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 Summary
 Bibliography














Group Title: Bulletin / University of Florida. Agricultural Experiment Station ;
Title: Angular leaf spot and fruit rot of cucumbers caused by Bacterium lachrymans E.F.S. & Bry. /
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026749/00001
 Material Information
Title: Angular leaf spot and fruit rot of cucumbers caused by Bacterium lachrymans E.F.S. & Bry. /
Series Title: Bulletin / University of Florida. Agricultural Experiment Station ;
Physical Description: 32 p. : ill., chart ; 23 cm.
Language: English
Creator: Weber, George F ( George Frederick ), b. 1894
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla
Publication Date: 1929
Copyright Date: 1929
 Subjects
Subject: Cucumbers -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 32).
Statement of Responsibility: by George F. Weber.
General Note: Cover title.
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Bibliographic ID: UF00026749
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - AEN4065
oclc - 18173262
alephbibnum - 000923514

Table of Contents
    Front Cover
        Page 1
    Main
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
    Summary
        Page 31
    Bibliography
        Page 32
Full Text


October, 1929


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilnion Newell, Director





ANGULAR LEAF SPOT AND

FRUIT ROT OF CUCUMBERS

Caused by Bacterium Lachrymans E.F.S. & Bry.



By GEORGE F. WEBER


Fig. 1.-Cull cucumber fruits discarded at field packing shade because of
infections of Bacterium lachrymans. Near Williston, Florida.


TECHNICAL BULLETIN


Bulletins will be sent free upon application to the
Agricultural Experiment Station
GAINESVILLE, FLORIDA


Bulletin 207







BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola
E. W. LANE, Jacksonville
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry


FRANK J. WIDEMAN, W. Palm Beach
J. T. DIAMOND, Secretary, Talla-
hassee.
J. G. KELLUM, Auditor, Tallahassee


STATION EXECUTIVE STAFF


WILMON NEWELL, D. Sc., Director
S. T. FLEMING, A.B., Asst. Director
J. FRANCIS COOPER, M. S. A., Editor
R. M. FULGHUM, B. S. A., Asst. Ed.


IDA KEELING CRESAP, Librarian
RUBY NEWHALL, Secretary
K. H. GRAHAM, Business Manager
RACHEL MCQUARRIE, Accountant


MAIN STATION-DEPARTMENTS AND INVESTIGATORS


AGRONOMY
W. E. STOKES, M. S., Agronomist
W. A. LEUKEL, Ph. D., Asso.
C. R. ENLOW, M. S. A., Asst.*
FRED H. HULL, M. S. A., Asst.
ANIMAL HUSBANDRY
A. L. SHEALY, D.V.M., Veterinarian,
in Charge
D. A. SANDERS, D.V.M., Asst. Vet.
E. F. THOMAS, D.V.M., Asst. Vet.
C. R. DAWSON, B. S. A., Asst.
Dairy Investigations
CHEMISTRY
R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph. D., Asso.
C. E. BELL, M. S., Asst.
H. L. MARSHALL, M. S., Asst.
J. M. COLEMAN, B. S., Asst.
J. B. HESTER, B. S., Asst.
COTTON INVESTIGATIONS
W. A. CARVER, Ph. D., Asst.
M. N. WALKER, Ph. D., Asst.
E. F. GROSSMAN, M. A., Asst.
RAYMOND CROWN, B.S.A., Field Asst.


ECONOMICS, AGRICULTURAL
C. V. NOBLE, Ph. D., Ag. Economist
BRUCE McKINLEY, A.B., B.S.A., Asst.
M. A. BROKER, M. S. A., Asst.
ECONOMICS, HOME
OUIDA DAVIS ABBOTT, Ph. D., Chief
L. W. GADDUM, Ph. D., Asst.
C. F. AHMANN, Ph. D., Asst.
ENTOMOLOGY
J. R. WATSON, A. M., Entomologist
A. N. TISSOT, M. S., Asst.
H. E. BRATLEY, M. S. A., Asst.
HORTICULTURE
A. F. CAMP, Ph. D., Horticulturist
M. R. ENSIGN, M. S., Asst.
HAROLD MOWRY, B. S. A., Asst.
G. H. BLACKMON, M. S. A., Pecan
Culturist
PLANT PATHOLOGY
W. B. TISDALE, Ph. D., Plant Path.
G. F. WEBER, Ph. D., Asso.
K. W. LOUCKS, B. S., Asst.
ERDMAN WEST, B. S., Mycologist


BRANCH STATION AND FIELD WORKERS

R. R. KINCAID, M. S., Asst. Plant Pathologist (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (Lake Alfred)
W. L. THOMPSON, Assistant Entomologist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)
R. V. ALLISON, Ph. D., Soils Specialist (Belle Glade)
J. H. HUNTER, M. S., Assistant Agronomist (Belle Glade)
L. O. GRATZ, Ph. D., Associate Plant Pathologist (Hastings)
A. N. BROOKS, Ph. D., Associate Plant Pathologist (Plant City)
A. S. RHOADS, Ph. D., Associate Plant Pathologist (Cocoa)
STACY 0. HAWKINS, M. A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
R. E. NOLEN,. M. S. A., Field Assistant in Plant Pathology (Monticello)
FRED W. WALKER, Assistant Entomologist (Monticello)

*In cooperation with U. S. Department of Agriculture.







ANGULAR LEAF SPOT AND FRUIT ROT OF
CUCUMBERS
Caused by Bacterium Lachrymans E.F.S. & Bry.
By GEORGE F. WEBER*
INTRODUCTION
Angular leaf spot and fruit rot of cucumbers in Florida are
considered by growers to be diseases of first importance in the
production of a profitable crop. These diseases make their ap-
pearance almost every year, causing considerable loss to grow-
ers. Since it has been observed that fruit rot never appears in
any cucumber field except in association with angular leaf
spot, the investigations reported herein were inaugurated for
the purpose of determining their relationship to each other and
methods of their control.

