THE RELATION OF TEMPERATURE AND HUMIDITY
TO INFECTION BY CERTAIN FUNGI

A THESIS

Presented to the Faculty of the Graduate School
of Cornell University for the Degree of
Dector of Philosophy

By
JOHN IRVIN LAURITZEN

Reprinted from PHYTOPATHOLOGY, VoL. 1X, No. 1,
January, 1919.

Reprinted from PayropatHouoey, Vol. IX, No. 1, January, 1919

THE RELATION OF TEMPERATURE AND HUMIDITY TO
INFECTION BY CERTAIN FUNGI

Je le 15 ASu Ree ZEN,

INTRODUCTION

Very early in the history of plant pathology a fundamental relation be-
tween weather and plant diseases was recognized, not only by the pa-
thologist but by the farmer. Even before anything was known about the
nature of diseases, the weather was thought to have an intimate connee-
tion with their causes, and by many to be responsible for their production;
and yet very little work has been done to analyze the exact manner in
which weather conditions affect diseases or disease production, except in
an observational way.

The effects of temperature, humidity, rainfall, and dew have not been
isolated, except in a few cases, and then chiefly from observation or under
partially controlled conditions. Never, so far as the author is aware, has
the influence of temperature and humidity upon infection been studied
separately where both have been under control.

The importance of taking cognizance of the one while studying the
other in connection with any growth phenomenon will be emphasized from
the following examples of the influence of temperature and humidity on
the growth of bamboo. Shibata (28), working under field conditions in
Japan, gives a table which indicates a close relation between the daily
growth of bamboo and temperature (16°C. to 20°C.) and scarcely any re-
lation to humidity. Lock (19), working at Peradeniya, on the other
hand, found that the daily growth depends largely upon the water supply
and the moisture content of the air, and has little relation to the tempera-
ture, which in his experiments fluctuated beween 19° and 26°C.

The difference in the temperature of the two places will account for the
seeming discrepancy, as far as the temperature is concerned. At Pera-
deniya the temperature is apparently the optimum for the growth of bam-

1 Also presented to the Faculty of the Graduate School of Cornell University,
_ March, 1916, as major thesis in partial fulfillment of the requirements for the
degree of doctor of philosophy. The writer is indebted to Dr. Donald Reddick and
Dr. V. B. Stewart under whose immediate direction the work was performed for
valuable assistance and suggestions in connection with the investigation and in the
preparation of the manuscript.

8 PHYTOPATHOLOGY [Vou. 9

boo, and covers a range of several degrees, while in Japan it falls below
the optimum, consequently the growth curve follows closely that of the
temperature. A comparison of the humidity of the two regions, as far as
a comparison is possible from the data that are available, reveals very
little difference in the moisture content of the air. It is apparent that
this humidity, which varies largely between 70 per cent and 90 per cent
influences the amount of growth under the favorable temperature at Pera-
deniya. Its influence is evidently obscured by the unfavorable tempera-
ture in Japan. Whether the humidity can become so unfavorable as to
obscure the effects of temperature is not known from the data at hand,
but it is probable. One thing seems certain, however, that in studying
either of these factors one cannot afford to ignore the one while the other
is under observation; in fact, it would be preferable to hold one of these
factors constant when observing the other.

In earlier work in pathology a clear distinction has not been drawn
between the infection period and the period of incubation? Such a dif-
ferentiation is not always possible, and perhaps it is never possible to
state definitely the exact point at which the infection period ends or the
period of incubation begins. However, in most cases they can be sepa-
rated sufficiently to study each apart from the other. Considerable work
has been done to show the influence of temperature on the production and
development of disease, but the two periods have been studied con-
jointly. Less work has been done upon the relation of humidity to this
phenomenon but a sharper separation has been made between the infee-
tion and incubation periods.

Balls (4) conducted temperature-infection experiments with Rhizoc-
tonia (Corticium vagum B. and C., var. Solani Burt) on cotton (Gossypium
spp.) in which he found that infection took place and became evident in
twenty-four hours at a temperature of 20°C. At 33°C. no infection oc-
curred. Here the infection and incubation periods are crowded into such
a short space of time and apparently so fused together that probably it
would be difficult to separate them. The experiments were conducted by
placing mycelium of the fungus in contact with seedlings placed upon
several layers of moist filter paper in a petri dish, which in turn was placed
in an infection chamber.

Gilman (11) performed some soil infection experiments with Fusarzum
conglutinans Wollenw. on cabbage (Brassica oleracea L.) which are of inter-
est in this connection chiefly because he worked in a greenhouse in which
the temperature was automatically controlled. He also conducted some

2 Infection period as here used is the period during which the pathogen penetrates

the host until it becomes established with the host. Incubation period is the period
of development that follows until the symptoms of the disease become visible.

1919] LAURITZEN: INFECTION RELATIONS 9

experiments in a glass infection chamber where the temperature was con-
trolled by an electric thermo-regulator. The difficulty of studying in-
fection apart from the incubation period is here apparent. It is not,
however, so important in this instance that they should be studied sep-
arately, because the environmental factors are not so variable except in
the case of temperature.

Tisdale (29) studied the infection of flax by Fusarium Lint Bolley. He
found that the lower temperature limit for infection was about 15°C., and
makes the statement that most of the infection occurs between 20° and
30°C. The temperature was controlled in one set of experiments by em-
ploying positions at different distances from a radiator in a green house,
in another by means of a circulating water jacket about the plant con-
tainers. He also investigated the influence of temperature upon the growth
of the fungus in culture media, and determined the limits to be 10° and
37°C. with an optimum temperature at 26° to 28°C.

Johnson (14), in working with Thielavia basicola Zopf. to test the range
of parasitism ona large number of plants, controlled the moisture content
of the soil and recorded the soil and air temperatures. The temperature
of the air and soil depended upon greenhouse conditions.

Fromme (10) was unable to produce infection on oats (Avena sativa L.)
by Puccinia coronifera Kleb. with a relative humidity of 75 per cent to 80
per cent and a temperature of 55° to 85° F. He conducted an experiment
designed to determine what conditions of humidity were necessary for
infection. He grew his plants in an open case made of window sashes
where the humidity averaged 93 per cent with a variation of about 2
per cent to 3 per cent. Although he inoculated thoroughly, he obtained
only slight infection. In an experiment where one pot was covered and
another stood in an open box there was an average of 161.6 lesions per
plant in the first case as compared with 10.4 or 6 per cent in the latter.

Some interesting results were obtained by Levin (17) in connection with
an experiment planned to determine the time required for the infection
of tomatoes (Leyoporsicum esculentum Mill.) by Septoria lycopersici Speg.
He sprayed ten plants with a water suspension of spores, placing 9 of them
in a Wardian case, where a high humidity was maintained by means of a
fine spray of water. A plant was taken out at intervals of 6, 12, 24, 36,
48, 60, and 72 hours and dried immediately by an electric fan and placed
in an open window until infection became evident. After a lapse of five
days all the plants, including the one left on the outside, showed charac-
teristic lesions of the disease. This experiment was repeated in detail,
except that the plants after inoculation were exposed to a current of air
from an electric fan until the disease appeared. The results were similar
to those secured in the previous experiment. Infection was also obtained
by applying dry spores.

10 PHYTOPATHOLOGY [Vou. 9

From the results of these experiments the author concludes that it is
questionable whether a film of water over the plant surface for at least a
number of hours is essential to infection.

