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_PHYTOPHTHORA DISEASE OF GINSENG

-A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF CORNELL UNIVERSITY FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

BY

JOSEPH ROSENBAUM

Reprint of Cornell University Agricultural Experiment Station Bulletin 363.
October, 1915.

PHYTOPHTHORA DISEASE OF GINSENG

A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF CORNELL UNIVERSITY FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

BY

JOSEPH ROSENBAUM

Reprint of Cornell University Agricultural Experiment Station Bulletin 363.
October, 1915.

Ta exchange
FEB 4- 1916

7d

aah

CONTENTS

PAGE

BB TMT OS PRE Ne eee earsrcr pees acta a atte st ESE at cla cieovk & lis Syuhcn de: aherayeRs onion neta 65
DIMI RGU SSC eeene eR R Me esr tere ere nen ctr amare ps senile Set chair ar aedsl ete or Sie Sine GR Ran ROS Re: 65
DistrlottiOmeprye es cy ter eerotne rector sel cre voneh ye coy rare eee At ara aman cracstskey eae Piawa & 65
Story ielcceCOnOnmucadM pPOntanee. ts dat eho eats acs a ceape sos LAVA WSE We Nes 66
RS iiEO US lytic CISCASE. tr Matlipct. (lhl sets anor ibe etic ya wa aie< lavals slays obapstael vedas 66
Symptoms of other diseases which may be confused with Phytophthora.. 70
PMiipereta cctete Olto tab eee Mees Arak, Ae Se ERS wc cicy oer err Naa nape ee 70
ScleLovimia WhHibe TOG ies atrias.cc0s ec = suena Be Men eS State te 70
Sclerotinia iblackero troscy. eismic ts cvaiscore's everett Geto s uate asthe cea eeee ae 71
ANerostalacmatis Wilt ter acm ninrcnha ects lathe A eet rutin walt, Siecds. Saxlele Ameen ee 71
PASE SO bbe. b serene. che oh ho caster ch ace: 61 ako cement aM orcsie eau ean Oe IS 71
STU yee see asks aod et Cuero dn wl a Sito bug, cna + Ge ne es Ri atorace eee Ae 71
iBall WOT Oly CUlG LOR Vin eres as ees suse accle © age age Monga pats eee Memee s 71
aOR etd CLEVE wae gc tn aot castiye tern SGN Las Euonas tere Ohetady er cv ana ene ten Mec ey 72
deatity.Om bherOrpamismi att. Siai. tN As Sci eta cust ts « aioe eT ha iret Re 83

IB xariiiniatl Ouro lslperattineys vies neue ha ornate Oe Eee | eA 83
Gomparisonyoly coliares 6) fo: A a otians aot Se ees a Be RO hae ee 84
Macroscopic srowthvion! variousimediay 9242. ..4.2. os eens ae 84

Kinds of spores produced on various media................... 85
Comparative:morpiolopiy.:...1.Ghon be dels Get oe uke Hae oe eee 87
EAeMISCORY ale wats. ais het see tell bic is ch a acntypant nahin her aR Re 89
Miormiialo py Othe Rum SUS... slo ans orate e aed sesh Aadane es Bir ys tata deen 94
IMinycelitatia ey ts Saye aut Sausmte ove ents cet alwys covc-ad ate cane Mts eee ey Geer 94.
(ComiGiophonesienamrccers oo Gea ions ene PEA aL OS en Eee aoe 95

OMIA eee eh ee ae re SS oie Steck Ran 95
(Germunationkoliconidialryear see eri rne Aine ee cee ene eee 97
Germinationtby, cenmatubes a seme) a suieeta eae aces ree 97

Genmuina tions bysswarm Sporesars. ea ee een oe eee 98

SWAGIMIES POLES ccsteeec es a borers eda ee Teak RIS Riny Ieee arn SEE Pots 98
SERUAIORCAIMS Mersememes lor mies teeaas cle Aad Meron cups acre gee ree ne eee 99
Mentiliza tio timers tre ter entire ire cue gees sore ae eee es ae 100

@OSPOTS eae y ee eety hae each ate ooee ie NAN e Se Buel e's eecdeel ce hepa isa oor 100
Oospore-eemuuiaL om ss Key, ee<rs army Mois chs «6c sale ar eoeneiepeey ee oe ROE 100

(Connor eee etme er eR nS yo Uae cael wher awta ot Richa noe Fae en CRN eRe ea ee aes 102
‘SOC aol sep para Mee Rcd CACRERB DEN RCN APR NET CRIES eR Pa rire Erte or Are Baan ee 102
RemovalvomadiseasedsmantSiprd. eee aac ake cle © aietetorsa tare aisaey Meuseer ene ores 103
MOV Sesionya td CITA a. mesh rene cas a Mls “syaeicith ate, eu eeere rake eae ASISTS hoes Sch 103
ROUT OM Ole CLO MS Eleiarya see eiseue is ners weve tae es sleet el veneer atenee, acer nella ae pielan tne s Suks 103
Stemlizabionion colleges on Claes teewencveiele eeiysi tach ease sets tere cloves cue peainmay satiny re 104.
UD) east NO CMe bagey arte fewchretoh sheucewe Manes yee reu oy slew syortel ou sicuseevenenaretenen nis ossye. sient saucy) hue cold wenciots 104.
Bey tied ICCAD LV oe sci nyo ene ee ater eee aKolez N's oye ote Sve nayoi'0y 0) 3) 6: oh ayobelle mile eailese eva lobe oiG.6 wha saeco ace 105

63

PHYTOPHTHORA DISEASE OF GINSENG
JOSEPH RosENBAUM!

THE HOST

The American ginseng, Panax quinquefolium L., is a member of the

family Araliacee. It was brought under cultivation about twenty years

ago, but either the same or a closely related species has been cultivated
‘in Korea for more than two centuries.

According to Jartoux (1714)?, ginseng is a native of the North Tem-
perate Zone. It grows in rich, damp soils, such as prevail in hardwood
forests. The Chinese ginseng is found principally between the 126th
and 136th meridians, east longitude. The American species has about
the same range of latitude, but extends farther south. The natural
environment of the plant indicates three factors as favorable to its growth,
namely, shade, good drainage, and an acid soil. The failure of the grower
to take these factors into consideration when removing the ginseng plant
from its natural habitat to his Begens has been primarily responsible
for most of his losses.

In 1821 (U. S. Secretary of the Areas Hy: 1822) 352,992 pounds of
ginseng were exported from this country and sold for $171,786, an average
of nearly 49 cents a pound. In 1913 (U. S. Department of Commerce,
1914), the exports amounted to but 221,901 pounds. This was sold
for $1,665,731, an average of about $7.50 a pound. This falling off in
the number of pounds exported since the first shipments must be attributed
in part to the diseases that attack this crop. It is becoming a common
opinion among ginseng growers that the men who would grow ginseng
successfully must first know all about the diseases to which the plant is
subject.

THE DISEASE
DISTRIBUTION

The disease known as mildew, Japanese mildew, or soft rot, attacks
leaves, stems, and roots of the host. In this country it probably exists
in every State in which ginseng is grown — Washington, Oregon, Nebraska,
Kansas, Minnesota, Missouri, Arkansas, Wisconsin, Michigan, Indiana,
Ohio, New York, Pennsylvania, New Jersey, and Maryland. It is de-
structive in Japan also, where it was first reported by Hanai (1900). It is
known there as Kosht-ore, meaning bending at the loins.

1JIn making these investigations, the author had the cooperation of W. A. Orton, in charge of Cotton
and Truck Disease Investigations, United States Bureau of Plant Industry. The author wishes to
acknowledge also the many suggestions received during the progress of the work from D1. Donald Reddick
and Professor H. H. Whetzel, of the Department of Plant Pathology, Cornell University,
2 Dates in parenthesis refer to bibliography, page 105.

05

66 BULLETIN 363

HISTORY AND ECONOMIC IMPORTANCE

Hori (1907), who was the first to study this disease rather carefully,
states that it has long been known to Japanese ginseng growers. In the
United States the disease was first discovered on ginseng in the State
of Ohio by J. M. van Hook (1906), and it has since been observed more
or less commonly in the ginseng-growing regions of the United States.
Because of its general occurrence in ginseng gardens in many States, and
the fact that it attacks all parts of the plant, both above and below the
ground, it forms one of the most serious disease problems that confront
the grower.

PHOTOGRAPH BY WHETZEL

1nke, Be CHARACTERISTIC SYMPTOM OF GINSENG MILDEW
One or more leaflets droop and hang limp and shriveled

Hori (1907) reports a loss of $25,000, due to the disease, in one prov-
ince of Japan in the spring of t904. From observations by the writer
in ginseng gardens for the past four summers, it is safe to say that in the
eastern United States from twenty to thirty per cent of the plants are
lost through the attacks of the disease before they reach the age of five
or Six years.

SYMPTOMS OF THE DISEASE

The tops of the plants are affected in a characteristic manner. Usually
there is a drooping of a single one or all of the leaflets at the top of the

PHYTOPHTHORA DISEASE OF GINSENG 67

petiole (Fig. 2). It happens in many cases that the disease attacks the
main stem at the crown, or point where the leaf petioles are attached,
and all the leaves droop and hang limp from the top of the stem (Fig. 3).
Some other ginseng diseases exhibit similar symptoms, and microscopic

PHOTOGRAPH BY WHETZEL

Fic. 3- SYMPTOM OF GINSENG MILDEW IN LATE STAGE

The stage here shown is much later than that shown in figure 2. All the leaflets hang shriveled
and dry

examination and identification of the causal organism is often necessary
in order to determine definitely what disease is present. The tissues
at the point of infection are rapidly injured and lose their turgidity,
and the leaflets hang limp from the petiole.

68 BULLETIN 363

The leaf blades also show characteristic lesions or spots. The spots
appear dark green and water-soaked, much like those of the Alternaria
blight in its early stages. A week or two after the first appearance of
the spot, the center becomes white, the margins remaining a dark water-
soaked green. The spots vary in size from one centimeter in diameter
to lesions involving the entire leaf. The demarcation between diseased
and healthy tissue is not sharply defined. The spotting shows on both
sides of the leaf, but in general the differently colored regions within
the spot are better shown on the upper surface (Fig. 4).

