Rajasthan downy mildew of maize incited by Peronosclerospora heteropogoni is a unique example of ontogenic predisposition of a crop to a pathogen from wild grass host. Since its first record on maize in 1968, several outbreaks have been reported during 1973-80 and losses of up to 60 per cent have been recorded. The pathogen can infect maize, teosinte, Heteropogon melanocarpus, and H. contortus. The latter seems to be the natural reservoir of the pathogen. Some extent of variability has been observed among populations of P. heteropogoni. Young maize seedlings, 3-4 days after germination, are most susceptible to RDM. The mycelium has been observed in seeds collected from systemically infected plants, but the studies on seed transmission suggest that seed transmission may not be of much significance. The most conducive condition for disease development are temperatures 22.9 to 28.6° C and RH > 85.0 per cent. Management strategies for RDM include early sowing with onset of monsoon to avoid inoculum from P. heteropogoni, use of systemic fungicide metalaxyl as seed treatment @ 4 g/kg or spray 0.1 per cent, and use of host plant resistance. Future research thrusts on pathogenic variability, search for other collateral hosts, inheritance of resistance, use of genotype mixture in hot spot areas, and evaluation of botanicals for eco-friendly management of RDM are suggested.

English

0502|AGRIS 0501|AL-Maize Program

Juan Carlos Mendieta

CIMMYT Publications Collection