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

strands of pigmented hyphae. Sclerotia are numerous, round,
0.4-2.0 mm in diameter, white when young, then tan, and dark
brown when old. [he hasidial stage. I'elliculariarolfvii (Sacc.)
West, is uncommon, with basidiospores approximately 3.5-5 X
6-7 j.m, elliptical to obovate, rounded above and either rounded
or pointed at the base. Basidiospores do not seem to be
important in the disease cycle,
Histopathology
Hlyphae are both intracellular and intercellular and are constricted
at the point of penetration of the cell wall. Host cells are
killed well in advance of fungus hyphae. The hyphae produce
oxalic acid in considerable quantities and also the enzymes
polygalacturanase and cellulase, which hydrolyze and disrupt
cell walls.
Disease Cycle
The fungus is soilborne as selerotia or mycelia on decay'ing
vegetable
vgtae ungusaistsoibor matter. Scle rotia nclerotia permit mitorlong-term y survival vival d5) but
contain relatively low energy reserves. They produce short-lived
mycelia unless a suitable living or dead plant part is available.
Mvcelia infect seed tubers, sprouts, grown plants at any stage,
and tubers. As an energy supply is exhausted, the mycelia
aggregate, and sclerotia are formed. Disease spread in the field is
by mycelial growth or by dispersal of mycelial fragments and
sclerotia in debris or infested soil. Spread is therefore slow.
Disease incidence within a field is often erratic, with infected
plants
plant
as foci. Long
parts
distance
containing
spread
hyphae
is by
or
transfer
sclerotia,
of infected
by movement of
sclerotia by wind or surface water, or by mechanical means.
Epidemiology
Germination of sclerotia and mycelial growth are favored by
aerobic conditions, high temperatures (28-30'C), and high
relative humidity. Vegetative survival is in the upper few
:'"';,: ' ­
,. .. ..4
*fruiting
Fig. 56. Stem rot. Symptoms on tuber: A, radiating white
mycelium; B, later stage with sclerotia. C,Clamp connections in
hyphae of Sclerotium rollsii. (A, Courtesy L. W. Nielsen; B,
courtesy T. A. de Icochea; C, courtesy T. A. de lcochea and L.J.
Turkensteen)
centimeters of the soil but may be deeper if the soil is dry and
well aerated. Cool climates (elevations above 1,000 m in the
tropics) are not favorable for disease development.
Other Hosts
S. rol'ii infects cultivated and noncultivated plants such as
ferns, certain mosses, gymnosperms, grasses, cereals, banana,
and many dicotyledonous plants including certain woody trees.
It also grows on plant residues, including wood, in appropriate
temperature and relative humidity.
Control
I) Use pentachloronitrobenzene as tuber seed treatment.
2) Fumigate soil with 3M%sodium N-monomethyldithiocarbamate
dihydrate.
3) Bury plant debris by deep plowing.
4) Avoid throwing sod or organic material (weeds) onto
lower stems of potato plants during cultivation.
lae Control nsi defoliating ufcs diseases to prevent accumulation of
Selected References
AYCOCK, R. 1966. Stem rot and other diseases caused by Scerotium
ro~llfii. N. C. Agric. Exp. Sin. [ech. Bull. 174. 202 pp.
AYCOCK. R.. chairman. 1961. Symposiumn on Schrotiuo rollii.
Phytopathology 51:107-128.
ED)INS, A. H., and F..WEST. 1946. Sclerotium rot of potato seed
pieces. Phytopathology
FRENCH,
36:239-240.
FRIBOURG, 1. R., F.N.FERNANDEZ, 11. TORRES, T.A.de
A.
ICOCIIEA,
MARTIN.J. I.. SAt.AZAR,
FRANCO,
C.
M.
M.de SCURRAtt, I.A. HERRERA, C. VISE, L.L.AZOand 0. A.
HIDAI.GO. 1972. Enfermedades de ]a Papa en el PeriL Bol. recn.
No. 77. Est. Exp. Agric. La Molina, 36 pp.
(Prepared by T. A. de lcochea)
Rosellinia Black Rot
The disease is prevalent in the tropics, where temperate and
moist climates are found during the growing season. Especially
heavy yield losses, rivaling those of late blight, are reported from
Costa Rica and Ecuador. The disease has also been reported
from Bolivia, Colombia, Peru, and Chile.
Symptoms
Plants become stunted and wilted. Leaves yellow, and plants
slowly die. Stems may be cankered, Roots and stolons may be
partially or completely destroyed, dark colored, and covered by
a mat of rough, loose, fast growing strands of a grayish white
mycelium (Fig. 57A). Affected tubers are partially or completely
covered by the loose fungus strands at harvest (Plate 39). A
hard, dark brown carbonaceous mass soon forms in affected
tissue under the white mycelium. When cut, tubers often show a
band of striate projections growing inward from the tuber surface
(Fig. 57C). Single plants or groups of plants may be
attacked in,the field. Infection expands from affected phmts in
the fungus are found to extend from one plant to another.
'ubers frequently rot before harvest.
Causal Organism
Morphology of the mycelium
istic swellings
and, especially,
of the hyphae
the character­
above the septa (Fig. 57B) are
characteristic of the genus Rosellinia, which produces no known
bodies and should be considered a member of the
Mycelia sterilia.
Rosellinia black rot can be distinguished from stem rot
because the fungal strands from Rosellinia may be present on all
parts below soil level, whereas Sclerotium rolfiiaffects only the
parts close to the soil surface. Rosellinia does not form round
sclerotia. It also differs from the perfect stage of Rhizocionia
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