Characterization of Sclerospora graminicola Isolates from Pearl Millet for Virulence and Genetic Diversity

Abstract

Virulence and genetic diversity were studied using 21 isolates of Sclerospora graminicola, the pearl millet downy mildew pathogen collected from major pearl millet growing areas of India. Variability for virulence was determined by inoculating a set of 10 differential hosts with the S. graminicola isolates in a greenhouse. The isolates varied for latent period (6.4 to 11 days), disease incidence (0 to <TEX>$98\%$</TEX>), virulence index (0 to 18.7) and oospore-production potential (1 to 4). Among the 21 isolates, Sg 139 (Rajasthan) was the most virulent and Sg 110 (Tamil Nadu) the least virulent. Based on virulence index (disease incidence<TEX>$\time$</TEX>slatent <TEX>$period^{-1}$</TEX>), the 21 isolates were classified into eight virulence groups. Genetic diversity among isolates was studied using AFLP markers. Based on similarity index of banding pattern, the 21 isolates were clustered into eight genotypic groups. The AFLP groupings, however, did not match with that of the virulence groupings, and these two were found independent. The isolate Sg 139 that remained distinct in both pathogenic and genetic groupings indicated its highly virulent nature. Implications of these results in downy mildew resistance breeding are discussed.