Collection and characterization of grey mildew ( Ramularia areola Atk.) pathogen of cotton

摘要

Grey mildew/false mildew of cotton caused by R. areola regarded as destructive on desi-cotton genotypes. Generally, causes premature defoliation of leaves and immature bolls in many susceptible cultivars/genotypes. The prolonged low temperature coupled with high humidity micro-climate conditions were predisposing factors for disease spread in resistance genotypes. Highest diseases incidence of grey mildew was observed in the transitional zone of Karnataka (Dharwad, Gadag, Haveri and Belgaum districts) and zero disease incidence was recorded in northern dry-zones of Karnataka. Direct transfer of conidia or transfer of germinated conidia on modified Kirchoffs?+?cotton leaves decoction medium was best for the sporulation and isolation of fungus. The molecular variability of isolates was confirmed through RAPD primers, 18–67% coefficient variation was observed in the isolates. Conidia of the fungus were short-lived in a natural condition, perpetuate for long times in leaf debris by producing dormant ascospores. However, low temperature and high soil moisture increase the viability of conidia under field condition. Out of 25 G. arboreum lines, EIPSD-4 entry showed resistant reaction followed by moderately resistant in A-1 and A-4 entries and none of the entries were immune to grey mildew.