Sorghum Diseases in India

eases, their pathogens and host pathogen relationships,
is needed and will be researched.
The existence of races of Colletotrichum graminicola
clearly shows the importance of continuous
monitoring of that pathogen population in
the principal production areas of Brazil, especially
in view of the highly virulent race 31H
detected in Jatai, Goias. A better understanding
of the Sorghum bicolor-Colletotrichum graminicola
relationship is essential, considering that it fits in
a "gene-for-gene" disease category.
Studies of the inheritance of vertical resistance
to Colletotrichum graminicola have been initiated at
the NMSRC to evaluate segregating generations
of crosses made between the differential cultivars
and inoculations with appropriate races. This information,
associated with continuing race surveys
of Colletotrichum graminicola, will permit
more accurate determination of genetic associations
in the host. This should be of value in developing
a more stable vertical resistance or, in
other words, the major virulence dissociation in
the pathogen (Vanderplank 1982).
Stable resistance to Colletotrichum graminicola
also implies the identification of dilatory resistance,
characterized by a reduced rate of epidemic
development, in spite of a susceptible
reaction class. Field evaluations conducted at
the NMSRC have indicated the existence of variability
for this form of resistance to Colletotrichum
graminicola in sorghum genotypes.
Some observations have shown small, but significant,
interactions between races of the pathogen
and sorghum cultivars, but not to the extent
that extreme changes in the ranking of cultivars
are suggested.
The increasing incidence of rust in Brazil indicates
that it will become a serious disease. The
appearance of Puccinia purpurea on some previously
resistant cultivars, such as Brandes, indicates
that detailed study of the physiological
specialization of the pathogen is necessary. The
"slow rusting" phenomenon in many sorghum
hybrids indicates that success in developing stable
resistance to rust is likely.
A continuous screening for resistance to sorghum
downy mildew in southern regions of
Brazil is necessary, due to the area's importance
as a grain producer.
The increasing importance of sorghum in
double-cropping systems, mostly following soybeans,
demonstrates the importance of charcoal
rot (Macrophomina phaseolina). This pathogen can
62
attack soybeans as well as sorghum and many of
the other crop species that may be included in
this system. Development of sorghum cultivars
specifically adapted to double-cropping will be
necessary, and charcoal-rot resistance is an
essential quality in these genotypes. Cultural
measures—such as irrigation during the postflowering
period, balanced fertilization, and the
appropriate plant populations—are also important
factors in reducing the incidence of charcoal
rot in these areas.
Finally it is obvious that continuous and integrated
efforts by pathologists and sorghum
breeders working together are essential for solving
sorghum disease problems.
References
Nakamura, K., and Fernandes, N.G. 1984. Resultados
dos ensaios de mildio do sorgo realizados
no ano agricola 1983/84 em colaboracao
com o CNPMS-EMBRAPA-Universidade Estadual
Paulista, Jaboticabal, Brazil: Universidade
Estadual Paulista, Jaboticabal. 5 pp.
Pinto, N.F.J.A. 1984. Virus do mosaico da canade-afucar
em sorgo [Sorghum bicolor (L.) Moench.]:
Caracterizacao de isolados, reacao de cultivares
e heranca da resistenca. Ph.D. Thesis
University of Sao Paulo. Piracicaba, Brazil. 136 pp.
Schaffert, R.E. 1986. Desenvolvimento de cultivares
de sorgo para uso na alimentacao humana.
Informe Agropecuario 12(144): 13-14.
Sharma, H.C 1983. A technique for identifying
and rating resistance to foliar diseases of sorghum
under field conditions. Proceedings, Indian
Academy of Sciences 42(3):278-378.
Vanderplank, J.E. 1963. Plant diseases: epidemics
and control. New York, NY, USA: Academic
Press. 349 pp.
Vanderplank, J.E. 1982. Host-pathogen interactions
in plant diseases. New York, NY, USA: Academic
Press. 207 pp.
Veiga, A.C. 1986. Aspectos economicos da cultura
do sorgo. Informe Agropecuario 12(144):3-5.
Vianna, A.C., Borgonovi, R.A., and Freire, F.M.
1986. Alternativas de cultivo para exploracao do
sorgo granifero. Informe Agropecuario
12(144):28-32.