FIG. -.- LESIONS OF GINSENG MILDEW ON LEAVES
The water-soaked margin of the lesion, particularly in the leaflet at the right, should be noted

In the early stages of the disease, especially on the stalk or the petiole,
the surface of the affected parts may show an almost indiscernible silvery
white coating. During periods of sunshine the diseased tissues dry up
quickly, leaving the dead and shriveled leaves at the top of the stem.

Under such conditions the disease does not spread down the stem with
great rapidity. If atmospheric conditions remain moist and cloudy,
the entire stalk 1s gradually involved. On pressing a diseased stalk
between thumb and forefinger it is found that, in contrast with the
ordinarily firm stalk, the diseased one is hollow. The hollowing of the
stem is preceded by a watery discoloration of the tissues.

PHYTOPHTHORA DISEASE OF GINSENG 69

The roots may be attacked, showing a semi-soft rot. The lesion may
start at any point on the root and in a short time involve all the tissues.
When such roots are allowed to remain in the soil for any considerable

FIG. 5. SYMPTOM OF GINSENG MILDEW ON ROOT

The two rcots have been cut longitudinally and show external and internal appearance. The root on
the right was kept in a moist chamber for two days, and the external view shows well the growth of
mycelium on the surface

time, various organisms, such as Fusaria and bacteria, invade the diseased
tissues, causing them to become soft. At this stage the disease is often
accompanied by a disagreeable odor characteristic of vegetable decays.

79 BULLETIN 363

In some cases the disease starting in the root spreads up the stem. Roots
cut longitudinally, showing the characteristic rotting, are illustrated in
figure 5.

When the disease originates in the root and does not extend rapidly
into the stem, the leaves may take on various shades of yellow and red,
resembling the colors that they naturally assume toward the close of the
growing period. Such'‘discoloration of the tops in the early part of the
season, however, while indicating some pathological condition, is not
to be associated necessarily with the Phytophthora rot. Any disturbance
in the functions of the root may cause such discoloration, and this condition
may occur in the case of other rots, as, for example, the Sclerotinia white
rot (Sclerotinia libertiana Fckl.).

SYMPTOMS OF OTHER DISEASES WHICH MAY BE CONFUSED WITH PHYTOPHTEORA

The symptoms of a number of other ginseng diseases may be confused
with those of the Phytophthora disease. Such are the Alternaria blight,
the Sclerotinia white rot, the Sclerotinia black rot, the Acrostalagmus
wilt, and an undescribed fusarial rot.

ALTERNARIA BLIGHT

Alternaria blight is a very widespread disease caused by a fungus of
the genus Alternaria, designated by Whetzel as species panax, although
a technical description has not been published. It attacks stems, leaves,
and roots of the host. The first symptoms in the spring appear as dark
brown cankers on the stem near the surface of the soil. The spots on the
leaves are similar in size to those caused by Phytophthora, but may be
distinguished from the spotting caused by the latter in that they exhibit
a broad, rusty brown border. The Alternaria lesions may also appear
on the top of the plant as the point where the leaflets are attached to the
petiole or where the petioles arise at the top of the stem, as in plants
affected with the Phytophthora disease. The lesions are, however,
readily distinguished from those of Phytophthora in that they exhibit
a velvety brown coating at the point of attack. The Alternaria disease
also occurs on the roots in the form of a dry rot. The tissues of the root
are shrunken, and are darker in color and firmer to the touch than roots
affected by Phytophthora.

SCLEROTINIA WHITE ROT

Inoculation experiments have proved that the disease known as
Scierotinia white rot is caused by Sclerotinia libertiana Fckl. Affected
plants wilt and sometimes fall over. This is due to a rotting of the stem
at its base, which usually involves also the crown of the root. The roots

PHYTOPHTHORA DISEASE OF GINSENG ar

become very soft and watery, but non-elastic. When placed in a moist
chamber, an affected root invariably becomes covered with the white
felt of the vegetative growth of the fungus. After a time numerous
black sclerotia appear.

SCLEROTINIA BLACK ROT

The cause of the disease known as Sclerotinia black rot is Sclerotinia
panacts Rankin.’ The roots only are affected. When the disease is in
an advanced stage the entire root, as the name indicates, is coal black.
In the earlier stages the rot is in all external symptoms similar to that of
Phytophthora; any dissimilarity before the root has turned. black can
be detected only by the aid of a microscope. Sections through tissue
affected with the black rot disease show an abundance of dark brown
mycelium.

ACROSTALAGMUS WILT

The disease known as Acrostalagmus wilt is said by van Hook (1904)
to be caused by a species of Acrostalagmus. The roots are the only parts
attacked. The first external symptom is a wilting of the tops. The
leaves finally become dry and papery to the touch. The limp appearance
of the top at once suggests the possibility of a lack of moisture in the
soil. Externally the roots show no lesions, but cross sections of affected
roots exhibit to the naked eye a brown ring in the region of the sap tubes.

FUSARIUM SOFT ROT
The disease called Fusarium soft rot is caused by a species of Fusarium
and is the most likely of these diseases to be confused with Phytophthora
rot of roots. Roots attacked by the Fusarium are softer, however, and
are always accompanied in the last stages by a strong odor.

ETIOLOGY

The cause of the Phytophthora disease of ginseng is a fungous parasite,
Phytophthora cactorum (Cohn et Leb.) Schrét. The genus Phytophthora
was founded by de Bary (1876) on the potato blight fungus, P. infestans.
The genus as it now stands includes more than a dozen species.

EARLY WORK ON ETIOLOGY

The history of the study of the organism associated with the disease
can be summed up as follows: Hanai (1g00:28) and Hori (1907:153)
demonstrated the constant association of the Phycomycete with the
lesions of the ginseng leaves. Hori, in the article cited, makes the following
statement: ‘‘ Since this decaying process proceeds downward to the

3 Recent inoculations indicate that Sclerotinia panacis Rankin is probably identical with Sclerotinia
smilacina Durand.

72 BULLETIN 363

roots, the entire plant begins to wilt and drops to the ground.” No |
experimental evidence is furnished to show that the roots really rot, or
that when this does occur it is due to the attacks of Phytophthora. Van
Hook (1906) reports the constant presence of odspores of the same fungus
in the stems of ginseng. Whetzel (1910) appears to be the only one
who has done any work on the pathogenicity of the fungus previous to the
studies herein presented. In ro09g he made a series of inoculations,
employing pure cultures of the Phytophthora isolated from ginseng,
and reports that ‘‘in every case there was prompt infection, with the
resulting lesions characteristic of the disease.” Little stress is laid,
however, on the Phytophthora causing injury to the roots. In a bulletin
by Whetzel and the writer (1912) the following statement is made:
“Observations in the gardens show that the roots of plants, the tops
of which are killed by the mildew, invariably rot unless promptly removed
enevel Ghaleel

For the past four seasons the writer has been investigating the diseases
of ginseng, studying for the most part the root rots. During the course
of the work it has developed that a large proportion of the soft rot is
due to Phytophthora. This bulletin presents a study of the life history
and identity of Phytophthora as it exists on ginseng.

PATHOGENICITY

Several methods have been employed for isolating the fungus and
growing it in pure culture. In 1914 the organism was obtained from
roots sent from a number of places — Ithaca, Scott, and Alden (New
York), Kutztown (Pennsylvania), Mentor (Ohio), and Cassopolis (Michi-
gan). Isolation from diseased roots was successful only when made from
roots on which the disease had just started. Later the lesion is invaded
by other soil organisms to such an extent that isolation of Phytophthora
is difficult or impossible.

In most cases in which the fungus was isolated directly from the root,
bits of tissue from the inside of the root at the junction of the healthy
and the diseased areas were placed in tubes of oat agar. In some cases
isolations were made directly from the root by placing the root in a moist
chamber and carefully transferring to bean pod plugs the surface growth
of mycelium which appeared in from two to three days.

Pure cultures of the fungus are obtained most readily, not from the
roots, but from the stems. The method of procedure is as follows:
Diseased stems are immersed in a 1-1ooo solution of mercuric chloride
for from two to three minutes, the stems are split longitudinally, and
tissue plantings are made on poured plates of oat or bean agar. In three
or four days the fungus usually will have grown out from the bits of tissue,

PHYTOPHTHORA DisEASE OF GINSENG 73

and subcultures can be made to test tubes of oat or potato agar. Good
results may also be obtained, in case the disease is in its early stages,
by washing the stems in mercuric chloride and placing them in a moist
chamber. Conidia of the fungus usually appear within a period of from
twenty-four to thirty-six hours. Transfers made from the surface growth
usually give pure cultures.

When the fungus is obtained in pure cultures it grows readily on a
number of media. The writer has grown it on oat agar as made by
Clinton, on Thaxter’s hard potato agar, on corn meal agar, on sterilized
ginseng stems,.on a ginseng decoction, on bean pods, and on lima bean
agar.4 The growth on synthetic media has been very slight.

After the ginseng fungus was isolated and grown in pure culture it
was used for inoculating healthy plants. The experiments in inoculation
of the tops have extended over a period of four years, but it was only
in the spring of 1913 that inoculation of the roots was attempted.

Inoculation of the tops was made in the following ways: (1) The
stems and leaves were sprayed with a water suspension of conidia and
swarm spores, an atomizer being used for the spraying. The plants were
covered with a bell jar for four or five days. Check plants were treated in
a similar manner, with the exception that conidia were not added to the
water. (2) By means of a platinum needle a bit of the fungus was removed
from a pure culture and placed in the crotch of the plant. The inoculum
was covered with moist cotton. For checks, the crotches of other plants
were likewise covered with moist cotton. (3) By the use of a flamed scalpel
a slight injury was made in the crotch of the plant and the inoculum
was placed in the cut.

