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GAL 0 AY, Chih of Bruyn :

HERMANN: VON SCHRENK,

Ageyr 1 IN, CHARGE OF THE Mississirrt Vise
_ Larorarory,

"VEGETABLE PATHOLOGICAL AND PHYSIOLOGICAL
é _ INVESTIGATIONS.

——

MN

| WASHINGTON:
GOVERNMENT PRINTING OFFICE,

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[Continued or. p, 3 of cover.]

Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE l.

APPLES AFFECTED WITH BITTER ROT.

Inoculation from a canker.

Clo DEW RVieNr OF AGRICULTURE.
BUREAU OF PLANT INDUSTRY —BULLETIN NO. 44.

B. T. GALLOWAY, Chief of Bureau.

YHE BITTER ROT OF APPLES.

HERMANN VON SCHRENK, ,
SPECIAL AGENT IN CHARGE OF THE Mississippr V ALLEY
LABoraTory,

AND

PERLEY SPAULDING, Sprcrarn AGENT.

VEGETABLE PATHOLOGICAL AND Pres LOO GLC ATE
INVESTIGATIONS.

Issuep Jury 18, 1903.

aS =
ANN

= = A) Mi \ WF =
ig Tei i SZ OT
Ea

iS

WASHINGTON:
GOVERNMENT PRINTING OFFICE.
1903.

BUREAU OF PLANT INDUSTRY.
B. T. Gattoway, Chief.
VEGETABLE PATHOLOGICAL AND PHYSIOLOGICAL INVESTIGATIONS.
SCIENTIFIC STAFF.
ALBERT F. Woops, Pathologist and Physiologist.

Erwin F. Smita, Pathologist in Charge of Laboratory of Plant Pathology.
GEORGE T. Moore, Physiologist in Charge of Laboratory of Plant Physiology.
HERBERT J. WEBBER, Physiologist in Charge of Laboratory of Plant Breeding.
Newton B. Pierce, Pathologist in Charge of Pacific Coast Laboratory.
HERMANN VON ScHRENK, Special Agent in Charge of Mississippi Valley Laboratory.
P. H. Rotrs, Pathologist in Charge of Sub-Tropical Laboratory.

M. B. Waite, Pathologist in Charge of Investigations of Diseases of Orchard Fruits.
Mark A. CaRLeton, Cerealist in Charge of Cereal Investigations.
Water T. SwInaie, Physiologist in Charge of Life History Investigations.

C. O. TownsEnn, Pathologist.

P. H. Dorserr, Pathologist.

Ropyey H. Trvue,@ Physiologist.

T. H. Kearney, Physiologist, Plant Breeding.

CorneLius L. SHEAR, Pathologist.

WixiramM A. Orton, Assistant Pathologist.

Fiora W. Parrerson, Mycologist.

JOSEPH S. CHAMBERLAIN, Physiological Chemist.

k. E. B. McKenney, Physiologist.

CHARLES P. Harriey, Assistant in Physiology, Plant Breeding.

DEANE B. SwINGLe, Assistant in Pathology.

JAMES B. Rorer, Assistant in Pathology.

Luoyp 8. TEenny, Assistant in Pathology.

JESSE B. Norton, Assistant in Physiology, Plant Breeding.

A. W. Epson, Scientific Assistant, Plant Breeding.

Karu F. KELLERMAN, Assistant in Physiology.

GEORGE G. HEepGcock, Assistant in Pathology.

PERLEY SPAULDING, Special Agent.

a Detailed to Botanical Investigations and Experiments.

bo

EET RROOF TRANSMIT EAL.

U. 8S. DEPARTMENT OF AGRICULTURE,
Bureau oF Piant INDUSTRY, OFFICE OF THE CHIEF,
Washington, D. C., April 8, 1903.
Str: I have the honor to transmit herewith a paper on ‘*The Bitter
Rot of Apples,” by Dr. Hermann von Schrenk, Special Agent in

Charge of the Mississippi Valley Laboratory, and Perley Spaulding,

Special Agent, Vegetable Pathological and Physiological Investiga-

tions, ard respectfully recommend that it be published as Bulletin No.
44 of the series of this Bureau.

This paper was prepared under the direction of and was submitted

for publication by the Pathologist and Physiologist. The illustrations,
_ which comprise nine half-tone plates and nine text figures, are an essen-
tial and important part of the paper.

Respectfully,
B. T. GaLLoway,
Chief of Bureau.
Hon. JAMES WILSON,
Secretary of Agriculture.

|

PRE EAC E.

For the past four or five years the bitter rot of apples has been the
cause of heavy loss to growers and handlers of this fruit. As stated
in our report for 1901, the president of the National Apple Shippers’

Association estimated that the damage to the apple crop of the United

States in 1900 from bitter rot was $10,000,000. In some orchards
there was a total loss of fruit; in others from one-half to two-thirds
of the crop was destroyed. The disease is especially severe in the
Mississippi Valley and the States along the Ohio River. At the
request of numerous growers this Bureau undertook extensive inves-
tigations to determine more definitely the life history of the fungus
causing bitter rot with the hope of discovering a more effective method
of holding it in check. The report presented herewith contains a
general account of the history of the disease, a description and life
history of the fungus causing it, and some facts which have been

recently discovered in regard to the mode of life of the parasite.

During the year 1901 cooperative experiments, conducted along lines
suggested by this Bureau, were carried on with the Illinois Experi-
ment Station, but during the last season the work was conducted inde-

| pendently by both the station and the Department. Cooperative
| experiments on the control of this disease were started the past year

with the Missouri Fruit Experiment Station, and will be continued
with this station and fruit growers in various apple sections during
the present season.
ALBERT F. Woops,
Pathologist and Physiologist.
OFFICE OF THE PATHOLOGIST AND PHYSIOLOGIST,
Washington, D. C., April7, 1903.
5

COUNT EN lS:

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LEP US deka Tins:

PLATES.

Page.

PuaTE I. Apples affected with bitter rot. Inoculation from a canker. . . Frontispiece.
Il. Apples affected with bitter rot. Inoculation from a diseased apple. - 54

EEL Diseased-apples-under, trees: 225 Jae 5. oe re ee 54

IV. The bitter-rot fungus on various fruits. Figs. 1, 3, and 7.—Various
stages of growth on apples. Fig. 2.—An early stage of the disease
Fig. 4A mummified apple from the preceding year. Fig. 5.—
Growth of the bitter-rot fungus on a pear, with controlfruit. Fig.
6.—Growth of the bitter-rot fungus on squash..............----- 54
V. Drawings showing various stages of the bitter-rot fungus. Fig. 1.—
_ Spores of the bitter-rot fungus ( Glomerella rufomaculans) growing
in pure culture. Fig. 2.—Germinating conidia of the fungus. Fig.
3.—Starch grains from diseased apple, showing corrosion. Fig.
4.—Resting spores of Glewosporium cactorum. Fig. 5.—Perithecia
of bitter-rot fungus from apple canker. Fig. 6.—Asci of the bitter-
rot fungus (Glomerella rufomaculans). Fig. 7.—Perithecium with
ascl trom-apple canker . 2.2 ee ee eee 54
VI. Stages of growth of the bitter-rot fungus. Fig. 1.—Plate culture of
the bitter-rot fungus ( Glomerella rufomaculans), showing masses of
perithecia. Fig. 2.—Enlarged group of pustules on an apple
affected with the bitter rot, showing the tendril-like spore masses.
Fig 3.—Apple diseased with bitter rot. The infection was made
with spores from a pure culture obtained from a canker. Fig. 4.—

Control Tuite Sso5 eee oo i See ee 54

VII. Three limbs with bitter-rot cankers from living apple trees. _....--- 54
VIII. Cankers on living apple limbs. Fig. 1.—Cross section of four cankers.

Figs. 2, 3, and 4.—Cankers on living apple limbs -------..--.---- 54

IX. Artificial cankers produced on living apple limbs by sonia
spores of Glomerella rufomaculans into bark slits. Fig. 5 is an
enlarged: view OP fig..4 2255.2 ee ee 54

TEXT FIGURES.

Fic. 1. Map showing geographical distribution of bitter rot......:..--.------ 13
2. Diagram showing how the bitter-rot fungus decays an apple. --------- 17
3. A later stage of bitter-rot decay 322-2 32 e222 8 ee 17
4. Berkeley’s grape-rot fungus (Septoria rufo-maculans Berk. ) SUre Sees 26
5. Berkeley’s apple-rot fungus (Glewosporium fructigenum Berk.)--.------ 27
6. Diagrammatic cross section of an apple canker -..-...-.------------- 32
7.” How-to cutiolf a large limib!: 2. 22 2. Se ee og
8. Method of cutting large limb which should be avoided. .....-.------- 39
9. Arrangement of vats used in making Bordeaux mixture...-.....----- 43

8

B. P. 1.—60. V. P. P. I.—102.

Pile bi Eke ko? OF. APPLES:

INTRODUCTION.

The bitter rot or ripe rot of apples has for many years formed one
of the most serious enemies of this fruit. It made its first appearance
in the United States before 1867, according to Curtis’s catalogue, but
it was not specifically described until 1874, when M. J. Berkeley and
_ M.A. Curtis published the first descriptive notice concerning its occur-
rence in America. With the increasing number of apple orchards
throughout the central belt of States, its range and destructive action
_ have steadily increased.

__ The bitter rot is a disease of the ripening fruit, which appears late
in the summer, affecting whole orchards at once and destroying vast
| quantities of fruit when it is almost ready for marketing. Estimates
_ of the loss resulting to apple growers from the ravages of the bitter
Tot in various sections of the country have been made repeatedly.
_ The bibliography beginning on page 46 of this bulletin gives in full
_ the titles to which the short citations of authorities in the text of this
| paper may be referred.

A few statements from various sources will show what this pest is
-eapable of doing:

This orchard that appears so vigorous and healthy is almost worthless. Last year
It had at least 1,000 bushels of apples on, and the proprietor did not get a bushel of
_ winter apples. The bitter rot blasts them like the breath of ruin, and the promise
of spring ends in disappointment and decay. * * * This orchard was in its prime
_ from the time it was 8 until it was 18 or 19 years old. For ten or eleven years it
| gaye most bounteous returns and produced wagonloads of the finest fruit. It then

began to decline. The fruit commenced to speck, and the evil increased until the
_ trees are little more than an incumbrance on the ground. (Murray, 1870.)

An Arkansas man relates his experience as follows:

The man from whom I purchased my place told me that the Fameuse had always
been subject to the rot. For the last three years the disease has steadily increased,
_ so that this year (1887) my old orchard of 75 trees will not yield 25 bushels of sound
_ apples. (Galloway, 1887.)

| In 1900 it was estimated that the loss in four counties of Illinois for
that season was $1,500,000. (Burrill and Blair, 1902.)

10 THE BITTER ROT OF APPLES.

The Pathologist and Physiologist of the Bureau of Plant Industry |
of the U. 8S. Department of Agriculture in 1901 says: @

The losses caused by bitter rot in the Middle States often amount to half or three-
fourths of the entire fruit crop, single large growers sometimes losing 10,000 barrels of
apples. One firm estimated that their losses in 1900 on apples bought in the orchard
in Missouri alone amounted to $20,000 to $30,000, and orchards which in midsummer
promised a yield of 25,000 barrels of choice apples produced only about 5,000 barrels
of indifferent fruit, owing to this disease. The president of the National Apple
Shippers’ Association estimated that the damage to the apple crop of the United
States in 1900 from bitter rot was $10,000,000.

In some years the destruction was so great as to cause many fruit
growers to abandon the business, and instances have been known
where men have leased their bearing orchards at $5 per acre for
periods of five years, preferring to be assured of that small amount
rather than risk getting nothing from their trees because of the work
of this fungus. :

Older reports make mention of extensive destruction. Galloway
reported in 1889 that ‘‘in certain places in Virginia, Kentucky, Ten-
nessee, Missouri, and Arkansas our agents report this season a destruc-
tion of from 50 to 75 per cent of the crop.”

Garman in 1893 stated that bitter rot probably caused more loss to
Kentucky fruit growers than any other disease, and statements of this
character have appeared from time to time and with increasing
frequency in the reports of experiment stations and horticultural
societies. |

The sudden appearance of the disease at a time when the grower has
spent time, money, and energy in producing a large crop, and the
almost total destruction of the apples in a few days, causes the disease
to be universally feared. It has probably done more to discourage
apple growing in many regions than all other troubles, including both
fungous and insect diseases combined.

In spite of the universal and destructive appearance of this disease,
comparatively little had been accomplished until recently toward pre-
venting or even checking the bitter rot, although its cause was clearly
established by Berkeley in 1856, as described more fully hereafter,
while other observers have given detailed accounts of spraying experi-
ments. Ever since the experiment stations were established inyesti-
gations have been conducted looking toward preventive measures.
Many papers on the subject have been written, an idea of the number
of which can be gathered by referring to the bibliography at the end
of this Bulletin.

In the following pages a general account of the disease, a description
of the fungus and its life history, and some facts which have recently
been discovered in regard to its mode of life, etc., are presented.

« Annual Reports, Department of Agriculture, 1901, p. 47.

HISTORICAL ACCOUNT. 11

HISTORICAL ACCOUNT OF THE BITTER ROT.

‘The early accounts of the bitter rot deal mainly with the fungus
causing the disease, which for the present we will call by the name
which it has held for so many years— Glaosporiwm fructigenum Berk.
Rey. M. J. Berkeley described a fungus causing a ripe rot of grapes
in 1854, which was probably the same as the bitter-rot fungus (see fig.
4). Two years later he described a fungus causing ripe rot of the
apple, calling it Glwosporium fructigenum n. sp. He describes (1856)
the disease (see fig. 5) as follows:

It (the apple) presented a spotted appearance externally as well as internally.
* * * The spots were perfectly circular and well defined, and exhibited traces of
vegetation. On cutting through the apple the flesh was found to be discolored in
various places from the effects of incipient decomposition which was not confined
to the surface but penetrated into the center of the fruit. * * * Ina few days
some of them (the spots) were studded with pearl-like specks bursting through the
cuticle and swelling above it in the form of little flat cushions. Sometimes there
was but a single speck in the very center, but more frequently there wasa more or less
perfect ring of satellites, * * * the cuticle was raised into little shining pustules,
and a tendril of minute spores * * * was protruded through it.

In 1859 Berkeley described a fungus causing a disease of peaches
and nectarines, which he called Glwosporiwm laeticolor n. sp.:

Nearly a month since we observed on the peaches little dark specks with a bleached

center. * * * Two days ago he (the gardener) called our attention to its present
condition. The specks were prevalent on the nectarines as well as the peaches.
* * * ‘YJtisof the disease, then, as developed on the nectarines more especially
that we are speaking. * * * The white spot and the dark ring around it were
most beautifully defined, seated in the center of a regular circular depression, the
borders of which were pale, but not completely bleached like the center. The whole
surface of the depression was studded with little salmon-colored warts, disposed more
or less in circles, from the center of some of which, but especially of those in the
bleached cuticle, a little curled tendril of salmon-colored spores was protruded. After
a time, however, the several spots run together, and form a depression an inch or
more across, still teeming with the red spores.

This fungus is apparently the same as Glewosporium fructigenum
Berk. Berkeley in his description gives most of his attention to the
fungus rather than to the disease caused by it, but we can very easily
recognize the fungus of the bitter rot as being the same that he
described. |

In 1867 Rev. M. A. Curtis in a catalogue of the plants of North
Carolina mentions a fungus, Glwosporiwm versicolor n. sp., as occur-
ring upon rotten apples. This was the first use of the name, and also
was the first record of the occurrence of a fungus causing bitter rot in
this country, as far as can be determined. The bitter rot was very
probably known at that time, and possibly quite extensively known, as
the article by Murray in the Illinois Horticultural Society publication
only three years later (1870) would seem to indicate. In 1874 Berkeley
and Curtis published the first description of Glwosporium versicolor
n. sp., so that the name really dates from 1874.

