Compendium of Potato Diseases - (PDF, 101 mb) - USAID

Immature tuber surfaces are easily infected, whereas those of
mature tubers are much more resistant. Wounds are generally
necessary for infection through mature tuber skins. A period of
3-4 days or more between vine killing and digging considerablv
increases tuber resistance.
Epidemiology
Maximum mycelial growth of*A.so/ani in pure culture occurs
at 280C, whereas optimum temperature for formation of
conidiophores and conidia is 19-23'C. Conidiophore
formation is inhibited, but not irreversibly, at temperatures
greater than 320 C. Temperatures above 270 ( stop conidia
formation. Conidiophores develop in light, whereas light
inhibits conidia formation at temperatures above 150C.
Maximum spore production in the field occurs between 3:00
1.O ,
'
' !41
I
/1
H °A
C I D
Fig. 48. Early blight: A, leaf lesions with concentric targetlike
markings, somewhat limited by the larger veins; B,tuber lesions;
C, dormant spores of Alternaria solani with short-beaked A.
alternata type near top (bar represents 50 pm); D, germinating
spore.
44
a.m. and 9:00 p.m. Spores in water germinate within 35-45 min
at the optimum temperature (24-30' C) and within 1-2 hr at
6-34' C. Optimum temperature for tuber infection is 12-16' C
but varies with cultivar.
Most rapid progress of the disease occurs during periods of
alternating wet and dry weather. Early blight can be severe in
irrigated desert regions because of prolonged periods of dew.
The disease is often more severe when the host has been
predisposed by injury, poor nutrition, or other type of stress.
Field resistance to foliage infection is associated with plant
maturity. Late maturing varieties are usually more resistant.
liarly blight does not red uce yields when inlection occurs late in
lhe season.
Other Hosts
The fungus is pathogenic on tomato and other solanaceous
crops and has been reported on other genera such as Brassica
spp.
Control
I) Cultivars with levels of field resistance are available, but no
cutivars are immune.
2) Protectant fungicides such as the dithiocarbamates, fentin
hydroxide, and chlorothalonil effectively control early blight on
loliage.
31) Fungicide applications scheduled by spore trapping or
other methods so as to coincide with secondary spread of the
disease are most effective. Early season applications of
.fgicides before secondary inoculum is produced often have
little or no effect on the spread
permit tubers
of the
to inature
disease.
in the ground before digging, and
avoid bruising in handling.
5) Avoid disturbing seed tubers until ready to plant.
Selected References
)OUGLAS, 1). R., and M. I). GROSKOIPIP. 1974. Control of c:arlv
blight ineastern and soutlicentral Idaho. Am. Potat .I.51:361-368.
I)OtJGL.AS. I I). R., andt i. .t. FPAVE K. 1972. Screening potatoes for field
EI.IIS, resistance M. .B., to and early I. A, blight. S. GIBSON, Am. Potato 1975. .1.49:1-6. .lhernariasolani. No. 475
in: Descriptions of Pathogenic Fungi and Bacteria. Comnmonw.
Mycol. Inst.. Kcn. Sorrey. Ingland. 2 pp.
IIARRISON, M. )., C. II. LIVINGSIION. and N. OSFIIMA. 1965.
Control of potato carly blight in Colorado. I. Fungicidal spray
schedules in relation to the epidemiology of the disease. Am. Potato
J. 42:319-327.
IIARRISON, M. I)., C. If. 1IVINGSTON, and N.OSIIIMA. 1965.
Control of potatocarly blight in Colorado. 1I.Spore traps asa guide
for initiating application%ol
VFNETTE,
hngicidcs.
.1.R.,
Am.
and
Potato
M.
,I.42:333-340.
1). IIARRISON. 1973. Factors affecting
infection of potato tubers by .lhernariasolani in Colorado. Am.
Potato .1.50:283-292.
WAGGONER, P. E.. and J. G. IIORSFAI.L..
simulator
1969. Epiden.
of plant
A
disease written fora computer. Conn. Agric. Exp.
Stn. [lull. 698. 811pp.
(Prepared by D. P. Weingartner)
lternaria alternata
Alernaria ahernata (Fries.) Keissler (syn. A. tenuis Nees.)
infects potato and other solanaceous crops, forming lesions on
potato leaves similar to those of early blight. Spores
x
(20-63
9- 18 Mpn) are snialler than those of' . solani,are formed in
chains, and lack the typical long beak (Fig. 49A). Their sizeand
shape may vary considerably. The fungus is often associated
with considered other diseases
a
and
weak
isfrequently
parasite,
isolated. It isgenerally
which attacks plants weakened by
viruses, deficiencies, stress, or senescence.
Selected References
EIIIS. M.B. 1971. Dernatiaceous Ilyphomycetes. Commonw. Mycol.