THE DISEASE
History.-Angular leaf spot and cucumber fruit rot have been
known in the United States for almost 20 years.
Smith and Bryan (20)** first reported a bacterial fruit rot of
cucumbers, but inoculations made with an organism isolated
from decaying fruits were unsuccessful. In 1911 Burger (1) re-
ported a new cucumber fruit disease in Florida. He found this,
disease bacterial in nature and associated it with the angular
leaf spot of that plant. He had the disease under observation for
several years afterward and reported a single organism causing
both leaf spot and fruit rot (1, 2, 3, 4). More recently these dis-
eases have been found in a majority of the states east of the
Mississippi River and in certain of the northern states. How-
ever, the general distribution is limited to sections of certain
central states north of the Ohio River; Atlantic and Gulf Coast
States, Colorado, California and Canada (Plant Disease Bulletin
19). Eriksson (10) reported a cucumber leaf disease from Rus-
sia, and Traverso (22) reported a fruit rot from Italy.
In Florida the diseases have been found in all cucumber grow-
ing sections, which are scattered more or less in the south cen-
tral and northern portions of the state. However, they have
been found most destructive and most prevalent from year to
year in the central portion of the state with the center in Levy
and Alachua counties.
*Photographs by David G. A. Kelbert.
**Figures in parentheses (italic) refer to citations in the bibliography,
page 32.






Florida Agricultural Experiment Station


Hosts.-The diseases were first noticed in destructive form
on the leaves and fruits of the cultivated cucumber plant (Cucu-
mis sativa). A study, however, revealed that the flowers and
vines also were attacked and that the young fruits and young
leaves were somewhat more susceptible to infection than older
portions of the plant. Carsner (7) lists 12 cucumber varieties,
the West Indian gherkin, Bryanopsis, Lociniosa (a tropical cu-
cumber) and three gourd species as being susceptible to these
diseases. Eriksson (10) adds Cucumis anguria, C. acutangulis,
C. dipsaceus and Lagenaria vulgaris. No cross inoculations have
been attempted in Florida, on other than the commercial cu-
cumber varieties, so that the host range other than cucumbers
has not been determined.
Varietal susceptibility.-All varieties of cucumbers tested
showed 100 percent infection. A plot of the commercial varieties
of cucumbers was planted on a piece of good cucumber land in
the center of a commercial field. This location offered conditions
for comparing the various varieties as to susceptibility to the
diseases. The seed planted in the variety plot were disinfected
with corrosive sublimate 1:1,000 for 10 minutes, while the seed
planted in the commercial planting surrounding the variety plot
was not treated.
The leaf disease showed up quite uniformly on the large field
in the seedling stage. Under the favorable conditions both leaf
and fruit became infected and caused a 50 percent loss in yield
and showed 100 percent infection of the plants. The variety plot
was planted, one variety to a row and each row containing about
150 plants. The leaf disease was first found at both ends of
the variety rows and on the two outside rows of the plot, where
they came in contact with the commercial plantings. It spread
rapidly toward the center of the plot. Shortly after the first
picking 70 percent of the plants were infected and at the end
of the season there was 100 percent infection. There was some
slight difference in severity of infection in certain areas in the
variety plot but none of these differences coincided with definite
rows and were considered due to other factors. Although the
severity varied somewhat, it was not enough to be considered sig-
nificant.
The varieties grown were as follows: Kirby Staygreen, Earli-
green, Vickers Forcing, Davis Perfect, Long Green, Early White
Spine, Extra Long Green Prolific, Henderson, Arlington White






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 5

Spine, Everbearing, Extra Long White Spine, Livingston's Ever-
green, Early Cluster, Livingston's Emerald, Improved Long
Green, Klondike, Early Fortune, Improved Arlington White
Spine, Thorburns, Parmure Long White, Black Diamond, Sham-
rock, Chicago Pickling, 40 Day, Prolific Pickle, Extra Early
White Spine, Green Prolific, Cool and Crisp, Jersey Pickling,
Fordhook, E a r y Cyclone, Snow's Pickling, Cumberland and
Early Green Cluster.
Economic Importance.-Since 1911, when these diseases were
first discovered in destructive form, they have caused more or
less damage every year. They are apparently retarded somewhat
by the weather conditions that prevail during and immediately
following the planting season. If the season is cool and wet at
the time the seed are planted and when the young plants are
emerging, cotyledon infection is very common and causes a con-
siderable loss of plants. Under these conditions young plants
were killed in a short time. When conditions were not so favor-
able, the damage was much lighter and the cucumber plants grew
to maturity and bore fruit, although they suffered more or less
loss of leaf surface from the lesions on them.
The disease on the fruits is important, both in the field and
in transit.
Carsner (5) considered these diseases destructive and of
greatest importance in Indiana, Michigan and Wisconsin of the
northern states. He also considered the losses in transit of great-
er importance than losses in the field. He attributed the decay
in transit to invasion by secondary organisms. Meier & Link (17)
stated that the effects of this disease of the fruit makes them
almost unsalable. However, they state that the decay of the
fruit is caused by invasion of secondary organisms. Weber (23),
after making a careful survey, reported a 50 percent reduction in
yields in large numbers of fields in Levy and Alachua counties,
Florida. The losses to Florida growers are considerable during
years favorable for the development of the diseases. If the fruits
were picked when of pickling size, the losses would be negligible,
but the Florida crop is grown to larger sizes for northern mar-
kets and is consumed fresh. During this latter period of growth
the disease develops rapidly, and the fruits rot in the field and
later in transit.
Symptoms.-The leaf disease first becomes apparent in the
cotyledon stage as more or less irregular shaped spots, usually






Florida Agricultural Experiment Station


along the margin of the cotyledon. The spots frequently involve
the cotyledons to the point of their attachment to the main
stem. At this latter place practically all of the seedling damage
occurs as the lesions spread rapidly to the growing point, involve
it, and thus kill the plant. The disease on the cotyledons is a
source of infection for the true leaves that appear later and for
other plants.




























Fig. 2.-Lower surface (left) and upper surface of cucumber
leaf showing lesions, in various stages of development, caused
by Bacterium lachrymans.
The lesions on the true leaves at first are merely specks of a
water-soaked appearance, slightly darker green than the sur-
rounding leaf tissue. These water-soaked areas enlarge rapidly
under favorable conditions and in the course of 18 to 36 hours
after the first appearance they are 2 or 3 mm. in diameter, more
or less angular in outline and delimited by the larger veins of
the leaves. During the next 24 hours the spot increases rapidly






