• TABLE OF CONTENTS
HIDE
 Front Cover
 Front Matter
 Tuber symptoms
 Losses
 Early observations
 Miscellaneous observations
 Experimental work
 Conclusion
 Literature cited






Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 187
Title: Infection of potato tubers by Alternaria solani in relation to storage conditions
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026683/00001
 Material Information
Title: Infection of potato tubers by Alternaria solani in relation to storage conditions
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 163-182 : ill. ; 23 cm.
Language: English
Creator: Gratz, L. O ( Levi Otto ), b. 1894
Bonde, Reiner, b. 1896
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1927
 Subjects
Subject: Potatoes -- Storage -- Diseases and injuries -- Florida   ( lcsh )
Alternaria solani -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 182.
Statement of Responsibility: by L. O. Gratz and Reiner Bonde.
General Note: Cover title.
General Note: "In cooperation with Maine Agricultural Experiment Station"--T.p.
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Florida Sea Grant technical series, the Florida Geological Survey series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00026683
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: aleph - 000923494
oclc - 18172833
notis - AEN4045

Table of Contents
    Front Cover
        Page 165
    Front Matter
        Page 166
    Tuber symptoms
        Page 167
    Losses
        Page 168
        Page 169
    Early observations
        Page 170
    Miscellaneous observations
        Page 171
        Page 172
    Experimental work
        Page 173
        Page 174
        Page 175
        Page 176
        Page 177
        Page 178
        Page 179
    Conclusion
        Page 180
        Page 181
    Literature cited
        Page 182
Full Text


Bulletin 187


AGRICULTURAL EXPERIMENT STATION
UNIVERSITY OF FLORIDA
In Cooperation with
MAINE AGRICULTURAL EXPERIMENT STATION



Infection of Potato Tubers by

Alternaria Solani in Relation to

Storage Conditions

By L. O. GRATZ AND REINER BONDE


Fig. 109.-Tuber spotting caused by "early blight" (Alternaria solani (E.
& M.) J. & G.). The tuber was taken from top of barrel of potatoes
remaining in the weather 20 days in September in Aroostook County,
Maine. The barrel was covered with blight-infected foliage.


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


June, 1927








BOARD OF CONTROL
P. K. YONGE. Chairman. Pensacola
E. L. WARTMANN, Citra
E. W. LANE, Jacksonville
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee
STATION STAFF
WILMON NEWELL, D. SC., Director
JOHN M. SCOTT. B. S.. Vice Director and Animal Industrialist
SAM T. FLEMING, A. B., Assistant to Director
J. R. WATSON, A. M. Entomologist
ARCHIE N. TISSOT, M. S., Assistant Entomologist
H. E. BRATLEY, M. S. A., Asst. in Entomology
R. W. RUPRECHT, Ph. D., Chemist
R. M. BARNETTE. Ph. D., Assistant Chemist
C. E. BELL, M. S. Assistant Chemist
HOUSDEN L. MARSHALL, M. S., Assistant Chemist
JACKSON D. HESTER, M. S., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
O. F. BURGER, D. Sc., Plant Pathologist
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. L. SEAL, M. S., Assistant Plant Pathologist
ROBERT E. NOLEN, M. S. A., Lab. Asst. in Plant Pathology
K. W. LOUCKS, A. B., Lab. Asst. in Plant Pathology
ERDMAN WEST, B. S., Lab. Asst. in Plant Pathology
D. G. A. KELBERT, Field Asst. in Plant Pathology
W. E. STOKES, M. S., Agronomist
W. A. LEUKEL, Ph. D., Assistant Agronomist
A. F. CAMP. Ph. D., Associate Horticulturist
HAROLD MOWRY, Assistant Horticulturist
G. H. BLACKMON, B. S. 'A., Pecan Culturist
M. R. ENSIGN, M. S., Truck Horticulturist
M, N. WALKER, Ph. D., Assistant Cotton Specialist
W. A. CARVER, Ph. D.. Assistant Cotton Specialist
EDGAR F. GROSSMAN, M. A., Assistant Entomologist, Cotton Investigations
RAYMOND CROWN, B. S. A., Field Asst., Cotton Investigations
A. L. SHEALY, D. V. M., Veterinarian
D. A. SANDERS, D. V. M., Assistant Veterinarian
C. V. NOBLE, Ph. D., Agricultural Economist
BRUCE MCKINLEY, B. S. A., Assistant Agricultural Economist
H. G. HAMILTON, M. S., Assistant Agricultural Economist
OUIDA DAVIS ABBOTT, Ph. D., Head, Home Economics Research
LEONARD W. GADDUM, Ph. D., Assistant in Home Economics
IDA KEELING CRESAP, Librarian
J. FRANCIS COOPER, B. S. A., Editor
RUBY NEWHALL, Secretary
HENRY ZEIGLER, Farm Foreman
W. B. TISDALE, Ph. D., Plant Pathologist, in charge Tobacco Experiment
Station (Quincy)
Ross F. WADKINS, M. S., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman Tobacco Experiment Station (Quincy)
L. O. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
A. N. BROOKS, Ph. D., Assistant Plant Pathologist (Plant City)
STACY O. HAWKINS, Field Asst. in Plant Pathology (Miami)
J. H. JEFFERIES, Superintendent Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (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)
FRED W. WALKER, Assistant Entomologist (Monticello)