Inoculation of the roots was made in the following ways: (1) The soil
was removed from one side of the root. The root was slightly cut with
a flamed scalpel and a bit of a pure culture of the fungus was placed in
the cut. The checks were treated in a similar manner, but no fungus was
placed in the cut. All the roots were then covered with soil. (2) Roots
were placed in pots and were inoculated by watering with a solution
containing conidia of the fungus. Previous to inoculation certain roots
were punctured with a flamed needle. As checks, similarly treated
roots were kept moist with water not containing the fungus. (3) Freshly
dug roots were immersed in a solution of mercuric chloride for ten minutes,

4 The media used were composed as follows:
Hard potato agar: 200 grams of potato, 20 grams of glucose, and 30 grams of agar, for every 1000
cubic centimeters of water.

Oat agar was made according to the directions given by G. P. Clinton in the Report of the Connecticut
Agricultural Experiment Station for 1909 and 1910, page 760.

Corn meal agar was made according to the formula given by C. L. Shear and Anna K. Wood in Bulletin
252 of the United States Bureau of Plant Industry, page 15.

Lima bean agar: 100 grams of ground lima beans and 15 grams ol agar for every 1000 cubic centi-
meters of water.
Bean pods: pods of ordinary string beans placed in test tubes with a small quantity of water and sterilized.

74 BULLETIN 363

rinsed several times with sterile water, and placed in sterile test tubes.
The inoculation was made in the test tube in much the same way as a
subculture is made. The roots in the test tube were cut with a flamed
scalpel. By means of a platinum needle bits of the pure culture were
inserted into the cuts. The checks were likewise injured with the flamed
scalpel, but no fungus was placed in the cuts. The test tubes were then
placed in a moist chamber for from two to three days. Later this was
found to be unnecessary.

Results of inoculations on tops, on roots placed in the soil, and on
roots placed in test tubes, are shown in figures 6, 7, and 8. It should

FIG. 6. GINSENG PLANTS INOCULATED WITH A PURE CULTURE OF PHYTOPHTHORA
CACTORUM

be stated here that when plants were injured, either on the tops or on
the roots, a higher proportion of infection was obtained than when the
tissues were not injured. As far as root rot in the garden is concerned,
however, this makes very little difference, for one seldom finds a root
in the soil without some injury due to rodents, insects, transplanting,
or other causes.

In all the inoculation work, in addition to the ginseng Phytophthora
a culture marked Phytophthora cactorum was used. The latter was
isolated by D. L. Peters, of Berlin, from Phyllocactus. This culture
was found to be as pathogenic to ginseng as the Phytophthora isolated
from ginseng.

PHYTOPHTHORA DISEASE OF GINSENG

tS

An attempt was made to determine whether the use of the different
organs of the fungus for inoculating — mycelium, conidia, or odspores —

made any difference in the ability to
produce infection. These various organs
were obtained from pure cultures of
different ages and from different media.
The mycelium was obtained from very
young cultures on hard potato agar; the
conidia were obtained from older cultures
‘on the same medium, also from corn
meal agar; the odspores, from old cultures
on bean pods. No doubt mycelium was
present in every case. No difference in
ability to infect was found. The period

of incuba-

tion—that
is, from the
time when

the parasite
is placed on
the host to
the time
when the
first visible
symptoms
appear — is
from three
to five days
on roots and
from four to
six days on

Fic. 8. GINSENG ROOTS INOCU-
LATED WITH A PURE CULTURE
OF PHYTOPHTHORA CACTORUM
Two-years-old roots of ginseng were

disinfected, placed in sterile test
tubes, and inoculated with a pure
culture of Phytophthera cactorum.
The root on the left was treated simi-
larly but was not inoculated. The
inoculations were made on May 15,
1913; the photograph was made ten
days later

BIG. -7.
WITH A PURE CULTURE OF PHYTOPH-

GINSENG ROOTS INOCULATED

THORA CACTORUM

Growing roots two years old were slit with
a scalpel and inoculated with a pure culture
of Phytophthora cactorum. The root on the
left was treated similarly but was not inccu-
lated. The inoculations were made on
August 4, 1913; the photograph was made
seven days later

tops.

The length of time during which the
fungus has been in artificial cultures does
not seem to have any appreciable effect on
its virulence.
summer of ro11 was employed, and another
isolated in the spring of 1913.
almost identical results in all the inoculation
work. Wherever the rot was produced, it
was always possible to make re-isolations by

One culture isolated in the

They gave

cutting out pieces of tissue at the boundary between the healthy
and the diseased regions, and planting these on oat agar or bean pod

BULLETIN 363

plugs. In a few instances the re-isolations were made by placing
the rotted root in a moist chamber and then making plantings on
oat agar from the mycelium appearing on the surface. Re-isolations
from the tops were made by washing the stems for from two to three
minutes in a 1-1000 solution of mercuric chloride, cutting them length-
wise, and making plantings from the interior on oat agar. The fungus
obtained from such re-isolations was identical with the original culture,
as regards both morphology, behavior on culture media, and ability
to produce the disease. Koch’s rules of proof were carried out for the
Phytophthora isolated from ginseng, and also for Phytophthora cactorum
from Phyllocactus.

In 1913 inoculations were made as shown in table rt. The percentage
of infection obtained in all these inoculations leaves no doubt as to’the
conclusions to be reached. In 1014 a greater number of inoculations
were made and the results obtained were almost identical with those

of 1913.
TABLE 1. INocULATIONS MADE IN VARIOUS WAYS WITH PHYTOPHTHORA CACTORUM
FROM PHYLLOCACTUS AND FROM GINSENG. SUMMER OF I913
Condition Number Number
Source of of plants Manner of lof plants] Percent- lof plants
Date organism at time of inoculation inocu- |@ge of M-| used as
used inoculation lated* |fection* | checks +
April 19 Phyllocactus |Four years |Tops sprayed 3 | 66.6 I
and ginseng jold, begin- — with sus-
ning to push pension
through soil of spores
April 19 Phyllocactus |Same as Plants not Ryall eager I
and ginseng |jabove injured,
IQIt inoculum 3. |166.6Gar
‘placed in crotch
|
April 19 Phyllocactus |Same as \Plants slightly 3) |TOOnOsR I
and ginseng jabove injured, 3 | 66.6G.
IQII inoculum
placed in crotch
April 19 Phyllocactus |Same as Soil removed, 4 |100.0 2
and ginseng jabove root injured,
IQII inoculum placed
in injury
April 19 Phyllocactus |Same as jRoots in test 3 |100.0 2
and ginseng jabove tubes ;
IOI

*The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for
ginseng unless otherwise stated.
+ All checks remained healthy unless otherwise stated.
t“P.” indicates percentage for Phyllocactus; ‘‘G.,’’ percentage for ginseng.

PHYTOPHTHORA DISEASE OF GINSENG re

TABLE I (continued)

Condition “Number re Number
Dat eet of plants Manner of _jof plants enor of plants
Be a ae at time of inoculation inocu- Bae » | used as
inoculation lated * checks fT
April 19 Phyllocactus |Same as Roots placed in 2 fo)
and ginseng jabove pots and
IQTI watered with a
suspension of
inoculum
April .19 Phyllocactus |Same as Same as above, 3.|66.6.2.4 I
and ginseng |above but roots R | Ba AG it
IQII pricked
April 20 ‘Phyllocactus |Same as Roots in test 3 |100.0 2
and ginseng |above tubes
IQII
April 20 Phyllocactus |Same as Tops sprayed Bl 2B I
above with a
suspension of
inoculum
April 20 Phyllocactus |Same as Plants injured, 2, |LOOLO 2
above inoculum
placed in crotch
April 20 Phyllocactus |Same as Soil removed, 3 |100.0 2
above root injured,
inoculum
placed in
injury
April 20 Phyllocactus |Same as Roots in test 3 |100.0 I
above tubes
April 20 'Phyllocactus |Same as Same as above, 3 Ce) 2
above but roots
pricked
May 16 Phyllocactus |Five years |Inoculum 3 |100.0 I
land ginseng old, full- placed on
IQII grown in leaves in drops
garden of water
May 16§ Phyllocactus |Same as Same as 3 |100.0 I
above above
May 27 Phyllocactus |Same as Same as above By, |lioxo) s(o) 1 e7. I
and ginseng jabove 3 | 66.6G.
1913
May 27 Phyllocactus |Same as Tops sprayed Ale Se Ole. I
and ginseng |above with a 4 |100.0G.
1913 suspension of
inoculum

* The number of plants inoculated and the percentage o* infection are the same for Phyllocactus and for
ginseng unless otherwise stated.

+ All checks remained healthy unless otherwise stated.

{°‘P.” indicates percentage for Phyllocactus; ‘‘G.,”’ percentage for ginseng.

§ Inoculations were made on the same day as the preceding ones, but either in a different garden or in
a different part of the same garden.

BULLETIN 363

TABLE I (continued)

78
Source of Sere On
Date organism ‘ ie ¢
sees at time 0
inoculation
May 27 Phyllocactus |Same as
and ginseng jabove
1913
May 27 ‘Phyllocactus |Same as
and ginseng jabove
1913
May 27 Phyllocactus |Same as
and ginseng |jabove, but
‘1913 with roots
removed
May 27 Phyllocactus |Same as
and ginseng |jabove
1913
May 27 Phyllocactus |Same as
and ginseng |above, with
1913 roots pricked
June 13 Phyllocactus |Four years
and ginseng jold, roots
IQII removed
from garden
June 13 Phyllocactus |Same as
and ginseng [above
1913
June 13 Phyllocactus |Same as
above
June 13 Phyllocactus |Four years
and ginseng Jjold, plants
IQII standing in
garden
June 13 Phyllocactus |Same as
and ginseng |jabove
June 13 Phyllocactus |Same as
above
June 14 Phyllocactus |Same as
and ginseng |jabove

IQII

Number Number
Manner of jof plants ete alGh plants
: ‘ : age of in-
inoculation inocu- |"Foobon* used as
lated* checks t
Plants slightly 4 |100.0 2
injured,
inoculum
placed in crotch
Soil removed, 4 |100.0 2
root injured
and inoculated
Roots in test A<\) 75cOR er 2
tubes 4 |100.0G.f
Roots placed 3 (e) I
in pots and
watered with a
suspension of
inoculum
Same as above B fe) I
Roots in test 4 |100.0 I
tubes
Same as above 4 |100.0 I
Seer
Same as above aay a 4 |100.0 I
Soil removed, 3 |100.0 I
root injured
and inoculated
Same as above 3, |100.0 | I
Same as above 3 |100.0 | I
Plants slightly 3 |100.0 | I

injured in
crotch and
inoculated

*The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for
ginseng unless otherwise stated.
+ All checks remained healthy unless otherwise stated.