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 7

in size and reaches its approximate diameter. The spot remains
in this condition for a very short period, during which time an
exudate often appears, usually on the lower surface of the leaf.
Occasionally the upper surface shows a film of exudate. During
the periods of high humidity, the exudate is present in the form
of glistening, somewhat clustered drops. Often two or more
drops unite and fall from the leaf. During the day these drops
evaporate and when completely gone, leave a white, chalky coat-
ing over the lower surface of the entire lesion. The exudate
makes its appearance under most favorable conditions intermit-
tently during two or three successive days. However, if the
weather is excep-
tionally dry during
the daytime, the
invaded cells are
killed and dry out
completely. D u r -
ing the following
day or two the in-
vaded tissues drop
out, leaving a
more or less irreg-
ular hole. Under
unfavorable condi-
tions from one to a
half dozen lesions
are usually found
on the leaves. Un-
der favorable con-
ditions for develop-
ment of the dis-
ease, t h e lesions Fig. 3.-Chalky residue on lower surface of cu-
cumber leaf lesions resulting from drying exu-
are o n 1 y distin- date.
guished as individ-
uals during the early stages. After a day or two they coalesce, in-
volving the entire leaf, which rapidly dies and dries out.
The younger leaves of the plant near the tips of the runners
are much more susceptible than the older leaves of the plants.
It was determined through inoculation experiments that the
most susceptible leaves were those frop T%/3 to 3 mature size.'
In severe cases the plants may becoirie entirely killed within
a very short period. This, however, occurs only under the most






Florida Agricultural Experiment Station


favorable condi-
tions for the de-
velopment of the
disease. Lightly
infected plants
will continue to
grow and produce
fruit without
showing any hin-
drance in their
development.
When the pis-
tillate blossoms
become infected,
they often fail to
set fruit. Young
fruits that are
beginning to de-
velop and are
from one to two
inches in length
when infected
turn yellow,
shrivel up, and
drop from the
vines in two to
four days with-
out showing def-
inite lesions. This
effect of the dis-
ease on young
fruits is often
mistaken for fail-
ure of fertiliza-
tion, as the
young unfertil-
ized fruits be-
Fig. 4.-Cucumber fruits of the same age. The five come yellow and
at the top were inoculated with Bacterium lachry- drop from the
mans when they were in the blossoming stage;
the three below were inoculated with sterile dis- plant in a very
tilled water at the same time. similar manner.







Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 9

However, under controlled conditions in the greenhouse, where
hand pollination was necessary for setting of the fruit, these
conditions were studied and it was found that early infection of
flowers and fruit by the organism could occur and that such in-
fections were more severe in this stage than at any other stage
in the development of the fruit. Such infection resulted in the
non-setting of fruit and a dropping of fruit just beginning
growth.


Fig. 5.-Two stages of severity of natural infection of cucumbers in the
field by Bacterium lachrymans.

In a majority of cases cucumber fruits that were inoculated
when more than two inches long developed local lesions. After
8 to 12 days these fruits were usually two or three times as
large as when inoculated and the infection appeared in the form
of circular, water-soaked, slightly sunken spots about 1 to 2 mm.
in diameter. Under normal conditions these spots enlarged very
slowly and it was unusual to find them twice as large on fruit
that was ready to be picked.







Florida Agricultural Experiment Station


Fruits in the field were usually infected on the top and occa-
sionally on the sides. These spots appeared on the flat or concave
surfaces of the more or less triangular fruits rather than on the
rounded or convex sides. Spots on a fruit vary in number from
one to several, depending on the source of inoculum and weather


Fig. 6.-Longitudinal sections of infected cucumber fruits showing man-
ner of early invasion and tendency of decay to follow the placentas.

conditions. In some cases they may be so numerous as to be in-
distinguishable as spots. In very few instances, however, do all
of the lesions actually penetrate to the inside of the fruit. In
fact, on practically every fruit collected in an infected field, one
is able to distinguish surface lesions that have abruptly stopped







Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 11

when only the epidermis is penetrated. In such cases after ap-
proximately a week the lesion dries out, the epidermis cracks
in one or more places and curls back and bleaches to a light color
which is characteristic of arrested development of these infec-
tions.
The decay of the fruits that takes place is exceedingly char-
acteristic. The organism gains entrance through the stomata
and invades the fruit between the cells, advancing directly to-
ward the central portion. If infection occurs immediately above
the spongy tissue surrounding the placentas, invasion is more
rapid than when infection takes place between the placentas. As

















Fig. 7.-An infected cucumber fruit of the same age as those in Fig. 6 sec-
tioned to show effects of imitated transit jogging.

soon as the soft, spongy tissue is penetrated the most rapid
progress is made toward each end, which results in light brown
streaks running the length of the fruit. Often there are sev-
eral points of invasion along the same groove on the outside of
the fruit into the same placenta, involving it more rapidly and
more completely. The only symptoms showing on the surface of
a fruit so invaded are the small circular, slightly sunken, water-
soaked spots. The development of the inner decay apparently
depends to a certain degree on the growth and expansion of the
fruit. The internal invasion advances rapidly until the fruit is
fully expanded, after which time there is a sharp decline in the
rate of its progress. Severe early infections usually result in







Florida Agricultural Experiment Station


heavy losses, while infections occurring later show less destruc-
tion. Fully developed fruits are seldom invaded in an area more
than 1 inch in diameter and 1/4 inch deep.
If cucumber fruits were to be consumed locally, fruit infec-
tion would not be so important. However, the continued jarring
from railroad transportation associated with considerable pres-
sure on bottom layers of fruit in loaded cars produces a favor-
able environment for the rapid spread of the organism in the
soft, spongy tissue surrounding the inner portions of the fruit.
Because the disease develops so rapidly in transit, growers spare
no pains in culling out all fruits that show a single infection
spot or even a suspected spot. In order to approximate transit
conditions a hamper of culled fruit was packed and stored for a
week with daily, gentle jogging. Upon examination the hamper
showed 30 percent mashed and decayed fruits. A similar num-
ber of culled fruits placed on the ground in the shade during the
same time did not show a single fruit in which the internal de-
cay became apparent on the surface. The above evidence shows
that the disease develops rapidly under imitated transit condi-
tions and that its progress is slow or does not occur when the
fruit is left under out-door conditions.