K. H. GRAHAM, Auditor.
RACHEL MCQUARRIE, Assistant Auditor








INFECTION OF POTATO TUBERS BY
ALTERNARIA SOLANI IN RELATION TO
STORAGE CONDITIONS
By L. O. GRATZ AND REINER BONDE1
Alternaria solani (E. & M.) J. & G. (Fig. 110), the cause
of "early blight" of Solanum tuberosum L. (Fig. 111), was
formerly considered non-parasitic on the tubers. As a tuber
parasite it was first described in 1925, as observed on Spaulding
Rose seed potatoes before and after shipment from Maine to
Florida (1 & 2).


,e ,



.. -1



Fig. 110.-Conidia of A. solani, the cause of early
blight and tuber spotting of white potatoes.


TUBER
SYMPTOMS
The lesions pro-
duced on the tubers
are dark, sunken
areas of various
shapes, sometimes
surrounded by ir-
regular, raised
borders of a pur-
plish or gunmetal
hue (Figs. 109 and
112). They are
usually shallow w,
but the depressions
may become deep
and crater-like
(Figs. 113 and
115) or, remaining
shallow, may spread
over an area 1 to 2
cm. in diameter.
Any part of the
surface of the tu-
ber may be affect-
ed. These lesions
have been confused


1L. O. Gratz, assistant plant pathologist, Florida Agricultural Experi-
ment Station. Reiner Bonde, assistant plant pathologist, Maine Agricul-
tural Experiment Station.
'Reference is made by number (italic) to "Literature Cited," page 182.


< L N"






Florida Agricultural Experiment Station


with those caused by the late blight organism (Phytophthora
infestans (Mont.) de By. (Figs. 116 and 117). A difference,
however, is observed from the very beginning, at which time
Alternaria lesions are dark brown, while Phytophthora lesions
are water-soaked and reddish brown, and are larger and not
so definite in outline. In the later stages the difference in area
is still greater, the late blight lesions are more shallow, and cut-
ting shows them spreading rather irregularly into the flesh and
exhibiting a discoloration adequately described by the term
"mahqgany rot." Early blight lesions are delimited by more
definite borders near the outer surface of the tuber (Fig. 117).
The tissue just beyond the edge of the spot has a light yellow
discoloration similar to that produced by the fungus on potato
agar. After the continuous development of the fungus, the
severely affected tubers may shrivel to less than half their orig-
inal size, while in the absence of secondary organisms, those
affected with Phytophthora rot retain their original size, to a
much greater extent.