The purpose of the present study is to determine the influence of tem-
perature and humidity upon infection, and to find out whether a film of
water covering the surface of the plant is essential for the fungus to become
established upon the host.

APPARATUS

The apparatus consists of two double chambers with thermo-electric
connections to furnish heat, and power to run fans. The outer chambers
are 40 by 54 by 48 inches in size and are made of glass. The inner are 11
inches smaller in each dimension and so placed that there is an air space
of 5 inches on all sides. They are constructed of wood except the lids,
which are of glass and slope at an angle of 40° from the horizontal. The
wood portion is coated on the inside with paraffin of a high melting point’
to prevent the absorption of water. Both inner and outer chambers are
provided with heating coils and thermostats. In the latter case a relay
was employed to prevent sticking of the thermostat, which was occa-
sioned by the use of larger wire necessitated to produce the required heat
for the outer chamber.

The evaporation surface for the control of the humidity was supplied
by open pans containing either pure water or saturated salt solutions. The
humidity was read directly from psychrometers upon which was directed
a constant current of air from a fan.

FACTORS

In approaching any physiological problem one is confronted with cer-
tain difficulties. One of these is the isolation of the particular factor to
be studied. The conditions affecting physiological processes are not only
numerous, but complex, and sometimes so interrelated as to make their
separation impossible.

The usual procedure is to hold all the other factors constant in order to
get at the facts of the particular one to be observed. Having thus reduced
the problems to simple terms, one might think he cculd proceed directly
to the solution of his problem, but he soon finds that the procedure is not sc
simple. One should not only have the conditions constant, but they should
be at their optimum, and such an accomplishment is by no means easy,
if indeed possible, with our present knowledge of the nature of physiologi-
cal processes, the factors affecting them, or methods of investigation.

In the present study an attempt has been made to keep the known and
possible factors affecting infection constant as far as possible with the

1919] LAURITZEN: INFECTION RELATIONS iat

means accessible. An attempt has been made to control, in part, condi-
tions influencing the growth of the host plant, such as the fertility, physi-
cal properties, organic matter and water content of the soil, light, tem-
perature, and humidity. The first four of these conditions are fairly easy
to control; the latter three involve more difficulties. Temperature and
humidity have been controlled as far as is possible under greenhouse con-
ditions. Light is the most variable factor and no attempt has been made
to control it. The greatest difference in light is between summer and
winter. Whether this difference is sufficient to alter the susceptibility of
the host plant to the attack of the fungus, or in any way influences the in-
fecting ability of the fungus, is not known. No such influence has been
noticed in the present experiments. It would seem that influences of
light become less important when making comparison between the suc-
cessive periods required for the growth of the plants while they attain
sufficient size for inoculation purposes.

Temperature and humidity may affect each plant differently, which of
course is true of the other factors. The exact range of temperature and
humidity favorable for the growth of the plants employed in these experi-
ments has not been determined. A variation in the range with the plant
is, however, generally recognized. It would have been desirable to have
grown these plants under optimum conditions, but these conditions were
not available, besides the optimium for each of these plants is not known.
These same conditions also come into operation during the incubation
period.

Light as it exists under greenhouse conditions is not known to be a
factor. Since light under natural conditions is not usually regarded as the
limiting factor in photosynthesis, upon which host and parasite alike
largely depend for their organic nutrition, it would seem that the reduc-
tion in food due to the reduction in light under greenhouse conditions would
not be sufficient to alter the number of infections more than slightly, if
at all.

. It would seem reasonable to assume that temperature and humidity
during the incubation period do not influence the total number of infec-
tions if sufficient time is allowed for the viable spores to establish a rela-
tion with the host. It is possible that the border-line temperatures and
humidities might cause a variation in the susceptibility of the host to the
parasite. There is some evidence to support this position in the case of
temperature.

Ravn (25), in studying the influence of temperature upon the infection
of barley by Helminthosporium, found that the incubation period was
forty-eight hours in a warm greenhouse as compared with seventy-two
hours in a cold house. The total amount of infection was slightly in favor

12 PHYTOPATHOLOGY [Vou. 9

of the cold house. Fifteen out of 16 plants were infected in the cold
house, while 12 out of 15 in the warm house were infected. He concludes
from this experiment that temperature does not alter the total amount
of infection.

Fromme (10) obtained similar results with Puccinia coroncfera on oats.
Plants inoculated and grown at a temperature ranging from 20° to 30°C.
showed evidence of infection on the fourth day, while plants inoculated
at the same time and grown in a greenhouse at a temperature varying-
between 14.5° and 21°C. showed indications of the disease only after seven
days. This experiment was repeated with similar results. There was a
slight difference in time due to a difference in temperature, but the varia-
tion was in the same direction. The degree of infection was not, however,
different in the two cases.

It seems in the foregoing cases that the temperature employed, whether
high or low, was sufficiently favorable to permit of the maximum amount
of spore germination, or at least these temperatures allowed about the
same percentage of germination; otherwise there would be a difference in
the number of infections, unless we assume an alteration in the capacity
of the fungi to cause infection or of the hosts to resist it. The latter seems
less feasible because it would be a remarkable coincidence if there should
be a shift of virulence or susceptibility in such an exact ratio that we
would have the same number of infections even though there were a shift
in the percentage of germination, especially when we are dealing with
two different host plants as well as two pathogens.

Mains (20) by altering the humidity during the incubation period
obtained more infection on corn by Puccinia sorght Schw. under high
humidity than under low. He employed only 12 hours as an infection
period and it is possible that there would have been more infection
where the plants were under low humidity had the infection period been
extended.

CONDITIONS AFFECTING THE INFECTION PERIOD

The light in the infection chamber was much reduced. First, because
the inner chamber was partially constructed of wood; second, the light that
reached the plants passed through two panes of glass; and third, the source
of light was the diffused light of the headhouse. (It would have been de-
sirable for the inner chamber to have been of glass, but such a chamber
was not available.) Whether this subdued light for a period of twelve
hours was sufficient to alter the relation cf host and parasite can not be
stated from our present knowledge. It would be expected to affect the
host more than the parasite, because of the autotrophic character of the
host. Furthermore if this diffused light had any effect in the short.

1919] LAURITZEN: INFECTION RELATIONS 3

period of time during which the plants were in the infection chamber it
would be to reduce the photosynthetic processes. The reduced food would
probably affect only the last stages of infection, after the germ tube had
penetrated the host and the energy of the spore was exhausted or reduced.
On the other hand the assumption might be made that there is an altera-
tion in the susceptibility of the host, due to a disturbance of an osmotic
or chemical equilibrium. The usual time required for starch to be re-
moved from the plant in total darkness seems to indicate that there would
be no actual food shortage.
TABLE 1

Record of infection in total darkness as compared with the light of the headhouse in case
of bean and buckwheat and the greenhouse in case of wheat

LIGHT DARKNESS

DATE OF INOCULATION HOS! LUANe |S REMARKS
_Plants| Plants} Plants} Plants
infected} wilted |infected} wilted

July Qi lOve. 2. ..|| Bean 3-3 | 33] 3-3] 3-38] No apparent differ-
ence
Jialive2 Sel Oilh7= ee ee Sean 3-3 | 3-3] 38-3] 3-3 | No difference
Total Total

Plants |number| Plants |number
infected of |infected of
spots spots

August 6, 1917....... Buckwheat] 3-3 28 | 3-3 28 | The number _ of
August 28, 1917...... Buckwheat} 3-3 | 300| 3-3] 250 plants infected
and the number
of spots are the
criteria for the
amount of infec-
tion