THE ORGANISM
The organism as described by Smith and Bryan (20) and
named Bacterium lachrymans E. F. S. & Bry. is undoubtedly the
cause of both the angular leaf spot and fruit rot. There is ap-
parently some discrepancy in the description by Smith and
Bryan (20) of the organism causing the leaf spot and that given
by Burger (3) for the organism causing the disease of the fruits.
The organisms causing the disease of both leaves and fruits with
which the field experiments and the inoculation work were con-
ducted, however, agree almost wholly with the description given
by Smith and Bryan. The cardinal temperatures for the growth
of the organism, according to Smith and Bryan (20) are 1; 25-
27; 300 C. They stated that it was very sensitive to sunlight
and was killed in several days by drying on glass slides.
Carsner (5) stated that the organism was killed by drying
on glass in 4 days and that it lived in fruit tissue and leaf tissue
for 32 days and in culture tubes for 30 days. The thermal death
point was 49-500C., the organism remaining viable below freezing
temperature for six days. Further experiments showed that it






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 13

was killed in 10 minutes in formaldehyde solution 1:1,000, cop-
per sulphate 1:100,000, mercuric chloride 1:1,000,000. It has been
found during the experimental work conducted in Florida that
the organism lost its pathogenicity in culture in the laboratory
in a very short time; in fact, it was almost impossible to keep
it in such condition that it would infect plants over a period
longer than 20 days. It is very sensitive to sunlight and high
temperature, it being almost impossible to secure infection on
plants in the field at 300 C. or above. Furthermore, abundant in-
fection occurred on plants inoculated in cages as compared with
little or none on the plants in the field not caged, even though
the moisture was almost the same. However, there was almost
50 C. difference in the temperatures of the two places.
Pathogenicity.-The fruit disease when first discovered by
Burger (1) was believed to have been of bacterial origin, since
no fungi were found. Bacteria were isolated from infected fruits
and infection developed on both leaves and fruits when they
were inoculated with the cultures thus obtained. Flower infec-
tion produced 50% loss in yields. Diseased leaves were pinned
upon healthy leaves and in these instances the disease was re-
produced. Likewise when plugs were transferred from diseased
to healthy fruits, the disease was transferred. On the other
hand when plugs were transferred from healthy fruits to healthy
fruits, no disease developed. The organism causing the angular
leaf spot was obtained in pure culture and inoculations were
made with a broth culture of the organism to leaves, fruits and
flower stigmas by the use of a camel's hair brush. Both injured
and uninjured plants were inoculated and in each case the dis-
ease was transmitted. Forty-two out of 50 fruits developed
typical symptoms of the disease, whereas the check plants in-
oculated with distilled water remained healthy. In contrast to
the work of Burger (1, 2, 3, 4), Smith and Bryan (20) state
that the organism causing the leaf spot does not cause the fruit
rot, but that the disease produced in the fruits is caused by a
secondary organism which cannot gain entrance to the fruits
until the epidermis is penetrated by the leaf spot organism. In-
oculation experiments made by them in 1914 with an organism
isolated from a diseased fruit produced no fruit infection.
During the past few years in Florida, especially in 1926 and
1928, the organism was isolated from both leaves and infected
fruits many times in the course of the experimental work re-






Florida Agricultural Experiment Station


ported herein. The isolated organisms were identified by inocu-
lation experiments. Isolations were made from leaves and fruits
originating in widely separated sections of the state and almost
without exception Bacterium lachrymans was successfully ob-
tained from both sources. Infections produced on the leaves
with pure cultures of the organisms isolated from both leaves
and fruits were indistinguishable at any time. Likewise fruit
infection comparable to the typical disease in the field under


Fig. 8.-Exudate on lesions on cucumber fruit (above) and leaf (below)
resulting from infection by Bacterium lachrymans.

natural conditions, was produced from artificial inoculations
with the organism isolated from both the leaves and the fruits.
Experiments During 1926.-The disease appeared in a small
field near LaCrosse in Alachua County in April, 1926. Specimens
of spotted leaves and infected fruit from this field yielded prac-
tically pure culture qf the organism corresponding to the orig-
inal description of Smith and Bryan (20). Transfers of single
colonies of these cultures were used for inoculation purposes.
Some of the plants to be inoculated were grown in the field with-
out protection; others in outside cheesecloth cages, and others
in the greenhouse. A series of inoculations were made on plants
in each of these places, as well as in moist chambers. Each of






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 15

the plants inoculated was in a good growing condition and pro-
ducing fruit. Leaves and fruits in different stages of develop-
ment were inoculated by atomizing them with a water suspen-
sion of the organ ism.
Another parallel
series of plants
was inoculated in
the same manner,
the only different
being that the or-
ganism used was
isolated from the
i n n e r, discolored
area of a carefully
surface-disinfected
fruit, which show-
ed typical lesions.
The results of the
inoculations a r e
given in Table I.
During July and
August of 1926
all cultures of the
organisms 1 o s t
t h e i r pathogen-
icity. Consequent-
ly, further work
was prevented
during that year.
The 1927 season Fig. 9.-Greenhouse cucumber plants used for leaf
and fruit inoculations with the organisms.
was extremely dry
and hot and no angular leaf spot or fruit rot was reported from
the state during that year. Whether these conditions were actu-
ally responsible for the non-appearance of the disease is not def-
initely known. During the summer of 1926 the disease was re-
ported from northern sections of the United States and since
the disease is seed-borne and practically all cucumber seed plant-
ed in Florida is grown in northern sections, it is hardly probable
that these seed were disease-free. It is the contention of the







Florida Agricultural Experiment Station


writer, however, that the dryness and the high temperature
were responsible for the scarcity of the disease during 1927.

TABLE I.-SUMMARY OF EXPERIMENTS CONDUCTED IN 1926 IN WHICH UN-
INJURED CUCUMBER PLANTS WERE INOCULATED BY ATOMIZING THEM
WITH A SUSPENSION OF Bacterium lachrymans E.F.S. & BRY. AND INCU-
BATED UNDER VARIOUS CONDITIONS. CHECKS REMAINED HEALTHY.

Inoculated Plants


Source
of In- Parts
oculum

leaves


Leaves fruits


blossoms


leaves


Fruits fruits


blossoms


Date Environment

June 1 open field
cloth cages
i greenhouse
moist chamber
open field
cloth cages
greenhouse
I moist chamber
open field
cloth cages
greenhouse
moist chamber
June 2 open field
cloth cages
greenhouse
I moist chamber
open field
cloth cages
greenhouse
!moigt chamber
[ open field
| cloth cages
| greenhouse
moist chamber


Incubation I Number
Period in Inocu- Number
Days lated Infected
S 4 118 101
2 26 26
2 14 14
112 7 7
12 41 37
11 16 14
9 27 26
9 7 5
4 22 17
2 13 13
2 26 26
2 17 17
3 137 111
2 49 49
2 78 78
1-2 14 14
12 37 23
9 11 7
9 27 27
9 6 6
4 47 47
3 18 18
2 21 21
2 11 11


Experiments During 1928.-With the advent of the 1928 sea-
son there was plenty of moisture and lower temperatures. The
disease appeared in abundance in widely scattered sections.
When the diseases were first observed in 1928 the organisms
were isolated from leaves and fruit from various sections of the
cucumber-growing area and the cultures verified by inoculation
experiments. The experimental work of 1926 was repeated in
part and the results obtained coincide with those obtained in
that year. The results of the experiments conducted in 1928 are
given in Table II.
These data are the summary of a number of inoculation experi-
ments conducted over a period of four months under varying
conditions. The results coincide with those obtained in 1926
and show that the bacterial organisms causing angular leaf spot







Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 17

TABLE II.-COMPARISON OF RESULTS OBTAINED IN 1928 BY ATOMIZING IN-
JURED AND UNINJURED CUCUMBER PLANTS WITH DISTILLED WATER SUS-
PENSIONS OF Bacterium lachrymans FROM ANGULAR LEAF-SPOT OF CU-
CUMBER AND FRUIT ROT OF CUCUMBER.

