Sorghum Diseases in India

or six leaves only towards maturity Abundant
sporulation occurs in very wet areas.
It would appear that leaf anthracnose causes
more damage than gray leaf spot. All leaves can
be heavily infected during grain formation. In
many instances, complete drying of the top
leaves occurs before the grain matures. However,
there are many local genotypes in which
leaf anthracnose appears only as midrib infections;
abundant tiny dark brown necrotic spots
on the leaf lamina resemble a hypersensitivetype
reaction. In this type of host reaction, the
top four or six leaves are rarely killed whereas
the lower leaves are completely dry. Formation
of acervuli is rare in either type of infection.
High incidence of oval leaf spot, zonate leaf
spot, and leaf blight occurs but not at severe
levels, in many farmers' fields in the Northern
Guinean Zone and the Sudanian Zone. Bacterial
stripe has been observed in many local genotypes
and is mostly restricted to the lower
leaves.
Panicle diseases
Grain molds are rare in farmers' fields. Most local
sorghum varieties in normal years develop
the grain after the rains cease. This enables the
plant to produce grain virtually free from seed
molds (Zummo 1984). Head smut, long smut,
and covered smut occur at low levels. Head
smut is, however, more common.
Parasitic weeds
Striga hermonthica occurs abundantly in farmers'
fields in all the agroecological regions of western
Africa. Some genotypes do not show typical
Striga symptoms, even under heavy infection.
Diseases Prevalent in Introduced
Sorghums
Leaf diseases
Gray leaf spot and leaf anthracnose are the more
prevalent leaf diseases in introduced genotypes
in the northern Guinean Zone and in very wet
areas of the Sudanian Zone. In the absence of
conclusive data from western Africa, it is diffi­
cult to comment on the effect of these two leaf
diseases on grain yield. Experiments show that
in highly susceptible genotypes (eg., IS 18696,
ICSV 20-1 BF, and ICSV 16-3 BF) grown under
favorable conditions for disease development,
first symptoms of gray leaf spot can appear anytime
within 10 days after infection. The disease
progresses slowly, at about 20 to 30 days after
flowering. Infection usually affects less than 50%
of the leaf area in the top four leaves. The progress
of the disease increases slightly after this;
at physiological maturity the leaf area infected
(LAI) usually exceeds 75% in any of the top four
leaves. In many other susceptible genotypes,
symptoms appear even later and disease progress
is even slower (unpublished data 1987).
This pattern of disease progress implies that
gray leaf spot may not cause serious loss in
yield. Odvody (1986) suggested that the economic
impact of gray leaf spot is hard to assess,
because epidemic conditions only develop near
crop maturity
With leaf anthracnose, the situation is completely
different and perhaps less ambiguous. In
susceptible genotypes—IS 18442, IS 2139, IS
4585, or IS 1552—leaf anthracnose symptoms
appear early and the disease progresses rapidly
and kills top leaves during grain formation. The
same is true for IS 18696 growing under conditions
favorable for leaf anthracnose. For example,
LAI in the top four leaves for IS 2139 and IS
1552 was between 26% and more than 75% at
flowering. Within 3 weeks after flowering, the
four top leaves were dead. The same general
pattern of infection and disease progress was
evident in IS 18696 and IS 18442 (unpublished
data 1987). This supports the view that anthracnose
is a major threat to sorghum production in
some areas of western Africa, because of the
rapid rate at which the anthracnose pathogen
can damage sorghum plants approaching maturity
(Frederiksen 1984).
When conditions are favorable, damage from
sooty stripe can be serious. More than 50% LAI
in the top four leaves may occur between flowering
and maturity. Dry conditions in the Sudanian
Zone appear to favor development of sooty
stripe. However/preliminary observations at
Farako-Ba and Kamboinse in Burkina Faso and
at Cinzana in Mali suggest that sustained high
humidity may be necessary for successful infection
and subsequent initiation of symptoms during
early stages of the disease. This might be
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