LOSSES

The determination of actual losses due to this trouble is dif-
ficult. First, the lesions are relatively small at shipping time, in
December, and are mostly hidden by the adhering soil unless
the tubers are carefully brushed or washed. Instances have
been reported where commercial lots were racked three times
before being shipped, in order to remove spotted tubers. This
requires the expenditure of much time and labor which still
does not result in satisfaction because, in spite of the racking,
most of the tubers will exhibit lesions upon arrival at their
destination.
Observations and experimental work have demonstrated
that with temperature and other conditions suitable the lesions
may increase several times in size within a period of from five
to ten days. Ten days to two weeks is the time required for
shipment from Maine to Florida, and in that time the tem-
perature of the tubers is changed from the minimum for rot
development to the optimum and possibly upon arrival may
approach the maximum. At this last temperature the lesions
develop slowly unless secondary organisms follow. The Florida
grower, upon observing this slow development, concludes that
the lesions must have been on the tubers long before the ship-







Bulletin 187, Infection of Potato Tubers 169


Fig. 111.-Early blight of potato caused by A. solani.







Florida Agricultural Experiment Station


ment started, and suggests this to the buyer or to the shipper,
meeting with a prompt denial. This results in a general mis-
understanding when, as a matter of fact, both sides are partly
correct.
The actual losses to the buyer occur in several ways. Sec-
ondary organisms, including Fusarium spp., may become in-
vaders as in the case of late-blight rot. The primary lesions
may involve the eyes, kill the sprouts, thus lowering the per-
centage of stand and finally decreasing the yield. These effects
of primary lesions may be reduced by discarding badly spotted
seed pieces. However, many seed pieces with injured sprouts
reach the fields. Further, some growers are not able to dis-
tinguish between the various potato rots and unnecessarily dis-
card many seed pieces that are usable in spite of their bearing
Alternaria lesions. The general dissatisfaction arising from
this condition has an importance that should not be minimized.

EARLY OBSERVATIONS

Early-blight rot has been observed for a number of years on
Spaulding Rose potatoes shipped to Florida. The causal organ-
ism was isolated
from diseased tubers
in Maine in March,
1922 (2, p. 282), and
in Florida consis-
tently in December,
1923 (3, p. 9). The
condition of the seed
potatoes i n Florida
was finally called to
the attention of the
Maine pathologists,
which resulted in
demonstrating t h a t
the "early blight"
fungus was the cau-
sal agent (1; 2; 3, p.
9).
Fig. 112.--Typical appearance of lesions on Alternaria tuber
Spaulding Rose No. 4 tubers on arrival in
Florida from Aroostook County, Maine. spotting is not pe-






Bulletin 187, Infection of Potato Tubers


culiar to any particular section, as the fungus has been isolated
from Spaulding Rose tubers received from Maine, New York,
New Jersey, Wisconsin, Michigan, and Minnesota. This trouble
is observed more often on tubers of the Spaulding Rose variety
than on those of any other variety, but similar lesions on the
tubers of the Early Rose, Irish Cobbler, Green Mountain, and
Smooth Rural varieties consistently yielded A. solani.
It was observed early that moisture and temperature condi-
tions were important contributing factors in the development of
















Fig. 113.-General appearance of the tubers in the shipments arriving in
Florida from Aroostook County, Maine, in November, 1924. Lesions
caused by A. solani.

the disease. Both in 1923 and in 1924 the tubers of the very
early shipments (November) were disfigured by lesions from
1 to 2 cm. in diameter (Fig. 113). The later shipments, though
spotted (Fig. 112), exhibited very much less infection. No
spotting was ever observed by the authors at digging time.
This indicated that storage and transit conditions were chiefly
involved in the development of the disease.

MISCELLANEOUS OBSERVATIONS

Many separate lots of tubers were observed in Aroostook
County, Maine, during August and September, 1925. On Sep-
tember 8, two barrels were filled with freshly dug Spaulding
Rose tubers, were covered with foliage, and were left in the
field. When examined 20 days later every tuber was infected.