Inoculation Methods and Results
No. Plant
Source of P.ant No. of Inoculaions Parts
Inoculum Parts With Injury Without Infected
Inoculated (needle) Injury

S 741 728
leaves
87 87

Cucumber frus 66 50
leaves fru
49 41

blossoms 217 217
blossom s -- --
103 103

S 617 597
le s 183 161

Cucumber fruits 119 94
fruits fruits ---

o so 136 13640
136 136
blossoms _72 136 70
72 I 70


20 0 0
Distilled 40 0
water fruits -
(check) 40 0


blossoms 20 0
____20 0


and fruit rot are identical. Plant parts that were injured by
sterile needle punctures before they were inoculated with sus-
pensions of the organism developed almost 100 percent infec-
tion, while those that were uninjured developed slightly less
infection. The most significant part of these experiments is the
fact that injured uninoculated fruits failed to show invasion and







Florida Agricultural Experiment Station


breaking down by secondary organisms. If the theory were true
that the causal organism only opens ways through the epidermis
for invasion by secondary organisms, then it is reasonable to sus-
pect that secondary invasion should have taken place through
the needle wounds. However, such did not occur in a single in-












Fig. 10.-Greenhouse cucumber plants used for testing pathogenicity of
bacterial organism isolated from leaves and fruit and for testing lon-
gevity of organism in culture. Left, check plant; two plants showing
lesions caused by B. lachrymans isolated from naturally infected fruit.

stance. Therefore it is reasonable to conclude that Bacterium
lachrymans is directly responsible for the great loss of infected
fruit.

SEASONAL DEVELOPMENT

The planting season for cucumbers in central Florida ranges
from the middle of February to the middle of March. Usually
at this time of year, rainy periods are not frequent and as a gen-
eral rule angular leaf spot is not common. However, certain
seasons are extremely wet and these wet seasons are accom-
panied by temperatures that are lower than normal. Under such
conditions, seed germination and subsequent development of the
young seedling are somewhat retarded. On the other hand these
conditions favor the development of the organism and, as a re-
sult, the disease is much more common and widespread. The
disease appears as soon as the cotyledons have expanded and,
if cool periods continue, considerable killing of plants occurs. The
infection is readily spread from the cotyledons to the newly de-
veloped leaves which continue to act as sources of inoculum for
the developing plants. When the weather becomes dry and is






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 19

accompanied by high temperature, the severity of the disease on
seedlings is considerably lessened and under these circumstances
seldom results in the killing of the plants. The
disease, however, is not entirely eliminated and
can be found on the plants as they con-
tinue to develop.
In this particular section of the
state the picking season begins
about the middle of April.
By this time, under con-
ditions favorable for the
development of the dis-
ease, it is not uncom-
mon to find 100 percent
infection in the fields.
An individual plant
may have from one to
fifty lesions on every
leaf that is old enough
to have passed the in-
cubation period of the
organism. It is at this
time or slightly before Fig. 11.-Typical lesions on naturally in-
fected cucumber leaf from which was
that the effects of the isolated the organism that was used in
disease are brought to making cross inoculations on fruits.
the attention of the
growers. Dropping of blossoms is the most noticeable symptom.
In most instances this is attributed to non-fertilization or to the
effects of fungicides. This early mortality of blossoms and young
fruit is of the most importance to the grower because it is the
first fruits which develop most rapidly and bring the highest
price. When the fruits are about half grown, there often appear
water-soaked spots on their surface from 1 to 2 mm. in diameter,
circular in outline with an apparent central point. These spots
are early infections caused by the bacteria from the leaves.
During the following 4 or 5 days the spots double in size and be-
come more distinct' in outline and slightly sunken. Their surface
diameter is usually riot more than 3 or 4 mm. These spots usually
appear on the upper surface of the fruits. An average number
of infections on a fruit is small, usually less than a half dozen,
although frequently fruits are collected on the surface of which






Florida Agricultural Experiment Station


the lesions are so numerous that they have coalesced and in-
volved the entire upper surfaces. These lesions remain in this
condition as far as the surface of the fruit is concerned until the
cucumbers are picked and ready to pack for shipment. At the
time they are graded, they are culled out. The number of the
infected fruits and, naturally, the resulting importance of the
disease after the beginning of the picking season, depends













Fig. 12.-Typical lesions on naturally infected cucumber fruit from which
was isolated the organism that was used in making cross inoculations
on leaves.

almost entirely upon the weather conditions. If frequent rains
and heavy dews occur during the latter part of April and May,
the grower usually suffers heavy losses. On the other hand, if
the season is quite dry with rising temperatures, the disease is
practically held in check and little or no damage results from
infected fruit. The average season for cucumbers in this sec-
tion is somewhat adverse for the best development of the dis-
ease. This period of the year is usually quite dry and the tem-
perature is usually high enough to check the development of the
disease.
The records kept during the past three years on the occur-
rence of angular leaf spot and fruit rot of cucumbers in Central
Florida show that there was a general distribution of these
troubles during the spring growing seasons of 1926 and 1928,
while no observations or reports of the disease were made dur-
ing the spring season of 1927. The reason for their non-appear-
ance is not known and recent investigations have failed to re-
veal the true cause. It was thought, however, that temperature







Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 21

and moisture or a combination of them are probably more re-
sponsible than any other factors.
A careful review of the weather data kept at Gainesville, lo-
cated in a large cucumber growing area and where these investi-
gations were conducted, has been made and the temperatures
and precipitation records examined and certain data recorded.
The records of temperature and precipitation selected for consid-
eration include the periods beginning March 20 and ending May
20 of each of the three years, 1926, 1927 and 1928. These data
are shown graphically in the following figure. (Fig. 13.)