1A

indicates percentage for Phyllocactus;

“G.”

percentage for ginseng.

PHYTOPHTHORA DISEASE OF GINSENG 70
5 TABLE 1 (continued)
Condition Number Number
Date eee of plants Manner of of plants ae of plants
8 aa at time of inoculation inocu- 2 ction* used as
bi inoculation lated* checkst
June 14 Phyllocactus |Same as Same as above 3 |100.0 I
and ginseng |above
1913
June 14 Phyllocactus |Same as Same as above 3 |100.0 I
above
June 14 Phyllocactus |Same as Soil removed, An e2 solar I
and ginseng jabove root uninjured, 4 oG.t
IQII inoculum
placed on
surface
June 14 \Phyllocactus |Same as Same as above 4 O I
and ginseng jabove
1913
June 14 Phyllocactus Same as Same as above 4 ) I
above
July 1 ‘Phyllocactus |Five years _|Tops sprayed Bu eaa ae: I
and ginseng jold, plants j|witha 3 |100.0G.
‘IQII standing in |suspension of
garden inoculum
July 1 Phyllocactus |Same as Same as above 3 | 66.6 I
and ginseng |jabove
1913
July 1 Phyllocactus |Same as Same as above 2 16626 I
above
July 1 \Phyllocactus |Same as Inoculum 3 |100.0 I
and ginseng |above placed on
IQII uninjured
leaves
July 1 |Phyllocactus Same as Same as above 2 100.0 I
and ginseng |above
|I9Q13
July 1 Phyllocactus Same as Same as above 3 |100.0 I
above
July 1 Phyllocactus |Same as Soil removed, 4 |100.0 I
land ginseng |above root injured
IQII and inoculated
July 1 Phyllocactus |Same as Same as above 4 |I100.0 I
and ginseng jabove

1913

* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for
ginseng unless otherwise stated.
+ All checks remained healthy unless otherwise stated.
£‘‘P.” indicates percentage for Phyllocactus; ‘‘G.,”” percentage for ginseng.

80 BULLETIN 363
TABLE I (continued)
Condition Number Number
wate Se of plants Manner of _ jof plants mbes of plants
Ban di at time of inoculation inocu- a ction* | sed as
inoculation lated * checks f
July 1 Phyllocactus |Same as Same as above 4 |100.0 I
above
July 1 Phyllocactus |Five years _|Roots in test 4 |100.0 I
and ginseng jold, roots tubes
I9II removed
from garden
July 1 Phyllocactus |Same as Same as above 4 |100.0 I
and ginseng |above
1913
July 1 Phyllocactus |Same as Same as above 4 |100.0 I
above
July 16 Phyllocactus |Three years Plants slightly 3 |100.0 I
and ginseng jold, plants injured,
IQII standing in jinoculum
garden placed in crotch
July 16. ‘Phyllocactus |Same as Same as above 3 |100.0 I
and ginseng |above
jIQI3
July 16 | Phyllocactus |Same as Roots not 3 oO I
and ginseng |above injured,
IQII inoculum
placed on
surface
July 16 Phyllocactus |Same as Same as above 3 (0) I
and ginseng labove
1913
July 16 |Phyllocactus |Same as Same as above 2B e) I
| above
August Phyllocactus |Four years {Soil removed, 4) | 752OR SE I
and ginseng jold, plants [root injured 4 |100.0G.}
IQII standing in jand inoculated
garden af |
August |Phyllocactus |Same as Same as above 4 |100.0 I
and ginseng |jabove
1913
August ‘Phyllocactus |Same as Same as above 4 |100.0 I
above
August Phyllocactus |Four years |Roots 3 |100.0 I

and ginseng
IQII

old, roots
removed
from garden

disinfected and
placed in test
tubes

* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for
ginseng unless otherwise stated.
+ All checks remained healthy unless otherwise stated.
.” indicates percentage for Phyllocactus; ‘‘G.,” percentage for ginseng.

t*

PHYTOPHTHORA DISEASE OF GINSENG 81
TABLE I (continued)
Condition Number Number
Source of Percent-
Dike organism of plants Manner of _ jof plants Bee ofan of plants
eee at time of inoculation inocu- | fe ction* used as
; inoculation lated * checks f
August I Phyllocactus |Same as Same as above 3 |100.0 I
and ginseng |above
1913
August I Phyllocactus |Same as Same as above 3 |100.0 I
above
August I Phyllocactus |Four years |Plants injured, 4 |100.0 I
and ginseng |old, plants [inoculum
IQII standing in |placed in crotch
garden
August 1 Phyllocactus |Same as Same as above 4 |£00.0 I
and ginseng |above
1913
August I Phyllocactus |Same as Same as above 4 |100.0 I
: above
August 15 |Phyllocactus |Same as Plants not 4 fo) i
and ginseng |above injured,
inoculum
placed in crotch
August 15 |Phyllocactus |Same as Same as above 4 ) I
above
August 15 |Phyllocactus |Three years |Tops sprayed z 0) I
and ginseng Jold, plants [witha _
standing in {suspension
garden of inoculum
August 15 |Phyllocactus |Same as Same as above 3 fo) I
above
September 3 /Phyllocactus |Same as Roots not 4 ) I
and ginseng Jabove injured,
1913 inoculum
placed on
surface
September 3 |Phyllocactus |Same as Same as above 4 fo) I
above |
September 3 |Phyllocactus (Same as Roots injured, 3 |100.0 | I
and ginseng [above inoculum
1913 placed on |
surface |
September 3 |Phyllocactus |Same as Same as above 25 TOKO: | || I
labove |

* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for
ginseng unless otherwise stated.
+ All checks remained healthy unless otherwise stated.

82 BULLETIN 363
TABLE I (concluded)
Souresior Condition Ree Percent-| Numbes
Wate organism of plants Manner of of plants age of in- of plants
eer at time of inoculation inocu- | faction® | used as
inoculation lated* checks f
September 3 !Phyllocactus |Three years |Roots placed in 3 oO I
and ginseng |old, roots pots and
1913 removed watered with a
from garden |suspension
of inoculum
September 3 |Phyllocactus |Same as Same as above, B Co) I
and ginseng jabove but roots
1913 pricked
September 3 |Phyllocactus |Same as Roots 4 | 50.0P.f I
and ginseng jabove disinfected and 4 |100.0G.f
1913 placed in test
tubes
September 3 |Phyllocactus |Same as Same as above 4 | 50.0 I
above | |
October 2 Phyllocactus |Four years |Same as above 3 |100.0 I
and ginseng |jold, roots
1913 removed
from garden
October 2 Phyllocactus ;Same as Same as above | 25 LOOROnmma, I
above |
October 2 Phyllocactus |Same as Roots placed in 3, |100.0 I
and ginseng jabove pot, injured,
1913 inoculum
placed on
surface
October 2 Phyllocactus |Same as Same as above 3 |100.0 I
and ginseng jabove but not injured
IQI3
October 2 Phyllocactus |Same as Roots placed in 3 Oy | I
and ginseng jabove pot and
1913 watered with a
suspension |
of inoculum ¥
October 2 Phyllocactus |Same as Same as above, Cl awlogyles | I
and ginseng |above but roots 3 oG. |
1913 pricked |

* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for
ginseng unless otherwise stated.
+ All checks remained healthy unless otherwise stated.
{‘P.” indicates percentage for Phyllocactus; ‘‘G.,’’ percentage for ginseng.

PHYTOPHTHORA DISEASE OF GINSENG 83

IDENTITY OF THE ORGANISM
EXAMINATION OF LITERATURE

A careful examination of the fungus from pure culture on various
media shows that it resembles most closely Phytophthora cactorum (Cohn
et Leb.) Schroeter (1889). Saccardo (1888) lists as synonyms of this
species the following: Peronospora cactorum Cohn et Leb., P. Fagi
Hartig, P. Sempervivt Schenk, Phytophthora omnivora de Bary. It may
be well to briefly review here the history of the species.

Lebert and Cohn (1870) observed a rot on Cereus giganteus and Melo-
cactus nigrotomentosus. From their description of the symptoms it appears
that the nature of the disease was a dissolution and separation of the
individual cells, resulting in a more or less soft rot. An abundance of
mycelium, conidia, and odspores was found. From the nature of the
fungus Lebert and Cohn rightly determined that it was a Phycomycete,
and described it as Peronospora cactorum. As far as they could deter-
mine, haustoria were lacking.

Hartig (1876:121) describes a fungus, Peronospora Fagi, as causing a disease
of beech. A similar fungus was described the previous year by Schenk
(1875), under the name Peronospora Sempervivi, found by him to be
causing a disease of Sempervivum. De Bary (1881), in order to settle
the identity of these forms — which he held to be identical — with little
regard for priority or rules of nomenclature gave them collectively the
name Phytophthora omnivora. Hartig (1882:42) wrote as follows in com-
menting on this change: ‘‘ I accept this new name, since it behooves me
above everything else to desire a name for the parasite that shall bear no
false significance. Since I have, from the earliest time, observed that the
disease attacks maple, pine, larch, and fir, I believe omnivora is- better
deserved than Fag?. In opposition to many systematists of later times
who from their researches on priority have changed the customary name for
another never accepted as valid by the science of the past one hundred
years, I have been of the opinion that names existed, not for the authors,
but for the scientific public.” °

De Bary was aware of the work of Cohn and Lebert when he
wrote that there was not a doubt in his mind that the two forms were
identical. He proposed the specific name omnivora as better expressing
the nature of the organism. Schroeter (1889: 236), recognizing the work
of Cohn and Lebert, adopted the original specific name cactorum and
simply classed the fungus in the more recently formed genus. The
name as it stands, therefore, is Phytophthora cactorum (Cohn et Leb.)
Schroeter.