February 24, 1918....| Buckwheat] 3-3 | 230 | 3-3] 295 | Under plants in-
January 25, 1918....| Wheat 23-24 19-21 fected 3-3 indi-
January 28, 1918....| Wheat 13-14 13-14 cates that three
out of three plants
were infected

Some experiments (table 1) were conducted to show whether total
darkness as compared with the light of the greenhouse in one case and the
light of the headhouse in two other cases alters the total infection of the
host plants employed, under the conditions of the experiments. The
following pathogens and host plants were used in the experiments: Col-
letotrichum lindemuthianum (Sacc. & Magn.) Bri. and Cav. on bean (Pha-
seolus vulgaris L.); Ascochyta fagopyrum Thuen. et Boll. on buckwheat
(Fagopyrum esculentum Moench.); Puccinia graminis Pers. on wheat (Tri-
ticum sativum Lam.). Both the bean and buckwheat experiments were

14 PHYTOPATHOLOGY [VoL. 9

conducted in the headhouse mentioned above. In each experiment three
plants were placed under a bell jar covered with black paper and three
under a jar not so covered. The jars stood on a table before a window.
The reason for using the headhouse instead of the greenhouse was that in
the latter, during the time in which the experiments were running, the sun-
light became so intense at times that under the high humidity of the
bell jars the plants were liable to injury. The wheat experiments were
performed in the greenhouse during the winter months when the sunlight
was not so intense; in fact, cloudy weather prevailed most of the time.
The other conditions of the wheat experiments were the same as those
mentioned above except that there were more plants used. The experi-
ments were repeated in each case and were run for twenty-four hours,
after which the plants were removed to the greenhouse, where they re-
mained until infection became evident. The temperature range was largely
between 70 and 80° F. The results are represented in table 1.

It seems fairly safe to conclude from these experiments that light in
the infection chamber is not a limiting factor in case of the plants used.
It is possible, however, that at the border temperatures and humidities
light may manifest itself as a limiting factor. —

The carbon dioxide relation

When plants are’ placed in a closed chamber there is an accumulation of
carbon dioxide whenever it is not used up by photosynthesis. The extent
of this accumulation depends upon the tightness of the chamber and the
amount of circulation provided. The question arises as to whether the
concentration of the carbon dioxide becomes sufficiently great in the in-
fection chamber to become deleterious to the host and parasite. If there
is an injurious effect, it is possible that the effects are the same in both
host and parasite, in which case there probably would be no change in
the number of infections. There would be a greater accumulation of ©
carbon dioxide at the higher temperatures, at least until the optimum for
respiration was reached, and consequently the effects would be more seri-
ous than at low temperatures.

The chambers were not perfectly air-tight. This was indicated by the
fact that whenever the electricity was cut off from the heating coils the
fall in temperature was sufficiently rapid to show some interchange of
air between the inside and outside of the chamber. The greater the dif-
ferences in temperature on the inside and outside, the greater would be
the exchange consequently the tendency for accumulation of CO, at high
temperatures would be compensated for (at least in part). It would
seem therefore that the source of error from carbon dioxide injury would
be slight if not negligible.

1919] LAURITZEN: INFECTION RELATIONS 15

Influence of sudden change of temperature

When the host plant and pathogen are introduced into the infection
chamber they are subjected to a more or less sudden change of tempera-
ture, especially when working at low temperatures.

A number of investigators have studied the influence of a sudden change
of temperature upon growth in flowering plants, with contradictory results.
Sachs (26) and Pedersen (22) conclude that the growth curve follows
closely that of temperature. Koeppen (15), Askenasy (3), True (30),
Price (23), and Lehenbaur (16) claim that the change itself has a tem-
porary effect, the time varying from one-half to three hours, depending
upon the investigator and the amount of change. The evidence seems to
be in favor of the latter conclusion. How much this temporary effect
may influence infection is not known. Eriksson (9) exposed aeciospores
of Puccinia graminis to a temperature of 3°C. for two hours and then
raised the temperature to about 20°C. He claims that such a change has
a beneficial effect and increases the percentage of germination. Melhus
(21) found that intermittent temperatures, whether changing from high
to low or vice versa, tend to slightly check germination, but suggests that
the small variation may be due to experimental error.

Duff (6) found that urediniospores of Cronartium ribicola F. de Wal.
(which become less viable with age and lose their power of germination ‘in
four weeks) which were placed in a refrigerator two weeks after collection
germinated only in a small percentage, but a reduction in temperature
stimulated a large increase in germination. Spores subjected to a sudden
change of temperature three weeks after being collected were stimulated
to a slight degree to germinate.

The control of temperature and humidity

On the whole, with the sizé of the chambers employed the temperature
can be kept within a variation of 1°F. The constancy of the tempera-
ture is greatly facilitated by the double chamber arrangement with two
heating systems and by the use of fans both in the inner and outer
chambers.

The temperature control was limited by outside conditions. The cham-
bers were situated in a potting room of a greenhouse where it was possible
to maintain a fairly low uniform temperature during the winter. The
temperature of the room could be altered by ventilation and the use of
steam radiators. This arrangement was sometimes convenient when
working at higher temperatures.

The control of humidity was accomplished by means of open pans of

16 PHYTOPATHOLOGY [Von. 9

water or saturated salt solutions in combination with temperature
manipulations.

Humidities above 95 per cent were difficult to attain whenever the tem-
perature on the inside of the chambers was much higher than that of the
outside air, because of inequalities in temperature in the outside chamber.
This difficulty was partly overcome by the use of an electric fan and by
placing beakers of water on the heating coils. A device was developed
during the later stages of the investigation by which it was possible to
maintain a saturated condition of air. Instead of using the air heating
coils as a source of heat a water heating coil was placed in an evaporating
pan containing water, thus insuring a slightly higher temperature of the
evaporating surface than of the air and consequently a saturated
atmosphere.

Whenever a lower humidity than 95 per cent was desired saturated salt
solutions were used. An excess of salt insured a definite vapor pressure
at a given temperature and hence a constant humidity. The wide range
of vapor pressure of saturated salt solution made it possible to obtain
almost any humidity desired.

It is not possible to predict the exact humidity that will result from a
given saturated solution. First, because the vapor pressure of the ma-
jority of saturated solutions has not been worked out for the various tem-
peratures; second, the vapor pressure of the entire system is altered by the
introduction of plants. The leaf surface presents an evaporating surface
very near that of pure water, tending to increase the humidity of the
system. However, as soon as the system comes to an equilibrium, the
bumidity becomes constant. It is possible by the inspection of the vapor
pressure of the various salts at a given temperature to predict what salt
to employ in order to obtain an alteration in humidity in the desired direc-
tion. The humidities obtained from the various salts vary in the same
direction as the vapor pressures of those salts. Some of the salts*used are
as follows:—Potassium sulphate with a vapor pressure of the saturated
solution of 17.21 mm. mercury at 20°C., Barium chloride V.P. at 20°C.
15.45, Sodium nitrate V.P. at 20°C. 13.7 mm., Cadmium chloride V.P. at
202@: 1222 mm,

Relative humidity as a unit of comparison

As has been pointed out by Livingston and others, relative humidity
is not a satisfactory unit of comparison whenever more than one temper-
ature is employed. Livingston (18) suggests the use of vapor pressure
deficit, which equals the difference between the maximum vapor pressure
of water vapor at a given temperature and the actual pressure of water
vapor in a given space at a given temperature.