76
74
72




nZIT







4kio 411
Fig. 13.-Curves and graphs showing the average mean temperature and
da.ly precipitation at Gainesville, Florida, from March 20 to May 20
during the years 1926-1928, inclusive.

The temperatures are shown in degrees F. by the three curves
which are distinguished by the figures showing the year. The
precipitation is shown in inches of daily precipitation, the spe-
cific years distinguishable by shading. The total precipitation
during the periods for each year is shown in the legend in the
figure.
The curves show a considerable higher temperature over the
entire season of 1927 than either the 1926 or 1928 seasons,
whereas the curves representing the temperatures of the two
latter seasons are almost parallel. It is also worthy of note that






Florida Agricultural Experiment Station


the precipitation during the selected period in 1927 amounted
to exactly two inches while the precipitation for a comparable
period in 1926 was 9.4 inches and for 1928 it was 10 inches. These
figures show almost five times as much rainfall during the years
that the cucumbers were diseased as during the year when no
disease was found. Further checking to prove the point was not
done, as it appears that temperature and precipitation furnish
sufficient circumstantial evidence to show that they are factors
in determining the amount of disease which occurs.

SOURCE OF INOCULUM

It is the consensus of opinion among cucumber growers and
investigators that the organism causing these diseases is seed-
borne. This has been reported by Carsner (6), Gilbert and Gard-
ner (13) and Jones and Doolittle (16). In these specific cases
this means of transmission has been proved. There are some in-
timations, however, that the organism lives over in the soil, but
under Florida conditions this is not the case. No signs of the
disease appeared on seedlings which developed from disinfected
seed planted in samples of soil from diseased fields. Neither has
it been found in fields where disinfected seed were planted, even
though these fields showed 100 percent infection the previous
season. Similar observations have been made in a large number
of commercial fields over a series of years.
There is no positive evidence that the organism remained
viable in dead plants, stems, leaves or fruits from one season to
the next. During 1926 a number of heavily infected plants were
collected, including the infected fruit, and stored under differ-
ent conditions in an attempt to carry the organism over in this
material to the next season. Portions of the vines were covered
lightly with soil, other portions were left entirely on the surface
of the ground and others were put in wire cage and suspended a
short distance above the ground. During the following cucum-
ber season these samples were collected and distributed over and
around hills of young cucumber plants developing under condi-
tions favorable for the development of the disease. These plants
were caged in an attempt to keep temperature down and to sup-
ply additional humidity during the day. Of 37 trials of this sort
under varying conditions, no infection was obtained. Conse-






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 23

quently, it appears that the occurrence of this disease in Florida
is entirely associated with the planting of infected seed.

DISSEMINATION

Once the disease appears in the field, its subsequent spread
can be readily traced. Infected hills have been located in fields
that showed very little disease. These hills have been marked
and at definite intervals observations were made as to the dis-
semination of the disease and it was found that infection oc-
curred in almost circular areas around these primary infected
plants up to the beginning of the picking season. At this time
there was evidence of some carrying of the organism by pickers
to healthy plants in certain rows. This was particularly evident
in one field in which the pickers always started at the same end
of the row. In this case the disease was spread about twice as












Fig. 14.-Greenhouse cucumber showing typical disease symptoms follow-
ing inoculation with B. lachrymans isolated and cultured from the cu-
cumber leaf shown in Fig. 11.

far in the direction of the picking as it was in the opposite direc-
tion and infection occurred on the rows often at considerable
distance from the original source of infection. This particular
field was practically flat, so that the action of the drainage wa-
ter was eliminated and the general wind direction was across
the rows, when there was enough wind to blow sand. Sand
blowing in this field was not frequent because of the wetness of
the soil.
It remains, however, that wind and rain dissemination of the
disease is more important than the dissemination by pickers
and cultivators. The dissemination of the disease in the field






Florida Agricultural Experiment Station


previous to picking time can be accounted for almost entirely
by the action of wind and rain, where primary infection is of
high percentage. Under favorable conditions for the develop-
ment of the disease, such as continued rainy weather, or rains
interspersed with dry windy periods, the disease has been ob-
served to have spread over large fields within a very short period.
The dissemination of the disease as it occurred in the variety
plot has already been partially described. However, it may be
restated that the disease spread over the entire plot beginning
at the edges and gradually involving all plants therein. It was
not possible to detect the most rapid direction of advancement.

RELATION OF PARASITE TO HOST

The incubation period of the disease reported by Burger (4)
was from 5 to 10 days on uninjured fruit and 3 to 5 days on
injured fruit. The experiments recently conducted have shown
that the incubation period on uninjured fruits is much longer
than the incubation period on the leaves. Inoculations of leaves
made in the evening have shown first symptoms of the disease
after 36 hours. This incubation period is about the average
under greenhouse conditions where plants have been subjected
to high humidity for the first 24 hours. Fruit inoculated under
the same conditions show lesions after the seventh or eighth
day. No lesions have been found on any inoculated uninjured
fruit under any conditions in less than seven days. The exudate
that appears on the lesions of leaves in the early morning is the
result of the continued flow of cell sap and the lack of evapora-
tion under humid conditions. During dry periods of the day
this exudate dries out, leaving a chalk-like residue, which con-
tains the organism and which falls away from the leaf readily
and is blown by the wind with the sand across the field. When
these bits of dry exudate come in contact with dew or rain, the
bacteria become active and, if they are in contact with cucum-
ber leaves under favorable conditions, infection results.
The bacteria enter the host plant through the stomata and
occupy the intercellular space (Smith & Bryan (20)). The organ-
ism develops between the cells of the host plant, destroying the
middle lamella and advances between the cells into the intercel-
lular spaces. The enlargement of the lesions is checked by the
larger veins and as a result the lesions are more or less angular






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 25

in outline, thus suggesting the name of the disease. The organ-
ism enters the fruit through the stomata and makes its way
into it by dissolving the middle lamella and gradually destroying
the cell walls and occupying the cells. The progress of invasion
is rapid in fruits during their period of expansion and enlarge-
ment. When they cease to enlarge the progress of the bacteria
is slowed up. The greatest amount of inoculation resulting in in-
fection takes place on fruits by the time they are half grown.



















Fig. 15.-Cucumber fruit shown in Fig. 14 cut longitudinally, showing the
development and progress of the decay within the fruit.