* Translation from the German,

84 BULLETIN 363

Syn. Peronospora cactorum (Cohn et. Leb.). Bietr. biol. pflanz. 1:51-57. 1870.
Peronospora Sempervivt Schenk. Bot. ztg. 33:690-693. 1875.
Peronospora Fagi Hartig. Zeitsch. forst.- u. jagdw. 8:117-123. 1876.
Phytophthora omnivora De Bary. Bot. ztg. 39:585-595, 6001-609, 617-626. 1881.
Phytophthora cactorum (Cohn et Leb.) Schroeter. Krpyt-fl. Schlesien 3:235-
236. 18809.

The following is the original description as given by Lebert and Cohn
(1870):

“ Mycelii tubi graciles nonnunquam torulosi ramosi, ramis angulo
recto patentibus, haustoriis destituti. Stipites conidiophori tenues, in
modum cincinni unilateraliter pauce-ramosi, sub apicibus ramorum coni-
diferis non raro vesiculoso-inflati. Conidia in stipitibus pauca hyalina,
ellipsoidea vel ovata, apice papilla prominente munita majuscula =
0,048 mm. (1/28-1/15 mm.).

“* Oogonia conglomerata membrana tenui marcescente munita, singula
oosporam singulam exacte globosam episporio valido luteo-fusco pellucido
laevi praeditam foventia, diametro = 0,024 mm. (1/40 mm.).

“Habitat in meatibus intercellularibus parenchymatis variorum Cac-
torum quorum morbum putredine quadam finitum efficit. Observ.
hieme 1868-1869 in viridario excellentissimi ducis a Jacobi Vratislaviae.”

Unfortunately it has thus far been impossible for the writer to examine
the type material or to make isolations from the original host, and he is
compelled to rely entirely on the above description and the descriptions
of the later workers for the identity of this fungus. For comparison,
a culture marked Phytophthora cactorum was obtained from the Bureau
pour le Distribution de Cultures de Moisissures, of the International
Association of Botanists in Amsterdam, with the information that it
was isolated from Phyllocactus by D. L. Peters, of Berlin.

COMPARISON OF CULTURES

Since the Phytophthora of ginseng resembles the culture marked Phy-
tophthora cactorum, a detailed comparison is here given.®

MACROSCOPIC GROWTH ON VARIOUS MEDIA

Phytophthora from ginseng and Phytophthora cactorum from Phyllo-
cactus were grown on hard potato agar, oat agar, corn meal agar, bean
pod plugs, and sterilized ginseng stems. Various synthetic media were
also employed, but the growth on these was so small as to make them
unsuitable for this work. On all the media no difference in the two forms
was noticeable, either in rapidity of growth or in luxuriance of growth.

Hard potato agar—A white, fluffy, aérial growth was produced in
five or six days on hard potato agar. The growth was profuse.

6 A comparison of the Phytophthora of ginseng was also made with nine other species of Phytophthora.
The results of this study will be published in a subsequent paper.

PHYTOPHTHORA DISEASE OF GINSENG

85

Oat agar.—The growth on oat agar was profuse and was beneath the
surface as well as at the surface, making a slightly yellowish, mealy growth.
Corn meal agar.—On corn meal agar there was a slight growth, mostly

subsurface.

Bean pod plugs.— The growth on bean pod plugs was aérial as well
as embedded in the tissues of the pod. The growth was white, but was
less fluffy than on hard potato agar.

Ginseng stems.—On ginseng stems there was a very scanty surface

growth.

KINDS OF SPORES PRODUCED ON VARIOUS MEDIA
The kinds of spores produced and the time of appearance of these are
shown in table 2:

At the end of two weeks

n
: On On On On O
Organism ginsen
§ potato oat. corn meal bean pods SUSE 's
stems
Phytophthora Numerous Oégonia, Few Few Numerous
from ginseng conidia odspores, conidia oogonia conidia,
conidia few o6go-
nia, few
odospores
P. cactorum Numerous Odgonia, Few Few Ntmerous
from Phyllo- conidia oospores, conidia oogonia conidia, few
cactus conidia odgonia, few
oospores
At the end of six weeks
n
Organism Xo On On va ee
8 potato oat corn meal bean pceds Pee
Phytophthora Numerous | Conidia, Few conidia,; Numerous | Numerous
from ginseng conidia few odgo- few od6gonia,| Odspores conidia,
nia, numer- | few odspores} and conidia | few o6gonia,
ous O6spores few odspores
P. cactorum Numerous Numerous Few conidia,| Numerous Numerous
from Phyllo- conidia conidia, few od6go- odéspores | conidia,
cactus few odgonia,| nia, few and conidia | few oégonia,
numerous odspores few odéspores
oospores

It was found in several series of the above that, while the time of ap-
pearance of the different spore forms may vary for the different strains
of Phytophthora, eventually the same spore forms appear on a given

86 BULLETIN 363

medium. Oat agar and bean pods are especially favorable for the pro-
duction of the sexual bodies. In the case of bean pods, the conidia appear
mostly on the aérial growth, while the odspores are imbedded in the
tissues of the pod.

FIG. 9. MYCELIUM OF PHYTOPHTHORA, (A) FROM GINSENG, (B) FROM :PHYLLOCACTUS

The drawings were made from mounts of mycelium of the two organisms growing on oat agar, No con-,
stant difference can be noted

PHYTOPHTHORA DISEASE OF GINSENG 87

COMPARATIVE MORPHOLOGY

The morphological studies were made from cultures of the same age,
grown on the same medium. No differences were noted in the mycelium
of the two cultures (Fig. 9). In very young cultures there is a slight
tendency to branch at right angles, but there is such great irregularity
in the mycelium that such can hardly be taken to be a constant character.

The conidia vary greatly in shape and size, but no difference between
strains could be detected either when grown on the same or when grown
on different media (Fig. 10). Over four hundred measurements were
made for each form from cultures of different ages and grown on different

FIG. 10. CONIDIA OF PHYTOPHTHORA, (A) FROM GINSENG, (B) FROM PHYLLOCACTUS

The drawings were made from mounts of cultures of the two organisms growing on oat agar. Both
drawings are made to the same scale

media. The measurements most commonly obtained are the same for
the Phytophthora from ginseng and for P. cactorum from Phyllocactus,
Gana x 27 1:

Inoculations were made on freshly disinfected ginseng roots in test
tubes and the two forms were re-isolated from the inoculated roots. Pedi-
greed single-spore cultures were then made, and conidia and odspores
were again measured.

The same differences appeared as were shown previously. Different
workers have given different measurements, though working presumably
with the same species. This is brought out in table 3, in which the
measurements given by individual workers for the same species are
presented,

88 BULLETIN 363

TABLE 3. SHOwING VARIATION GIVEN BY DIFFERENT WORKERS FOR
PHYTOPHTHORA CACTORUM

Measurements of Diameter of
Author conidia odOspores
(micromillimeters) (micromillimeters)
Connvandtteberts-t44-0 ee acer ee VAS 215 OB ck sul, ee | 20-70
[BIBS B kesieg Sele eet emi ANA GS Re Hae 25 =A Os icratat eee seers ad
S Chie milcgars meat shite Wes eeeeaer tre gat tke tere 7 a A ich Wer hae ae ee et ee | 20 (odgonium)
ID) Sa Mayet ace ee ee cee 35-40 x 50-60-90....... | 16-24T
SCMTOCtEIpe aa soos ee Pom eee. B B5-AO x 150-0055 en e430
@stenwalldens) 63 as totes cio ee 14.64-24.4 x 119.56.....| 24 (o6gonium)
lapamel bares. gece. ON ee oy Notigivent 025s. seen | 30-45
Jbsrantaavessootshal caklenalo! st cic ee cree a eer: 17-30 x 25-60...........| None found
FO RING con oe NN ete ct [i | 30—50'5 150.00 Peauromm a leis
Abnormal 29 x 85.5.....|{ 7 *
Bulnallce Sewers teat e ark nd. os eas 15-25 KX 15-120..........| Not given
Wanl THOOKeS Ae Jas Geary ya rien sas 30-42) & AO—58..5.5--44..2\° Not given
PAULIN © Dee mr teaceercreioy sie cetscenees tis cgeur Sa BASU Disc erave. eae ie | 27
|
* Measurements cf conidia given by Schenk areas follows: ‘‘ Die kleinsten derselben sind 5, die gréssten

36 Theilstriche meines Zeiss’schen Mikrometers lang und 4 bis 25 Theilstriche breit ”

+ De Bary states that the odspores are in general from three-fourths to four-fifths the diameter of the
odégonium. He gives the measurements of the latter as from 24 to 30 microns in diameter. The meas-
urements given above for the diameter of the odspores were derived accordingly.

It is thus shown that great variations may occur, apparently in the
same species. De Bary, knowing of these variations as given by Lebert

FIG. 11. THE SEXUAL PROCESS IN PHYTOPHTHORA FROM GINSENG

Various stages are shown in the development of antheridium, odgonium, and odspores, Fertilization
tubes are very evident in a number of cases

PHYTOPHTHORA DISEASE OF GINSENG 89

and Cohn, by Hartig, and by Schenk, did not hesitate to place all forms
in a single species. Likewise, Osterwalder (1906), notwithstanding the
fact that his measurements do not agree with the others, does not con-
sider this of sufficient importance to establish a new species.

FIG. 12. fHE SEXUAL PROCESS IN PHYTOPHTHORA FROM PHYLLOCACTUS

More than four hundred measurements of o6gonia were made for each
form. Measurements of odspores taken from various media, and the
cultures of different ages, show this spore form to be very constant. The
measurements of the two forms are identical, being 274 in diameter. The
method of fertilization likewise does not differ in the two forms (Figs.
It and 12).

A summary of the above comparisons, taken together with the results
of the inoculations as shown previously, proves that the Phytophthora
isolated from ginseng is identical with the culture marked Phytophthora
cactorum (Cohn et Leb.) Schroeter isolated from Phyllocactus.