12 THE BITTER ROT OF APPLES.

Practically all of the publications in regard to the bitter rot until
1887 were mere reprints of the articles already mentioned, and the dis-
ease was treated apparently as a rather uncommon one and not of
much importance.

Galloway seems to have been the first to treat upon the subject of
thisdisease from an economic standpoint, the first accounts dealing with
the bitter rot as a destructive orchard disease being published by him
in 1887. He called attention to the damage caused and the results of
experiments made to check the disease. At that time the bitter rot had
appeared in many States from the Atlantic seaboard to Kansas, and the
destruction of apple crops was large. These experiments were fol-
lowed by many others: Garman (1889), Galloway (1889), Jennings
(1890), Curtiss (1890), Galloway (1890), Churchill (1890), Chester (1890),
Garman (1890), and others. The results of these various experiments
were very conflicting. A few investigators succeeded in totally check-
ing the disease even after it had become well established, while others
had no success whatever. In the more northern States experimenters
seemed to succeed in checking the disease by spraying affected trees
with the ordinary fungicides. In the region south of the fortieth par-
allel, i. e., in the territory extending from the eastern coast to Kansas,
Indian Territory, and Texas, where the fungus seems to flourish best,
it was found much more difficult to control the disease. Spraying
experiments indicated that the disease could be checked to some extent,
but only in one or two instances was it stopped entirely. From the
time of its first appearance in July until the latter part of September
the bitter-rot fungus was active. What became of the spores, where
they remained over winter, and how they infected the fruit the fol-
lowing year was unknown, but the opinion was generally accepted
that many of the spores survived in the mummified fruits which
remained on the trees or on the ground throughout the cold season.

Up to within three years ago it was generally accepted that G/wos-
porium fructigenum Berk. was the cause of the bitter rot of apples.
During the last two years, owing to the increased ravages of the dis-
ease, attention was directed toward the investigation of the life history
of the bitter-rot fungus, with the result that a number of new facts
of considerable importance have been determined. These facts have
been discovered almost simultaneously by a number of observers, and
their exact bearing on preventive measures has already been tested.

DISTRIBUTION OF THE BITTER-ROT FUNGUS.
GEOGRAPHICAL DISTRIBUTION.

The bitter-rot fungus, like other species of the form genus Glceospo-
rium, has an almost world-wide distribution. In the United States it
has been found in nearly all of the States east of and including Kan-
sas, Oklahoma, and Texas. <A careful search through the mycological

GEOGRAPHICAL DISTRIBUTION. ~ 13

literature available at the Missouri Botanical Garden has shown that
under one name or another this fungus has been reported from Maine,
New Hampshire, Vermont, Connecticut, New York, New Jersey,
Delaware, Maryland, West Virginia, Virginia, North Carolina, South
Carolina, Alabama, Mississippi, Kentucky, Ohio, Indiana, Illinois,
Michigan, Wisconsin, Missouri, Arkansas, Kansas, Oklahoma, Indian
Territory, and Texas. The States east of the Mississippi from which
the fungus has not yet been reported are almost unexplored mycolog-
ically. It is extremely probable that it occurs in all States where
the apple is being grown, even in the most northern latitudes. (See
ioe Me)

The bitter-rot fungus was first described in England from English

Fig. 1.—Map showing geographical distribution of the bitter-rot fungus in the United States. The
shaded sections show where bitter rot occurs, the heavier shading indicating where the disease is
most prevalent.
specimens. On one or another host the bitter-rot fungus has been
found in all parts of the world. It is reported by Trail (1888), from
Perth, Scotland; by Saccardo (1881), from Italy; by McAlpine (1895),
from Queensland and New South Wales; by Cooke (1892), from
Queensland; by Speschnew (1897), from Tiflis, in Transcaucasia; by
Klein (see Frank, 1896), from Baden, Germany; also by Kirchner
(1890), from various parts of Germany; by Nypel (1896), from Liege,
Belgium; by Viala (1887), from France. It is probable that the fungus
occurs to some extent in every country where the apple is grown,
which is not surprising when one considers the manner in which apples
are sent to all parts of the world and the excellent chances which
spores of this fungus have for dissemination with the fruit.

14 THE BITTER ROT OF APPLES.
OCCURRENCE ON VARIOUS HOSTS.

The first bitter-rot fungus was described in 1854 (Berkeley) as
growing on grapes. Some years later the same writer described a
fungus causing ripe rot of the apple. Berkeley in some later papers
describes the ripe-rot fungus (under various names) as occurring on
grapes, apples, peaches, and nectarines. In 1871 Berkeley, referring
to a manuscript description of a fungus growing on grapes (G/qo-
sporium uvicola), takes occasion to say that in his opinion it is the
same as the fungus causing ripe rot of peaches and nectarines (Glwo-
sporium lzticolor Berk.). He states that ‘‘where grapes are grown
in the same house with stone fruits the malady may spread upward,”
which may be taken to imply that he considered that the ripe-rot fun-
gus of grapes may cause the disease of peaches and nectarines. He
further emphasizes their probable identity by saying (p. 1163): ‘* Both
on grapes and stone fruits the spores of the fungus are very variable
in size, so that no stress can be laid on mere measurement.”

Von Thiimen (1887) added the pear and the apricot to the list of
hosts. Galloway, in 1890, demonstrated for the first time that the
ripe-rot fungus of the grape, when transferred to the apple, caused the
ripe rot or bitter rot of the apple, and vice versa. Miss Southworth,
in 1891, confirmed these results.

Halsted, in 1892, published the results of a large number of experi-
ments in which he had inoculated fruits with spores from different
ripe-rotted fruits to determine whether the numerous forms of ripe
rot or bitter rot were really due to the same fungus. His experiments
seemed to prove that the same fungus caused the ripe rot of the apple,
grape, peach, pear, pepper, tomato, and eggplant. The fungus was
found to grow on bananas, quinces, lemons, and beans, in addition to
the other hosts mentioned.

Chester (1893) corroborated Halsted’s results so far as the tomato,
grape, pepper, and apple were concerned. He came to the same con-
clusion as Halsted—i. e., that the fungus on the apple, grape, tomato,
and pepper is biologically the same species. Alwood (1894) states
that all pomaceous fruits are attacked by Glawosporium fructigenum
Berk. During the last year Spaulding grew the fungus successfully
on squash. (PI. IV, fig. 6. See also Pl. IV, fig. 5, showing the
fungus on the pear.)

From the evidence at hand it appears that this fungus can adapt
itself to numerous hosts. Itseems probable that all the forms are one
and the same species, but it will be necessary to develop the perfect
or ascus stage of many of them before any positive statement on this
point can be made.

GENERAL DESCRIPTION. 15

GENERAL DESCRIPTION OF THE BITTER ROT.
TIME OF APPEARANCE.

The bitter rot appears in an apple orchard at different times during
the months of July and August, the time of its first appearance vary-
ing with the climatic conditions during any particular season. The
first spots (Pl. IV, fig. 2) usually develop on the apple fruits when
they are nearly full grown. From that time on until the fruit is
entirely ripened the disease is likely to occur with increasing severity.
In the Southern States bitter rot may destroy some fruit in the early
part of July. Ina number of cases apples only three-fourths of an
inch in diameter were found affected with the disease. One of the
writers collected apples affected with bitter rot in Vermont on Octo-
ber 20. The spots were small but well developed, and were present
on a large number of individual fruits on one tree.

The factors which determine the time of appearance are probably
(1) the age of the fruits; (2) the temperature and humidity of the air;
(3) the presence of spore-distributing centers. The age of the fruit
isa factor of considerable importance. Asa rule, the green fruit is
comparatively immune, which may be due in part to the large amount
of malic acid present in the unripened fruit. It is possible to produce
the disease on green fruits by artificial inoculation by allowing such
fruits to he on a shelf for several days after being picked. Different
varieties of apples show a different susceptibility with respect to the
time of attack. No hard and fast rule can, however, be laid down in
respect to this matter, as the climatic conditions may hasten or retard
attack.

Warm, sultry weather, particularly after a rain, forms the ideal con-
dition for the development of the bitter rot. In cool, dry summers the
bitter rot is usually present but sparingly. A short series of hot, wet
days in August may bring about a sudden and very destructive attack.
Nights with a heavy fall of dew alternating with hot days are usually

followed by an extensive development of the disease. Numerous

instances might be mentioned where the disease appeared in an orchard
during the latter part of August, after a few hot days, destroying the
whole crop in three days. A notable case of this kind occurred during

the summer of 1900. Cold weather usually checks the disease and

may stop it altogether.

The time of appearance of this disease is probably influenced also
by the condition of ripeness of the spores in the cankers (as described
later) and in the mummies. A cold spring may retard their develop-
ment and consequently bring about a late attack on the fruit, or vice
versa.

16 THE BITTER ROT OF APPLES.
CHARACTER OF THE SPOTS.

The first signs of the bitter rot appear in the form of a very faint
light-brown discoloration under the skin of the apple. The spots are
exceedingly small at first, and as they grow larger they appear cir-
cular in outline. (PI. IV, fig. 2.) The spots rapidly increase in size,
becoming darker brown. When the spot is one-eighth of an inch in
diameter the area appears distinctly sunken. The borders of these
spots are usually very nearly circular and sharply defined. When
about one-half an inch in diameter small black dots appear at more
or less regular intervals beneath the epidermis in the sunken area.
These increase in size and project as tiny raised points. At a later
stage they break through the epidermis of the fruit and allow large
numbers of spores to escape. (PI.1V, figs 1 and 7.) These spores, when —
not washed from the fruit, form pink masses, sticky when moist. As
the spore mass dries it cakes and adheres to the epidermis. On quiet,
dry nights the spores are discharged in long tendril-like threads
(Pl. VI, fig. 2), oozing out slowly from the mouths of the black
bodies, which are the fruiting bodies of the bitter-rot fungus. These
black bodies or pustules are often arranged in the form of a ring.
(Pls. Land Il.) As the rot progresses other rings of pustules appear
outside of the first one, and at regular intervals six to eight, and
sometimes more, well-defined rings may form in rapid succession.
Each ring will have hundreds of pustules, each producing spores at
the same time, so that some rings appear almost continuous. (Pls. I,
II, and IV, figs. 1 and 7.) The formation of these rings depends on the
rapidity with which the fungus grows. The most perfect rings of
pustules are formed when the fungus grows most rapidly. (Pls. I and
Il.) Cold weather will be followed by a more or less irregular devel-
opment of the pustules. (PI. LV, fig. 3.) They then break through the
epidermis at many points, as shown on Pl. IV, figs. 3 and 7. The
arrangement of the fruiting bodies in rings is a common phenomenon
among fungi. Where a single spore germinates in a medium where
the food supply is abundant on all sides, the hyphe generally grow in
all directions with equal rapidity. When the period for the deyelop-
ment of spores has arrived, the spores will be formed from hyphe of
the same age, 1. e., at points equally distant from the original point of
infection. The phenomenon of fairy rings is a notable instance among
the higher fungi. Alternate periods of low and higher temperature
may account for the intermittent development of fruiting bodies, and
hence the formation of successive rings.

The pinkish appearance of diseased fruit is due to the spore masses
which exude from the pustules. After a rainstorm the interior of the
pustules looks sooty black and the mouths ragged, all the spores
having been washed off.

f

CHARACTER OF THE SPOTS. £0

The brown coloration of the spots on the apple fruit is an indication
of the decayed condition of the tissues immediately under the spots,
in which region the threads of the bitter-rot fungus are bringing about
changes in the firm tissue of the fruit which make it appear decayed.
The lateral progress of the disease, evidenced by the increasing
diameter of the brown area, is accompanied by a corresponding prog-
ress of the disease into the fruit (figs. 2
and 3). The rotted mass, which is an
inch in diameter at the surface, usually
extends inward to the core of the fruit.
The rotted mass shrinks somewhat in
volume, hence the sunken character of the
spot outside. There is usually a sharp
dividing line between the rotted mass and
the sound tissue. In this respect the bit-
ter rot differs from the black rot of the

Fig. 2.—Diagram showing how the
apple. bitter-rot fungus decaysanapple.
The size of the diseased areas on the

fruit increases rapidly after an infection, and eventually the whole
fruit may be affected. Where two or more separate infections
take place the diseased masses fuse (Pl. I). The separate rings of
fruiting bodies join and the two sets of hyphe then grow on just
as if there had been but one. The completely rotted fruit appears
considerably shrunken, especially if there have been several cen-
ters of infection. The fruit hardly ever decays entirely, as do apples
attacked by the black rot; as a rule there
are small patches of healthy cells which
hold out a long time. The affected fruit
falls from the tree during all stages of
the disease. (See Pl. III.) In this case,
as in other instances of fruit diseases due
to fungi, a hastening of the ripening proc-
ess takes place. The diseased fruits are
heavier than ripe fruits, and are readily
shaken from the trees. There are proba-
Cae ees of bitterrot bly other changes taking place in a dis-

si eased fruit which influence its condition and
bring on premature fall, much as with fruits stung by various insects.

CAUSE OF THE BITTER ROT.

The bitter rot of apples is due to a fungus, Glwosporium fructige-
num Berk., which grows in the ripening tissues of the fruit, thereby
inducing decay. The earliest accounts of this fungus deal largely with
its systematic position, but it was recognized at an early date that the

26892—No. 44-08

2

; 18 THE BITTER ROT OF APPLES.

bitter rot or ripe rot of both apples and grapes was in some way con-
nected with this fungus. A complete description of the fungus and
its various stages 1s given ina succeeding chapter, and it will be neces-
sary at this point to simply mention in brief the general appearance of
the fungus in the orchard and the reasons for connecting this fungus
with the bitter rot.

Reference has already been made to the appearance on diseased
fruits of more or less regular rings of pustules. In these pustules
small one-celled spores are formed, which exude from the pustules
after they have broken through the epidermis. In the orchard these
spores seem to be produced abundantly only when the air is heavy
with moisture. Heavy dews and rain wash away the pink spore
masses, leaving the ragged mouths of the pustules freely exposed. The
appearance of the pustules and the discharge of the spore masses are
the only evidences of fungus activity visible during the attack.

These pustules and spores are, however, always present in apples
affected with the bitter rot, and no cases of this disease are known
where these spores have not appeared at one stage or another. More-
over, inoculations of sound fruit with the spores of Glewosporium
Jructigenum Berk., made by many experimenters, have invariably
produced the disease (Pl. Il). There is, therefore, no doubt whatever
that the bitter rot or ripe rot of apples and of some other fruits is
caused by the bitter-rot fungus (Glwosporium fructigenum Berk.).

RATE OF DEVELOPMENT OF THE BITTER ROT.

The rate with which this disease develops depends largely upon con-
ditions of temperature and moisture. During some summers it may
take several weeks for the disease to develop to any extent after its
first appearance. Then, again, it may start ona fruit during the night
and in three to four days entirely destroy it. Apples inoculated
with the bitter-rot fungus and kept in incubators at a temperature
of 87° C. (98.6° F.) will show spots three-fourths of an inch in diame-
ter, with numerous pustules, in forty-eight hours after inoculation.
As has been stated above, the disease will develop in several days in
epidemic form when heavy dews fall during the night, followed by
hot, cloudy days. The condition of the apple fruit at the time of
the attack influences to some extent the rate of development. Thus
green fruits do not suffer as severely from the disease nor does the
disease progress as rapidly as with fruits which are almost ripe. The
disease progresses at different rates on different varieties of apples.
Some are more easily affected than others. In general, it may be said
that hot, muggy weather is most favorable for the rapid development
of the bitter rot.

f

THE BITTER-ROT FUNGUS. 19

THE DISEASED APPLE.

