Sorghum Diseases in India

acylalanine fungicides (Odvody, unpublished).
However, the metalaxyl-resistant strains that
have occurred in other Peronosporales were also
resistant to other acylalanines (Cohen and
Samouche 1984). The same cross protection
would be probable in metalaxyl-resistant biotypes
of P. sorghi
The use of fungicide mixtures in some disease
systems effectively prevents or slows the
selection and increase of pathogen strains tolerant
to specific fungicides in the mixture (Cohen
and Coffey 1986). This is currently impractical
for graminaceous mildews, because all effective
fungicides are in the acylanilide group. An exception
is the phosphonate fosetyl-Al, but even
at high rates fosetyl-Al is sometimes inconsistent
in control (Odvody, unpublished). In addition,
recent research demonstrated that metalaxyl-resistant
strains of Phytophthora infestans
and Pseudoperonospora cubensis were also resistant
to fosetyl-Al (Cohen and Samouche 1984).
Conclusion
The combined use of the best available hostplant
resistance with metalaxyl should simultaneously
provide the best protection against
fungicide-tolerant strains and conserve resistant
germplasm. Virulent, metalaxyl-sensitive pathotypes,
and avirulent metalaxyl-resistant pathotypes
would not survive. The probability of a
pathotype occurring which combines virulence
to the resistant host and resistance to metalaxyl
is comparatively small. However, this option
may soon be lost in regions where protection of
susceptible sorghum genotypes with metalaxyl
has become routine.
References
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Use of systemic fungicides metalaxyl and fosetyl-Al
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