LIFE HISTORY

Careful studies’ of the fungus have been made in order to determine
its various relations to its host and the morphological characters of the
parasite itself. These studies have been made with fresh material from
the garden and with pure cultures on various media. Plants which
early in the spring show characteristic drooping usually exhibit no external
evidence of the fungus. They show a slight shrinkage and browning of
the tissues of the stem, and often the shrunken tissue appears water-
soaked. If the stems are placed in a moist chamber for a day, a silvery

go BULLETIN 363

white coating of conidia appears, characteristic of Phytophthora. Mi-
croscopical examination shows an abundance of the large ovate conidia of
the pathogen. An excess of moisture in the chamber will force the fungus
to the production of a large amount of mycelium with little conidial
formation. In a few cases, by taking a microscope directly into the field
the writer was able to find conidia on the surface of the stems. This
was the case during a continuance of from two to three days of warm,
muggy weather, accompanied by dews in the mornings.

The conidia are spread by the wind or by other usual means of dis-
semination; very often, no doubt, by the bodies of the workers while
weeding. One who knows the conditions in a ginseng garden can readily
understand how such is the case, since the weeders get down on their
hands and knees. The rows, and the individual plants in a row, are so
close together that it is almost impossible not to disseminate the spores
when these are present. A spore falling on a healthy plant, under the
right conditions of temperature and moisture, germinates, and within
from four to six days infection becomes apparent.

When a plant is infected in the tops, the fungus travels from the petioles
into the main stem, through that, and into the root, where it rots the
root. That the fungus travels downward is shown by the following
experiment: On July 11, 1913, twelve plants were inoculated in the
tops with a pure culture of the fungus. Six other plants were used as
checks. Half of the plants inoculated were injured by means of a flamed
scalpel and the inoculum was placed inside the cuts; for the uninjured
plants the inoculum was placed at the base of the petioles and covered
with moist cotton. The check plants were treated in a similar manner,
both as regards injuring half of them and covering the others with moist
cotton, but the inoculum, of course, was not placed on them. Four
days later (on July 15) the moist cotton was removed. On the same
day all the plants injured and inoculated showed the characteristic drooping
of the leaflets from the crotch of the plant. Within three days more
four of the uninjured inoculated plants likewise showed the characteristic
wilting. All the checks, whether injured or not, remained healthy. On
July 20 it was apparent, by the hollowing out and discoloration of the
stems, that the fungus was traveling downward. On pressing a stalk
between thumb and forefinger, it was found that the ordinarily firm
stalk felt hollow in the region of the discoloration. By marking the
point of discoloration on the stem with india ink, it was ascertained that
the fungus traveled about one-half to two-thirds centimeter each day,
as indicated by the new limit of discoloration. On August 1 the stems
were hollow for the entire distance to the ground. On that day one of
the hollow stems was examined microscopically, mounts of tissue taken

PHYTOPHTHORA DISEASE OF GINSENG QI

from the inside being used, and odspores were found in great abundance.
The odspores were most abundant near the origin of infection, and grad-
ually diminished in numbers as the distance from this point increased.
Thus all developmental stages of the fungus were found on the inside of
the stem — odspores, odgonia, and mycelium. On August 7 the roots of
some of the infected plants were completely rotted, and the crowns of
others deeper in the soil were just beginning to rot. All the checks re-
mained perfectly healthy during the entire time.

Similar sets of inoculations were made on August 1 and August 15,
with identical results. On inoculated plants that were slightly injured,
too per cent of infection was obtained in every case; on plants that were
not injured, the percentage of infection was only from 25 to 50 per cent.

In the early stages of the rot in the root, mycelium may be found in
the tissues. In the summer of 1913 an examination of a rotted root
showed that one of the smaller rootlets contained numerous odspores.
In the fall of the same year, an inoculated four-years-old root was placed
in a test tube filled with sterile distilled water. An examination of the
root ten days later showed numerous odspores. This experiment has
since been repeated many times, but in all cases it has given negative
results. In general, in the later stages of the rot the roots become soft
due to the presence of soil organisms. When the roots are in this condition,
nothing definite can be learned of the relation of the Phytophthora to the
host.

The preceding data show how the fungus starts in the tops by infections
from conidia and travels down through the stem to rot the root. It was
found, however, that in many cases of artificial infection of the top, if
the root was some distance below the surface of the soil the fungus did
not attack it. In order to determine this point more definitely eighteen
plants were carefully transplanted at varying depths in the soil. The
depths used were 4, 1, 2, 3, 4, and 5 inches below the surface, three roots
being planted at each depth. The depth at which roots are commonly
found varies from } to 2 inches below the surface. The plants used as
checks were likewise transplanted. After transplanting, sufficient time
was allowed for the plants to establish themselves before inoculations
were made. The plants were inoculated by slightly injuring the tops
and placing the inoculum in the injured parts. As before, the fungus
traveled down the stems, this being made evident by a discoloration
and hollowing of the stems. In the case of roots 3, 1, and 2 inches below
the surface, all the roots rotted; of those planted 3 inches below the sur-
face, one root rotted and two remained healthy; while of those planted
4 or 5 inches below the surface, none rotted. The experiment was re-
peated, but instead of transplanting plants at various depths the stems

02 BULLETIN 363

of a number of plants were covered to various heights with soil. In these
experiments, while the number of plants rotting at each depth did not
correspond with the former, the experiments did agree in that they showed
a correlation between the number of roots rotting and the depth at which
they were planted. They also showed that in case of infections of plants
of the same age and with stems of approximately equal length, the fungus
took much more time to reach the root in the case of those stems that
were deepest in the soil. These facts are suggestive in considering the
control of the disease in the garden.

It was supposed that the fungus might pass from the tops to the roots
by conidia being washed down into the soil by rain water, and that those
coming into contact with the tissues of the roots would produce infection.
Numerous experiments were performed in order to determine this point,
by planting roots at various depths in both heavy and light soils and
drenching the plants with water containing conidia of the fungus. Con-
flicting results only were obtained, and in no case were there any signs
of infection unless the roots had previously been injured. Infection by
this method, if it occurs at all in nature, is of relatively slight importance.

The primary infection may start in the tops or in the roots. When
the roots are first attacked, the spread of the pathogen may be just the
opposite from that already described. Instead of traveling down the
stem and rotting the root, the fungus rots the root and continues its course
upward into the stem. Root infection may start from mycelium in the
roots or from odspores that have wintered in the soil. Hartig (1875)
has shown that odspores of the Phytophthora on beech, left in the ground
for four years, are still capable of germination and infection of healthy
plants. Repeated inoculations of ginseng roots placed in soil have
shown that the fungus, after rotting the root, can travel upward (Fig 13).
The following details of one series of these inoculations are offered: On
June 15, 1913, six roots of four-years-old plants were inoculated with a
pure culture of the fungus by removing the soil from one side of each
root, making a slight incision near the top, or crown, of the root with a
flamed scalpel, and placing a bit of inoculum at the point of injury. Four
check plants were injured in a similar manner, but were not inoculated.
On July 17 all the tops of plants with inoculated roots showed a character-
istic drooping and evidence that the roots were rotting. An examination
proved this to be the case. The tops were carefully removed, and mounts
were made from the inside of the stem at different distances from the
crown of the root, which was the original point of infection. The following
conditions were found: Two centimeters above the crown the stem was
hollow, and mounts showed an abundance of odspores, odgonia, and
mycelium. The tissues of the stem were brownish and water-soaked.

PHYTOPHTHORA DISEASE OF GINSENG

Fic. 13. CHARACTERISTIC SYMPTOM OF GINSENG MILDEW

The drying and shriveling of the stem near the crown of the root is an indication
that the Phytophthora is spreading from the root upward

94 BULLETIN 363 ’

e
Five centimeters above the crown the stem was firmer to the touch, though
still showing an abundance of odspores, odgonia, and mycelium. The
stem still presented a water-soaked appearance. Seven centimeters above
the crown the stem was not hollow, but was still slightly discolored and
mounts showed an abundance of mycelium. Evidently the mycelium at
this point was not old enough for a differentiation into spore forms. Ten
centimeters above the crown the stem was perfectly healthy and the
microscopic examination showed no evidence of the fungus. In order to
make sure that the mycelium and the spore forms seen belonged to Phy-
tophthora, plantings from the interior of the stem from these various
points were made on poured oat agar plates. The fungus obtained from
these plantings was Phytophthora, identical with the fungus with which
the roots had been inoculated.

MORPHOLOGY OF THE FUNGUS
MYCELIUM

The mycelium of the fungus in culture is very characteristic and can
be distinguished readily as a Phycomycete if examined carefully. Septa,
as a rule, are absent, except for an occasional one in very old cultures.
The branching is irregular, and consists of
threads of varying diameter, as well as
knoblike and button-shaped protuberances.
The protoplasmic contents are granular,
intermingled with oil globules and other
larger bodies. The larger bodies are found
for. the most.) part in mycehumMormrsan
advanced stage.

In plant tissue, especially in the root,
Se the mycelium is scanty. The main branches

eee are intercellular. Small branches are often

seen to penetrate the cell walls. There is
FIG. 14. PASSAGE Or MycELIUM = @ constriction at the point of passage and
FROM CELL TO CELL a broadening out on each side of the cell
sricted af the point where it pases wall (Fig..tq). In. other words ‘iheyigganes
Tarn) eo neet “or ceveciun are reduced! )to) mere. threads amatpeceme
pees within the host cell. uit through the wall. Hartig 882) deserbes
Bee B with a 4millimeter and illustrates the haustoria of P. omnivora
as spherical. Klebahn (1909:75) and Cole-

man (1910:61), however, figure them as rather elongate and finger-like, in
which case they agree closely with those of the Phytophthora of ginseng.

In making mounts of affected stems, it was found in many cases that
where the conidiophores arose in great abundance the mycelial branches

PHYTOPHTHORA DISEASE OF GINSENG 95

had also penetrated within the cells. Morphologically the haustoria-like
branches are not particularly specialized, since the conidiophores arise
directly from them or from short inner branches extending from these
swollen threads.

CONIDIOPHORES

The conidiophores arise from the mycelium within or between the
epidermal cells. When about to produce conidiophores, the branches
of the mycelium within these cells become slightly swollen at their tips.
On emergence from the tissues, the swelling is immediately followed
by a reduction in the
diameter of the thread.