An apple affected with the bitter rot or ripe rot is a most objection-
able fruit. The name of the disease is derived from the peculiar bitter
taste of the decayed tissues of the fruit which is noticed almost as soon
as the fungus has begun its growth in the cells. One observer (Alwood,
1894) states that this bitter taste is not always present. The partially
decayed fruit leaves a bitter taste in the mouth, resembling the after
effect of quinine, yet not quite the same. The bitterness increases as
the rot becomes more pronounced. The tissues of the apple are hard
and firm when first affected; the cells look somewhat watery and are
pale brown. As the rot advances the flesh of the apple softens and
turns darker in color, until at an advanced stage the whole tissue 1s
soft and mushy, very watery, and without any resemblance to the
original healthy tissue. Attention should be called to the fact that in
no case does the apple become as soft and mushy as it does when
affected with most other fruit-rotting fungi, for instance, the black
rot. The decay starts at the surface of the fruit and gradually extends
inward toward the core, making a sort of cone-shaped mass of dis-
eased tissue, as described above (figs. 2 and 38).

During the early stages of the disease there is a marked accumula-
tion of starch around the affected spots, which calls to mind similar
phenomena described by Halsted (1898) for various leaf-spot fungi.
The cells of the apple tissue separate from one another as the disease
progresses. The middle lamella of the cells is dissolved by the fungus
hyphe, but the cell walls themselves remain intact.

THE BITTER-ROT FUNGUS.

LIFE HISTORY ON APPLES.

The spores of the bitter-rot fungus germinate on the apple fruit
when it is nearly ripe. In some cases the fungus has attacked apples
when they were only three-fourths of an inch in diameter (Garman,
1893), which, however, may be regarded as exceptional. The hyphe
from germinating spores enter the apple and begin to grow in the
layer immediately under the epidermis. Whether the young hyphe
can pierce the uninjured epidermis of the apple seems to be a some-
what disputed point. In making infections of apple fruits in the lab-
oratory it was found that the greatest numbers of successful infections
were obtained by puncturing the epidermis with a sterile needle and
then spraying the spores on to the broken epidermis. Clinton (1902)
states that the spores placed on unpunctured apples, ‘‘if successful,”
brought about the rot two or three days later than when placed on
punctured fruits. It is probably true that the young hyphe can enter
through the unbroken skin, possibly through the stomates, but at the

20 THE BITTER ROT OF APPLES.

same time it is probable that a large percentage of the infections in
an orchard start in fruits which have been wounded in some way, gen-
erally by insects. When one reflects that the number of spores which
fall on a fruit is generally very large, it is strange that there should
be only very few infections or sometimes only one infection. This
point is one which will require additional careful study.

After the first hypha has entered the tissue below the epidermis it
branches rapidly. The hyphe grow in the intercellular spaces, absorb-
ing the sugar and other products from the apple cells. (See Pl. V, fig.
3.) The affected cells turn brown and separate, and after a time they
collapse. It is then that the presence of the fungus becomes noticeable
on the outside in the form of the brown, sunken spots mentioned above
(Pl. IV, figs. Land 2). The fungus hyphe grow in all directions from
the original point of infection with great regularity. As they extend
outward the cell groups attacked become brown in turn and collapse
more or less. This regular development gives the affected mass of
cells the circular form visible on the outside.

Early in the season the brown areas are about one-half of an inch in
diameter before there is any evidence of spore formation; later on,
during the height of an epidemic, the spores’*begin to form when the
affected areas are still very small. The spore-forming stage is evi-
denced by the appearance of numerous small raised points, which push
up the epidermis in a brown spot at irregular intervals. These points
are composed of masses of parallel hyphe which grow outward from
the cells just underlying the epidermis. These hyphe are short and
so arranged as to form a low cone, whose apex pushes against the
epidermis as the hyphe composing it grow in length. These hyphe
are at first colorless and then turn olive colored. Ultimately, either
by pressure or because of the solvent action of an enzyme, the tip of
this cone breaks through the epidermis. On the outside the tips of
the cones appear as small dark specks. The unicellular spores are
formed by abstriction from the ends of the hyphz composing the
cone, Many spores being formed from each hypha. Great masses
of these spores issue from the hole made in the epidermis and
remain on the outside as bright pinkish, glistening masses, adhering
to the tips of the cones. The latter are the pustules or sori. When
the fungus is growing rapidly the pustules or sori may form when the
spots are but one-fourth of an inch in diameter. The spore masses
are sticky and adhere firmly to the mouth of the pustules. Some-
times, especially during nights when a heavy dew has fallen and there
is an abundance of moisture in the air, the spores will be discharged
forcibly in the form of tendril-like masses. (PI. VI, fig. 2.

As stated above, the sori appear in irregular groups early in the
season. Later in the summer, when the fungus is growing rapidly,
they break through the epidermis in groups, forming very regular
rings (Pl. I). These rings are striking objects shortly after the dis-

LIFE HISTORY OF FUNGUS. 2]

charge of the spores and form one of the most characteristic features
of the disease. The spores disappear from the tip of the pustules
after a time. Rain or dew may wash them away or insects rub
them off. The empty sori remain behind and have a sooty, black
appearance.

The time elapsing between spore germination on a fruit and the
ripening of the first spore crop differs with the season from three or
four days toa week. In hot days of August the cycle is completed
with great rapidity. In one and the same spot on a fruit spores may
be forming at the center, while a quarter of an inch farther out the
pustules have not yet begun to develop.

The foregoing description of the growth of the fungus pertains to
the development on apples still on the trees. Spores inoculated into
apples after they have been picked will give rise to similar phenomena.
The rate of growth of the fungus and the formation of spores will
depend entirely on the temperature and moisture conditions under
which the inoculated apple is kept.

The spores of Glwosporium fructigenun Berk. germinate on grapes
when they are almost or quite ripe (Southworth, 1891). The bitter
taste which follows the attack of this fungus on apples is absent in
diseased grapes. Hence the more common designation of ‘‘ripe rot”
for the same disease of the grape. On white grapes small reddish-
brown spots appear, which spread and become darker as they grow
older, until the spots have an almost purple center with a bright brown
border. The pustules on the grape are at first white, then darker,
until they arealmost black. The spores are flesh-colored. The berry
ultimately dries up, but does not turn black. Dark-colored grapes
how no color changes when attacked.

|
|
|

THE CONIDIA

The spores of Glawosporium fructigenum Berk. produced in the
sori, and commonly called conidia, are pinkish-colored en masse. This
color varies from a light fresh pink to a darker reddish pink.* When
highly magnified they have a very delicate light-green color. This
color is quite distinct, and it seems strange that of many observers
Alwood (1894) seems to be the only one to recognize this greenish
color. Clinton (1902) states that the conidia are colorless, while Miss
Southworth (1891) says that they are hyaline.

In size and form the conidia are extremely variable. The great
variability in these respects has probably been responsible for the
difficulties which many observers have labored under when it came to
deciding which of the several fungi causing similar diseases of fruits

«One of the writers noted apples which had been inocu'ated in the laboratory and
bore only cream-colored spore masses. The spores seemed to be perfectly normal in
other ways.

22 THE BITTER ROT OF APPLES.

properly belonged to this particular species. Alwood (1894) was able
to produce in the same culture spherical, dumb-bell-shaped, oblong,
ovoid, and cylindrical conidia. Although such extreme forms were
not found by the present writers, they agree with Alwood and others
that the form variation is certainly large. The general form of the
conidia developed on fruits and in cultures may be characterized as
oblong or cylindrical, sometimes slightly curved (PI. V, fig. 1).

Extremes in sizes, gathered from all other writers, were from 6 to
40 4 in length and from 3.5 to 7 ” in width. The dimensions given
by some may be mentioned. Alwood gives 10 to 12 ux 4 to 6 mu.
Saccardo’s measurements, 20 to 30 “x5 to 6 “, are probably of
exceptionally large spores. The average size, as determined by the
writers, is 12 to 16 ~ xX 4406 -.

Miss Southworth says of the conidia: ‘*They are apt to be shorter
and thicker on the apple [than in cultures], and in dry than in moist
surroundings.”

The spores can not and should not be taken as a criterion in deter-
mining whether any particular fungus is Glwosporium fructigenum
Berk., since the spores of other species of Glceosporium closely
resemble those of the bitter rot. The great variability in size and
form of many fungi of a more or less saprophytic nature is coming to
be more widely recognized, and the former method of lumping or
separating many forms simply by spore characteristics is rapidly giy-
ing way toa clearer conception of the relationship based upon more
constant characters. 3

The ripe conidia are filled with a finely granular protoplasm. Near
the middle and usually a little to one side a clear hyaline area is gen-
erally visible (Pl. V, fig. 1). It is at this point that the septum forms
during germination. Normally, the conidia are one-celled until they
germinate. They resemble the ascospores of this same fungus, and
the two can hardly be distinguished. Asa rule the ascospores are
slightly curved, while the conidia are straight.

GROWTH IN CULTURES—CONIDIAL AND ASCUS STAGES.

Freshly-formed conidia of the bitter-rot fungus germinate in three
or four hours when put in water at room temperature. Just before
germination a septum frequently forms at or near the middle of the
spore, thus making a two-celled spore (Pl. V, fig. 2). A spore may
produce one, two, or more rarely three, germ tubes (Pl. V, fig. 2).
Where a wall forms, these two germ tubes start, one from each end of
the spore. Short spores generally have but one tube. When the
spores germinate in drops of water they become vacuolated after a
few hours, and after five or six hours they become entirely empty.
When germinated in bouillon or on agar, the protoplasm remains
finely granular for some time and the cells rarely become entirely
emptied.

GROWTH IN CULTURES. 23

The germ tubes grow in length with great rapidity, reaching a
length three or four times that of the spore (Pl. V, fig. 2) in three-
fourths of an hour. Ina water medium the first hyphe grow to con-
siderable length before branching. In bouillon or agar they branch
when two to three times as long as the spore. Septa form very early
in the development of the mycelium (PI. V, fig. 2).

Fusions between neighboring hyphe are common both in the apple
fruit and in cultures. The young hyphe are colorless and are filled
with a granular protoplasm. When growing in the tissues of the
apple, the young hyphe soon turn darker and ultimately become
brown. When an abundant food supply is at hand the mycelium
grows to large dimensions, and it may be several days before any
fruiting bodies are formed. These are usually conidia formed by a
process of abstriction at the end of short lateral hyphe (PI. V, fig. 7).

These conidia develop with great rapidity (Clinton, 1902), so rapidly
that in twelve hours an agar plate will appear as if covered with a
powdery mass. When growing under unfavorable conditions, so that
the mycelium is starved, some of the hyphal tips will swell consider-
ably, and a wall will cut off the swollen end (Pl. V, fig. 2). The walls
of this swelling turn dark red-brown and thicken somewhat, forming
what appears to be a spore (PI. V, fig. 2). A bright translucent spot
is usually present near the center. These brown bodies have various
shapes and appear to be formed by most species of the genus Glao-
sporium. Miss Stoneman (1898) figures them for @. fructigenum and
G. naviculisporium. Miss Southworth (1891) and Clinton (1902)
obtained them in cultures of Glewosporium fructigenum. Gleosporium
cactorum forms very fantastic bodies which bud and develop short
tubes (Pl. V, fig. 4). Halsted (1892) published an extended account
dealing with some of these secondary spores. Many attempts were
made to cause the bodies formed by Glawosporium fructigenum to ger-
minate, but so far without success. They probably represent a form
of chlamydospore, which may have to undergo a resting period before
developing.

The conidia formed freely from rapidly growing mycelium on agar
resemble those from the pustules on apples in allrespects. They ger-
minate in a similar manner, and the mycelium which they give rise to
may produce similar conidia, pustules, or perithecia, as the case may
be, depending upon the age of the fungus, the food supply, etc. The
fungus can be made to grow continuously, producing crops of conidia
without the production of the other stages.

When kept growing on apple agar several crops of conidia usually
form, as described above, and when the food supply has been partially
exhausted the production of conidia gradually stops. The first lot
of conidia have germinated by this time and have produced mycelia,
so that a petri dish with a pure culture of the bitter-rot fungus

24 THE BITTER ROT OF APPLES.

is covered with a dense growth of mycelium after a period of from
ten to fourteen days. At about the time when the conidia cease to be
formed small black knots appear among the tangled mass of hyphe,
looking much like warts. Drops of a yellowish liquid frequently
exude from these black bodies (PI. VI, fig. 1) | The latter increase in
size and frequently form masses one-fourth of an inch in diameter.
Cultures on apple agar will show good-sized masses of this kind in
from twelve to eighteen days. These black masses contain the peri-
thecia of the bitter-rot fungus.

The perithecia and asci were first described by Clinton (1902), who
proved their connection with the bitter-rot fungus (Glwosporium Fruc-
tigenum Berk.) by inoculating ascospores into apples and producing
the bitter rot. The formation of perithecia was found by the writers
to occur with great constancy under appropriate conditions. As a
rule the perithecia form in older cultures only.

The black nodules in which the perithecia are embedded are hard
masses of mycelium, which may be characterized as carbonaceous.
They are very irregular in shape and vary in size froma small pin
head to one-fourth of an inch in diameter. The perithecia, from one
to many, are embedded in this carbonized mass. In apple-agar cul-
tures the perithecia form when the black nodules are still very small.
When there is: but one perithecium in a nodule it is almost spherical;
when there are several, they are somewhat flattened laterally, and
sometimes very irregular in form. There is no beak. Clinton (1902)
found the perithecia to be from 125 to 250 “in length. These meas-
urements agree fairly well with those found by the writers. The
walls of the perithecia show marked reticulations about 6 to 14 4 in
diameter. These are quite marked in the early stages, but become
obscured as the perithecium matures.

The asci (Pl. V, fig. 6), which occur in considerable numbers in a
perithecium, are oblong-clavate in form, 55 to 70 4 by 9 “4, often with
a slight pedicel, and are comparatively thin walled. When mature
they break open and disappear rapidly. They contain. 8 ascospores,
which are usually arranged in pairs, more rarely in oblique scries.
The spores resemble the conidia formed directly on the mycelium, so
much so that they might easily be taken for conidia. They are per-
haps curved a little more than the conidia, a character which can some-
times be used to separate the two, but not always. The ascospores
and the conidia are about the same size, though the former are not as
variable as the conidia, measuring 12 to 22 «by 3.5 tod uw. Their
great resemblance has probably led to the ascospores remaining undis-
covered for so many years. The asci are short lived and after they
have discharged the spores they vanish. When found in apples it is
practically impossible to tell whether any particular spore is an asco-
spore or a conidium. The ascospores germinate much in the same

THE NAME OF THE FUNGUS. 25

manner as the conidia, and the description given for the germination
of the conidia will hold for the ascospores.

Conidia were found in the bitter-rot canker during the summer of
1902, and in the latter part of 1902 perithecia and asci were found in
the canker. (Science, 17: 188, 1903.) The description of these will be
given below in discussing the cankers.