Ee eee

1919] LAURITZEN: INFECTION RELATIONS 17

METHODS AND MATERIALS

The following pathogens and host plants were employed in these ex-
periments: Collectotrichum lindemuthianum (Sace. & Magn.) Bri. & Cav.
on red kidney bean (Phaseolus vulgaris L.) Puccinia graminis Pers. var.
tritici Erick on wheat (Triticum), and Ascochyta fagopyrum on buck-
wheat, gray variety,(Fagopyrum esculentum Moench.). The fungi employed
were all pure line strains to which the respective hosts were susceptible.
An attempt was made to secure pure line strains of the host but this
could not be done except in the case of wheat.’

The bean and buckwheat plants were grown in two inch pots and the
wheat in an inch and a quarter pots in a greenhouse with a temperature
ranging from 60° F. to 85° F. and relative humidity varying from 60 per
cent to 85 per cent.

Plants of the game age were used as far as possible. Some variation
was inevitable, however, even under greenhouse conditions. The beans
were usually from sixteen to twenty days old, the wheat from seven to
ten, and buckwheat from twenty to twenty-four days old. An effort was
likewise made to use spores of the same age. Here some variation oc-
curred, due to the necessarily different conditions under which the organ-
isms were grown. Colletotrichum was grown on bean pods, Ascochyta on
potato agar, and the spores of Puccinia graminis obtained directly from
pustules on the host plant.

Twenty pots were used in each experiment, with one plant in each pot,
except in case of wheat, where the number of plants varied from three to
five. These cultures were divided into five series of four pots each and
designated by the following symbols: Ch 1, Ch 2, Ch 3, F, and D. The
plants in Ch 1 were taken directly from the greenhouse when the particu-
lar experiment was started, and placed in the infection chamber. The
purpose of this series was to show whether or not any infection that oc-
curred was due to spores that may have come in contact with the host
before inoculation. The remaining four series were sprayed with a spore
suspension from an atomizer (except in case of wheat) and used as fol-
lows. The plants in Ch 2 were placed in a special chamber at tempera-
tures and humidities known to be favorable for the development of the
disease. This procedure was to determine whether the spores were viable
and whether infection would take place if conditions were favorable.
The plants of Ch 3 were dried immediately by means of an electric fan
and left in the greenhouse as a check to show whether infection occurred

> The wheat seed for these experiments was furnished by Dr. E. C. Stakman.
This strain was given the number 169 by him and was used because of its suscepti-
bility to the attack of Puccinia graminis.

18 PHYTOPATHOLOGY [Vou. 9

in the infection chamber or in the greenhouse. Series F consisted of plants
placed in the infection chamber directly after inoculation and covered
with a water suspension of spores. In series D the plants were dried at
once and placed in the infection chamber. This series was employed to
determine whether a film of water over the surface of the plants was es-
sential to infection. Sometimes series D was omitted in the temperature
experiments.
TABLE 2

Record of amount of infection on wheat plants by Puccinia gramints tritici at various
low temperatures, the humidity being practically constant

EXTENT OF INFECTION

DEPRES-| RELA- 1 1 1 1

DATE OF INOCULATION eon See | Raa z pe ga ee
TEMES Ee BULB ITY Number| Number| Number} Number

fo} of fo) of

plants | plants | plants | plants
infected | infected | infected | infected

December 18, 1917..... 53.0-52.6 0.4° | 97.5 | 12-342} 0-17 | 17-18 0-16
December 19, 1917..... 53.0-52.6 0.4° | 97.5 8-28 0-20 | 14-24 | 0-16
December 31, 1917..... 52. 7-52.2 OFd Se OO 9-43 0-24 | 22-25 0-16
December 21, 1917..... 51.7-51.2 0.5° | 97.0 | 23-43 0-18 | 16-22 0-20
January 3, 1918.....| 50.8-50.4 ORAS 9 7e0 2-30 0-15 | 18-22 0-14
January 10, 1918.....) 49.8-49.75 | 0.05°| 99.0 5-44 0-18 | 19-20 | 0-17
December 10, 1917..... 47 .2-46.7 0.5° | 96.0 0-380 0-16 | 16-19 0-12
January 6, 1918..... 47.1-46.75 | 0.85°| 97.0 2-44 0-16 | 19-20 | 0-16
December 11, 1917..... 47 .0-47.0 0.0° |100.0 1-40 0-20 | 17-25 | 0-22
January 19, 1918.....| _46.85-46.75} 0.1° | 99.0 1-41 0-22 | 25-35 0-22
January 22, 1918.....| 46.48-46.2 | 0.28° 98.0 7-35 0-16 | 27-27 0-16
January 21, 1918.....) 45.5-45.3 0.2° | 98.0+] 5-31 0-17 | 12-24 0 26
December 14 ......... 42.2-42.0 0.2° | 98.0+] 0-88 0-20 | 23-23 0-14

1 An explanation of symbols is given on page 17.
2 In this table the number of diseased plants is the criterion of infection. 12-34,
0-17, 17-18, 0-16, etc., means that 12 out of 34 plants, 0 out of 17, etc., were infected.

The wheat was inoculated by removing the spores from pustules of
diseased leaves by means of a scalpel and spreading them on the wheat
leaves. Ch 2 and F were then sprayed with water from an atomizer.

The plants were allowed to remain in the infection chamber for twenty-
four hours and were then returned to the greenhouse, where they remained
until the disease developed. The time for the development of the dis-
ease varied somewhat with the greenhouse conditions, but since the time
is influenced little during the infection period it was not considered in
recording data. Sufficient time was allowed in each case for any possible
infection to become manifest. Bean plants were allowed ten to fourteen
days, wheat thirteen to twenty, and buckwheat ten to fifteen days.

ee ee ee ea ae

1919] LAURITZEN: INFECTION RELATIONS 19

An electric fan was placed in the greenhouse in such a position as to
blow a current of air between and above the plants in order to prevent
the accumulation of higher humidities immediately around the plants.
This procedure was found necessary in some instances to prevent infection
of buckwheat. The bean and wheat never showed any tendency to the de-
velopment of the diseases in the greenhouse. In one instance Ch 3 plants
showed infection in case of wheat.

TABLE 3

Record of infection on buckwheat plants by Ascochyta fagopyrum at various low
temperatures, the humidity remaining practically constant

- EXTENT OF INFECTION!
A
B F Ch. 1 Ch. 2 Ch. 3
I es
PSYCHROME- a 8 ro) B @ S 2
mrocicanmon) ymeeeerinss; 8) 3 | a le le |e 5 =
6 | a | sel 2, | 3s | se g oo
aw > Se ag gS a+ ag S2
g a or |) 2 || cer | dag aS a2
ae |e ee Se ae $3 Bie
8 Bie ze Rein ah eel, a Z
December 21, 1917 |59.50—-59.15] 0.35°| 98.0] 7-8 | 52 | 0-4 | 442|} Numerous] 0-4
December 22, 1917 |56.70-56.10} 0.6° | 96.0) 0-8 0 | 0-4 | 4-43 43 0-4
December 19, 1917 |56.10—55.40} 0.7° | 95.5} 2-9 4 | 0-4 | 44 55 0-4
January 14, 1918...)54.25-54.18) 0.07°} 99.0} 1-8 1 | 0-4 | 44 60 0-4
January 7, 1918.../58.25-53.00} 0.25° 98.5} 1-8 1 | 0-4 | 44 20 0-4
December 11, 1917 |48.40-48.00) 0.4° | 97.0) 0-8 0 | 0-4 | 4-4 ay 0-4
January 22, 1918.../46.48-46.1 | 0.38°| 97.0) 48 15 | 0-4 | 44 100 0-4
January 21, 1918.../45.60—-45.35) 0.25° 98.5} 1-8 3 | 0-4 | 44 150 0--4
December 13, 1917 |42.80-—42.60} 0.2° | 98.5} 0-8 0 | 0-4 | 44 | Numerous} 0-4
December 10, 1917 |41.70—40.65} 1.05°| 92.0] 0-6 0 | 0-4 | 4-4 36 0-4
December 14, 1917 |38.00-37.80} 0.2° | 98.5] 0-8 0 | 0-4 | 4-4 All dead | 0-4

1 Two methods of measuring the amount of infection are employed in this table,
for example, in column 1 under F the number of diseased plants is used as a basis,
while in column 2 the total number of lesions occurring on all the plants marked F
are given.

