MORPHOLOGICAL CHARACTERIZATION OF BIPOLARIS ORYZAE CAUSING BROWN SPOT OF PADDY IN BIHAR

An extensive survey was conducted during kharif season of 2012 and 2013 in major rice growing areas of Bihar for observing disease incidence of brown spot of paddy and for collection of diseased samples of paddy ( leaf as well as seed) to study morphological variability amongst the isolates of Brown spot fungus, Bipolaris oryzae. These samples from 25 districts were used for isolation of desired pathogen from spotted leaf and seeds with infection of brown spot disease. The disease was prevalent at all the locations surveyed. 52 isolates of Bipolaris oryze from rice were characterized morphologically. On the basis of colony morphology and growth pattern on PDA, these all isolates can be grouped into 5 categories: Black with fluffy growth (16 isolates), Black with suppressed growth (10 isolates), Grey with cottony growth (9 isolates), Grey and white mix with cottony growth (12 isolates) and white with cottony growth (5 isolates). Based on colony diameter all these isolates can be grouped into 3 different categories: Slow growing 9 isolates), Moderate growing (15 isolates) and Fast growing (28 isolates). Maximum sporulation was observed in Samastipur (Pusa), Vaishali, Patna and Supaul isolates while minimum was observed in Rohtas, Bhojpur and Aurangabad isolates. Virulence of these isolates were also tested and those isolates which were highly sporulating were found most virulent but this was not true for all isolates. The virulent isolates established from this study can be used by plant breeders for screening varieties in pipeline against Brown spot disease which is the most threatening disease of Paddy in Bihar.