Ly
The reduced thread Uy
pushes or dissolves its
way directly through \
the cuticle and the vf
cell wall. In many
De

cases the conidio-

phores arise at the
point of junction of pe
two cell walls, but yy

this is by no means
always the case. The A ]

. . B
conidiophores, after

passing through the Fic. 15. coNmropHORES OF PHYTOPHTHORA FROM GINSENG

i (A) Manner in which the conidia are borne on the conidiophores (16-
small opening: th the millimeter objective); (B) manner in which the conidiophores emerge

cell wall, may swell] ‘om the tissue of the host

slightly and then grow into a long, almost straight stalk, which is
usually not more than one-half or one-third the diameter of the hyphe of
the mycelium from which it arose. The conidiophores never exhibit the
peculiar swelling just back of the point where a conidium is borne which
is so characteristic of Phytophthora infestans. (Fig. 15.)

CONIDIA

The conidia are ovate, with a prominent apical swelling, or papilla
(Fig. 16). The papilla is lighter in color than the remainder of the
cell, and apparently thinner also. At the larger rounded end of the spore
the short broken attachment of the conidiophore is seen in some cases.
The walls are smooth and hyaline. The double walls of the conidium,
which indicate its sporangial nature, are quite evident, the inner one
being much thinner than the outer. The contents are alveolate and
granular. Often the center of the spore shows a large, clear spot, re-

96 BULLETIN 363

sembling a large vacuole. Conidial measurements, as pointed out pre-
viously, average 34.5 by 27n.

The conidium arises as a swelling. At first, and often until near
maturity, it is almost globose in form. It gradually becomes ovate,
the papilla being the last part of the spore to take its form. This appears
about the time of maturity. In many instances, especially in cultures
of considerable age, a tube is sent out from a little below the papilla,

Fic. 16. GERM_NATION OF CONIDIA OF PHYTOPHTHORA CACTORUM
Various stages in the germination of conidia by tubes, with the production of secondary and tertiary
conidia, are shown above. Below are shown the germination of conidia by means of swarm spores, and
the germination of swarm spores

and at the apex of this another conidium is formed. The contents
of the first conidium pass through the tube into the second conidium.
The process may be repeated two or three times, giving the appearance
of a chain of conidia. As a rule, each succeeding conidium is slightly
smaller in size than the preceding one.

PHYTOPHTHORA DISEASE OF GINSENG 07
O7

GERMINATION OF CONIDIA

The conidium is potentially a sporangium. It germinates normally
in one of two ways, either directly by the production of numerous germ
tubes, or by the production of swarm spores.

GERMINATION BY GERM TUBES

The most usual and most abundant type of germination observed is
by means of germ tubes produced directly from the sporangium itself
(Fig. 17). The number of germ tubes varies. The tubes are large and

Fic. 17. GERMINATION OF CONIDIA OF PHYTOPHTHORA CACTORUM

Various stages in the germination of conidia of Phytophthora cactorum from ginseng by means of
germ tubes

rather straight, with relatively few branches. They arise most commonly
from the ends of the sporangium. Those arising from the proximal end
of the sporangivum ordinarily are fewer in number than those arising
from about the apex. Moreover, the germ tubes from the proximal end
commonly emerge directly from the point where the spore was attached
to the conidiophore. At the apex the germ tube very seldom arises from
the papilla, but usually from the side of the spore a short distance below the
papilla. It is very characteristic of many of these germinations that the

98 BULLETIN 363

germ tubes at the distal end arise in a whorl, or cluster, around the papilla.
These germ tubes are densely granular, the contents of the sporangium
passing out into them. The first evidence of loss of protoplasmic contents
of the sporangium is the appearance of rather large vacuoles here and there
through the spore.

GERMINATION BY SWARM SPORES

Germination by means of swarm spores (Fig. 16) was observed a number
of times by making mounts from fresh cultures in drops of water in van
Tieghem cells or on object slides. Swarming has also been seen on an
object slide in a drop of water under a cover glass. The time for such
germination varies. The first evidence of the presence of swarm spores in a
sporangium is the movement of the protoplasmic granules in certain centers,
or areas, in the sporangium. In some cases swarming is seen fifteen
minutes after the conidia have been placed in drops of water. In other
cases no signs of swarming are evident for from two to three hours. In
examining a mount made for this purpose, there is often noticed a sudden
and tremendous swarming in practically all of the sporangia. The swarm
spores appear in the mount by hundreds, and a rapid review of the spo-
rangia under low magnification shows swarm spores rolling out of nearly
every one. It is a most exciting and extraordinary sight.

The manner of emergence varies. Usually the swarm spores emerge
singly and very quickly from the thin, narrow, papilla-like opening.
The time usually required for the emergence of the mass of spores is
from four to ten seconds. After emergence the spores are usually held
together at the opening for from two to three seconds, after which they
all swim apart in different directions. Often they do not congregate
near the opening, but swim away as fast as they emerge. It often happens
that for some reason two or three swarm spores do not emerge when the
majority escape. In one case those left were noticed apparently trying
hard for fifty-five minutes to get out, without success. At times, in
- their movements, they were at the very opening. It gave the impression
that the opening where the majority of swarm spores escaped became
closed again, and thus prevented the emergence of those left behind.
In one particular case the spore came to rest and germinated inside the
sporangium, the germ tubes extending through the walls of the sporangium.
Very often two swarm spores, after emerging together, seem to stick
together for two or three seconds, held by a fine protoplasmic thread
or connection, after which each darts off by itself.

SWARM SPORES

The number of swarm spores in a sporangium varies with the size
of the sporangium — the larger the sporangium, the greater the number

PHYTOPHTHORA DISEASE OF GINSENG 99

of swarm spores produced. The greatest number ever observed was
thirty-six. Each swarm spore is provided with light-colored spots,
or vacuoles, which are located nearer one end of the concave side. The
concavity is near the smaller end of the pyriform swarm spores. It
appears that here also are attached the flagella. These are two in number
and of unequal size, varying in size from one and one-half to two times the
length of the body of the swarm spores.

After swimming for a time, the swarm spores come to rest, withdraw
their flagella, become round, and germinate by sending out germ tubes.
Germ tubes of considerable length are formed within a short time after the
swarm spores have come to rest. Ordinarily one single germ tube is formed
by each spore.

It has always been a matter of interest to discover what determines
whether germination is to be by swarm spores or by germ tubes. Different
investigators have attributed the phenomenon to different causes. Klebahn
(1909) cites a case showing that oxygen apparently is necessary for the
emission of zodspores, while Coleman (1910) states that the formation
and emission of zodspores in a sporangium is clearly influenced by external
factors, chief of which is a certain strength of light. Coleman states
further that zodspores can be obtained in the Areca Phytophthora by
suspending sporangia in water, placing them on the stage of the micro-
scope, and illuminating them by means of the mirror and the condenser.
This has been tried by the writer, not only for the ginseng Phytophthora
but for the Areca Phytophthora as well, but for some unknown reason
without success. In the same paper Coleman cites an experiment in
which a number of cultures were kept in the dark and an equal number
in the light. He draws no conclusions from the experiment, but from
the results obtained one is led to believe that light is necessary for the
formation of sporangia. In the writer’s experience with Phytophthora
cactorum from ginseng, this has not been the case.

After numerous attempts to germinate conidia both from plants in
the field and from growths on various media, the writer is inclined to the
opinion that the age of the conidium has more to do with its manner
of germination than external conditions. Conidia taken from young
cultures — that is, cultures just beginning to form conidia — are more
likely to germinate by swarm spores than are older conidia. In the case
of conidia formed on the host, those having favorable conditions for
germination soon after formation will germinate by swarm spores, while
the others will germinate by germ tubes.

SEXUAL ORGANS

The antheridia and the odgonia form from the mycelium of the fungus
when the fungus reaches a certain age. This varies with the medium

TOO 1e> BULLETIN 363

on which it is grown. The antheridium and the odgonium mey arise
as branches of the same thread or from different threads (Figs. 11 and 12),
but always the threads are close together. The antheridium and the
oogonium are terminal swellings of their branches. The formation
of the two structures takes place simultaneously. In some cases the
stalks bearing the antheridium and the odgonium are on the same side,
and the antheridium then falls on the odgonial stalk. Under the micro-
scope, such a condition may present the appearance that the odgonium
has grown through the antheridium (Fig. 11).

The antheridium at maturity is from elliptical to reniform in shape,
and is cut off by a cross wall from the main part of the thread. The
odgonium is globose and much larger than the antheridium, and is also
cut off by a septum. The protoplasm in the early stages, in both the
antheridium and the odgonium, is finely granular, with a number of
oil globules varying in size.

FERTILIZATION

Preceding the formation of the odsphere a change takes place in the
odgonial contents. The protoplasm becomes denser, and, together
with the oil drops, collects in the center. After the odsphere has been
formed in the odgonium, one may detect in some cases a fine, lght-
colored passageway extending from the antheridium to the wall of the
odsphere (Fig. 11). This is the fertilization tube. The passage of any
contents into the odsphere from the antheridium has never been observed,
though it undoubtedly takes place as an examination of later stages
shows that the contents of the antheridium are less dense. But at
this time the fertilization tube has disappeared. In one case on five-
days-old oat agar culture numerous fertilization tubes were seen. The
tubes were present also on the following day, but on the seventh day
all signs of them had disappeared. In no case do all the contents of
the antheridium pass into the odsphere in the act of fertilization, as is
the case in many of the Phycomycetes.

OOSPORE

After fertilization has taken place the odspore gradually changes color,
from hyaline to yellow or brown. During this change in color there is
a gradual thickening of the wall of the odspore. The odgonial wall per-
sists, but without any change. In most cases, however, in this species,
careful focusing will show that the antheridium is superimposed on the
oogonium.

