Sorghum Diseases in India

with grain mold resistance was recently introduced
from ICRISAT for testing in the southern
African region. Screening methods need to be
adapted to the region and local pathogens and
sources of resistance need to be identified.
C. Smuts
Covered smut (Sporisorium sorghi), head smut
(S. reilianum), long smut (Tolyposporium ehrenbergii)
and loose smut (Sphacelotheca cruenta)
were all reported in the region.
Covered smut. This sorghum smut, commonly
found in most of the 12 southern African countries
on local and introduced germplasm alike, is
of importance to small-scale farmers in several
countries (Ndimande, personal communication
1982, Botswana: Ministry of Agriculture 1987).
Chemical control of covered smut has been recommended
in Tanzania since the 1950s (Doggett
in Williams et al. 1980), and appears to be of
importance in all 12 southern African countries.
Lesotho has actively tested control methods
since 1985, making use of artificial inoculation at
sowing. This disease can be controlled effectively
with seed-dressing fungicides; low-cost
seed dressings have been identified and many
others are available for evaluation.
Head smut. Head smut, confirmed in six nations
(Table 2), can be expected in all southern
African countries (Sundaram in Williams et al.
1980). In the last 10 years, incidence levels have
been very low. Sources of resistance (Texas
A&M University, INTSORMIL) were introduced
to test for local adaptation and performance.
Considering the complicated development of resistance
due to high chance of the development
of new races, continuous monitoring for this disease
is required.
Long smut. This smut is commonly found in
areas affected by drought. In recent droughts it
was observed in Botswana, Lesotho, Malawi,
Tanzania, Zambia (first record, 1987) and Zimbabwe
(first record, 1985). In 1987, at Hombolo
in Tanzania, up to 40% of the head area in susceptible
genotypes was affected. In susceptible
genotypes, in other countries, less than 10% of
the head area was affected. Verification of the
resistance of entries tested in Kenya is important
in particular for use in Tanzania.
Loose smut. Loose smut affects local and introduced
germplasm in many countries, before
and after ratooning, but has not reached high
incidence.
Witchweeds. Three witchweeds were of importance
in the region: Striga asiatica, S. hermonthica,
and 5. forbesii. S. asiatica were reported
in most countries (Riches et al. in SADCC/ICRI-
SAT Sorghum and Millets Improvement Program
1987), in particular on poorly drained soils
with a low nutrient status. S. hermonthica occurred
in specific areas mainly in Tanzania, and
S. forbesii in specific areas in Tanzania and Zimbabwe.
In the 1985/86 season, SADCC/ICRISAT
began researching the Striga spp. S. asiatica was
studied intensively in Botswana by the Department
of Agricultural Research (Botswana: Ministry
of Agriculture 1987). ICRISAT provided
sources of resistance to S. asiatica from India,
and the New Dominion University, USA, provided
scientific cooperation. A field identification
guide for the region was published and
distributed (Obilana et al. 1987).
Conclusion
Doggett (in Williams et al. 1980) hypothesized
that the importance of diseases is positively related
to yield levels. Sorghum yields surpassing
3 t ha -1 have been achieved under experimental
conditions. In Malawi, Swaziland, South Africa,
Tanzania, Zambia, and Zimbabwe, yields in trial
plots were 3 to 12 times higher than the national
sorghum grain yields. In developed countries,
chemical control was used to obtain high yields
in wheat, but in sorghum, disease-resistant lines
appear to be the most promising method to increase
grain yields. With Doggett's hypothesis in
mind, it appears that this is an appropriate time
to put more efforts into developing disease resistance,
with increased yields.
Acknowledgment. D. Rohrbach assisted with
the preparation of the Introduction and the material
on Grain Yield.
17