Florida Agricultural Experiment Station


During this 20-day interval several hard rains occurred which
presumably washed the spores from the blight-infected foliage
down into the barrelful of tubers. The most lesions per tuber
were found in the top of the barrel directly beneath the foliage.
These lesions were on the upper side of the tubers (Fig. 109).
One or two spots per tuber were found in the lower parts of
the barrel.
Four lots, each of a bushel or more, were dug from hills dis-
eased with Verticillium wilt and were cut across the stem ends
and examined for stem-end browning. Twenty days later these
lots showed, respectively, 35, 42, 57, and 67 percent Alternaria


Fig. 114.-Tuber showing the extent of
development of an Alternaria lesion
about a rake wound in about two
months under optimum to maximum
temperature conditions. Note the de-
velopment of two new lesions just be-
neath the primary lesion. Isolations
from this tuber yielded pure cultures
of A. solani, and the lesion never had
any indication of Fusarium or any
other dry-rot organism.
amined in 24 different storage houses


infection. Of these
lesions, 80, 93, 98, and
98 percent respective-
ly were immediately
adjoining the cut sur-
faces of the tubers.
Lesions are frequent-
ly observed in associa-
tion with cuts and
bruises (Fig. 114).
In 1923 and 1924
very few potatoes
could be found which
were not spotted
when they arrived in
Florida. In 1925, in
spite of an epiphy-
totic outbreak of ear-
ly blight in Aroostook
County late in the
growing season, only
27 percent of the tu-
bers which were ex-
were found affected at


shipping time in December. About 100 cars were inspected on
arrival in Florida, only 40 percent of the tubers were spotted,
and the lesions in all cases were comparatively small and rela-
tively few per tuber. The ease with which it was possible to
inoculate the tubers artificially (as will be described later)







Bulletin 187, Infection of Potato Tubers


leads to the conclusion that the difference between the amounts
of infection of the last two years was due to the fact that in
1925 severe frosts killed the foliage several weeks before dig-
ging, while in 1924 the tops were still rather heavy when the
Spaulding .,Rose fields were dug. It was also observed that
early harvested potatoes of this variety had a higher percent-
age of infected tubers than those which were harvested later
in the season.
EXPERIMENTAL WORK

As a result of some of the observations described above,
more than 5,000 tubers were inoculated at the Aroostook lab-
oratory during the growing season of 1925. Freshly dug tu-
bers (50 tubers in each lot) were inoculated and stored under
various conditions. 'Some were inoculated by stirring them
about in potato foliage spotted by early blight, and others were
stored in contact with diseased foliage. During digging the
precaution was taken to prevent the tubers from coming into
contact with leaves.
Some lots of tubers were inoculated with moist diseased foli-
age, and other lots with dry foliage. After the freshly dug tu-
bers were inoculated, they were put into storage either im-
mediately while still moist, or after having been air-dried in-
doors for from 24 to 36 hours. After having been inoculated,
each lot was placed in a cloth or a paraffined cloth bag and
was stored either in the cool basement or in the warm attic of
the laboratory. Temperature readings were taken three times
daily and observations were made at 10-day intervals.
The results of this experiment are detailed in Table 1. It
will be seen therein that lesions became apparent in every in-
oculated lot within 10 days. In general the number of infected
tubers and the number of spots per tuber then increased slight-
ly during the next 10 to 20 days. The untreated control lots
remained comparatively free from lesions and there was mark-
edly less infection on the tubers packed in unspotted foliage
than on those packed in infected leaves. When the tubers were
stored in paraffined cloth bags, in the majority of comparisons
lower percentages of tubers were infected, and fewer and small-
er lesions per tuber developed, than where ordinary cloth bags
were used. The tubers in the latter type of bag remained dry






Florida Agricultural Experiment Station


while those stored in the paraffined bags were comparatively
moist throughout the period of the experiment.
In basement storage where the temperature was from 12 to
16 degrees C., higher percentages of tuber infection and larger
and more lesions per tuber generally were obtained, than in
attic storage where the temperature was consistently higher.
Under certain suitable conditions the amount of infection was
uniformly high from the different successive inoculations, even
though the times they were made ranged from early in Aug-
ust when the tu-
bers were but
half grown, to
digging time,
October 1, when
the tubers were
mature. Slightly
better results in
general were ob-
tained where the
tubers were
Stirred about in
moist foliage and
allowed to dry
for a day or so
before being
placed in stor-
age, than where
Fig. 115.-A tuber affected with Alternaria lesions they were store
split lengthwise to show the appearance of the
lesions on the surface and the rotting within the while still moist.
tuber. Isolations from this tuber yielded cultures It is worthy of
of A. solani. note that the
most typical lesions were obtained when the leaves and tubers
were dry at the time of inoculation. Several times tubers were
packed in soil mixed with diseased foliage, but the percentage of
tuber infection thus obtained was low, and the lesions were not
typical.
In the experiments described above, about as many lesions
were observed on unbruised as on bruised tubers.- Inoculations
were consequently made to test further the effect of bruising
on the amount of infection. Fifty Spaulding Rose tubers with
no apparent skin abrasions were infected by stirring them in