The greatest detrimental effect of the parasite does not usually
occur until the organism has invaded the placentas and the im-
mediate vascular tissue. Observations in the field disclose that
98 percent of the infections that actively involve the internal
tissues take place on the flat or concave surfaces of the fruits
rather than on the convex surfaces. This overwhelming situ-
ation arouses one to determine the reasons. The possibility of
the action of gravity on water droplets containing bacteria in
relation to the convex and concave surfaces is evident and im-
portant. This explanation is not the whole solution, however,
since the points of invasion of the epidermis are often well dis-
tributed.
Following this entrance stage, which is detected by minute,
circular, water-soaked spots, only a few spots continue to en-






Florida Agricultural Experiment Station


large. These in most instances include the spots in the concave
sides of the fruit. The host tissue immediately under these con-
cave surfaces is made up of smaller cells, thus appearing more
compact and contains more numerous vascular strands than
that tissue under the convex surfaces. A few millimeters below
the epidermis (depending on size of fruits) on the three concave
surfaces are the placentas which are made up of exceptionally
spongy tissue and numerous large bundles of vascular tissues.


Fig. 16.-Cross section through healthy cucumber fruit stained with methyl
blue and cleared, revealing vascular tissue, placentas, carpel and seed.
Concave and convex sides are designated.

Close to the placentas are found numerous small, vascular strands
parallel with the placentas and the long axis of the fruit. In con-
trast, the host tissue under the convex surfaces is less compact,
there are fewer vascular strands and the distance from the epi-
dermis to the carpels is three times as great. The path of such
invasion does not come in contact with the spongy tissue or






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 27

the abundant vascular tissue in conjunction with it. Table III
shows the average distances in millimeters from the epidermis
to the carpels and placentas, respectively, of 20 cucumber fruits
of various diameters.

TABLE III.-DISTANCE IN MM. FROM EPIDERMIS TO CARPELS AND PLA-
CENTAS OF CUCUMBER FRUITS OF VARIOUS DIAMETERS.
Distance in mm. from Epidermis to
Diameter of Fruits in
cm., x-Section Carpels-Convex Sides Placentas-Concave
Sides

0-2 5-6 1-2
2-3 9-12 2-3
3-5 12-15 3-4
5-7 15-18 4-5


The depth of parenchymatous tissue to be penetrated before
the carpels are involved is about three times as great on the
convex sides as on the concave sides. In fruits under 2 cm. in
diameter, the distance from epidermis to placentas is often 1
mm. or less. In fruits of larger diameters these distances rapid-
ly increase. It is obvious from these figures that infections tak-
ing place on a concave surface would penetrate to the central
softer area quicker than from the convex surface. The entire
inner portion of the fruit may be involved, due to the rapid
spread of the decay along the placentas. This is what actually
happens in Nature. The large percent of early infection result-
ing in losses as compared with late infection can be explained
as above.
Field observations and inoculations have shown that the great-
est amount of infection resulting in internal decay takes place
on the concave sides of fruits and that these infections occur
during their early development.

CONTROL
Experiments planned for the control of angular leaf spot and
fruit rot of cucumbers have shown that strict sanitation or rota-
tion in cucumber fields is unnecessary since the organism does
not live in the field from one season to the next in the soil nor
in portions of the vine, leaves or fruit. Burger (2) attempted





Florida Agricultural Experiment Station


to control this disease in the field by the application of Bor-
deaux mixture. Some of his experiments show that the checks
produced more fruit than the sprayed plants. However, in ex-
amining the data further, it showed that 17 percent of the
sprayed fruits was infected, while 35 percent of the unsprayed
fruit was infected. Carsner (7) does not believe that spraying
is economical and believes that dry periods and high tempera-
ture will control the disease. Seed treatment, however, seems
to be the most logical means of control and has proven entirely
satisfactory during the past six years in dealing with this dis-
ease in Florida. Out of 26 cucumber fields observed in the vicin-
ity of Williston, Florida, it was found that the seed planted in
20 of these fields had not been treated and that the disease ap-
peared in 18 of these 20 fields. The seed planted in the 6 re-
maining fields had been treated and showed no signs of the dis-
ease. This evidence points to the advisability of seed treatment.
Since seed treatment offered the best means of controlling
the disease it was found that necessary information was lacking
concerning certain phases of disinfection. A review of the litera-
ture reveals the recommendation of treatment with various dis-
infectants for different lengths of time. Necessary data con-
cerning the effect of disinfectants on the viability of the seed
were also lacking. Consequently, experiments were conducted in
order to determine this point. A presoaking method was tried
in which commercial cucumber seed were soaked in water for
different periods of time before the disinfectant was applied.
Two thousand seed of the Davis Perfect variety were used in
each lot for the experiment. All lots of seed except lots 1, 11,
and 12 were submerged in water for 10 minutes and were then
kept damp for different periods of time previous to disinfection.
The final treatment consisted of submerging the seed for 10
minutes in bichloride of mercury solution (1:1,000) and then
washing and planting them.
Table IV gives the results of these tests and is self-explana-
tory. Lots of seed No. 1 and No. 13 were checks (not disin-
fected), the former planted dry and the latter soaked in water 2
hours previous to planting. Lots of seed No. 11 and No. 12
were not pre-soaked, but disinfected and planted.
The average germination for the dry checks was 67%, for the
pre-soaked checks 69%, for the disinfected seed 70% and the
non-pre-soaked disinfected seed 65.5%. Since 26,000 seed were






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 29

used in this experiment, it may seem that the difference is sig-
nificant. However, for the grower such differences are not
worthy of consideration.

TABLE IV.-EFFECT OF PRE-SOAKING AND TREATMENT WITH BICHLORIDE
OF MERCURY SOLUTION (1:1,000) ON THE GERMINATION OF CUCUMBER SEED.

Ave. %
Lot of seed.. 1* 2 3 4 5 6 7 89 101 11 1213* germ.
SI! I che'ksl treated
Hours Pre- |
riod ............ 0 1 2 3 4 5 6 7 81/6 0 0 2

% germ......... 67 74 62 73 721 75 73 741 73 62 65 66 69 68 69.9

*Not disinfected.