The bitter-rot fungus grows readily on most culture media. It grows
vigorously on apple agar, on sterilized apple wood or leaves, on sterile
pine blocks, bean stems, etc. It is in many respects a true saprophyte.
It is questionable whether it ought to be considered a parasite at all
times when growing on the ripe fruit in the orchard, for at the time it
attacks such fruit the latter is practically full grown and 1s no longer
composed of cells or tissues which will react when stimulated. The
fungus develops best at temperatures ranging from 33° to 38° C.
(91.4° to 100.4° F.). Apples which were kept in incubators at 38° C.
after infection showed decayed spots 1 inch in diameter in from
one to three days. Cold checks growth materially, and at 2° C. or
35.6° F. (cold-storage temperature) no further growth takes place.

THE NAME OF THE BITTER-ROT FUNGUS.

About the middle of the last century a number of fungi were
described by M. J. Berkeley as growing on various fruits and bring-
ing about their decay. In 1854 he published the discovery of a fungus
growing on grapes which caused ripe rot. He says of this:

The surface of the spots is rough, with little, raised, orbicular, reddish bodies
arranged in concentric circles and easily separating from the matrix, which is per-
forated for their protrusion. The outer surface of these bodies consists of delicate
cells, with a distinct darker nucleus, and when this is removed a lobed hymenium
is seen within, rough, with distinct sporophores, each of which is surmounted by an
oblong spore, sometimes constricted in the center, and occasionally so much so as to
become pyriform, and varying in size from 7545 to z4y inch. In age the perithecia
fall away, leaving a little aperture, the border of which is often stained with biack.

Berkeley named this fungus Septoria rufo-maculans, n. sp. He fig-
ures pycnidia and spores, and for reference the latter are reproduced
herewith (fig. 4). In 1860 he changed the name to Ascochyta rufo-
maculans. Von Thimen (1879) renamed this grape fungus Gla@osporiumn
rufo-maculans (Berk.) v. Th.

In 1856 Berkeley described a fruit-rotting fungus growing on apples,
which he called Glwosporium fructigenum, n. sp. This is the first
authentic description of a fungus causing bitter rot, or ripe rot, of
apples. Berkeley says of this fungus:

On examination each plant was found to consist of a branched inosculating myce-
lium, giving rise to simple or forked subfastigiate irregular threads, each tip of which

was surmounted by an oblong, curved, or irregular spore about ;3,5 of an inch in
length. There was not the slightest trace of an investing membrane or perithecium.

26 THE BITTER ROT OF APPLES.

He refers to the description of a grape-rotting fungus two years
before, and seems inclined to doubt the wisdom of considering the
apple fungus a new species.

The spores (of the apple fungus) are more inclined to be curved, rather longer,
and not so variable in size, and the want of a perithecium separated the two widely
from each other. * * * At the same time these organisms are so different in dif-
ferent conditions that I would not affirm that the two productions are essentially
different, and the more especially because in external appearance and habit they are
so perfectly identical.

Berkeley’s figures of this fungus are reproduced in figure 5.

In 1859 Berkeley published the name Glwosporium leticolor n. sp.,
applying it to a fungus growing on peaches and nectarines. He eyvi-
dently regarded this species as quite distinct from the apple and grape

ARs t
WZ

IN
A\RYT\\

YN
ON)

Fic. 4.—Berkeley’s grape-rot fungus (Septoria rujo-maculans Berk.). [Drawn from the original
figure. |
fungi, as he speaks of these in the following words (p. 676): “*A plant
of the same genus, destructive to apples, is figured and described in
this journal (Gardeners’ Chronicle, 1856, p. 245). * * * We may
also refer to the very similar production on grapes.”

In 1874 Berkeley and Curtis described a fungus growing on apples
in South Carolina, calling it Glaosporium versicolor n. sp. They
appeared anxious to emphasize the fact that this new fungus was not
Glaosporium fructigenum, as they say: ‘‘ It is very different in habit.”

In the years following this last description the accounts dealing with
the bitter-rot fungus on apples in the United States speak of it as
Gleosporium fructigenum Berk., using the name given for the fun-
gus on apples by Berkeley in 1856.

When Miss Southworth, in 1891, published an article on the bitter-
rot fungus she reviewed the older accounts of fungi causing bitter rot

THE NAME OF THE FUNGUS. Sot

or ripe rot of fruits, and decided to accept the name Glewosporiwm
Fructigenum Berk. for the fungus causing the bitter rot of apples.
She gives her reason for so doing in the following words:

The strict law of priority might demand that we now make the specific name rufo-

maculans, but since the better-known G. fructigenum is also Berkeley’s name it will
remain so in this paper.

At this point it will be necessary to refer again to the results which
Miss Southworth obtained by inoculating grapes with spores of the
apple bitter-rot fungus (Glawosporium fructigenum Berk.) and apples
with the grape ripe-rot fungus (Glwosporium rufo-maculans (Berk.) v.
Th.). In both cases a bitter rot or a ripe rot of the respective fruits
followed, which led Miss Southworth to regard the bitter-rot fungus
and the ripe-rot fungus as one and the same species. The experiments
of Halsted (1892) seemed to verify Miss Southworth’s experiments

Fig. 5.—Berkeley’s apple-rot fungus (Glawosporium fructigenum Berk,). [Drawn from the original
figure. |

and to show that the same fungus caused the ripe rot not only of

apples and grapes, but also of quinces, pears, peaches, nectarines,

peppers, and other fruits.

Summing up the foregoing, it appears that several fungi causing
fruit rots have been described under the impression that they were
distinct species. More recent investigations have demonstrated that
in all probability the same fungus has caused the various ripe rots of
fruits. The different forms variously described as Gla@osporium fruc-
tigenum, Gleosporium rufo-maculans, Gleosportum versicolor, and
Gleosporium leticolor probably differ only in minor characters, such
asin the size and form of the spores. The effects which they produce on
different fruits vary as to color, size of spots, etc. These differences
are readily intelligible in view of the better knowledge which we now

28 THE BITTER ROT OF APPLES.

have concerning the influence of different substrata on morphological
characters of plants. This is particularly true of saprophytic fungi,
which, like the ripe-rot or bitter-rot fungus, can grow on media of
widely different chemical compositions. An abundant food supply
may result in the production of very large spores, just as a meager
supply may be followed by the formation of smaller spores.

The various fruits under consideration have a different structure and
they differ chemically. It might, therefore, be expected that there
would be slight differences in the structure of the fungus, and also in
the external appearance of diseased fruits.

In cultures the various forms behave similarly. No such distinet
physiological strains as were described for Veocosmospora vasinfecta
by Erwin F. Smith (1899, p. 39) could be established. This is prob-
ably due to the more or less saprophytic nature of the fungus.
Gleosporium fructigenum Berk. is not bound so strictly to the apple
cell as the root-rot fungus is bound to the cowpea, the cotton, or the
watermelon.

Assuming, then, that the four species mentioned above are one and
the same, it becomes necessary to choose one of the four specific names.
According to the generally accepted rules of nomenclature, the name
under which the fungus was first known takes precedence, and in this
case it is Glwosporium rufo-maculans (Berk.) vy. Thiimen.

This would have been the name of the bitter-rot fungus but for the
discovery of the perfect or ascus stage. In 1902 Clinton placed the
bitter-rot fungus in the genus Gnomoniopsis Stoneman.

In 1895 Miss Stoneman described a new genus Gnomoniopsis in
which she placed (after obtaining in cultures the ascosporic stage) the
following fungi, hitherto known only in the imperfect stages as mem-
bers of the Melanconiacese: Glwosporium cingulata Atk., Glaosporium
piperatum KE. & E., Colletotrichum cinctum Berk. & Curt., and Col-
letotrichum rubicolum EB. & E. Clinton included the bitter-rot fungus
Gleosporium fructigenum Berk. in this group and named it accord-
ingly Gnomoniopsis fructigenum (Berk.) Clinton. It is under this
name that the fungus now stands.

In establishing the genus Gnomoniopsis Miss Stoneman, however,
overlooked the fact that six years prior to her publication Berlese
(1892) used the name Gnomoniopsis for a group of fungi very different
from the perfect form of the G/lwosporiwm which she described.
Clinton, in accepting Miss Stoneman’s name, likewise overlooked the
name published by Berlese. The latter raised the subgenus Gnomoni-
opsis of the genus Gnomonia as used by Winter (1887) to generic rank,
making the species Gnomonia chamaemori (Fries) the type, and includ-
ing in the new genus the former Gnomonia misella as a variety of
Gnomoniopsis chamaemor’-(Fries). Lindau (1902) accepts Miss Stone-
man’s genus Gnomoniopsis. The generic use of Gnomoniopsis by Ber-
lese in 1892 clearly invalidates Miss Stoneman’s name, and it becomes

THE NAME OF THE FUNGUS. 29
necessary to rename the genus. The name Glomerella is suggested by
the writers. The bitter-rot fungus would accordingly become Glom-
erella rufomaculans (Berk.) Spaulding & von Schrenk, with the fol-
lowing synonymy:

Glomerella rufomaculans (Berk.) Spaulding & von Schrenk. @

Septoria rufo-maculans, Berk. (1854, Gard. Chronicle, p. 676).

Ascochyta rufo-maculans, Berk. (1860, Outlines of British Fungology, p. 320).
Gleeosporium rufo-maculans, (Berk. ) v. Thtimen (1879, Fungi Pomicoli, p. 59).
Gleeosporium fructigenum, Berk. (1856, Gard. Chronicle, p. 245).
Gleosporium laeticolor, Berk. (1859, Gard. Chronicle, p. 604).

Gleosporium versicolor, Berk. and Curt. (1874, Grevillea 3: 13).
Gnomoniopsis fructigena, (Berk.) Clinton (1902, Bull. Ill. Agr. Exp. Sta. ).

The new genus Glomerella stands practically for the genus Gnomoni-
opsis Stoneman, and accordingly includes all the species, four in num-
ber, which were placed by her in the genus Gnomonzopsis, 1. e., they
become Glomerella cingulata (Atk.) Spaulding & von Schrenk, Glom-
erclla piperata (KE. & E.) Spaulding & von Schrenk, Glomerella cincta
(Berk. and Curt.) Spaulding & von Schrenk, Glomerella rubicolor
(EK. & E.) Spaulding & von Schrenk.

Glomerella rufomaculans may be described, using the description
given by Clinton (1902), which agrees with the finding of the writers
so well that it fully covers all points.

Glomerella n. n. (Gnomoniopsis Stoneman, not Berlese). Perithecia membrana-
ceous, dark brown, spherical to flask-shaped, often rostrate, sometimes evidently hairy,
cxespitose or more or less compound and immersed in a stroma with which they often
form an evident hard cushion; asci oblong to clavate, often fugacious, aparaphysate;
ascospores hyaline, apparently eight, distichous, oblong, usually slightly curved, uni-
cellular. Permanent stage of Gloesporium-like fungi.

Glomerella rufomaculans ( Berk.) Spaulding & von Schrenk. Permanent stage devel-
oping on decayed pomaceous fruits; forming stromatic cushions (often concealed by
dark olive mycelial felt), which contain immersed and more or less compounded,
subspherical perithecia; asci subclavate, often slightly pedicellate, fugacious 55-70 ju
in length, ascospores alantoid, with evident central hyaline area chiefly 12-22 4 by
3.9-9 4. Glcesporium stage causing rotting of pomaceous fruits; sori small, develop-
ing more or less in concentric circles, usually soon rupturing and oozing out spores
in small pinkish masses; spores greenish,” chiefly oblong, unicellular, with evident
hyaline areas when fresh, 10-28 u by 3.5-7 “, but chiefly 12-16 4 by 4-5 yu.

To this must be added: The fungus forms cankers on apple limbs, bearing both
conidia and perithecia.

THE CANKER STAGE.
DISCOVERY OF THE CANKER.

The sudden appearance of the bitter-rot fungus late in the summer
and its equally sudden disappearance in the early winter have long
excited conjecture as to where the spores which affected the first apples
every year came from. Diseased apples of a previous year hanging

“The writers have dropped the hyphen from rufo-maculans in order to simplify
the name, as was done by Cooke (1885).
6 Changed by the writers. The original says ‘‘ hyaline.”’

30 THE BITTER ROT OF APPLES.

in mummified condition on the trees, or lying on the ground under the >
trees, probably served as infection centers in many instances; but in
many cases, although all mummies and diseased apples were carefully
removed during the winter, the disease reappeared in the orchard. -
Another feature explained with difficulty until recently was the fact
that even with many specimens of bitter-rotted apples of the previous
season lying on the ground under the trees, the disease first manifested
itself in the tops of the trees and very rarely on the branches nearest
the ground. In other words, it was difficult to understand how the
spores of the bitter-rot fungus got on the fruits in the tree tops from
the mummies on the ground without first infecting those on the lower
branches. It had been noted repeatedly that the disease frequently
made its first appearance on the apple tree in a cone-shaped area, with
the apex of the cone near the top of the tree. It was this observation
oft repeated which led to the discovery during the past summer of
what is probably the winter stage of the bitter-rot fungus.

On July 10, 1902, Mr. R. H. Simpson discovered peculiar depres-
sionson many branches of apple trees in his orchard at Parkersburg, Ill.
Mr. Simpson was at that time employed as an agent of the Department
of Agriculture to conduct spraying experiments looking toward the
control of the bitter rot of apples by spraying with fungicides. Mr.
Simpson had been hunting for the source of the first infection, and
early in July he noted the peculiar cone-shaped distribution of the
fruit which showed the first signs of the bitter rot. On many trees_
the grouping of the infected fruit in the cone shape was so marked
that it seemed probable that the disease had started near the apex of
the cone and had spread downward and outward. In nearly every
instance Mr. Simpson found blackened depressions of a characteristic
appearance on one or more branches at or near the apex of the cone of
infected fruit. These black depressions in the apple limbs occurred
so constantly associated with early bitter-rot infection that Mr. Simpson
proceeded at once to cut out all blackened areas which he could detect.
The blackened sunken areas in the apple limbs have the appearance of
‘*cankers,” as this term is generally understood, and they have been
called cankers since their first discovery. Mr. Simpson was able to
locate the canker in more than 95 per cent of the cases by following
up the cone of infected fruit to the apex.

On the day following Mr. Simpson’s discovery at Parkersburg,
Professors Burrill and Blair, of the University of Illinois, visited the
orchard at Parkersburg and learned of Mr. Simpson’s find. Believing
that the causal relation between the cankers and the bitter rot was
thereby established, they published a preliminary note in a circu-
lar of the Agricultural Experiment Station of Illinois, in which they

«The discovery of the apple cankers was made July 10, 1902, in the afternoon, as
indicated by a telegram from Mr. Simpson to the writers on the same day, not July 11,
as stated in Circular No. 58 of the Illinois Agricultural Experiment Station, July, 1902.

DESORIPTION OF CANKER STAGE. ol

recommended cutting out all cankers in apple orchards. This prelim-
inary circular was followed by a bulletin on the same subject, giving
illustrations of the cankers and results of experiments, showing that
bitter-rot spores occurred in the canker and that apples could be
infected from cankers.

Investigations as to the relations of the cankers and the bitter rot
were begun by the writers two days after Mr. Simpson’s discovery.
These have been continued up to the present time and will be carried
on further.

DESCRIPTION OF THE CANKER STAGE.

The cankers found on apple trees in Illinois appear as blackened
depressions on apple limbs of various sizes, from last year’s fruit
spurs to limbs 3 to 4 inches in diameter. Thus far the cankers have
not been found on the main trunk. On these limbs rounded or oblong
sooty-black sunken spots occur from one to several inches long, which
have more or less ragged edges. (See Pls. VII and VIIL.)

