GENETIC AND PATHOGENIC VARIABILITY AMONG ISOLATES OF SCLEROSPORA GRAMINICOLA, THE DOWNY MILDEW PATHOGEN OF PEARL MILLET

Downy mildew, caused by the oomycete pathogen Sclerospora graminicola (Sacc.) Schroet, is economically the most important disease of pearl millet (Pennisetum glaucum (L.) R. Br.) in Asia and Africa. The pathogen induces systemic infection in pearl millet plants that manifests itself through foliar chlorosis and panicle malformation (also called “green-ear” or “crazy top”). The fungus is heterothallic (Michelmore et al., 1982) and reproduces both by sexual and asexual means, and is therefore highly variable (Ball and Pike, 1984; Thakur et al., 1999). The commercial cultivation of a number of genetically homogeneous single-cross F1 hybrids of pearl millet in India has led to increased virulence in S. graminicola populations, thus shortening the useful life of the hybrid cultivars (Thakur et al., 1999). Monitoring virulence changes in the pathogen population, identifying resistance to specific and multiple pathotypes, and directing pearl millet breeding programmes towards strategic utilization and deployment of resistance genes form the basis of a long-term downy mildew management research at ICRISAT (Thakur, 1999).