Sorghum Diseases in India

Breeding for resistance
The main objective of the sorghum breeding
program at ICRISAT is to develop high-yielding
breeding material, acceptable in food quality
and resistant to insect pests and diseases. The
program at ICRISAT includes projects on diseases,
Striga, insect pests, multifactor resistant
populations, sorghum conversion, and development
of hybrids and hybrid parents. At present,
our single project on disease resistance focuses
on grain molds. Sources of resistance to downy
mildew, stalk rots, and leaf diseases are used in
all the breeding projects, of course, and are selected
simultaneously with other specific traits.
Heritabilities for resistance to downy mildew
and leaf diseases are fairly high, therefore frequency
of these resistance genes in the breeding
material generated should be high. Rosenow
and Frederiksen (1982) summarized the inheritance
of resistance to several diseases. Mold resistance
is dominant in some F1 hybrids, and
over-dominant or intermediate in some others.
Resistance to downy mildew, anthracnose, and
rusts is dominant. That of charcoal rot is recessive
to intermediate.
Grain Molds
Grain mold (GM) has become a major and widespread
disease of sorghum in the SAT, especially
where flowering and grain development and
maturity coincide with the rainy warm weather.
Grain molds significantly reduce yields and
grain quality. Growing of high-yielding, earlymaturing,
mold-resistant cultivars is the only
practical control method suited to farmers in the
SAT.
At ICRISAT Center, the sorghum germplasm
collection was screened between 1975 and 1978
for sources of GM resistance; lines consistently
resistant were selected for breeding. Selections
from crosses involving these low-level sources
of mold resistance yielded improved breeding
lines with moderate grain yield potential but
with low levels of resistance. The mold resistance
of these lines is not sufficient for effective
mold control under moderate to high mold-disease
pressure. Several low susceptible lines were
intermated to generate variability and concentrate
the scattered resistance genes, but this did
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not provide significant improvement in GM-resistance
in the white-grained sorghums.
In the early 1960s, high-level GM resistance
was identified in colored-grain sorghums. These
maintain their resistance for 2 to 3 weeks following
physiological maturity (Bandyopadhyay et
al. 1987). We involved these colored-grain lines
in crosses and intensively screened the segregating
progenies for white-grained segregates with
high levels of mold resistance. Five whitegrained
selections with levels of mold resistance
as high as their colored-grained parental lines
were identified, specifically ICS x 62 K 140 B 3-1,
ICS x 62 K140 B 2-1, ICS x 119 K19 W 1-6-1, ICS
x 119 K 64 W 1-2-1, and ICS x 119 K 19 W 1-4-1.
These lines, however, are tall and low-yielding.
So we are now using them as sources of
high mold resistance in developing improved
breeding material with good yield potential and
desirable agronomic traits.
Mold resistance in the white-grained selections
appears to be associated with grain hardness,
(Mukuru; Waniska et al., this publication)
while mold resistance in colored-grain is associated
with tannin and flavan-4-ol content or grain
hardness, or a combination of these factors.
High flavan-4-ol content has not been identified
in white-grained sorghum lines.
We routinely screen for resistance to grain
molds in all breeding lines generated in the
many breeding projects at ICRISAT Center; all
have been found to be mold-susceptible. (Mukuru;
Waniska et al; Forbes et al., this publication).
Other Diseases
The other sorghum diseases of importance in
India are charcoal rot, downy mildew, anthracnose,
and rust. The sorghum germplasm collection
has been screened, and resistance to these
diseases identified (ICRISAT 1984).
Charcoal rots caused by a common soilborne
fungus, Macrophomina phaseolina is a destructive
disease of sorghums in the SAT (see Pande on
Stalk Rots, this publication) Plant lodging and
reduction of yields and quality of the grain result
from stalk rot infections. Charcoal rot-resistant
germplasm lines have been identified and
are used in various breeding projects. All breeding
material generated is grown during the postrainy
season; and those nonsenescing genotypes