The entire bark is killed for a considerable distance back (Pls. VII
and VIII), and the dead bark appears cracked and fissured and in some
instances broken away. In many cankers regular transverse cracks,
caused by the drying out of the bark, are very marked. As the bark
dries out it adheres very firmly to the underlying wood. As a result
of the decrease in volume of the affected bark and cambium, a
marked flattening and final depression take place on the affected limb.
Around the dead areas a healing callous layer usually forms (Pl. VII,
fig. 1; Pl. LX, figs. 1 and 4). This starts at the edges of the dead
areas and pushes toward the center, frequently lifting the dead bark
at the edges. The appearance of this callous layer makes the cankered
spots look more and more sunken. It will be noted that most of the
cankered spots show the presence, near the center, of a small branch
or of a branch stub. There may be some relationship between the
formation of the cankered spot and a diseased fruit borne on such a
small branch in a previous year. That is, however, a mere conjecture.

On cross sections of cankers one frequently finds that at its very
center the wood has been dead for two years. (See Pl. VIII, fig. 1.)
The small hole in the wood, two rings in, shows where the small branch
broke away. This dying and breaking away of the small branch
would point to the fact just mentioned, that the canker may sometimes
start in the branch.

The wood of the branch immediately below a cankered spot is dis-
colored for a considerable distance toward the center. (See Pl. VIII,
fig. 1.) The discoloration is brown and resembles that found in many
hardwood trees in the region below a wound. The wood cells and
medullary rays in the discolored region are filled with a light brown
_ mass, readily soluble in alkalis, which leads one to class it as one of

32 THE BITTER ROT OF APPLES.

the humus compounds. It is probably one of the decomposition prod-
ucts which forms when the bark and cambium are killed and which
infiltrates the wood. One finds numerous fungous hyphe in the
medullary ray cells and the larger vessels, but at this stage it is not
possible to say whether these are hyphe of the bitter-rot fungus.
Further studies in this direction are being made.

The formation of the cankered spot probably starts at some small
wound (or branch, as stated above). The fungus begins to grow in
the living bark and kills the bark and the cambium. Asa result no
new wood is formed at the point where the cambium is killed (see PI.
VIII, fig. 1), and a small depression forms as the wood at the edges of
the dead cambium increases in thickness. As the fungus grows out
from the original point of infection, more and more bark and cambium
are killed, until at the end of the growing season a large spot on the
limb is dead.

Since BEES is always a small series of wood cells formed at the
beginning of the year during which
the attack takes place, the fungus
probably starts to grow in the bark
early in June. (See fig. 6.)

The majority of the cankers found
during the last summer probably were
started two years ago. During the
first year the fungus made very little
headway. A very small central area
was killed, generally around and in-
cluding a small branch. The following
Fic. 6.—Diagrammatic cross section of year the larger part of the canker was

ous ae formed. Whether the cankers will con-
tinue to increase in size is as yet undetermined, but it does not seem
probable, for if such were the case cankers three or more years old
ought to have been secured in the orchards where the bitter rot has
been common for many years.

RELATION OF THE CANKERS TO THE BITTER ROT.

The discovery of the cankers was brought about directly by tracing
groups of diseased apples to these sunken areas on apple limbs. The
numerous observations made by Mr. Simpson and by those who fol-
lowed him seemed to prove beyond question that the cankers were in
some way responsible for the infection of the apples. Instances were
frequent where two or more apples hung just below a canker. These
were generally badly diseased, while all ‘other apples in their immedi-
ate vicinity were perfectly healthy.

Although it seemed extremely probable from Mr. Simpson’s obser-
vations, confirmed and extended by the writers, in his orchard and

RELATION OF CANKERS TO BITTER ROT. ao

in other orchards, that a causal relation existed between the canker
on apple limbs and the bitter rot, it was by no means positively proved
that the bitter-rot fungus (Glomerella rufomaculans (Berk.) Spaulding
& von Schrenk) produced the cankers on apple limbs. Experiments
were accordingly started to determine whether any such relation
existed. Examination of the cankers showed the presence of unicel-
lular spores resembling the spores of Glomerella rufomaculans Berk.
In most cases there also occurred numerous unicellular brown spores
of a fungus which was probably Spheropsis malorum Peck. There
were spores present now and then of Zricotheciwm roseum and a species
of Alternaria, but the unicellular colorless spores (Glomerella rufo-
maculans) and the unicellular brown spores (Sphwropsis malorum) were
quite constantly present. The mere presence of spores of any one
fungus, even when constantly associated with a canker, is no proof
that the fungus producing these spores causes the cankers. It is
strong presumptive evidence, but no more. That the colorless one-
celled spores were spores of Glomerella rufomaculans was proved after
a few days by inoculating some of these spores obtained from a canker
into healthy applies. These showed unmistakable signs of the bitter rot
inafew days. (See Pl. II.) This experiment was repeated many times,
using control fruits with every culture. In every case the bitter rot
appeared in inoculated fruits, while the check fruits remained sound.
Fearing that the spores which caused the disease in these cases might
have simply rested in the bark of the cankers, numerous cultures on
apple agar were made from pustules in the bark of cankers, and from
these pure cultures of the bitter-rot fungus were obtained.

Spores from such pure cultures were inoculated into sound apples,
using control fruits, and these also produced the disease (PI. VI,
figs. 3 and 4). These cultures, repeated for several months and under
different conditions, left little doubt that the cankers on apple limbs
contained spores of the bitter-rot fungus (Glomerella rufomaculans
Berk.).

A number of tests were made to determine whether the spores
could be washed from a canker onto apples by water falling on the
cankers. The first test of this kind was made by Mr. Simpson. To
insure rapid action on the part of the fungus, he punctured an apple,
and then allowed water to run from a canker on the fruit. After
several days this apple showed unmistakable signs of the disease.

It now became a matter of considerable importance to determine
what connection, if any, existed between the bitter-rot fungus and the
cankers. It was very possible that the cankers served merely as
lodging places for the bitter-rot fungus or its spores. The presence
of numerous spores of what was believed to be Sphwropsis malorum
suggested that this fungus, which is known to form cankers on apple
limbs (Paddock, 1899 and 1900) resembling those in the Illinois

26892—No. 44—03——3

34 THE BITTER ROT OF APPLES.

orchards, might be the canker-forming fungus. This supposition
was strengthened by the fact that many of the Illinois cankers had
the sooty black appearance characteristic of the black-rot apple
cankers.

To determine whether the bitter-rot fungus (Glomerella rufo-
maculans) could form cankers, a number of trees in the Missouri
Botanical Garden were selected. Small longitudinal slits were cut
into the bark, reaching the cambium layer, two slits on every branch.
Into the upper slit spores from pure cultures of Glomerella rufomacu-
lans (made from diseased apples and from cankers) were introduced.
The second slit, from 3 to 5 inches below the first, was used as a con-
trol. <A large number of control slits were used, as it was possible for
spores flying about in the air to enter the infected slits and thereby
vitiate the results. It may be said at this point that in no case did
any of the control slits show any signs of canker formation. A num-
ber of inoculations were made, using pure cultures of Glomerella
rufomaculans obtained from apple cankers in Illinois and from
diseased apples. Inoculations were likewise made with ascospores
obtained in apple agar cultures. The first infection of apple limbs
was made July 16, 1902.

The inoculations were made by inserting a needle with spores into
the freshly made slit, or by spraying water into the slit and then
placing some spores in the drop of water. Some of the slits were
covered with grafting wax or with cloth waxed with a cocoa-butter
mixture, as it was thought that the uncovered slits might be infected
by bitter-rot spores from the air. The results showed that this pre-
caution was useless, as none ot the uncovered control slits showed any
signs of being infected:

Several weeks elapsed before there was any ev idence of develop-
ment on the limbs. In both the inoculated slits and the control slits
the bark dried somewhat along the edges of the slit, making a gaping
wound. After some two weeks a distinct callous layer had formed
under the edges of the bark of the control slits. The two callous
layers joined after six to eight weeks and occluded the wound. In
the slits where bitter-rot spores had been inserted the callous forma-
tion was less marked. The exposed wood turned dark, almost black,
and the exposed edges of the bark turned back. The living bark
then began to dry out gradually and became depressed (PI. IX, fig. 3),
and after about two months a decided sharply defined depressed area
had formed, with the slit in the center. Shortly thereafter small
black pustules broke through the dried bark in a number of instances
(Pl. LX, figs. 2,4, 5, and 6). By that time the infected points showed
all the characteristics of small cankers.

On examination the black pustules were found to contain masses
of spores resembling those of the bitter-rot fungus (Glomerella rufo-

f

RELATION OF CANKERS TO BITTER ROT. 35

maculans). At this time there were no other spores in the canker,
such as the brown Spheropsis spores. Inoculations were immedi-
ately made with the spores which had formed in the pustules of the
cankers produced on the apple limbs, using healthy apples. |

Several days thereafter these apples showed all signs of the bitter
rot, and after three days quantities of bitter-rot conidia were produced
in the characteristic manner already described. These results proved
that the fungus growing in these cankers was actually Glomerella
rufomaculans.“ Some of the more striking cases of artificial cankers
are reproduced on Plate 1X. Figures 2, 3, and 4 show artificial can-
kers, with control cuts above. Figure 5 shows one of the cankers
(fig. 4) somewhat enlarged, with numerous black pustules.

These results showed beyond question that the bitter-rot fungus
actually produces the cankers on apple limbs, and is not merely present
in cankers which are produced by some other fungus. There was no
question as to the purity of the cultures used for inoculating the apple
limbs, and as there was no growth in any of the control cuts there is
no reason for doubting that the fungus inoculated into the cuts on
apple limbs grew in the bark and formed the pustules containing spores,
which in turn produced the bitter rot in apples.

A further proof that the fungus produced the cankers was brought
forward by the discovery (by Spaulding, December 24, 1902) of peri-
thecia and asci, with ascospores (Pl. V, fig. 7)of Glomerella rufomacu-
fans, in one of the cankers artificially produced on apple limbs by
inoculating conidia of Glwosporium fructigenum Berk. into apple
limbs. Spaulding found that many of the spores in the artificial can-
kers were curved very much like the ascospores of Glomerella rufo-
maculans obtained in cultures on apple agar. The conidia and asco-
spores of this fungus look very much alike—so much so that it is not
easy to separate them with any degree of accuracy. The only differ-
ence which is‘at all evident is that the conidia are usually straight,
while the ascospores are slightly curved. (PI. V, fig. 6.) Sections of the
canker made by Spaulding showed the presence of perithecia (Pl. V,
figs. 5 and 7), most of which were empty. Several were found, how-
ever, with asci and ascospores. (PI. V, fig. 7.) It seems that the asci
in the cankers have as little permanence as do those found in cultures.
Clinton refers to the comparatively evanescent character of the asci
which he found in the cultures, and we can testify to the same state-
ment. So far as could be determined, the perithecia and asci in the
cankers were identical with those of Glomerella rufomaculans formed
incultures. Up to this writing no perithecia or asci have been reported
from the cankers on apple limbs in the orchard.

“A preliminary note announcing the proof of a causal relation between the bitter-
rot fungus (Glaosporium fructigenum Berk.) and the apple cankers was published in
Science, 16: 699, 1902.

b See Science, 17: 188, 1903.

36 THE BITTER ROT OF APPLES.

Summing up the evidence now at hand as to the causal relationship
between the bitter-rot fungus (Glomerella rufomacilans) and the
apple cankers found in certain apple orchards in Illinois and other
States, we find (1) that conidial spores of this fungus which will pro-_
duce the bitter rot in apples occur with great regularity in the cankers;
(2) that such conidial spores taken either directly from diseased apples
or from pure cultures made from cankers or diseased apples, when
inoculated into the living bark of growing apple-tree branches, will
produce apple cankers resembling those found in the orchards; (3) that
conidial spores and asci and ascospores are contained in such artificially
produced cankers, which, when inoculated into apples, produce the
bitter rot.

Taken together, these facts seem to prove beyond question that the
bitter-rot fungus can grow in apple branches, that by so doing it
forms cankers, and that after a time spores are formed in such cankers,
which produce the bitter rot in apples. |

Although this fact seems established at present, the writers are by
no means convinced that sufficient proof is yet at hand which would
warrant the statement that a// of the cankers found in the Illinois
orchards were formed by the bitter-rot fungus. The resemblance
between the canker formed by the black-rot fungus Spheropsis malo-
rum Peck on apple limbs in New York (Paddock, 1899 and 1900) and
the cankers formed in Illinois suggested at first that the latter were
formed by the black-rot fungus. This supposition was strengthened
by the almost constant presence of spores of Spheropsis malorum
Peck in the Illinois cankers. The black-rot fungus is known to form
cankers on apple limbs with great readiness, and the black rot isa
common enemy of the apple in Illinois and adjacent States. The
writers are therefore of the opinion that it is not at all improbable
that the Illinois cankers are formed in part by Spheropsis malorum
Peck. The bitter-rot fungus may get into the young Spheropsis
cankers and both fungi may grow side by side. Considerable addi-
tional work will have to be done with these cankers before their exact
identity will have been established.

SPREAD OF THE BITTER ROT.

Nearly all those who have studied the bitter rot agree that the fungus
is very erratic in its time of appearance. The disease may be prevalent
year after year in a particular part of an orchard without occurring in
other places in the same orchard or in other orchards in the immediate
locality. It has been repeatedly noted that the rot seemed to start
in one tree or a group of trees close together and that it spread from
the center to adjoining trees.

Observation showed that the rot was more likely to appear on trees
which had once had the disease than on trees previously free from it.

SPREAD OF BITTER ROT. 37

One apple grower carefully marked the trees which were affected with
bitter rot in 1900. When the rot first appeared in his orchard in 1902
(there was hardly any rot in 1901) he went over the orchard and found
that every tree marked in 1900 had bitter rot, and not only that, but
that the rot was at first confined to these trees.

Another observation frequently recorded is that the disease often
starts on a few trees and, starting from this center, it gradually
spreads year after year and finally affects the entire orchard. Mr. J. W.
Beach, of Batavia, Ark., stated a typical case:

I came to this country in 1884, and that season there were four trees in my old
orchard affected. * * * For the last three years the disease has steadily increased,
so that this year (1887) my old orchard of seventy-five trees will not yield 25 bushels
of sound apples.

This apparently erratic behavior of the bitter rot can be explained
in part since the discovery of the canker stage of the fungus. After
its introduction into an orchard or on one tree the fungus attacks one
or more branches, probably early in the summer, and produces a
canker. The next year the spores from this canker will be washed
down on the ripening fruit by a rain. The water is sprayed from
the branch on which the canker is situated to the lower branches in
the form of a cone, and one or more spores will probably fall on every
apple within such a cone.

The presence of the winter stage of the fungus will explain why
the rot is apt to recur on the trees affected the year before with the
bitter rot, and also why the disease should first appear on such trees.
The cankers produce spores early in the season, and from the trees
which have cankers the disease spreads to neighboring trees.

The bitter rot is apt to appear in virulent form only once in two or
three years. During the intervening periods there may be little or no

rot in any one region. This may possibly be caused by weather con-

ditions generally unfavorable to the fungus, as was the case in the
summer of 1901, but 1t may also be due to conditions unfavorable to
the growth of he fungus in the cankers.

The exact agndtition: which favor the development of the bitter-rot
fungus on the branches are not known as yet, but it is conceivable that
these might be such as would retard its growth in the canker to such
an extent that few or no spores would be found during one year.

