Resistance to powdery mildew (Erysiphe cruciferarum) in mustard in relation to rate reducing factors

Progression of powdery mildew (Erysiphe cruciferarum Opiz. ex. Junnell) was studied in nine cultivars RH-30, RH-8812, RH-9801, RH-9304, RH-9901, RC-781, Purple mutant (Brassica juncea), HC-9603 (B. carinata) and GSL-1 (B. napus) of mustard for components of slow mildewing viz., number of specks/leaf, size of speck, number of conidia per speck, incubation period, latent period, disease progression and disease intensity. The disease appeared late in all the varieties and cultivar HC-9603 was free from the disease. The variety GSL-1 showed least number of specks per leaf (5.52) and minimum sporulation. All the cultivars showed incubation period and latent period of 3–4 and 1–2 days, respectively except GSL-1 where latent period was more (3 days). The progression of disease and mean speck size was lower in variety GSL-1. Stepwise multiple regression analysis revealed that the environmental factors played more than 80 per cent role in progression of disease in all cases whereas it was 47 per cent in variety GSL-1. Moreover, variety GSL-1 (Brassica napus) showed components for higher degree of partial resistance or slow mildewing and variety HC-9603 was resistant.