Prevalence of Pearlmillet Downy Mildew, Sclerospora graminicola in Gujarat and Pathogenic Characterization of its Isolates

Surveys were conducted in Gujarat state of India to assess the incidence of downy mildew (DM) caused by Sclerospora graminicola in pearlmillet hybrids during the seasons of 2005 rainy and 2006 summer. Of the 23 private sector hybrids, three (Pioneer 7688, Proagro 9330 and -9440) were free from DM during the rainy season, 2005 and 11 (Bioseed 8510, HY 555, M-50, Nandi 5, Nandi 52, PAC 982, Pioneer 85M34, Pioneer 86M52, Proagro 9444, Raasi 2246 and Ritu) during the summer 2006. A public sector hybrid GHB 558 and a private sector hybrid Proagro 9444 were found resistant (<10% incidence) during both cropping seasons. Pathogenic diversity studied in a greenhouse experiment using nine isolates of S. graminicola collected from different locations and hybrids revealed that isolate Sg 441 from Brahmanwada in Mehasana district was the most virulent (mean incidence of 84% across 9 differentials) followed by Sg 445 and Sg 439 from Banaskantha district. However, based on virulence index (percent disease incidence × latent period^-1), Sg 445 was identified as a highly virulent isolate (virulence index of 16.5). This study provided two highly virulent isolates Sg 445 (Banaskantha) and Sg 437 (Jamnagar) to replace less virulent isolates Sg 348 (Anand) and Sg 200 (Jamnagar) that are being used for greenhouse screening of breeding lines targeted for Gujarat.