TABLE 1.-PERCENTAGE OF TUBERS INFECTED, NUMBER OF LESIONS PER TUBER, AND DIAMETER OF LESIONS, TEN DAYS AND
THIRTY DAYS AFTER INOCULATION.


Storage



Series I-Inoculated ................ 8-8-25
Percent tubers infected ..............
No. lesions per tuber ................ Base-
Diam. of lesions (mm.) .............. ment
Percent tubers infected .............. at
No. lesions per tuber................... 120-160C.
Diam. of lesions (mm.) ............

Percent tubers infected ............
No. lesions per tuber .................
Diam. of lesions (mm.) ............. Attic
Percent tubers infected ............. at
No. lesions per tuber ................. 180-24oC.1
Diam, of lesions (mm.) .............

Series II-Inoculated .................... 8-21-25
Percent tubers infected ............
No. lesions per tuber ................. Base-
Diam. of lesions (mm.) ........... ment
Percent tubers infected .......... at
No. lesions per tuber ................ 120-160C.
Diam. of lesions (mm.) ..............

Percent tubers infected ............
No. lesions per tuber ..................
Diam. of lesions (mm.) ............. Attic
Percent tubers infected ............ at'
No. lesions per tuber .................. 180-240C.
Diam. of lesions (mm.) ..............


No.
Days Check
After (not treated)
Inocu-
lation


0
4
1-2
15

0
0
0
0
0
0


4
2-5
1-2
4
1
3

0
0
0
0
0
0


0
0
0
0
0
0

0
0
0
0
0
0


2
1-2
1-2
4
1-2
5-6

0 -


Packed
Not
spot-
ted


16
1-5
1-3
50
1-5
3-25

0
0
0
2
1
6


2
1-2
1-2
44
2-3
3-12

10
1-2
1-2
38
2-5
3-10


in Leaves
Spotted
with
A. solani


100
2-15
2-6
100
5-10
3-20

52
2-5
2-5
64
3-6
3-20


98
5-20
2-6
98
5-10
2-8

86
5-25
2-10
90
5-10
3-18


I PC


82
2-10
1-2
84
5-10
2-3

56
2-5
1-3
46
3-6
3-12


80
5-10
2-4
88
5-10
2-8

88
5-251
2-10
100
5-10
3-10


*Lesions beginning to coalesce.
**Accurate diagnosis vitiated by infection of Phytophthora infestans de By.
'C, in cloth bag; PC, in paraffined cloth bag.


Tubers


Inoculated with
Moist Foliage I Dry Foliage


-dried


C I PC


84
1-5
2-4
94
1-5
3-25

46
2-5
2-6
76
3-6
3-20


92
5-20
2-4
100
5-10
5-12

90
5-20
2-4
**
**


.And Stored With Tubers
Moist I Air-dried [ Air


C


24
1-2
2-4
72
2-5
5-12

22
1-2
2-4
32
3-5
3-12


28
1-2
1-2
**
**
**

88
5-20
2-5
**
**


100
5-15
2-6
100
*3-10
3-30

88
5-10
2-6
100
3-6
3-15


100
5-20
2-7
100
5-15
3-25

84
5-20
2-6
98
5-10
3-15


C PC


-- ----~----~-----i


100
5-15
2-8
100
*3-10
3-25

78
3-5
2-10
98
2-5
3-20


100
5-20
2-6
100
5-15
3-20

68
5-20
2-6
96
5-10
3-12


100
5-25
2-4
100
5-15
3-16

54
2-5
1-4
84
5-10
3-18


I


,


,


I


78
2-10
2-4
98
5-10
3-12

40
2-5
1-4
82
5-10
3-15






TABLE 1.-PERCENTAGE OF TUBERS INFECTED, NUMBER OF LESIONS PER TUBER, AND DIAMETER OF LESIONS, TEN DAYS AND
THIRTY DAYS AFTER INOCULATION.-Continued.


