Sorghum Diseases in India

(most systemically infected plants are barren).
Infected plants also produce conidia that become
airborne under favorable conditions. With
certain maize-sorghum intercropping schemes,
conidia produced by the maize plants may reach
the sorghum plants in time to cause systemic
infections. Infections can become systemic
mainly during the first 3 weeks of plant growth.
Systemically infected sorghum plants produce
numerous oospores that are released when the
dying leaves shed. These can infest the sorghum
seed produced on healthy plants, and carry over
in the soil. In a yield-loss study on sorghum in
the Honduras, an incidence of 43% SDM reduced
grain production by 44% (Wall et al.
1986).
Three different pathotypes of P. sorghi have
been found in the Honduras so far (Fernandez
and Meckenstock 1987). This development complicates
implementation of effective control
strategies based on resistance. Constant monitoring
of the pathogen population in different
production areas and deployment of the adequate
resistant genotypes in each is required.
Acremonium strictum invades vascular tissues
of sorghum, causing wilting and burning of the
leaves. The disease has been seen all over the
Honduras, on local sorghums as well as on improved
cultivars. Its prevalence is very high in
some areas, but its severity is usually low; only
certain susceptible materials are affected seriously.
Infected plants may produce no grain at
all; an average of 36% grain mass reduction
(Table 1) was observed on infected plants when
compared to healthy ones (Meckenstock and
Table 1. Yield loss of grain sorghum from systemic
diseases in the Honduras. 1
Disease
MDMV
SDM
Acremonium
wilt
1. Source: Wall (1986).
Typeof
comparison
diseased vs
healthy 2
3% vs 43% 3
diseased vs
healthy
2. Comparisons between paired plants.
Yield loss
(%)
52
44
36
3. Comparisons between resistant and susceptible
70
near-isogenic populations.
Wall 1987). The disease can be seed-transmitted
(Bandyopadhyay et al. 1987). Our own observations
in the field lead us to believe that acremonium
wilt can also become established on
plants after they suffer insect damage, either
from stalk borers or armyworms.
Stalk and panicle diseases
Covered smut (Sporisorium sorghi) and loose
smut (Sphacelotheca cruenta) are common, be
cause most farmers save part of their own harvested
grain for next year's seed. When seed is
treated with thiram, the problem is virtually
eliminated. Head smut (Sporisorium reilianum)
has been seen in an experiment station in El Salvador,
but does not occur regularly (R. Ortiz,
CENTA/MAG, San Andres, El Salvador, personal
communication).
With maicillos, the problem of grain mold is
minimal, as the flowering period coincides with
the end of the rainy season. Photoperiod-insensitive
sorghums must be sown so that their flowering
times coincide with dry weather, or they
can develop serious grain mold problems. Several
fungi are involved, but it is mainly Fusarium
moniliforme and Curvularia lunata that are involved
in grain molding in Central America.
They appear as pink and black discolored
grains, respectively, on the panicles.
Head blight can be caused by F moniliforme
and Colletotrichum graminicola. The basal node
area of the panicle is invaded, and shows a discoloration
if split open. Insect damage promotes
colonization by Fusarium, Conditions that favor
grain mold are conducive to head blight.
The basal part of the sorghum stalk can also
be attacked by F moniliforme, leading to premature
death of the plant. E moniliforme infections
are also associated with insect and mechanical
damage.
Charcoal rot (Macrophomina phaseolina) can affect
plants that are subjected to drought stress
during grain filling. This disease is important in
Panama (Jimenez 1984). It occurs mostly on
high-yielding sorghums that have been heavily
fertilized, particularly with high levels of nitrogen
and low levels of potassium, and then subjected
to drought stress (Frederiksen 1986).
Charcoal rot seldom occurs on maicillos, or in
maize-sorghum intercropping.