Other seed disinfection experiments were conducted in which
two commercial varieties of cucumber, Klondike and Davis Per-
fect, were used. They were disinfected with bichloride of mer-
cury 1:1,000 for different periods of time, washed and planted.
The seed were disinfected in lots of 100, and four replications
were averaged for each time period with each variety. Thus the
total check seed were 800, averaging 77 percent germination.
The total treated seed were 25,600, averaging 78.15 percent ger-
mination. Each lot of 100 seed was tied in a small cheesecloth bag
and all were immersed in the disinfectant. A lot of 100 seed
was planted after five minutes treatment and other lots were
removed and planted after having been treated for progressively
longer periods.
The results of these experiments (Table V) show that cucum-
ber seed are not easily injured by bichloride of mercury. Seed
soaked in a 1:1,000 solution for 2 hours and 45 minutes showed
only 2 percent less germination than the untreated check. The
extremes in germination of treated seed varied 20%, namely
from 68 percent to 88 percent. There appears to be no correla-
tion between the percent germination and the time of treatment
and it is concluded that other environmental factors not con-
trolled were responsible for these fluctuations. The average per-
cent of germination for 800 untreated seed of both varieties
was 77 percent. The average percent of germination for 25,600







Florida Agricultural Experiment Station


treated seed of both varieties was 78.15 percent. Considering
the large number of seed involved iii the experiments and the
final variation of less than 2 percent, it is concluded that the dif-
ference is not significant. However, such treatment is not neces-
sary to control Bacterium lachrymans, 10 minutes being suffi-
cient, as has already been demonstrated in field plots.

TABLE V.- EFFECTS OF TREATMENT WITH BICHLORIDE OF MERCURY
(1:1,000) FOR DIFFERENT LENGTHS OF TIME UPON THE GERMINATION OF
KLONDIKE AND DAVIS PERFECT CUCUMBER SEED.


Klondike
Time
Treated
Minutes

0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
86
90
95
100
105
110
115
120
125
130
135
140
145
150
155


Per-
cent
Germ.

74
80
68
68
77
71
66
62
80
79
80
76
80
80
82
81
82
83
75
72
80
72
84
76
81
76
85
81
77
75
75
72


Lot


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32



Final
Aver-
age


3
3


Davis Perfect
Time
Treated
Minutes G

1 0.
2 5
3 10
4 15
5 20
6 25
7 30
3 ' 36
9 40
0 45
1 50
2 -55
3 60
4 65
5' 70
6 75
7 80
8 85
9 90
0 95
1 100
2 105
3 110
4 115
5 120
6 125
7 130
8 135
9 140
0 145
1 150
2 155
3 160
4 165


Ave. germination
of all treated
lots.


7


Per-
cent
erm.

80
81
77
82
81
79
86
81
80
81
80
77
80
73
80
74
80
78
79
75
76
81
80
88
77
87
84
75
75
82
88
75
80
78

9.7%


Checks
Ave. Total Germ.

800 seed=77% checks






























S25,600 seed = 78.15%
disinfected seed.


Ave. germination
76.6% of all 1
treated lots. I






Bul. 207, Angular Leaf Spot and Fruit Rot of Cucumbers 31

SUMMARY

1. The organism Bacterium lachrymans E.F.S. & Bry. has
been found associated with and is the cause of angular leaf spot
and fruit rot of cucumbers in Florida.
2. The bacterial organisms isolated from angular leaf spots
and from fruit rots were grown in pure cultures and were not
distinguishable.
3. Fruit rot has never been observed in any cucumber field,
except in association with angular leaf spot.
4. Cross inoculations, in which the leaf organism and the
fruit organism were used to inoculate leaves, fruits and flowers,
showed that the diseases produced on specific plant parts by or-
ganisms from the two sources were not distinguishable.
5. The diseases were produced under varying environmental
conditions and on wounded and unwounded plant parts.
6. The wounded uninoculated cucumber fruits did not de-
velop decay.
7. Thirty-six commercial varieties of cucumbers became
naturally infected and showed little or no variation in suscep-
tibility to the disease.
8. High temperatures and lack of precipitation were prob-
ably responsible for the failure of the disease to show up in
1927.
9. The disease is transmitted through seed in Florida.
10. The fruit rot results from the bacterial organism pene-
trating the epidermis and advancing to the inner core of the
fruit.
11. Ninety-eight percent of infection spots that eventually
cause internal fruit rot originate on the flat or concave side of
the fruit, rather than on the convex sides and penetrate directly
to the placentas where the parasite spreads rapidly in the spongy
tissue lying parallel to the long axis of the fruits.
12. The disease can be entirely controlled by treating the seed
for 10 minutes in 1:1,000 bichloride 'of mercury solution. Seed
treated for much longer lengths of time showed no injury from
the disinfectant. Pre-soaked seed did not show improved ger-
mination.







32 Florida Agricultural Experiment Station

BIBLIOGRAPHY

1. BURGER, O. F. A new cucumber disease. Fla. Agr. Exp. Sta. Ann.
Rept.: c-ci. 1912.
2. Bacterial rot of cucumbers. Fla. Agr. Exp. Sta. Ann.
Rept.: xc-xciv. 1913.
3. -A bacterial rot of cucumbers. Phytopath. 3:169-170. 1913.
4: Cucumber rot. Fla. Agr. Exp. Sta. Bul. 121:97-109. 1914.
5. CARSNER, EUBANKS. Angular leaf spot, a bacterial leaf spot of cu-
cumbers. Abst. Phytopath. 6:105-6. 1916.
6. Do the bacteria of angular leaf spot of cucumber over-
winter on the seed? Abst. Phytopath. 7:61-62. 1917.
7. Angular leaf spot of cucumber: Dissemination, overwin-
tering and control. Jour. Agr. Res. 15:201-220. 1918.
8. CHUPP, CHAS. Angular leaf spot of cucumbers; Bac'erial rot of cu-
cumbers. Manual of Vegetable Garden Diseases. Macmillan. Pp.
198-200; 213-14. 1925.
9. CLINTON. J. P. Angular leaf spot of cucumber. Conn. Exp. Sta. Bul.
222:397-482. 1920.
10. ERIKSSON, JAKOB. Eckige blattflecken der gurken. Die Pflanzenk. der
Garten und Partgewachse. Stuttgart. Pp. 28-30. 1928.
11. GARDNER, M. W. AND GILBERT, W. W. Cucumber angular leaf spot
and anthracnose overwintering and seed treatment control. Abst.
Phytopath 8:79-80. 1918.
12. GILBERT, W. W. Cucumber diseases in the middle west. Abst. Phyto-
path 6:104-5. 1916.
13. --- AND GARDNER, M. W. Seed treatment control of overwin-
tering of cucumber angular leaf spot. Phytopath 8:229-233. 1918.
14. AND POPENOE, C. H. Angular leaf spot. U.S.D.A. Farm-
ers Bul. 1371:23-24. 1924.
15. HEALD, F. D. Angular leaf spot of cucumbers. Manual of Plant Dis-
eases. McGraw-Hill. P. 349. 1926.
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