That the spores of the bitter-rot fungus are spread to the fruit from
the cankers in the tree now seems proved beyond doubt. The dissemi-
nation of spores from the cankers probably begins early in summer
and continues until the apples are fully grown. :

Another source of infection is found in the dried mummies hanging
on the trees and lying on the ground under the trees. The diseased
apples of one season either fall to the ground (which most of them do)
or they remain on the trees, where they dry and shrivel up. When

38 THE BITTER ROT OF APPLES.

examined in the spring many of these mummified fruits are found to
contain spores of the bitter-rot fungus in quantity. Inoculations made
by us with such spores have shown them to be fully capable of remain-
ing alive over winter and of producing the disease in July and August
otf the following year.

It was formerly supposed that the fungus passed the winter in the
mummies, but as most of these were on the ground it was difficult to
understand how the apples high up in the trees became infected. It
now seems probable that the mummies play a comparatively small
part in serving as distributing points for spores from year to year.

After the fungus becomes started on a number of fruits it spreads
to neighboring apples and trees with great rapidity. The sticky
nature of the spore masses precludes any theory of wind distribution.
The spores are never dustlike, so that they could be blown about, but
are generally stuck together, forming a sticky, paste-like mass. Rain
and dew play an important part in distributing the spores.

Numerous small insects which frequent apple trees in the late sum-
mer, such as members of the genus Drosophila, probably carry the
bitter-rot spores from one tree to another. Clinton (1902) proved
that this was actually the case by placing some of these flies on sound
apples and thereby producing the disease.

REMEDIAL MEASURES.

Although the bitter rot has been so destructive to apple crops for thirty
years or more, little if any headway had been made until recently
toward combating it successfully. The disease may still be regarded
as one of the most difficult ones to control, although it now seems
probable that greater success ought to attend preventive measures,
These may now be placed under these heads:

1. Removal of diseased fruits and mummies.

2. Removal of limb cankers.

3. Spraying with fungicides.

REMOVAL OF DISEASED FRUITS AND MUMMIES.

Apples affected with bitter rot generally fall from the trees during
the later stages of the disease. In many cases the spores in these rotted
apples will live through the winter, and may be carried to sound
fruits the following season. Such apples as do not fall dry up and
hang on the trees all winter in a mummified condition. The next
year the spores formed in these mummies may infect sound fruits.
All diseased fruits on the ground should be carefully collected as soon
as they fall; they should be removed from the orchard and destroyed
either by drying and subsequent burning or by burying them in a
deep trench, which is carefully covered with soil afterwards. Under

REMOVAL OF CANKERS. 39

no circumstances should the rotted fruits be allowed to remain lying
on the ground under the trees through the winter.

Dried apples on the trees should be picked and burned as soon after
the fall of the leaves as possible.

Where the bitter rot appears in an orchard
at isolated points it will oftentimes pay to
watch the trees where the trouble first shows
itself and to pick every fruit showing the
slightest sign of disease. In that way the
chance of having the disease spread to adjoin-
ing trees will be materially lessened.

REMOVAL OF LIMB CANKERS.

It seems well established now that one of
the principal sources of infection of the ripen-
ing apples is to be found in the cankers on
apple limbs. ‘These cankers should accord-
ingly be removed and burned wherever they
are found, no matter where the affected limb
may be. It is often a difficult matter to find
these cankers on large trees, and a good deal of patience is necessary
to locate them. In cutting out the cankers the whole limb should be
sawed off some distance below the cankers. Where the branch is a
large one the diseased portion may be cut out without cutting off the
entire limb. The best time for cutting out
the cankers is during the late fall and dur-
ing the winter. The cankers can be located
most readily when there are no leaves on
the trees. In cutting off limbs which have
cankers on them, the same rules which hold
for pruning branches should be observed.
Small branches may be cut off with a saw
at one cut. Two cuts should be made for
larger branches, the first one on the under
side, the second on the upper side, so as to
prevent tearing off large areas of bark.
(See figs. 7 and 8.)

All cut surfaces should be carefully
trimmed, and after that they should be
coated with some antiseptic substance, such
as white lead paint or ordinary coal tar. The coal tar should be
applied with a brush, and if too thick, it may be warmed. It is
believed that by carefully removing and destroying all cankers the
damage from bitter-rot infection will be very materially lessened.

Fic. 7.—How to cut off a large
limb.

Fic. 8.—Method of cutting a large
limb which should be avoided.

40 THE BITTER ROT OF APPLES.

SPRAYING WITH FUNGICIDES.

Prior to 1887, at a time when the bitter rot had already a wide dis-
tribution, no attempts seem to have been made to control the disease.
Galloway said (1887): *‘ With our present limited knowledge of its hab-
its, it is impossible to suggest means for combating it.” Two years
later the same writer suggested spraying the fruit trees with sulphuret
of potassium when the apples were about half grown, and repeating
the operation every two or three weeks throughout the summer. In
a brief note during the same year (1889) Galloway referred to some
experiments made by Beach in 1888 with sulphuret of potassium, in
which he stated that ‘‘ Mr. Beach has full confidence in the remedy.”
Galloway (1889) reported some tests made with potassium sulphide and
ammoniacal copper carbonate by Curtiss. A good many apples were
saved by the spraying, little difference being noted in the results
accomplished by the use of the two solutions mentioned.

Chester (1890) sprayed with potassium sulphide, liver of sulphur,
and ammonium copper carbonate without decided success.

Garman (1894) published an account of a series of experiments to
control diseases of apples with Bordeaux mixture. In his general sum-
mary he states:

The proportion of rotting to nonrotting apples was in every case lessened by spray-
ing, and we are in a position to say, asa result of these experiments, that spraying
with Bordeaux mixture will save from rotting from 74 per cent to 31% per cent of the

whole number of apples. * * * Thespraying increased the yield of usable apples
from a little less than twofold to nearly sevenfold.

From the beginning of the nineties to the present time a number of
experiments in spraying have been made by several persons, notably
Alwood (1892, 1894), Stinson (1892, 1894, 1896, 1901, and 1902),
Whitten (1895), Clinton (1902), Staubenrauch (1902), Burrill and Blair
(1902, a and b).

Without going into details, it may be said that the results reached
were favorable in some cases, but not so successful In others.
Alwood (1894) states:

Our results with Bordeaux mixture and ammonia copper carbonate, as recom-
mended in bulletins mentioned above, are very satisfactory.

Whitten (1895) says:

Bitter rot began first on unsprayed trees and developed more extensively than on
sprayed trees. Bitter rot was less on trees sprayed with the 6-pound solution (of
Bordeaux mixture) than on those sprayed with the weaker solutions.

Stinson (1896) says:

There was much less bitter rot on the sprayed fruit than on the unsprayed. From
the results obtained it was concluded that the injury can be partly prevented with
three sprayings with Bordeaux mixture.

From a careful study of the results obtained up to 1900, it was
evident that, although it had been shown that the disease could be

f

SPRAYING WITH FUNGICIDES. 41

checked by spraying, there was much conflicting evidence at hand and
a great many unanswered questions. Most of the experiments made
were conducted for one year only. Many involved only a few trees,
and many others were conducted under unfavorable conditions.

The bitter rot is a disease which has always appeared with varying
virulence from year to year, sometimes destroying whole crops, then
again attacking only a few apples. It has likewise made its appearance
inadjoining orchards at different times in the same year. It is therefore
almost impossible to draw any definite conclusions from experiments
extending over one year only. Spraying in early summer may in
some years check the disease should it appear only a few weeks after
the spraying, while spraying at exactly the same time the next year,
when the disease appears late in September, may have absolutely no
effect. In order to be of value for a disease dependent upon so many
varying factors as is bitter rot all spraying experiments must be con-
ducted under exactly the same conditions in the same localities for a
series of years without interruptions. Isolated tests may be and doubt-
less are of value in indicating what may be expected, but they are at
best simply single instances, the results of which can by no means be
taken as conclusive. Realizing that such was the case, a comprehen-
sive plan for conducting spraying operations was drawn up by Mr.
Waite of the Bureau of Plant Industry, U.S. Department of Agri-
culture, in the winter of 1900-1901, and this plan was carried out for
two years in Virginia, Illinois, and Missouri, one year in cooperation
with the Illinois Agricultural Experiment Station.“ This plan was
stated as follows: The object of this experiment is to answer the fol-
lowing questions: (1) Can Bordeaux mixture by proper spraying be
made to protect apples from bitter rot? (2) Is winter treatment of
the dormant trees of any assistance in the process? (3) Is early
spraying more advantageous than late spraying in the treatment of
this disease? (4) Are any other fungicides superior to Bordeaux
mixture in the treatment of this special malady? To answer these
questions the following plan was followed. The parts of the orchards
experimented in were laid off in five plats, which were sprayed as
follows:

Plat 1. Winter spraying only.—Spray plat and duplicate with Bor-
deaux mixture before the buds swell, applying the spray until the
trunk and buds are blue. In duplicates, with controls.

Plat 2. Combined winter and spring spraying.—First treatment,
winter spraying before buds push; second treatment, when cluster
buds are open and flower buds exposed; third treatment, when the
last of the petals are falling; fourth treatment, seven to ten days later.
In duplicate, with controls.

@This plan was described in Circular No. 43 of the Illinois Agricultural Experi-
ment Station.

42 THE BITTER ROT OF APPLES.

Plat 3. Early spraying without the winter treatment.—Same as above,
with first treatment left off; that is, second, third, fourth, and fifth
sprayings.

Plat 4. Early spraying continued until summer.—Second, third,
fourth, and fifth sprayings, with four or five more treatments at inter-
vals of two weeks until about the middle of August.

Plat. 5. Late spraying.—Begin when the fruit is about an inch in
diameter and spray four or five times. These sprayings may be on
the same dates as the last four or five treatments of plat 4.

Before giving the results obtained from the spraying in Missouri
and Illinois, it may be well to state that the bitter rot appeared ina
comparatively ight form during both years in which the experiments
were made. The experiments illustrate once more the necessity of
carrying on tests of this character for a long period of years under
the same or similar conditions as previously stated. In view of the
fact that the attack of the disease for the past two years was a light
one in some of the orchards experimented in, the conclusions reached
must be considered as preliminary ones which simply go to swell the
number of isolated results of spraying operations already referred to.

Replying to the questions which are enumerated above, the follow-
ing general answers may be given at this time:

(1) Can Bordeaux mixture, by proper spraying, be made to protect
apples from bitter rot?—To a certain extent, varying from 10 to 75
per cent, Bordeaux mixture surely does prevent the ravages of the
bitter rot. The extent to which it will do so will depend largely on
the following factors:

(a) Making the Bordeaux mixture.—Although the literature dealing
with the making of this fungicide is voluminous, there is still much of
it made in an improper manner. The standard Bordeaux mixture,
i. e., 6 pounds of copper sulphate, 4 pounds of lime, and 50 gallons of
water, is still preferable. The copper sulphate should be dissolved in
one vat; the lime in another. Only freshly slaked lime should be
used, and the slaking should be brought about with small quantities
of water added from time to time, so as to get an even slaking. The
solutions of copper sulphate and of lime should be diluted separately
and then both should be run simultaneously into a third tank. A
very convenient arrangement which can be constructed anywhere is
shown in figure 9. The two smaller tanks are elevated on a rough
platform, high enough above the third tank to allow the solution to
be turned readily into the latter. This third tank in turn is elevated:
sufficiently to allow the finished Bordeaux mixture to run into the
tanks on the spraying wagon without pumping. Such an arrange-
ment can be built at the edge of the pond or well, from which the
water for the spraying mixture is obtained. A force pump drives the
necessary water into the upper smaller tanks. Great care should be

f .

SPRAYING WITH FUNGICIDES. 43

taken in weighing the proper amount of chemicals. The custom of
guessing at the amounts invariably results in a poor mixture. Stock
solutions of the copper sulphate, 1 or 2 pounds to the gallon, can be
made and kept without deterioration, evaporation being considered.
(b) On the thoroughness with which spraying ts done.—Only nozzles
which throw a fine spray should be used. The Vermorel is the stand.
ard nozzle for good work. In spraying, the old precept that all parts
of a tree should be reached by the spray holds good. With a fungus
like that of the bitter rot, where a large number of spores may reach
a fruit, thorough spraying alone will be effective. The apparent
failure to control the bitter rot in many instances is doubtless due to
the fact that even with the best spraying it is impossible to cover the

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entire fruit with the fungicide. Numerous fruits were found on
sprayed trees where the fungus had started to grow between points
on the fruit covered with the fungicide. It is very desirable that
further information concerning the number of sprayed fruits actually
rotted be obtained. —

(2) Ls winter treatment of the dormant trees of any assistance in the
process?—The spraying of trees before the buds opened showed no
apparent benefit. This, however, ought not to be taken as conclusive,
especially in view of the recent discovery of a stage in the life history
of the bitter-rot fungus in the wood and bark of the apple tree. In
the absence of any data as to the exact time when this bark stage—the
canker—is reached, it may be that winter spraying will to some extent
check the development of possible cankers.

44 THE BITTER ROT OF APPLES.

(83) Ls early spraying more advantageous than late spraying in the
treatment of this disease?—No evidence was obtained from the exper-
iments calculated to prove that early spraying is more advantageous
than late spraying. The later sprayings—that is, those made after the
apples were half formed—in our estimation were the most effective.
The early spraying resulted in a severe rusting of the fruit during one
year. The tissues of the young fruits developed very slowly under
the spots where the fungicide covered the epidermis, and rusted and
misshapen fruits resulted in many cases. Thick-skinned varieties like
the Ben Davis showed this rusting to a marked extent. The exact
explanation for this rusting as a result of spraying with Bordeaux
mixture is still to be determined.

(4) Are any other fungicides superior to Bordeaux mixture in the

our tests go, certainly superior to any of the other fungicides used,
i. €., ammonium copper carbonate and potassium sulphide.

Summing up the evidence from our own spraying operations as
well as those of others, the following recommendations can be made
at this time:

(1) For spraying to prevent bitter rot use the standard Bordeaux
mixture, 1. e., 6 pounds of copper sulphate, + pounds of lime, and 50
gallons of water.

(2) Spray at least once before the buds open. This spraying of the
trunks and branches should be thorough, so as to reach any possible
spores about to form cankers or coming from cankers.

(3) Spray during the middle of the summer, beginning about the mid-
dle of June, and continue several times until the fruit is almost ripe.
Should the attack come very late in the summer, use the ammonium
copper carbonate, so as to avoid damaging the fruit for the market,
because of a possible lime deposit from the Bordeaux mixture.

In addition to these sprayings aimed especially at bitter rot, it is
necessary to spray with Bordeaux mixture to which Paris green or
some arsenical poison has been added just after the petals have fallen
and again ten days to two weeks later. This is directed against apple
scab, codling moth, and leaf-eating insects, as well as bitter rot and
leaf blight.

SUMMARY AND RECOMMENDATIONS.

The facts presented in the foregoing pages may briefly be summarized
as follows:

(1) The bitter rot or ripe rot is one of the most serious diseases of
apples. The loss due to this disease in 1900 was estimated (for the
United States) as $10,000,000. It is one of the most difficult diseases
to control and is constantly on the increase. i

(2) The bitter rot is due to a fungus, Glomerella rufomaculans (Berk.)

f

SUMMARY AND RECOMMENDATIONS. 45

Spaulding & von Schrenk, hitherto generally known as Gla@osporiwm
Sructigenum Berk.

(3) This fungus until 1902 was known only in its conidial stage on
pomaceous fruits .and grapes. The perfect or ascus stage has since:
been discovered both in cultures on fruits and in artificial cankers on
the apple limbs.