2 All plants were wilted.

3 Infection on primary leaves only, 3 plants wilted, one leaf of remaining plant
wilted. bg

Influence of low temperature upon infection of wheat

From table 2 it will be seen that wheat can become infected by Puccinia
graminis at a temperature as low as 45.5° F. but the infection is very
slight and rapidly decreases at temperatures below 45.5° F. In the single
experiment run at 42° F. there was no infection. This experiment should

PHYTOPATHOLOGY

20

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LAURITZEN: INFECTION RELATIONS 21

1919]

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22 PHYTOPATHOLOGY * [Vou. 9

at least have been duplicated but the low temperature did not prevail at
the time. However, the humidity was very favorable and the infection
between this point and 50° F. was very slight. It seems therefore that
45° F. is near the lower limit of infection. This point is only about 9° F.
above the lowest temperature at which Johnson (13) was able to obtain
germination of spores of Puccinia graminis.

The amount of infection rises rapidly from within a few degrees of the
lower limit to almost a fair average for the higher temperatures, indicating
that there is no definite optimum temperature for infection. These results
correspond to those obtained by Johnson (13) for germination of spores
of Puccinia graminis. He found no definite optimum temperature when
percentage germination was used as a basis for measuring the amount of
germination.

Influence of low temperatures upon infection of buckwheat by Ascochyta
fagopyrum

No infection was obtained in buckwheat below 45.5° F (table 3). An-
other experiment at 42° F. and at high humidity should have been con-
ducted as a further check upon the lower limit but the outside temperature
was not sufficiently low to do so. Some variation in the amount of in-
fection between 45° F. and 59° F. will be noted, and even an absence of
infection in some cases. An observation of a certain phenomenon in con-
nection with spore germination of the pathogen suggests a possible ex-
planation of this variation. At times, and for reasons unknown, the fun-
gus produced one-celled spores. Whether these spores are merely imma-
ture spores is not known, because old cultures sometimes contain them.
These spores do not germinate nearly as well as the two-celled spores.
At higher temperatures, however, they seem to produce infection. It is
possible that these spores may fail to produce infection as the tempera-
ture becomes less favorable. This problem needs to be solved.

Low temperatures and infection of bean by C. lindemuthianum

From table 4 it will be seen that the lower limit for infection of bean
by Colletotrichum is 57°F. where the plants remain in the infection cham-
ber for twenty-four hours. It is possible that if this time were extended,
a lower limit might be obtained.

The rise in the amount of infection here as in case of wheat and buck-
wheat is rapid. Excellent infection was secured at 63° F.

1919] LAURITZEN: INFECTION RELATIONS 23

Infection of wheat at higher temperatures by P. graminis tritic

The highest temperature at which Puccinia graminis will produce infec-
tion in wheat (table 5) is 80° F., at least under the conditions of the experi-
ment. This temperature is 7.8° F. below the maximum at which the
spores will germinate. It is possible that in a saturated atmosphere this
temperature might be raised. It seems probable, however, that the
highest temperature at which infection will take place is below the maxi-
mum for germination.

TABLE 5

Record of infection on wheat plants by Puccinia graminis at various high temperatures,
the humidity remaining practically constant

- EXTENT OF INFECTION!
=)
Fe E pb: | Ch.1 | Ch.2 | Ch.3
a g
etiam || Ol Sie ects wipe Pa Boge by oh eee
DATE OF INOCULATION Pee aTon & < B25 223 ase 223 B29
FAHR. SCALE x, = crapgeg st: ||| cemete| | came rst ll alls alll eal es
B | Ba6 | BS6 | BSS] BS | Bas
a yal rcs lth gece (bers cs ee] trey ete] cas
a 2 | Ess |'sS| bes) bs8| 5e8
=) td a Z Z Z Zi
ATUISTISG ZO nl Oe se a ae ae = 82.4-81.70} 0.7° |97.0+] 0-4 0-4 0-4 4-4 0-4
September 3, 1917......../82.0-81.30) 0.7° |97.0+) 0-4] 0-4; 0-4]' 44) 0-4
PACT OUSiG 2s Qe meee ee 81.5-81.10) 0.39°/98.5 0-4 Q-4 Q-4 4-4 0-4
September MM ooconbos 80.8-80.00) 0.8° |97.0 0-4 0-4 0-4 4-4 0-4
September 24, 1917....... 80.0-79.10) 0.9° |96.0+] 0-4 1-4 0-4 4-4 0-4
September 27, 1917....... 80.0-79.00) 1.0° |96.0 1-4 0-4 0-4 4-4 0-4
September 29, 1917....... 78.0-77.00} 1.0° |96.0 1-5 1-2 0-4 4-4 O-4

1 In these experiments the number of plants diseased was not counted (there be-
ing 3 to 5 plants in each pot), but the number of pots in which infection occurred
was used as basis of measurement.

2 Explanation of symbols is given on page 17.

Infection of bean at higher temperatures by C. lindemuthianum

The highest temperature at which infection took place in bean was
80° F. (table 6). With both wheat and bean a large number of experi-
ments were run at temperatures above 80°. The increase in the number
of plants infected was rapid as the temperature was lowered. The range
covered is not sufficient to show the same decided increase in the amount
of infection. One finds this suggestion, however, in the data.

This maximum temperature for infection falls 7.8° F. below the tem-
perature at which Edgerton finds Colletotrichum to grow in culture
media.

