Sorghum Diseases in India

Breeding for Grain Mold Resistance
S.Z. Mukuru 1
Abstract
Colored-grained germplasm sorghum collection lines with high levels of mold resistance were used
for developing white-grained genotypes with good levels of resistance. Segregating progenies were
intensively screened for white-grained genotypes, and five white-grained advanced selections with
mold resistance similar to their colored-grain parental lines are now in the breeding program. Mold
resistance in the white-grained types was associated with grain hardness, while that of brawngrained
types was associated with either high-tannin or flavan-4-ol or grain hardness. Cultivars
with a combination of these factors were highly resistant. It appears that flavan-4-ol is not
produced in white-grained types, either mold-resistant or mold-susceptible. At present the only
factor known to be responsible for mold resistance in white-grained cultivars is grain hardness.
Intensification of efforts to breed mold resistance into high-yielding cultivars is in order so that
farmers can efficiently grow mold-free sorghums.
Introduction
Grain mold (GM), caused by several unspecified
fungi, is a major and widespread problem in the
semi-arid tropics (SAT) because of significant reductions
in yield and quality of the harvested
sorghum grain. The problem has become particularly
widespread where early-maturing improved
cultivars are cultivated and mature
under warm and wet conditions. Grain deteriorates
because of breakdown of grain structure
and eventual loss of viability from mold-induced
physical, physiological, and chemical
changes. Endosperm of molded grain appears
chalky because of partial hydrolysis of starch
and protein. Molded grains may be contaminated
with mycotoxins and present health hazards
to consumers (Castor and Frederiksen
1980).
The only practical and economical methods
for control of GM in sorghums are avoidance
and/or sowing GM-resistant cultivars. Chemical
control of GM in SAT nations is usually thought
to be impractical and too costly. Seed dressings
may be an exception, but many SAT farmers
who grow their own seed will be slow to adopt
this practice.
Most peasant farmers of limited means in Africa
and India have always used the avoidance
method of grain mold control—i.e., growing traditional
photoperiod-sensitive landraces. These
avoid, or escape, the mold problem because the
grains develop and ripen during dry weather—
after the rains. Pest and pathogen pressures are
much reduced at this time. These landraces,
however, are bulky plants with poor harvest indices,
and often are affected by terminal
drought-stress.
Another method of GM control used in some
areas is to grow high-tannin, colored-grain landraces;
these resist grain mold attack, and bird
damage as well.
Sources with low levels of mold resistance,
identified at ICRISAT Center in 1975, were used
to develop improved cultivars with mold resistance.
The high-yielding, white-grained cultivars
that were developed, however, do not have
sufficient levels of resistance to control grain
1. Principal Plant Breeder, Cereals Program, ICRISAT Center, Patancheru, Andhra Pradesh 502 324, India.
Mukuru, S.Z. 1992. Breeding lor Grain Mold Resistance- Pages 273-285 in Sorghum and millets diseases: a second world review,
(de Milliano, W.A.J., Frederiksen, R.A., and Bengston, G.D., eds). Patancheru, A.P. 502 324, India: International Crops Research
Institute for the Semi-Arid Tropics. (CP 739).
273