(4) The fungus attacks ripening apples during July and August,
and is most virulent during moist, hot summers. It is most active on
apples in the belt of States on the line of the Ohio River, from Virginia
on the Atlantic Ocean to Oklahoma in the West, and southward. (See
fol)

(5) During the past summer canker-like areas were discovered on
apple limbs from which the disease seemed to spread. These cankers
generally occurred in the upper parts of trees and contained spores of
the bitter-rot fungus, as proved by direct inoculations into apples.

(6) Inoculations into healthy apple limbs of bitter-rot spores from
pure cultures of the bitter-rot fungus (made both from diseased apples
and cankers) resulted in the formation of cankers similar to those
found in the orchards. Spores from these cankers produced the bitter
rot in sound fruits. This proves beyond doubt that the bitter-rot
fungus is the cause of the cankers on apple limbs in the orchard.

(7) The spores of the bitter-rot fungus are washed from the cankers
onto the apples below the cankers. Spores are carried from tree to
tree by insects, and possibly by raindrops.

(8) One of the best methods for combating this disease will consist
in carefully cutting out all cankers during the winter. These should
be burned at once. All diseased apples on the ground or in the tree
should be collected and destroyed. As a further precaution, trees
should be sprayed with standard Bordeaux mixture at least once before
the buds open, and again frequently from midsummer until the fruits
are almost ripe.

INDEX TO LITERATURE.
[All the papers in this list were consulted in the library of the Missouri Botanical Garden, St. Louis.]

1892. Autwoop, W. B. Bitter Rot. Bulletin Virginia Agricultural Experiment
Station, 17 :61-62, 65.

1893. Bitter Rot of Apples. Southern Planter, July: 414-416, and 2
plates.

1893. - Bitter Rot (Gleosporium fructigenum). Bulletin Virginia Agricul-
tural Experiment Station, 24:24.

1894. Ripe Rot or Bitter Rot of Apples. Bulletin Virginia Agricultural

Experiment Station, 40 :59-82.

1892. Arkinson, G. F. Gleosporium fructigenum. Bulletin Cornell Agricultural
Experiment Station, 49 :313.

1897. Gleosporium fructigenum Berk. Cornell Science Bulletin, 3, No. 1, 36.

1898. Barnes, W. H. The Kansas Apple.

1897. Beat, W. J. Bitter Rot, Ripe Rot, or Anthracnose. Proc. Michigan Horti-
cultural Society, p. 178.

1854. BerKeiety, M. J. Septoria rujo-maculans. Gardeners’ Chronicle, p. 676.

1856. Gleosporium fructigenum. Gardeners’ Chronicle, p. 245.

1859. Gleosporium leticolor. Gardeners’ Chronicle, p. 604.

1860 (1). Ascochyta rufomaculans. Outlines of British Fungology, p. 320.
1860 (2). Gleeosporium fructigenum. Outlines of British Fungology, p. 245.
1860 (3). Gleosporium lexticolor. Outlines of British Fungology, p. 325.
1871. Gleosporium lxticolor. Gardeners’ Chronicle, pp. 1159-1140, 1162-

1163.

1874. BerKetefy, M.J.,and M. A.Curtis. Gleosporiwm versicolor B. & C. Notices
of North American Fungi, Grevillea, 3:15.

1888. Beriese, A. N. Ascochyta rufo-maculans Berk. Nuovo Giornale Botanico
Italiano, 20 :441. :

1892. Gnomoniopsis n. gen. Icones Fungorum., Vol. 1, Fas. 3, p. 93.

1901. Bracxert, G. B. Bitter Rot. Yearbook of U. 8. Department of Agricul-
ture, p. 604.

1889. Brirron, N. L. Gleosporium versicolor B. & C. Report of State Geologist of
New Jersey, 11: 590.

1902. Britron, W. E. Bitter Rot of Apples in New Hampshire. Private Letter.

1908. Brirron, W. E., and G. P. Crinron. Bitter Rot. Bulletin Connecticut
Agricultural Experiment Station, 142 (Spray calendar).

1902a. Buatr, J. C. See Burrill, T. J. 1902 (a).

1902b. —, See Burrill, T J.1902 (b):

1902a. Burritt, T. J.,and J.C. Buatr. Prevention of Bitter Rot. Circular Illinois

Agricultural Experiment Station 58: 1-3.
Bitter Rot of Apples. Bulletin Illinois Agricultural Experiment
Station, 77: 351-366.

1902. Burritt, T. J. Bitter Rot of Apples. Science, 16: 909.

1890. Cuester, F. D. Experiment in the Treatment of Bitter Rot of the Apple.
Report Delaware Agricultural Experiment Station, 3: 78-79.

19025.

L893. The Ripe Rot or Anthracnose of Tomato. Report Delaware Agri-
cultural Experiment Station, 6: 111-115, and diagram.
L895. Ripe Rot of Apples. Bulletin Delaware Agricultural Experiment

Station, 29: 24.
46

1901.
1890.

1902a.
1902b.

1903.
1871 (

INDEX TO LITERATURE. 47

Cuester, F. D. See Sanderson. 1901.
CuurRcHILL, G. W. Bitter Rot. New York (Geneva) Agricultural Experi-
ment Station Report, p. 325.
Cunton, G. P. Bitter Rot. Bulletin Illinois Agricultural Experiment
Station, 69: 193-211, and 39 figs.
Gnomoniopsis fructigena n. n. Bulletin -Illinois Agricultural
Experiment Station, 69: 111, 206-211, and 6 figs.
See Britton, W. E. 1903.
1). Cooxn, M. C. Gleosporium fructigenum Berk. Handbook of British
Fungi, 1: 474.

1871 (2). Gleosporium leticolor Berk. Handbook of British Fungi,
1: 474, No. 1410.

1885. Ascochyta rufomaculans Berk. Grevillea, 14: 76, No. 460.

1886 (1). ———. Gleosporium fructigenum Berk. Grevillea, 14 : 124, No. 623.

1886 (2). ———. Gleosporium leticolor Berk. Grevillea, 14: 124, No. 624.

1892. ——_. Gleosporium fructigenum Berk. Handbook of Australian Fungi, p.
363.

1900. Corserr, L. C. Bitter Rot (Gleosporium fructigenum). Bulletin West Vir-

1893.

1890.

+

1867.

1874.
1892.
1892.

1897.
1898.

1899.
1885.
1885.
1891.
1888 (
1888 (
1896 (
1896 (
1896 (

1887.

1889a.

ginia Agricultural Experiment Station, 66 : 200-202.

Craic, Mossrs. Bitter Rot or Bird’s-eye Rot (Gleosporium fructigenum
Berk). Bulletin Oregon Agricultural Experiment Station, 27 : 22.

Curtiss, G. G. Treatment of the Bitter Rot of the Apple. Bulletin of Sec-
tion of Vegetable Pathology, U. 8. Department of Agriculture, 11 : 38-41.

Curtis, Rey. M. A. Gleosporium versicolor B. & C. Geological and Natural
History Survey of North Carolina. Botany (Containing a Catalogue of the
Indigenous and Naturalized Plants of the State), p. 126.

See Berkeley, 1874.

Davis, J. J. Gleosporium fructigenum Berk. A Supplementary List of the
Parasitic Fungi of Wisconsin. Trans. Wisconsin Academy of Science,
9 : 169, No. 340.

DancEARD, P. A. ©. Gleosporium fructigenum Berk. Les maladies du
Pommier et du Poirier. Le Botaniste, 3 : 66-67.

Ear.e, F. 8. See Underwood, 1897.

Summer Rots. Bulletin Alabama Agricultural Experiment Station,
98 : 266.

—.. Summer Rots. Bulletin Alabama Agricultural Experiment Station,
106 : 164.

Evuis, J. B. & B. M. Evernartr. Gleosporvwm versicolor B. & C. The
North American Species of Gleosporium. Journal of Mycology, 1 : 109.

EVvERHART, B. M. See Ellis, 1885.

FarrcuiLp, D. G. Grape Gloeosporium. Journal of Mycology 6:99.

1). Farrow, W. G. & A. B. Seymour, Gleosporium versicolor B. & C. A

Provisional Host Index of the Fungi of the United States, p. 41.

2). Gleosporium fructigenum Berk. A Provisional Host Index of
the Fungi of the United States, p. 41.
1). Frank, A. B. Gleosporium fructigenum Berk. Die Pilzparasitiiren

Krankheiten der Pflanzen, p. 379, No. 41 (c).

2). Gleosporium leticolor Berk. Die Pilzparasitiren Krankheiten
der Pflanzen, p. 379, No. 42 (a).

3). Gleosporium versicolor B. &C. Die Pilzparasitaéren Krankheiten
der Pflanzen, p. 379, No. 41 (d).

GaLLoway, B. T. Bitter Rot of the Apple. Report of the U. S. Depart-

ment of Agriculture, pp. 348-350.
Sulphuret of Potassium for Bitter Rot of the Apple. Journal of
Mycology, 5 : 37-38.

48

THE BITTER ROT OF APPLES.

1889). Gatioway, B. T. Bitter Rot of the Apple. Report U. 8. Department of

1889c.
1890.
1896.
1902.
1889.
1890.
1893.
1894.
1895.
1899.

1900.

1892da.

Agriculture, pp. 412-413.
Bitter Rot of Apples. Bulletin of Section of Vegetable Pathology,
U.S. Department of Agriculture, 8:61.
——. Ripe Rot of Grapes and Apples. Gleosporium fructigenum Berk.
Report U. S$ Department of Agriculture, p. 408.
Bitter Rot. Farmers’ Bulletin, U. S. Department of Agriculture,

oie

Bitter Rot. Report of the Secretary of Agriculture, Departmental
Reports, p. X VIII, 51, 65.

GarMAN, H. The Bitter Rot Fungus of the Apple ( Gleosporium versicolor).
Report Kentucky Agricultural Experiment Station, 2:43-45, and 2 figs.

. (Gleosporium) Rot Fungus, Report Kentucky Agricultural Experi-

ment Station, 3: 185.

. Gleosporium versicolor. Bulletin Kentucky Agricultural Experiment

Station, 44: 3-24, 30-31, and 2 figs.

. Apple Rot. Bulletin Kentucky Agricultural Experiment Station,

50:35, and Report 7:35.

. Apple Rot ( Gleosporium versicolor). Bulletin Kentucky Agricultural
Experiment Station, 59: 127.

GREEN, SerBy & Wesster. Bitter Rot of Apple. Bulletin Ohio Agricultural
Experiment Station, 102. (Spray calendar. )

Hau, F. H. See Stewart, 1900.
Hatstep, B. D. The Apple and Pepper Fruit Rot. American Agricul-

turist, p. 337, and 2 figs.

1892). . Apple Bitter Rot or Ripe Rot. Report New Jersey Agricultural
Experiment Station, p. 338.
1892c. . Anthracnoses of Solanaceous Fruits. Report New Jersey Agricul-
tural Experiment Station, pp. 330-383, and 1 fig.
1892d. . Secondary Spores in Anthracnoses. New Jersey Agricultural
Experiment Station Report, pp. 303-306. ;
1892e. . Laboratory Study of Fruit Decays. Report New Jersey Agricultural
Experiment Station, pp. 326-330, and 1 diagram.
18927. . Rot of Quinces. Report New Jersey Agricultural Experiment Sta-
tion, pp. 316-317, 324.
1892y. —. The Ripe Rot of Quinces. Bulletin New Jersey Agricultural Experi-
ment Station, $91: 11-12, and 2 figs. ;
1893u. Decay in the Apple Barrel. Popular Science Monthly, May:
76-84. .
1893). Gleosporium fructigenuum Berk. Report New Jersey Agricultural
Experiment Station, pp. 373-374.
1893c¢. A Study of Solanaceous Anthracnoses. Bulletin Torrey Botanical
Club, 20: 109-112. ;
1894. Ripe Rot. Report New Jersey Agricultural Experiment Station,
p- 324.
1896. The Ripe Rot of Quinces ( Gleosporium fructigenum Berk. ), in W.W.
Meech’s Quince Culture, pp. 155-157.
1898. Starch Distribution as Affected by Fungi. Bulletin Torrey Botan-
ical Club, 25:571-575.
1902. Anthracnose of Fruit or Ripe Rot ( Glwosporium fructigenum Berk.).
Report New Jersey Agricultural Experiment Station, p. 421.
1890. Jennines, H. 8. Bitter Rot of Apple. Bulletin Texas Agricultural Experi-

1894.

ment Station, 9:25.
Kerrer, C. A. Bitter Rot. Bulletin Missouri Agricultural Experiment Sta-
tion, 27:13,

INDEX 10 LITERATURE. 49

1894. Kinney, L. F. The Ripe Rot or Bitter Rot. Report Rhode Island Agricul-
tural Experiment Station, pp. 193-195.
1890. KrrcHNER, Oskar. Gleosporium leticolor Berk. Die Krankheiten und
Beschidigungen unserer landwirtschaftlichen Kulturpflanzen, p. 436.
No. 339.
1900. Lamson, H. H. Bitter Rot on Apples. Bulletin New Hampshire Agricul-
tural Experiment Station, 79: 26.
Bitter Rot (Gleosporium fructigenum).
Agricultural Experiment Station, 93:76.
1900 (1). Lirypau, G. Gleosporium fructigenum Berk., in Engler u. Prantl, Die
Naturlichen Pflanzenfamilien, 1, pt. 2 : 399-400.
Gnomoniopsis, Stoneman, in Engler u. Prantl, Die Nattirlichen
Pflanzenfamilien, 1, pt. 2 : 543.
1894. LopEman, E.G. Ripe Rot on Grapes. Bulletin New York (Cornell) Agri-
cultural Experiment Station, 76: 448.
Bitter Rot, Ripe Rot. The Spraying of Plants, pp. 240-241 and

1902.

Bulletin New Hampshire

1900 (2).

1899.

acteg,

1892 (1). Lupwic, F. von. Gleosporium fructigenum. Lehrbuch der niederen
Kryptogamen, p. 294.

1892 (2). Gleosporium leticolor Berk. Lehrbuch der niederen Krypto-
gamen, p. 294.

1892. Masser, G. Gleosporiwm lexticolor. Gardeners’ Chronicle (new series), 12:

D287.
1893. Gleosporium Jexticolor. Gardeners’ Chronicle (new series), 18 : 755.
18930). - Gleosporium leticolor. Gardeners’ Chronicle (new series), 14: 48,
75, 503.
1893c. ~Gleosporium fructigenum Berk. Gardeners’ Chronicle, 14 (new

series) : 568.

Bitter Rot of Apples. Gardeners’ Magazine, February 26, p. 1380.

Gleosporium fructigenum Berk. Text-book of Plant Diseases, pp.
281-284 and 1 fig.

1895 (1). McAupinge, D. Gleosporium fructigenum Berk. Systematic Arrange-
ment of Australian Fungi, pp. 176-177, No. 2127.

1895 (2). Gleosporium versicolor B. & C. Systematic Arrangement of
Australian Fungi, pp. 178-179, No. 2138.

1893. McCarrny, G. Bitter Rot. Bulletin North Carolina Agricultural Experi-
ment Station, 92 : 88-89, 116.

1901. Monr, Cuaries. Gleosporium fructigenum Berk. Plant Life of Alabama
(issued as Vol. 6 of the Contributions from the National Herbarium and
also as a Report of the Alabama Geological Survey), p. 250.

1902. Morse, F. W. Bitter Rot (Gleosporium fructigenum). Bulletin New Hamp-
shire Agricultural Experiment Station, 98 : 76.