Storage



Series III-Inoculated ..--........-..! 8-31-25
Percent tubers infected ...........
No. lesions per tuber ................. Base-
Diam. of lesions (mm.) ............ ment
Percent tubers infected ............. at
No. lesions per tuber .................. 120-160C.
Diam.' of lesions (mm.) .............

Percent tubers infected ..----..
No. lesions per tuber ..................
Diam. of lesions (mm.) .............. Attic
Percent tubers infected .............-- at
No. lesions per tuber ................ 180-240C.
Diam. of lesions (mm.) ..............


Series IV-Inoculated ................
Percent tubers infected ............
No. lesions per tuber ..................
Diam. of lesions (mm.) ............
Percent tubers infected ..............
No. lesions per tuber ................
Diam. of lesions (mm.) ..............


9-10-25

Base-
ment
at
120-160C.


No.
Days [ Check
After (not treated)
Inocu-I
nation
C' PC1

10 8 4
10 1-2 1-2
10 2-6 1-3
30 34 10
30 1-2 1-2
30 3-5 4-8

10 0 2
10 0 1-2
10 0 1-2
30 4 8
30 1 1
30 10 8

10 2 2
10 1 1
10 3 2 .
20 6 10
20 1 2-3
20 4 2-5


Packed
Not
spot-
ted
C 1

26
2-4
1-3
90 1
2-4
3-10

20
1-2
1-3
64
2-4
2-5


in Leaves
Spotted
with
A. solani
C I PC


30
5-10
2-8
00
2-10
3-8

56
1-4
2-8
84
4-8
3-10


88
3-5
2-6
94
5-15
2-7

54
1-4
1-4
92
2-5
2-5


Percent tubers infected ............ 10 2 0
No. lesions per tuber .................- 10 1 0 ............ ..............
Diam. of lesions (mm.) .............. Attic 10 10 0 ...................................
Percent tubers infected .............. at 20 12 4 ..................................
No. lesions per tuber .................. 180-240C. 20 1 1 ..............
Diam of lesions (m m.) .............. 20 4 3 ...................................
*Lesions beginning to coalesce.
**Accurate diagnosis vitiated by infection of Phytophthora infestans de By.
'C, in cloth bag; PC, in paraffined cloth bag.


Tubers
Inoculated with _
Moist Foliage Dry Foliage
_And Stored With Tubers


Moist


76
3-5
2-10
98
4-10
3-12

76
3-5
1-8
100
3-6
5-15


74
3-5
1-6
92
3-5
3-12

52
2-5
1-5
90
3-6
3-8


5-10 5-10
1-4 1-4
.- 100 100 1
... 2-10 5-15
2-6 2-6

S94 86
-. 2-5 2-5
--I 1-4 1-4
... 94 96
3-8 5-101
-. 3-6 3-7


Air-dried


50
2-5
1-5
98
2-7
3-15

46
2-5
1-5
84
2-5
3-15

100
2-5
1-3
00
5-15
3-10

58
2-5
1-5
68
2-5
2-6


PC

70
3-5
2-4
100
2-7
5-15

52
3-5
1-5
100
3-6
2-1(

92
5-1(
1-3
100
5-1l
3-1

88
2-1(
1-4
96
2-9
2-6


SAir-dried
C I PC

94 92
2-4 3-5
1-4 1-4
100 98
3-10 3-12
33-2 3-8

74 48
5-101 2-5
2-71 1-5
100 70
4-10 2-5
4-12 3-8


I1


98
5-10
1-4
98
5-20
1-5

96
2-5
1-5
100
5-20
2-6


0

51
0

0
3


84
5-15
1-4
96
1-10
2-10

82
5-15
1-4
94
1-6
2-8


111











T A B L E 2.-DATA SHOWING THE EFFECT OF BRUISING THE TUBERS BEFORE INOCULATION.