OOSPORE GERMINATION

All attempts by the writer to germinate odspores during the year 1912
and a part of 1913 met with failure, even though the odspores were taken

PHYTOPHTHORA DISEASE OF GINSENG IOI

from cultures almost a year old. Accordingly, in the fall of 1913 it was
decided to place the odspores under as nearly natural conditions as possible.
Transfers of pure cultures of the Phytophthora isolated from ginseng
and of Phytophthora cactorum from Phyllocactus were made on sterilized
bean pod plugs in test tubes. At the end of two weeks these were examined
and were found to contain numerous odspores. Some of the test tubes
containing the odspore material were sealed with paraffin and covered

Fic. 18. GERMINATION OF OOSPORES OF PHYTOPHTHORA CACTORUM

with small rubber caps. From the remainder of the test tubes the bean
pod plugs were removed and placed in small five-inch flowerpots con-
taining sand. On December 2, 1913, the covered test tubes and the
pots were taken out of doors and buried an inch below the surface of
the soil. On January 8 following, one of the pots was dug up. Small
bits of the bean pod material containing odspores were placed in hanging
drops of water to germinate. They were examined on several successive
days, but no signs of germination were visible. On January 29 one of
the covered test tubes was brought in and bits of material were placed

102 BULLETIN 363

in drops of water, but no signs of germination could be seen. Instead
of discarding the remaining material, the test tube was partly filled with
sterile distilled water. Mounts in van Tieghem cells and in drops of
water were again made from this test tube on February 20. An exami-
nation on the following day showed that many of the odspores had germi-
nated. On the next day the remaining material was brought in and
placed under water. At the end of two weeks no difficulty was encountered
in germinating odspores from any of the material. The germination of
odspores of the Phytophthora from both ginseng and Phyllocactus was
identical.

The odspores of the wintered material are granular, some being denser
than others. In some cases the odgonial wall is broken or entirely gone
and only the thick wall of the odspore is seen, in other cases the oégonial
wall still persists. Just before germination the granular substance becomes
denser near the periphery and the wall of the odspore takes on a striated
appearance. Through a break in the wall a germ tube is sent out. The
contents of the odspore gradually pass into this tube, which, when it
has attained a sufficient length, bears a conidium. More than one
conidium may be borne, as is the case with ordinary conidiophores. As
germination proceeds, the striations on the odspore wall disappear and
the wall itself diminishes in thickness. Various stages in the germination
of the odspores are represented in figure 18.

The conidia thus produced have been seen to send out ordinary germ
tubes, as well as to break up into swarm spores.

CONTROL

The various methods of control of Phytophthora of ginseng fall
under the following heads: (1) spraying with fungicides; (2) removal of
diseased plants or parts of plants; (3) deep planting; (4) crop rotation;
(5) sterilization of the soil; (6) drainage.

SPRAYING

As has been pointed out, the most favorable time for infection is very
early in the spring, just as the plants are pushing through the soil. At
this time the plant tissues are succulent and tender, and the temperature
and weather conditions, as a rule, are most favorable for spore germination
and infection. In order to prevent this early infection of the tops, a
fungicice should be applied as the plants are pushing through the soil,
and the application should be continued at intervals until all the plants
have made their appearance. Spraying after this period will depend
on weather conditions and on the amount of growth that the plants have
made since the last applicatien. Spraying should be done before rainy
periods, and all the new growth should be covered with the fungicide.

PHYTOPHTHORA DISEASE OF GINSENG 103

Various fungicides, such as lime-sulfur solution, bordeaux mixture,
and bordeaux mixture with arsenate of lead, have been tried for two
seasons. Lime-sulfur solution in some cases causes injury to the foliage.
As between bordeaux mixture with and without the addition of arsenate
of lead, the former has been found to be the more satisfactory. Arsenate
of lead seems to improve the adhesive quality of the mixture, which remains
on the foliage longer when this is used. The fungicide employed should
therefore be bordeaux mixture 3-3-50, to which has been added two pounds
of arsenate of lead for every fifty gallons of mixture.

REMOVAL OF DISEASED PARTS

It has been found that if the diseased tops — that is, those that show
a wilting and drooping — are removed just as soon as they are noticed,
the fungus will be prevented from traveling down the stem. When the
root is believed to be affected, it should be carefully removed from the
bed. It is a good practice to disinfect the soil with a fungicide at the place
from which the root has been removed. Formaldehyde, one part to
twenty-five parts of water, or copper sulfate, one pound to ten gallons
of water, is a good solution for this purpose.

DEEP PLANTING

During the summer of 1911, in a garden three-quarters of an acre
in size, almost every plant was lost through attacks of Phytophthora.
The disease seemed to start in the tops, and in ashort time nearly every root
in the garden was affected. There were, however, about a dozen plants
scattered throughout the garden which did not seem to be affected. These
came up again the following spring, and on examination it was found
that without exception the roots of the plants not attacked were planted
at least four inches below the surface of the soil. From artificial infections
recorded in the preceding pages, it is seen that the fungus can travel
down the stem and rot the root. When the crown of the root is several
inches below the surface of the soil, however, there is less likelihood that
the root will rot. In the case of the potato Phytophthora, hilling up
of the rows has been suggested as a means of reducing the rot of the tubers;
but the method appears to be impracticable, since it causes a consider-
able reduction in yield. In the case of ginseng, the roots are left in the
ground for five years or longer.

ROTATION OF CROPS

A garden once affected with Phytophthora cannot be again used for
ginseng for some years. A number of growers whose land had become

104 BULLETIN 363

infected allowed the land to he fallow for two years. They then planted
seed, and the seedlings were attacked to a considerable extent by the
disease. Hartig (1882) showed that the odspores can live for a number
of years in the soil. Financially the grower cannot afford to let his land
lie fallow for a period of years, since it is almost impossible to move
the shade. The writer therefore suggests that a rotation with some
other crop, requiring the same conditions of shade, be practiced. Golden
seal (Hydrastis canadensis) is a good plant for this purpose. A number
of inoculation experiments have been made with the ginseng Phytophthora
on golden seal, and in no case has there appeared any evidence of infection.

STERILIZATION OF SOIL

Where it is not desirable to practice rotation of crops, the sterilization
of soil by means of steam will prove of value. The steam pipe method
and the inverted pan method have been tried. The inverted pan method
is by far the more satisfactory, because of the greater ease with which
the pan is handled and because less of the steam is lost than in the pipe
method.

The pan should be of galvanized iron, of a width equal to that of the
beds in the garden, a length of ten or twelve feet, and a depth of from
five to seven inches. The sides should be provided with sharp edges,
which are forced down into the soil. The soil is prepared as for planting.
It is necessary to have a pressure of from seventy-five to one hundred
pounds for forcing the steam into the soil. The length of time required
for each pan will vary with the kind of soil, owing to the fact that steam
penetrates a sandy soil with greater ease than one of clay. Depending
on these conditions, the time will vary from twenty to forty minutes.

DRAINAGE

When plants are growing naturally in the forest, the excess water
in the soil is removed by the roots of trees and shrubs. Under culti-
vation some artificial means of removing the excess of water from the
beds must be employed. In one experiment it was found that a much
greater abundance of odspores was produced when the root was placed
in an abundant supply of water. Vegetable rots in general are favored
by an abundance of moisture. It is therefore suggested that some type of
underground drainage be employed to carry off the excess of water in the
soil. Ordinary hard-burned clay tiles have proved most effective and
permanent for this purpose. The depth, interval, and size of the drains
must vary with the character of the soil and of the subsoil and with the
amount of rainfall. In general the drains should be placed at a depth
of from two to three feet in sand and gravel, and from one and one-half

PHYTOPHTHORA DISEASE OF GINSENG 105

to two feet in clay. Where possible a tile drain should be placed under
the center of each bed, or the drains may be placed at intervals of from
six to eight feet. The size of the tile depends on the volume of water
to be carried. In the ginseng-growing sections of New York State a
three-inch tile has been found satisfactory.

| BIBLIOGRAPHY
Bary, Anton de
1876 Researches into the nature of the potato-fungus— Phytoph-
thora infestans. Roy. Agr. Soc. England. Journ. 2:12:
239-269.
1881 Zur kenntniss der Peronosporeen. Bot. ztg. 39:585—-595,
601-609, 617-626.
Coleman, L. C.
1910 _ Diseases of the Areca palm. I. Koleroga. Mysore State Agr.
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Hanai, I.
1900 [Japanese title.] On the culture and curing of the Idzumo
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Hartig, Robert
1876 Die buchencotyledonen-krankheit. Zeitsch. forst.- u. jagdw.
Scr 123"
1882 Phytophthora omnivora (Phytophthora Fagi und Peronospora
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Hook, J. M. van
1904. Diseases of ginseng. Cornell Univ. Agr. Exp. Sta. Bul.
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1906 A disease of ginseng due to Phytophthora. Spec. crops n. s.
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Hori, S.
1907 A disease of the Japanese ginseng caused by Phytophthora
cactorum (Con. et Leb.) Schrét. Imp. Cent. Agr. Exp. Sta.
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Jartoux, Father
1714 The description of a Tartarian plant, called ginseng; with an
account of its virtues. . . . Taken from the tenth
volume of letters of the missionary Jesuits. Roy. Soc.
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Klebahn, Heinrich
1909 Krankheiten des flieders, p. 1-75.
Lebert, H., and Cohn, F.
1870 Ueber die faule der cactusstamme. Beitr. biol. pflanz. 1: 51-57.

106 BULLETIN 363

Osterwalder, A.
1906 Die Phytophthorafaule beim kernobst. Centbl. bakt. 2:15:43 5-
440.
Saccardo, P. A.
1888 Phytophthora cactorum (C. et L.) Schroet. Syll. fung. 7:238.
Schenk, August
1875 Sitzungsberichte der Naturforschenden Gesellschaft zu Leipzig.
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Schroeter, J.
1889 Gattung Phytophthora De Bary. Krypt.-fl. Schlesien 3:23 5-
2306.
U. S. Department of Commerce, Bureau of Foreign and Domestic
Commerce
1914 The foreign commerce and navigation of the United States
for the year ending June 30, 1913, p. 394.
U. S. Secretary of the Treasury
1822 Letter from the Secretary of the Treasury, transmitting state-
! ments shewing the commerce and navigation of the United
States for the year ending the 30th September, 1821, p. 73.
Whetzel, H. H.
1910 The mildew of ginseng caused by Phytophthora cactorum (Leb.
& Cohn) Schroeter. Science n. s. 31: 790-791.
Whetzel, H. H., and Rosenbaum, J.
1912 The diseases of ginseng and their control. U.S. Plant Indus.
Bur Bul: aso217—10.

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