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LAURITZEN: INFECTION RELATIONS 25

1919]

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26 PHYTOPATHOLOGY [Vou. 9

Infection of buckwheat at higher temperatures by Ascochyta fagopyrum

The upper limit for the growth of buckwheat appears to be about 100° F.
(table 7). Most of the plants collapsed after having been in the infection
chamber at this temperature for twenty-four hours. Yet in one instance
typical Ascochyta lesions appeared on plants that survived. I have ger-
minated the spores of the fungus at a temperature of 106° F. The*’maxi-
mum temperature for germination has not been determined. Some ex-

TABLE 7

Record of infection of buckwheat by Ascochyta fagopyrum at various high temperatures
and within the humidity range at which infection takes place

t EXTENT OF INFECTION

4

cy F D |Ch.t| Gh2 |ch3

> ta

lal SI

psycHrome- | F A 2 3 oS ioe 3 @
DATE OF INOCULATION |TER READINGS| §& 5 A ae Sl by eB iB “= iS
FAHR. SCALE | _ S 2 £ ‘@ | 2 canbe Tee a rai

° a Roles} g S| 8 ‘oo lou! § woles)

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per
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March 12, 1918... .|100.0-100.0) 0° |100.0} 2-11! 2 —| — | 0-42 |4-4 37 |0-4
March 13, 1918... ./100.0-100.0} 0° |100.0) 0-83 0 —| — | 0-44 /4-4) 119 |0-4
Aueust 3, 1917.52.) 97 t= JoeZizso ole a) a Sev- |1-4/Few] 0-4 |4-4) Nu- |2-4°
eral mer-
ous

September 27, 1917} 93.3— 90.8/2.5°| 91.5} 1-4 1 |1-4| 3 | 0-4 |44 90 |0-4
September 28, 1917} 92.6— 90.3/2.3°| 92.0} 1-4 5 |1-4| 2 |0-4 |44 24 |0—4
September 6, 1917] 91.0— 88.0/3.0°| 89.0) 3-4 10 |1-4) 2|04 |44) 117 |0-4

1 Four out of 11 plants were dead. Remaining were all injured.

2 All 4 plants were dead at end of infection period.

3 Seven out of 8 plants were dead.

4 Two plants dead; 2 remaining plants injured.

> These plants show infection but they were at the end of the greenhouse, where

there was dropping from the roof.

periments were conducted at temperatures above 100° F., but the plants
~ always died.

The limits of temperature at which infection by Ascochyta occurred in
buckwheat were wider than in wheat and bean. In the latter two the
maximum temperatures for growth are higher than for infection. — It is
possible, at least in case of beans, to grow them at temperatures unfavor-
able for the fungus and thus escape the losses due to this disease where

. the other conditions for its development are favorable.

1919] LAURITZEN: INFECTION RELATIONS 27

Infection of buckwheat at various humidities by Ascochyta fagopyrum

In table 8 is shown the infection of buckwheat at various humidities,
the temperature remaining nearly constant. The lowest humidity at
which infection has been observed to take place on buckwheat is 91 per
cent. The humidity rises to 94.5 per cent where the plants were dried
before placing them in the chamber. It will be noted, however, that con-
siderable infection took place at this humidity. This table not only shows
that infection can take place at the temperatures considered, within a

TABLE 8

Record of infection on buckwheat by Ascochyta fagopyrum at various humidities, the
temperature remaining practically constant

EXTEND OF INFECTION
Q
4
B Ch. h
B . F D nl Chiba: 3
psycHRrom-| = 5 | a 3s |2 ly |2 la ls n
DATE OF INOCULATION pes a A 5 Bl le, oe i 2 z = E
FAHR.SCALE| z BP lee. ee police le B a
bee a |ool§ [Sulf [Suley| € [sx
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2 | & lefisalecigelecles| se lee
EB a |58/$.8ls8/58/5.8|58| 22 |58
Qa a if |b |j4@ la |4@ |&@ a Zz
November 15, 1917............|77.1-76.2] 0.9°)96.3 |38-4) 23/34) 11/0-4/4-4| 321 |0-4
November 20, 1917............|77.6-76.3} 1.3°/95.0+/2-3} 12/34] 17/04/44) 57 |0-4
November 13, 1917............|78.0-76.0} 2.0°/91.0 |1-4) 2/0-4| O|0-4/44) 54 |0-4
November ss, (9722-022... 78.7-76.9| 1.8°|91.5 |0-4| Oj|O-4) O|0-4)4-4) 100 |0-4
November 27, 1917............]77.3-75.2] 2.1°/90.6 |2-4) 410-4) O/0-4/4-4) 55 |c-4
October Oliienaes seer oe 77.1-74.5| 2.6°|89.0 |0-4| Oj0-4| Oj|0-4/4-4) 37 |0-4
October Ss IG meanness aie ee 77.2-74.7| 2.5°|89.0 |0-4| Oj0-4) O/0-4/4-4| 46 |0-4

1 Plant wilted (lesions not counted).

range from 91 per cent to 100 per cent humidity, but that a film of water
covering the leaf surface is not essential to infection.

The question may arise as to the possible presence of a film on the leaf
surface at such high humidities. It has been observed throughout these
experiments that plants placed in the chamber with a film covering the
leaf surface are dry when removed at the end of twenty-four hours. Since
the chamber is always run at a temperature above that of the surround-
ing atmosphere, evaporation must always take place because under these
conditions saturation is rarely ever reached. The only cases where a
condition of saturation has been observed are at the lowest temperatures.

98 PHYTOPATHOLOGY [Vou. 9

Infection of wheat at various humidities by P. graminis tritici

The range of humidity for infection in wheat (table 9) is a little nar-
rower than it is for buckwheat. The lowest humidity at which infection
has been observed is 95 per cent. No infection takes place at 92 per
cent and below. The same general difference is observed between the
plants with a film and those without. The dry plants require a slightly
higher humidity.

TABLE 9
Record of infection of wheat by Puccinia graminis tritici at various humidities, the
temperature remaining practically constant

EXTENT OF INFECTION
Q
A
Fy F D | Ch.1| Ch.2 | Ch3
Boy oP Hi 8 |
PSYCH ROME- z 2) 2 2 g 2 2
DATE OF INOCULATION TER READINGS 5 a a a qa qa
FAHR. SCALE 2 B ra Ta ra ra ra
9 6 Od Os os os Roles)
CD a) Ee heros Parsee |e
a SI 23 23 23 23 23
F < | 2 | 2 | 2 | Sa | 83
eS a 3.8 3.5 5.8 i 3.8
| a ? a Z Z A Z Z
February 18, 1918.......| 70.0-69.6 | 0.4° | 98+ | 12-15) 15-17} 0-27 | 22-22) 0-25
March 7, 1918...........| 68.9-68.4 | 0.5° | 97 5-22} 5-17) 0-26 | 14-18] 0-17
Marchi OS sesame 68.2-67.3 | 0.9° | 96 5-16} 2-19) 0-16 | 10-15} 0-13
February 24, 1918....... 67.5-66.7 | 0.8° | 96— 8-19) 3-16) 0-20 | 28-29) 4-24!
IMianchige 4 elOliS ie nreeae 68.9-67.9 | 1.0° | 95 7-16} 3-13) 0-15 | 10-11} 0-12
Meno 10), NOUS: 2 5585a600 68.0-67.0 | 1.0° | 95 6-17} O-17| 0-18 8-11) 0-17
November 17, 1917...... 68.0-66.5 | 1.5° | 93 0-16) 0-15} 0-17 0-14
November 22, 1917...... 68.2-66.7 | 1.5° | 93 0-15} 0-14) 0-12 | 12-17) 0-14
November 28, 1917...... 68.5-67.0 | 1.5° | 93 0-15) 0-15) 0-15 | 14-18} 0-14
November 12, 1917...... 68.1-65.6 | 2.5° | 88 0-20) 0-17) 0-18 | 12-16} 0-19
December 3, 1917........ 68.0-65.3 | 2.7° | 88 0-14] 0-16) 0-17 | 11-15) 0-13

1 In this case Ch 3 showed slight infection, the only case ever recorded on wheat.

The temperatures at which the humidities were studied were arbitrarily
selected, after considerable preliminary work. These temperatures were
thought to be within the limits of the optimum.

Influence of humidity upon infection of bean by Colletotrichum
lindemuthianum

The lowest humidity at which infection took place in bean is near that
of wheat. The data in table 10 do not show any infection at 95 per
cent humidity, but only one experiment was run at this humidity. Nega-
tive results were also obtained with wheat at 95 per cent humidity.