No. Days SERIES I SERIES II SERIES III
Storage After
Inocula- 00
tion Bruised Not Bruised Not Bruised I Not
Bruised Bruised .Bruised
Date inoculated ................................... ..8-21-25 8-31-25 9-10-25
Percent tubers infected .............I 10 70 32 76 52 96 66
No. lesions per tuber ........... Base. 10 3-10 2-5 2-5 2-5 5-10 5-10
Diam. of lesions (mm.) ............ ment 1 10 2-6 1-2 2-10 1-4 1-4 1-4 s
Percent tubers infected .............. at 30 100 88 98 88 100 88
No. lesions per tuber .................120-16C. 30 5-10 5-10 3-10 3-10 5-15 5-15
Diam. of lesions (mm.) ........... 30 3-15 2-15 3-12 4-10 2-6 3-8
Percent tubers infected ........... 10 48 2 76 0 94 54 5
No. lesions,per tuber .................. 10 2-5 1-3 2-5 0 2-5 2-5
Diam. of lesions (mm.) ............. Attic 10 1-4 1-2 1-8 0 1-4 1-3
Percent tubers infected .............. at 30 96 36 100 72 94 60
No. lesions per tuber .................. 18-240C. 30 5-10 2-5 3-6 2-3 3-8 2-5 0,
Diam. of lesions (mm.) .............. 30 3-15 4-10 5-15 6-10 3-6 8-7
Co














TABLE 3.-DATA SHOWING THE EFFECT OF STORING TUBERS AT DIFFERENT TEMPERATURES AFTER INOCULATION WITH A. SOLANI.


No. of
Days Not
After Inocu-
Inocula- lated
tion

Temperature ( Centigrade) ..................... 14-16

Percent tubers infected ............ 10 0

No. lesions per tuber ............... 10 0

Diam. of lesions (mm.) ............ 10 0

Percent tubers infected ............ 30 I 12

No. lesions per tuber ............... 30 1-2

Diam. of lesions (mm.) ............ 30 5-10


SERIES I


Inoculated on 10-6-25


4-6

18

1-2

2-4

66

2-3

3-5


9-12

24

3-4

4-6

90

3-8

3-8


14-16

38

2-3

3-4

84

4-7

4-10


19-22

18

1-2

4-5

18

2-3

5-15


24-25

2

1-2

4-5
8*

1-2

10-30


Not
Inocu-
lated


14-16

8

1-2

3-4

8

1-2

2-8


SERIES II



Inoculated on 10-13-25


9-12

50

1-3

2-4

86

3-10

2-8


*Several atypical lesions occurred which on culturing yielded Fusaria and other organisms.


14-16

96

3-8

3-8

98

3-8

2-8


19-22

26

2-3

3-5

26

1-4

6-10


24-25
0*

1-2

2-4
0*

1-3

10-30







Bulletin 187, Infection of Potato Tubers


diseased potato foliage and were compared with a similar, lot
of potatoes that had been bruised during the application of the
inoculum. The experiment was made three times during the
summer with a total of six 50-tuber lots. These lots were stored
like those described before. The results demonstrated that
bruising is an aid to infection but is not essential. Frequently
almost twice the percentage of tuber infection was obtained
where the tubers were bruised, but the size and number of le-
sions per tuber were approximately the same (Table 2). The
most typical or normal lesions were obtained when the tubers
were not bruised.
As mentioned above, the development of this trouble was
more rapid at a cool temperature than at ordinary room or at-
tic temperatures. The cardinal temperatures for the develop-
ment of lesions were more definitely determined by three series
of studies made at different intervals. Each series consisted of
the storage of five lots of tubers at approximately 5, 10, 15, 20
and 25 degrees. In all three series there was very slow growth
at from 5 to 7 degrees, none at 25 degrees or above, and a con-
sistent development at all of the other temperatures but with
the most rapid development at from 13 to 16 degrees C. To
further confirm this, two more series were placed in controlled
temperature chambers at the experiment station laboratory at
Orono, Maine, and held at the same five temperatures given
above. Here similar results were obtained (Table 3).
Several lots of different varieties were inoculated and com-
pared both in 1924 and in 1925 to obtain information on varie-
tal susceptibility. The varieties included were: Spaulding
Rose, Early Rose, Green Mountain, Irish Cobbler, and Bliss
Triumph. The Spaulding Rose variety was by far the most sus-
ceptible, but the others were not immune. The varieties are
listed above in the order of their decreasing susceptibility. The
Spauldings developed 100 percent infection for practically all
of the inoculations and the infection for the other varieties was
from 25 to 50 percent.
Tubers of one lot were inoculated by stirring them about in
tomato foliage spotted with early blight lesions. One hundred
percent infection resulted and the lesions were typical for the
disease. Isolations from these tubers yielded A. solani.
At the conclusion of the above experiments, tubers with typ-
ical lesions were selected at random from the various lots and