1870. Murray, C. H. Bitterrot. Transactions Illinois Horticultural Society (new
series), 4: 346.

1901. Norron, J. B.S. Bitter Rot (Gleosporium fructigenum Berk.). Report of
Maryland State Pathologist, p. 30.

1896. NY¥pet, Paut. Gleosporium fructigenum Berk. Les Champignons Nuisibles
aux Plantes cultivées, pp. 76-77, No. 81.

1901. Orton, W.A. Bitter Rot. Yearbook U.S. Department of Agriculture, p. 669.

1893. Peck, C. H. Gleosporium fructigenum. Report New York State Museum,
46:11.

1902. Ricker, P. L. Gleosporium versicolor B. and C. A Preliminary List of Maine
Fungi, p. 29.

26892-—No. 44—08

1898.
1899.

4

50
1900.
1875.

1881.
1884 (
1884 (

THE BITTER ROT OF APPLES.

Rours, F. M. See Stewart, 1900.

Saccarpo, P. A. Gleosporium fructigenum Berk. Fungi Veneti, series 5;
Nuovo Giornale Botanico Italiano, 7:202.

Gleosporium fructigenum Berk. Fungi Italici, No. 1042.

Ascochyta rufo-maculans Berk. Sylloge Fungorum, 3:395.

i).

2). ——. Gleosporium fructigenum Berk. Sylloge Fungorum, 3:718.

1884 (3). ———. Gleosporium lxticolor Berk. Sylloge Fungorum, 3:718.

1884 (4).

1902.
©1901.

1902.
19038«a.
19035.
1887.
1890.
1897.
1898.
1899.

1888.
1899.

1886.

1890.

1891.

1902.

1903.

1897.

1895.

1900.

1892.

1894.

1896.

1901.

1902.

1898.

1898.

Gleosporium versicolor B. and C. Sylloge Fungorum, 3:718.

Gnomonopsis n. gen. Stoneman. Sylloge Fungorum, 16:352-354.

SanpErson, E. D., and F. D. Cuester. Bitter Rot of Apple. Bulletin Dela-
ware Agricultural Experiment Station, 50. (Spray calendar. )

Scorenk, H. von, and P. Spautprnc. The Bitter Rot Disease of Apples.

Science, n. s., 16:669-670.
———. The Bitter Rot Disease of Apples. Science, n. s., 17:188.
The Bitter Rot Fungus. Science, n. s., 147:750-751.
Scripner, F. L. Gleosporium fructigenum Berk. Report U. 8. Department
of Agriculture, pp. 324, 325, 348-350.
——. Bitter Rot of Apples. Fungus Diseases of the Grape and Other
Plants, p. 82.

Secpy, A. D. Bitter Rot. Bulletin Ohio Agricultural Experiment Station,
79: 134-156.

Gleosporiuin leticolor Berk. Bulletin Ohio Agricultural Experiment

Station, 92: 225.

See Green, 1899.

Srymour, A. B. See Farlow, 1888.

SwirH, Erwin F. Wilt Disease of Cotton, Watermelon, and Cowpea. Bul-
letin No. 17, Division of Vegetable Physiology and Pathology, U.S. Depart-
ment of Agriculture.

Smita, W. G. Gleosporium leticolor. Gardeners’ Chronicle 26:53 (n. s.)._

-. Spot on Grapes. Gleosporium leticolor. Gardeners’ Chronicle, n. s.,

NOONE

eo E. A. Ripe Rot of Grapesand Apples. Journal of Mycology,
§:164-173, 1 plate.

SpauLpine, P. See von Schrenk, 1902.

See von Schrenk, 1903.

SprscHNEW, N. N. Gileosporium leticolor Berk. Les Parasites Vegetaux de
la Cakhetie. Arb. Tiflis bot. Gart., 2:242.

Srarnes, H. N. Ripe Rot. Gleosporium fructigenum. Bulletin Georgia
Agricultural Experiment Station, 28:282-283.

Stewart, Rours, and Haru. Bitter Rot. Gleosporium fructigenum. Bulletin
New York (Geneva) Agricultural Experiment Station, 191:297.

Srrnson, J. T. Bitter Rot. Bulletin Arkansas Agricultural Experiment
Station, 21:49-52.

Bitter Rot. Bulletin Arkansas Agricultural Experiment Station,

26:33-44.

Bitter Rot. Bulletin Arkansas Agricultural Experiment Station,

39:17.

Preliminary Report on Bitter Rot or Ripe Rot of Apples. Missouri

State Fruit Experiment Station Bulletin, 1:3-21.

Notes on Spraying for Bitter Rot. Missouri State Fruit Experiment
Station Bulletin, 2:3-20.

SroneMAN, Bertua. Gleosporium fructigenum Berk. Botanical Gazette,
26: 71-74. .

Gnomoniopsis n. gen. Botanical Gazette, 26: 99-101, 113-114.

f

INDEX TO LITERATURE. Sak

1902. SruspenraAucH, A. V. Field Work with Bitter Rot During 1901. Circular
Ulinois Agricultural Experiment Station, 43: 1-27.

1892. Srurais, W. C. Ripe Rot or Bitter Rot. Bulletin Connecticut Agricultural
Experiment Station, 111: 5.

1893. Ripe Rot or Anthracnose (Glwosporium. fructigenum Berk., Gleo-
sporium versicolor B. & C.). Report Connecticut Agricultural Experiment
Station, p. 260.

1894. Ripe Rot or Anthracnose (Gleosporium fructigenuin Berk., Gleo-
sporium versicolor B. & C.). ' Bulletin Connecticut Agricultural Experiment
Station, 118: 10.

1897. Anthracnose or Ripe Rot ( Glwosporium fructigenum Berk.). Report
Connecticut Agricultural Experiment Station, p. 189.

1900. Anthracnose of Fruit or Ripe Rot (Gleosporium fructigenum Berk.) .

Report Connecticut Agricultural Experiment Station, p. 257.
1895a. Tarr, L. R. The Ripe Rot or Bitter Rot of the Apple (Gleosporium fructi-
genum Berk.). Bulletin Michigan Agricultural Experiment Station,
121: 21, 46-47.

1895). The Ripe Rot of Quince ( Glaosporium fructigenum Berk.). Bulletin
Michigan Agricultural Experiment Station, 121: 21.
1895c. Bulletin 121 reprinted in the Report of the Board of Agriculture, p.

549-623.
1879(1). Toten, F. von. Gleosporium rufo-maculans (Berk.). Fungi Pomicoll,
DOU:
ESTO (2)\s Gleosportum versicolor B. & C. Fungi Pomicoli, p. 60.
1887 (1). ——. Ascochytarufo-maculans Berk. Die Pilzeder Obstgewachse, p. 116.

1887 (2). . Gleosporium fructigenwm Berk. Die Pilze der Obstgewichse,
On so whl

1887 (3). Gleosporium lexticolor Berk. Die Pilze der Obstgewiichse, pp.
3, 79.

1887 (4). Gleosporium versicolor B. & C. Die Pilze der Obstgewiichse, p. 91.

1888. Gleosporium lxticolor Berk. Die Pilze des Aprikosenbaumes, p. 6.

SOA Cy: Ascochyta rufo-maculans Berk. Die Pilze der Weinreben, p. 5.

1891 (2). Gleosporium versicolor B. & C. Die Pilze der Weinreben, p. 4.

1888. Trait, J.W.H. Gleosporium fructigenum Berk. Scottish Naturalist, April,
p. 48.

1895. Tuseur, Freiherr K. von. Gleosporium fructigenum Berk. Pflanzenkrank-
heiten durch Kryptogame Parasiten Verursacht, p. 502.

1897. Gleosporium fructigenum Berk. Diseases of Plants, pp. 482-483.

1897. UnpeErwoop, L. M., and F.S. Earte. Gleosporium fructigenum Berk. Bulle-
tin Alabama Agricultural Experiment Station, 80: 161.

1887. Viaua, P. Ascochyta rufo-maculans Berk. Les Maladies de la Vigne, p. 387,
No. 176. is

1897. Vooruegs, E. B. Bitter Rot or Ripe Rot. Bulletin New Jersey Agricultural
Experiment Station, 119: 19.

1899. Weszsrer, —. See Green, 1899.

1894. Weep, C. M. The Bitter Rot, Ripe Rot, or Apple Rot. Fungi and Fungi-
cides, pp. 33-36.

1895. Wauirren, J. C. Bitter Rot. Bulletin Missouri Agricultural Experiment
Station, 381: 3-4, 7-16.

1887. WriytTer, GEorGE. Gnomoniopsis. In Rabenhorst’s Die Kryptogamen Flora
von Deutschland, Oest. u. d. Schweiz. 1, pt. 2: 588.

1900. Woops, A. F. Bitter Rot. Yearbook U. 8. Department of Agriculture, pp.

a 729-730.
Bitter Rot of Apples. Annual Report, Department of Agriculture,
pp. 47, 53.

1901.

DESCRIPTION OF PLATES.

Puate IJ. Frontispiece. Apples affected with bitter rot resulting from inoculation
from a canker. Two rings of spore pustules have already formed in the apple
shown at the top of the plate.

Puate II. Typical examples of apples affected with bitter rot. These fruits were
inoculated with spores from a diseased apple.

Puare III. A view in a Missouri apple orchard during a severe epidemic of bitter rot.
Almost the entire crop of apples is diseased and has fallen from the trees within
a few days.
Puate ly. Figs. 1, 3, and 7.—Apples attacked by the bitter-rot fungus at various
stages of the disease. Fig. 7 shows an apple with a rotten spot only 2 or 3
days old; fig. 3, probably four or five days after the attack; and fig. 1, a little later.
They all show how the diseased area becomes sunken, and later on wrinkled.
They also show the rings of spore masses. Fig. 2.—An apple affected with
bitter rot. The small dark spots show the appearance of early stages of this
disease. Fig. 4.—A mummified apple which was attacked by the bitter-rot
fungus in summer, and remained on the tree the following winter. It is dried
up and shriveled. The spore masses dried, but are still present in quantities
in the mummy, as shown in the figure. This illustrates the necessity for
removing the mummies. Fig. 5.—Two pears, of which the one on the left was
inoculated at one point with bitter-rot spores and the other pear not inoculated.
After several weeks the inoculated fruit (which remained on the tree) showed
a typical bitter-rot spot, with well-developed spores of the bitter-rot fungus.
Fig. 6.—A small piece of a winter squash inoculated with spores of the bitter-
rot fungus. The fungus grew readily on the squash, and after a brief period
numerous pustules with spores formed, as shown in the figure.

| Puate V. Fig. 1.—A mass of spores of the bitter-rot fungus growing in a pure cul-
ture. These spores form in countless thousands in such a culture for a period
of 8 to 14 days. Fig. 2.—Various stages of germinating bitter-rot spores. Some
have but one germ tube, others have two. On some of the threads dark second-
ary spores form. Fig. 3.—Starch grains in various stages of solution by the fer-
ment given off by the fungus. The fungus threads growing in the cells of the
apple digest the starch grains. Fig. 4.—Peculiar spore-like bodies formed by
germinating spores of a cactus fungus (Glwosporium cactorum), which resemble
the black bodies shown in fig. 2. Figs. 5 and 7.—The perfect or perithecial
stage of the bitter-rot fungus as found during the winter of 1902-3 in the apple
cankers. Fig. 5 shows two empty perithecia from an apple canker; fig. 7 a
single perithecium much enlarged with some of the asci in place. Fig. 6.—A
group of three mature asci with ascospores of the bitter-rot fungus and one imma-
ture ascus. These asci were developedin a pure culture of the bitter-rot fungus.
The ascospores so much resemble the ordinary spores that it is difficult to dis-

tinguish them.

54 THE BITTER ROT OF APPLES.

PiaTtEe VI. Fig. 1.—A pure culture on apple agar, showing the luxuriant develop-
ment of the bitter-rot fungus, with large numbers of spores. After a time this
spore production stops and peculiar hard black masses develop. These masses
are shown in Fig. 1. From a number of them large drops of a yellowish liquid
are exuding. Each black mass contains one or more perithecia of the bitter-rot.
fungus, with asci, such as are shown on Plate V, fig. 6. Fig. 2.—Enlarged group
of pustules on a diseased apple. On quiet, moist nights the spore masses of the
bitter-rot fungus exude from the mouths of the pustules on the apple fruit in
long filmy threads. Some of these threads, composed wholly of spores, are
shown exuding from some of the pustules. Figs. 3 and 4.—Apple diseased with
bitter rot and control fruit. These figures show the result of an experiment to
determine whether the spores found in the apple cankers would produce the
bitter rot in apples. A pure culture was made with spores taken from an apple
canker. Spores from this pure culture were inoculated into an apple-(fig. 3),
while another apple was punched full of holes with a sterilized needle. As_
shown in the figures, the inoculated fruit (fig. 3) developed a typical case of the
bitter’ rot, while the control fruit (fig. 4) was still sound. This is one of
numerous proofs that spores from the apple cankers produce the disease.

Prate VII. Three typical cankers such as are now believed to be formed on apple
limbs during one stage in the life cycle of the bitter-rot fungus. Spores from
these cankers produce the bitter rot of apples. Such cankers should be cut out
and burned wherever found. .

Priate VII. Cankers on living apple hmbs. Fig. 1.—A number of cross sections of
apple cankers, illustrating the manner in which the wood turns brown immedi-—
ately under the dead bark. It also shows the healing callus forming at the edge ~
of the dead areas. The largest section shows two such healing layers, proving”
that this canker is at least two yearsold. Figs. 2 and 4.—Apple branches, fig. £7
showing probably early stages of canker. Fig. 3.—A branch swollen at the
point where an apple was borne the previous year. Many such were found to
contain bitter-rot spores. It is possible that the fruit spurs became inca
from diseased fruits through the stems of the apples.

Piare IX. Young apple cankers produced by inoculating spores from pure cultures |
of the bitter-rot fungus into bark slits on healthy apple trees. In all cases here
shown small cankers were formed, pustules with spores developed, and the
spores, when inoculated into apples, produced the bitter rot of the fruit. This _
formed the last link in the chain of evidence necessary to show the connection -
between the bitter-rot fungus and the apple canker.

QO

Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture.

APPLES AFFECTED WITH BITTER ROT.

Inoculation from a diseased apple.

PLATE II.

PLATE III.

Bul. 44, Bureau of Plant Industry, U. S, Dept. of Agriculture.

DISEASED APPLES UNDER TREES.

Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE IV.

THE BITTER-ROT FUNGUS ON VARIOUS FRUITS.

1, 3, and 7, Various stages of growth on apples; 2, An early stage of the disease; 4, A mummified
apple from the preceding year; 5, Growth of the bitter-rot fungus on pear, with control;
6, Growth of the bitter-rot fungus on squash.

Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture. PRATER.

VARIOUS STAGES OF THE BITTER-ROT FUNGUS.

i

Na fede ‘pes sl :

Bul 44, Bureau of Plant Industry, U. S. Dept. of Agriculture. : PLATE VI.

Fic. 1.—PLATE CULTURE. Fic. 2.—PuSTULES ON APPLE.

Fic. 3.—APPLE INOCULATED FROM A PuRE CUL- Fic. 4.—ConTROL FRuIt
TURE OBTAINED FROM A CANKER.

STAGES OF GROWTH OF THE BITTER-ROT FUNGUS.

Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE VII.

THREE LIMBS WITH BITTER-ROT CANKERS FROM LIVING APPLE TREES.

Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE VIII.

BITTER-ROT CANKERS ON LIVING APPLE LIMBS.

PlATEIxXe

OF THE BITTER-ROT FUNGUS.

Beira

see

ARTIFICIAL CANKERS PRODUCED ON LIVING APPLE LIMBS BY INOCULATION WITH SPORES

Bul. 44, Bureau of Plant Industry, U. S. Dept of Agriculture.