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LAURITZEN: INFECTION RELATIONS

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30 PHYTOPATHOLOGY [Vou. 9

A large number of experiments were run at humidities above 95 per
cent. The data given in the table are representative of the results ob-
tained. A large number of experiments were conducted at humidities of
92 per cent and below.

There is a rapid rise in the number and extent of infections from 95
per cent up to 100 per cent. At 97 per cent humidity, the highest hu-
midity given in the table, the amount of infection approaches closely that
in Ch 2, where saturation was attained at least part of the time and where
the film over the leaf was maintained throughout the infection period
due to precipitation because of alterations in temperature. The tem-
peratures in Ch 2 varied largely between 65° F. and 75°F. The same
influence of the presence of a film is to be noted as in the wheat and
buckwheat.

DISCUSSION AND CONCLUSIONS

Heretofore the study of the effects of temperature upon the relation of
parasite to host has been limited largely to the influence of temperature
upon the growth of the fungus and the germination of the spores. In a
few cases the effects of temperature upon the development and extension
of diseased tissue has been studied (Ball (4), Brooks and Cooley (5) ).
This phenomenon is largely one of growth and seems to obey, in the main,
the Van’t Hoff law. The growth of the fungus behaves in the same way
(Tisdale (29), Brooks and Cooley (5) ).

A number of methods have been employed to measure the effect of
temperature upon germination, with varied results. In some cases it
would seem that all the factors involved were not considered.

The extension of the germ tube ‘and the development of mycelium have
been used as a basis for the study of the influence of temperature upon
germination and infection (Johnson, E. C. (13), Wiesner (80), Balls (4),
ete.). Here one is dealing with a growth phenomenon, and when food is
not a limiting factor one would expect the behavior of this phenomenon
towards temperature to be the same as found among flowering plants and
the growth of fungi in culture media. For every increase of 10°C. (within
certain limits) there would be a doubling or trebling of growth in a given
time (Tisdale (29), Brooks and Cooley (5), Edgerton (7) ).

The time required for germination has been used as a measure of the
influence of temperature. The results have been rather uniform, and
there has been a general shortening of time with an increase of temperature
to a more or less optimum temperature in the same proportion as de-
manded by the Van’t Hoff law (Anderson (1), Hecke (12), Wiesner (31),
Ravaz (24), Melhus (21), Shapovalov (27)). Ames (2) obtained varied
results with different species. In some cases the optimum is very broad,

1919] LAURITZEN: INFECTION RELATIONS 31

while in others the time is shortened with an increase of temperature to a
rather definite optimum.

Where percentage germination has been used as a criterion for measur-
ing the effects of temperature, fairly uniform results have been obtained.
The optimum, as a rule, is broad, as one would naturally expect if suf-
ficient time were allowed at the lower temperatures for germination to
take place. If ashorter time were used different results might be expected.
Melhus’ (21) results with the spores of Phytophthora infestans show a fairly
broad optimum (5° to 13°C.) where he used the number of cultures in
which germination occurred as a basis of measurement of the temperature
effects. It is sharper, however, than that obtained by other investigators.
Where he used the percentage germination in the various cultures as a
criterion, there was a gradual rise in percentage from 5° to 13°C. He
states, however, that there was a variation from 13 to 80 per cent in
germination at the optimum. This fact may account for the difference in
the two curves. Ames (2) abandoned percentage as a basis of measuring
the effects of temperature upon germination because her results were not
uniform. Anderson (1) found the percentage germination of the spores
of Cylindrosporium scoparium Morg. was almost total between 12° and
30°C., ranging between 95 and 100 per cent. Johnson (13) did not ob- -
tain a definite optimum temperature for Puccinia graminis by percentage
germination, there being no uniformity between 9° and 25°C.

From these results it would seem that the number of spores which
germinate does not rise with an increase in the temperature to a definite
optimum, but that the range at which a large number of spores will germi-
nate is wide. One would expect, then, that there would be a wide range
of temperature at which the number of infections that would take place
would not vary much if sufficient time were allowed for the spores at lower
temperatures to cause infection, providing some other factor did not enter
in. This view corresponds to the results of the present experiments (tables
2, 3, and 4). Some experiments were conducted between the tempera-
ture limits given in the tables with results which conform to this conclu-
sion. These results have also been confirmed by Ravn and Fromme
(pages 11 and 12).

An understanding of this phenomenon is important wherever the num-
ber of lesions, such as in leaf spots, fruit spots, ete., is responsible for the
chief loss due to diseases. If there were a definite optimum, the number of
lesions that would develop would gradually decline as the temperature
was lowered from the optimum. The infection phenomenon viewed in
this light implies a different attitude towards control measures. Not
only must the degree of temperature be considered, but the time to which
the host plant is exposed to conditions of infection, in connection with

a2 PHYTOPATHOLOGY [VoL. 9

the number of infections that take place as well as the development and
extension of a particular lesion.

Some incidental data obtained in the present investigation in connec-
tion with infection of bean by C. lindemuthianum near the lower tempera-
ture limit indicate that the time element is important. The data point
to a lower temperature limit for infection where forty-eight hours were
used for an infection period than where twenty-four hours were used.

From the data presented, an interesting relation between host and
parasite is brought out. The temperature ranges for host and parasite
are not identical in any of the cases. The temperature range for growth
of bean and wheat is wider than for the germination of spores and of
infection by C. lindemuthianum and P. graminis. The maximum temper-
ature for infection by the two pathogens is about the same in the time
employed (tables 5 and 6) while the lower limit for infection by P. gram-
inis (compare tables 2 and 4) is lower than for infection by C. lindemu-
thianum. The upper temperature limit for the growth of bean is higher
than for germination of the spores of and infection by C. lindemuthianum,
which fact has made possible the control of anthracnose in the Southern
States. The optimum temperature for the growth of bean is probably
higher than that of wheat.

The exact temperature ranges for Ascochyta and buckwheat have not
been determined. There is no indication as to which has the wider
range. Their ranges do not coincide, because buckwheat is killed at a
temperature at which infection takes place and below the maximum tem-
perature for germination of spores of Ascochyta (table 7). These relations
are all important in connection with control measures.

The variation in the amount of moisture in the air in different regions —
is probably important in the distribution of diseases over the earth’s sur-
face. The absence of certain diseases in semi-arid and arid regions where
agriculture has been practiced for long periods of time may be due in part
to the small moisture content of the air.

Seasonal variation in the moisture content of the air plays an important
part in determining the amount of disease that may develop.

In the course of the present investigation (compare tables 8, 9, and 10),
a variation in the humidity in the air required for infection for the indi-
vidual plant has been exhibited. Infection occurred at a slightly lower
humidity in buckwheat than in case of bean and wheat. As mentioned
earlier, it was necessary to provide for circulation of air about the buck-
wheat plants to prevent infection in the greenhouse. This same provision
was found requisite in a few experiments conducted with Septoria lyco-
persici Speg. on tomato. The tendency for infection to take place in the
greenhouse was more marked with tomato than with buckwheat.

1919} LAURITZEN: INFECTION RELATIONS 33

The degree of humidity in the general environment of the plant may be
an inaccurate criterion of the amount of moisture required for infection,
at least when there is little air movement. The air movement created by
an electric fan over a bench in the greenhouse has been sufficient to pre-
vent infection of buckwheat by A. fagopyrum and of tomato by S. lycoper-
sict where in its absence infection took place. The higher humidity in
the immediate environment of the plant may be of considerable significance
in connection with infection in nature.