Florida Agricultural Experiment Station


isolations were made further to confirm the work. Of 186 iso-
lations thus made, 92 percent yielded A. solani, while various
Fusaria and other fungi were secured from the remaining 8
percent. These other fungi were in all probability secondary


Fig. 116.-Tubers showing stem-end lesions and the appearance of the
flesh just underneath the skin. This injury was caused by A. solani.
This illustrates how this trouble may be confused with other troubles.

organisms and Alternaria may still have been the primary cause
even though not isolated in these instances.

CONCLUSIONS

From the foregoing observations and results it is obvious that
Alternaria spotting of potatoes is not necessarily or solely a
soil trouble, although tubers dug with no early blight apparent
on the vines have become infected (3, p. 6).
The tubers are easily and effectively inoculated at digging
time by stirring them about in foliage spotted with early blight.
The leaves are usually blight-infected at this time and the ordi-
nary commercial digger may serve as the inoculating agent.
Covering the barrels standing in the fields with foliage is
another way of effecting inoculation. Bruising is an aid to
infection but is riot essential.


::~ ,:";







Bulletin 187, Infection of Potato Tubers


Storage conditions as they exist in October in the Maine po-
tato houses are ideal for the development of this trouble. As
the temperature of the storage houses decreases, the dust cov-
ered lesions become practically dormant, making it impossible



















Fig. 117.-The tuber on the left is affected with Alternaria rot and the
other with Phytophthora rot, further illustrating the ease with which
Alternaria spotting may be confused with late-blight rot, Rhizoctonia
pitting, or other troubles.

to detect a large percentage of the minute spots when the stock
is prepared for Southern shipment in December. Much time is
required to remove the infected tubers prior to shipment and
the unobserved lesions increase in size during transit and are
from two millimeters to half a centimeter or more in diameter
on arrival at their destination. Under favorable conditions the
lesions will continue to develop. This breeds dissatisfaction, as
the Florida grower is convinced only with difficulty that the le-
sions were not readily apparent at the time of shipment.
Secondary organisms may follow the invasion of Alter-
naria, thus further increasing the storage losses. Further
losses are caused by injury to sprouts. It has not been demon-
strated conclusively that epiphytotic outbreaks of early blight
may result from the planting of infected seed pieces but this
appears entirely possible.







Florida Agricultural Experiment Station


Definite control methods have not been evolved. The method
of attack is suggested. If the control of early blight in the field
is impossible, the only other point of attack is at digging time.
Whether it means the application of an inhibiting agent to the
tubers, or the elimination of tuber and foliage contact either
by removing the vines first or by digging later when the vines
have been killed, remains to be seen.

LITERATURE CITED
(1) FOLSOM, DONALD, and REINER BONDE.
1925. ALTERNARIA SOLANI AS A CAUSE OF TUBER ROT IN
POTATOES. (Abstract.) In Phytopathology, v. 15, p. 49.
(2)
1925. ALTERNARIA SOLANI AS A CAUSE OF TUBER ROT
IN POTATOES. In Phytopathology, v. 15, p. 282-286, pl. 5-7.
(3) GRATZ, L. 0.
1925. IRISH POTATO DISEASE INVESTIGATIONS, 1924-1925.
(A PRELIMINARY REPORT) Florida Agr. Exp. Sta. Bul. 176,
23 p., 6 fig.
(4) and REINER BONDE.
1926. ALTERNARIA TUBER ROT OF POTATOES. (Abstract.)
In Phytopathology, v. 16, p. 68.




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