Sorghum Diseases in India

Current Status of Sorghum Downy Mildew Control
J. Craig 1 and G.N. Odvody 2
Abstract
Resistance to sorghum downy mildew (Peronosclerospora sorghi) is vulnerable to the variability
for virulence found in P. sorghi. Several pathotypes (races) of P. sorghi have been identified.
Successive sorghum genotypes possessing monogenic, physiological resistance have become susceptible
to new virulent pathotypes of P. sorghi. The sorghum cultivar QL 3 with oligogenic
factors for resistance to downy mildew may provide a source of durable resistance to the pathogen.
The fungicide metalaxyl provides excellent chemical control of sorghum downy mildew. However,
the ability of fungi related to P. sorghi to produce metalaxyl-resistant strains raises the possibility
that a metalaxyl-resistant strain of P. sorghi will occur. The practice most likely to provide durable
control of downy mildew is use of metalaxyl only on DM-resistant sorghum genotypes.
Introduction
Research on sorghum downy mildew (SDM)
(Peronosclerospora sorghi) has successfully determined
most of the etiological aspects of this disease.
The pathogen's host range, environmental
requirements, modes of infection, and other
characteristics have been established (Frederiksen
1980; Safeeulla 1976; Williams 1984).
Disease-control procedures involving hostplant
resistance or fungicides have been developed
to reduce crop damage by SDM. These
procedures have been used successfully, but our
observations suggest that their continued effectiveness
is in question. The current status and
future possibilities of host-plant resistance and
fungicides in the control of SDM are discussed.
Host-plant Resistance
Host-plant resistance is the most widely used
method of reducing SDM losses. Downy mildew
resistance as presently utilized in sorghum-improvement
programs is expressed as a physi­
ological incompatibility between host and
pathogen that prevents infection. In most genotypes,
this type of resistance is probably monogenic
or infrequently oligogenic. Sorghum
improvement programs in Texas have made extensive
use of physiological resistance to SDM.
Sorghum downy mildew first appeared in
Texas in 1961. Within 6 years it became economically
important. Resistant sorghum hybrids
were developed and widely grown. Six years
after popular acceptance of those first resistant
hybrids, a new SDM pathotype (physiological
race), capable of attacking some of these hybrids,
appeared (Craig and Frederiksen 1980).
However, hybrids with the resistant sorghum inbred
Tx 430 as a parental line were resistant to
this new pathotype. Again, 2 years later, a third
pathotype of P. sorghi appeared, and was capable
of overcoming the resistance of Tx 430 (Craig
and Frederiksen 1983).
Again, sources of resistance effective against
the new race of P. sorghi were identified and utilized
in breeding programs. These new hybrids
are resistant to all the known Texas pathotypes
of SDM, but it is probable that a new race of the
1. Agricultural Research Service, United States Department of Agriculture, PO Drawer DN, College Station, TX 77841, USA.
2. Texas Agricultural Experiment Station, Route 2, PO Box 589, Corpus Christi, TX 78410, USA.
Craig, J., and Odvody, G.N. 1992. Current status of sorghum downy mildew control. Pages 213-217 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.
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