Just how the spore upon the plant surface obtains sufficient moisture
for germination and infection is an unsolved problem. Within certain
limits of humidity, that is, where the evaporation is not too great, the spore
is able to absorb sufficient water for germination. The absorption may
be from the host plant, at first by imbibition and later by osmosis. It is
possible that in the depressions of the leaf surface and especially immedi-
ately above the stomata a higher humidity prevails which may afford
sufficient moisture for germination.

There is a possible relation to hairiness because the juvenile leaves of
buckwheat have more hair than the secondary leaves and seem to be
infected more readily (the data contained in the tables are from the sec-
ondary leaves). The secondary leaves of the bean are more pubescent
and seem to be infected more easily at the limiting humidities. The hair
would tend to prevent evaporation and increase the humidity at the leaf
surface.

SUMMARY

The lower temperature limit for infection of wheat by Puccinia graminis
triticc is somewhere near 42°F. The amount of infection rises rapidly
and at 53° F. it approaches the average for higher temperatures.

The lower temperature limit for infection of buckwheat by Ascochyta
fagopyrum is about 45° F. There is some variation in infection between
this temperature and 59° F., possibly due to the one-celled spores some-
times produced in culture.

The lower temperature limit for infection of bean by Colletotrichum is
about 57° F. This limit may be influenced by the time the plants are in
the infection chamber.

The upper temperat re limit for infection of wheat is 80° F.

The maximum temperature for infection of buckwheat by Ascochyta
is about 100° F. At this temperature buckwheat plants are injured or
killed.

The upper temperature limit for infection of bean is 80° F. With the
decrease of temperature there is a rapid increase in the number of plants
infected.

34 PHYTOPATHOLOGY [Vou. 9

There seems to be no definite optimum temperature for infection in
the hosts and parasites used where the number of infections is used as a
measure of the amount of infection and sufficient a is allowed for the
fungi to establish a relation with the hosts.

The range of humidity for infection of buckwheat varies between 90
per cent and 100 per cent. Where the plants are dried off before being
placed in the infection chamber, it varies between 94.5 per cent and 100
per cent.

The humidity range for infection of wheat is between 92 per cent and
100 per cent. The lowest humidity at which infection has taken place
is 95 per cent. The range for the dried plants is a little narrower.

The range of humidity for infection of bean lies between 92 per cent
and 100 per cent.

A film of water covering the leaf surface is not essential to infection.

BureEAv OF PLANT INDUSTRY,

WASHINGTON, D. C.

LITERATURE CITED

(1) AnpERSON, J. P. Rose canker and its control. Mass. Agr. Expt. Sta. Bul. 183:
7-46. 1918.
(2) Ames, ADELINE The temperature relations of some fungi causing storage rots.
Phytopathology 5: 11-19. 1915.
(3) Askmenasy, E. Ueber einige Beziehungen zwischen Wachsthum und Temper-
atur. Ber. Deut. Bot. Ges. 8: 61-94. 1890.
(4) Batts, W.S. Temperature and growth. Ann. Bot. 22: 557-591. 1908.
(5) Brooks, CHarRLES, AND Cootry, J. 8S. Temperature relations of apple-rot
fungi. Jour. Agr. Research 8: 139-164. 1917.
(6) Durr, Grorce H. Some factors affecting viability of urediniospores of Cro-
nartium ribicola. Phytopathology 8: 289-292. 1918.
(7) Epererton, C. W. Effect of temperature on Glomerella. Phytopathology 5:
247-259. 1915.
(8) Epagerton, C. W. Effect of temperature on Glomerella. Science n. s. 41: 174.
1915.
(9) ErRtKsson, J. Ueber die Férderung der Hnespettenl seein durch Kalte.
Centb’. f. Bakt. II 1: 557-565. 1895.
(10) Fromme, F. D. The culture of cereal rusts in the greenhouse. Bul. Torrey
Bot. Club. 40: 501-521. 1913.
(11) Gruman, J. C. Cabbage yellows and the relation of temperature to its occur-
rence. Ann. Missouri Bot. Gard. 3: 25-82. 1916.
(12) Hecxre, Lupwic Untersuchungen iiber Phytophthora infestans De By. als
Ursache der Kartoffelkrankheit. Jour. Landw. 46: 97-142. 1898.
(13) Jounson, E. C. Cardinal temperatures for the germination of uredospores of
cereal rusts. Phytopathology 2: 47-48. 1912.
(14) Jounson, James Host plants of Thielavia basicola. Jour. Agr. Research 7:
289-300. 1916.

1919] LAURITZEN: INFECTION RELATIONS 35

Koeppen, W.P. Wirme und Pflanzenwachsthum. Bul. Soc. Imp. Nat. Moscou
43, 1870: 41-110. 1871.

LEHENBAUER, P. A. Growth of maize seedlings in relation to temperature.
Physiological Research 1: 247-288. 1914.

Levin, Ezra The leaf-spot disease of tomato. Michigan Agr. Expt. Sta. Tech.
Bul. 25: 1-51. 1916.

Livineston, B. E. The vapor tension deficit as an index of the moisture
condition of the air. Johns Hopkins Univ. Cir. 293:170-175. March,
1917.

Lock, R. H. On the growth of giant bamboos with special reference to the re-
lation between conditions of moisture and the rate of growth. Ann. of
Roy. Bot. Gard., Peradeniya 2: 211-267. 1904.

Mains, E. B. The relation of some rusts to the physiology of their hosts.
Amer. Jour. Bot. 4; 179-220. 1917.

) Metuus; I. E. Germination and infection with the fungus of the late blight

of potato. Wisconsin Agr. Expt. Sta. Research Bul. 37: 1-64. 1915.

) Peprerson, R. Haben Temperaturschwankungen als solche einen ungiinstigen

Hinfluss auf das Wachsthum? Arb. Bot. Inst. Wiirzburg 1: 563-583.
1874.

Price, H. L. The application of meterological data in the study of physiologi-
cal constants. Ann. Rpt. Virginia Agr. Expt. Sta. 1909/10: 206-212. 1911.

) Ravaz, L. anp Verax, G. Influence de la température sur la Germination des

conidies du mildiou. Prog. Agr. et Vit. 57: 170-177. 1912.

Ravn, F. Koupin Nogle Helminthosporium-Arter og de af dem fremkaldte
Sygdomme hos Byg og Havre. Bot. Tidskr. 23: 101-322. 1900.

Sacus, J. Textbook of botany. Translated by Alfred W. Bennett assisted by
W. T. Thistleton-Dyer. Oxford, 1875.

SuHapovaLov, Micwarut Effect of temperature on germination and growth of
the common potato-seab organism. Jour. Agr. Research 4: 129-1338. 1915.

Suipata, K. Beitrage zur Wachstumsgeschichte der Bambusgewiichse. Jour.
of Sci. Imp. Univ., Tokyo 13: 329-496. 1900.

TispaLe, W. H. Relation of temperature to the growth and infecting power of
Fusarium lini. Phytopathology 7: 356-360. 1917.

Truer, R. H. On the influence of sudden changes of turgor and of tempera-
ture. Ann. Bot. 9: 365-402. 1895.

WIESNER, JuLIuS Untersuchungen iiber den Einfluss der Temperatur auf die
Entwicklung des Penicillium glaucum. Sitzber. Akad. Wiss. (Vienna)
Math. Naturw. Kl. 68: 5-16. 1874.