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

Pleospora herbarum
Pleosporaherbarum (Pers. ex Fr.) Rabenh. and its imperfect
stage, Stemphyilium hotr'osuin Wallr., are often found
associated with potato plants poorly adapted to warm
conditions or to other environmental stresses. Round, rapidly
enlarging, light colored leaf lesions develop, affected tissues
appear as thin paper (Plate 34). The same fungus is commonly
isolated from dead and dried materials and wood, but is also
known as a pathogen for several crops.
Conidia are olive to brown and oblong, with three transverse
septa and 1-3 longitudinal septa The spores are 19.5 X 28.5 mm,
with asingle basal pore 8 um in diameter (Fig. 49B). Ascospores
are dark, yellow-brown, ellipsoid to clavate, muriform, and
26-50 X 10-20 ym (Fig. 49C). Transmission is by airborne
ascospores or conidia, and penetration is through stomata.
Selected References
BOOTH, C., and K.A. PIROZYNSKI. 1967. Ph'osporaherharum.No.
150 in: Descriptions of pathogenic Fungi and Bacteria. Commonw.
Mycol. Inst., Kew, Surrey, England.
ELLIS, M.B.
2 pp.
1971. Dematiaceous
Inst., Ke w ,
Hyphomycetes.
S u rrey. E n gla n d .
Commonw.
6 0 8 p .
Mycol.
(Prepared by L. J. Turkensteen)
Ulocladium Blight
Ulocladium atrum Preuss (syn. Stemphylium atrum (Preuss)
Sacc.) is a weakly pathogenic organism (Fig. 49D). In the high
(over 3,500 m) Andean region around I.ake Titicaca, it causes
a potato foliage blight that is associated with damage from
insects and, especially, from hail. Damage caused by the
frequent hail storms is increased considerably as torn edges of
leaves turn dark to black. When heavily attacked by U.atrum,
the whole foliage turns blackish and becomes necrotic. Also,
tiny, dark colored lesions up to 3 mm in diameter with irregular
margins are formed on healthy lcaves, apparently without
previous wounding. Peruvian natives call the disease kasahui.
Selected References
FRENCH, E.R., H.TORREST.A.de ICOCIEA, I.. SAI.AZAR, C.
FRIBOURG, E.N.FERNANDEZ, A. MARTIN.J. FRANCO, M.
M.de SCURRAH, I.A.HERRERA, C.VISE, .. .AZO, and O.A.
HIDALGO. 1972. Enfermedades de lapapa in el Peri6. Bol. Teen.
No. 77. Est. Exp. Agric. La Molina. 36 pp.
ELLIS. M. B. 1976. More )ernatiaceous |lyphomycctes. Commonw.
Mycol. Inst., Kew, Surrey, England. 507 pp.
(Prepared by .. J. Turkensteen)
, •
Lv~~ ~ -_..
Fig. 50. Leaf spot lesions of Septoria lycopersici.(Courtesy E. R.
French)
46
*
Stemphylium consortiale
Sternphvliuni consortiale (Thiim.) Groves & Skolko (syn.
Ulocladium consortiale (Thiim.) Simmons) causes lesions
occurring with and superficially resembling those caused by
Alternaria solani, except that lesions lack the concentric
markings of early blight and are lighter brown. Lesions develop
three to fourdaysafter inoculation and cause defoliation similar
to that of early blight.
Selected References
EI.l.lS, M. B. 1976. More t)ematiaceous Hyphomycetes. Commonw.
Mycol. Inst., Kew, Surrey, England. 507 pp.
WRIGIHT, N.S. 1947. A stemphylium leaf spot on potatoes in British
Columbia. Sci. Agric. 27:130-135.
(Prepared by W. J. Hooker)
Septoria Leaf Spot
Thedisease ispresent in Centraland South America. It occurs
T e d s a e i r s n n C n r l a d S u h A e i a t o c r
in cultivated potatoes at elevations that differ considerably from
one region toanother, e.g., at 1, 6 00-2,500 m in Venezuela and at
3,800-4,200 m in Peru. It occurs in wild potato at a wider range
of elevations.
Symptoms
Lesions on leaves are round to oval (Fig. 50) and have concentric
rings of raised tissue when viewed from the upper surface.
Rings are similar to those of early blight or Phoma leaf spot.
Septoria leaf spot can be distinguished with the help ofa good
hand magnifier by the presence of one or more relatively large,
erumpent pycnidia ( 9 0-230,um) in older lesions. Leaves in alate
stage of attack become bri'tle, deformed, and susceptible to
wind damage. In advanced stages, leaves become necrotic and
may drop from the plant. Yield reductions are considerable.
Causal Organism
Septoria l.vcopersici Speg. is similar on tomato and potato
plants but exhibits differences when isolates from the two hosts
are grown on artificial media. Dampened pycnidia release
masses of hairlike spores (1.8-2.4 X 25-135 pm or longer) with
three or four, sometimes up to seven, cross walls (Fig. 49E). On
artificial media, lead gray colonies expand very slowly, and
oatmeal agar becomes brown below the colony.
Epidemiology
The disease is present in regions characterized by cool, moist
weather during the growing season. Inoculum is transported by
rain splash and probably carries over on plant debris in soil.
Long moist periods during which leaves stay wet are thought to
be necessary for infection.
Other Hosts
Tomato is the principal other host.
Cntrol
I) Nonsystemic fungicides capable of controlling late blight
are effective agaist Septoria. Treatment should be started at an
early stage of infection because lesions, once present, form a
continuous source of inoculum.
2) Differences in susceptibility have been observed.
Selected References
PIGLIONICA. V., G. MAI.AGUTI. A. CICCARONE, and G. H.
BOEREMA. 1979. L.a Septoriosi della patata. Phytopathol.
Mcditerr. 17:81-89.
JIMENEZ, A. T., and E. R. FRENCH. 1972. Mancha anular foliar
(Septoria lycopersicisubgrupoA)de lapapa. Fitopatologia 5:15-20.