Morpho-pathological and Molecular Characterization of Bipolaris oryzae in Rice (Oryzae sativa)

Fifty isolates of Bipolaris oryzae from rice were characterized morpho-pathologically and molecularly. Based on colony morphology and growth pattern on PDA, these isolates were grouped into four categories: black with suppressed growth (21 isolates), black with cottony growth (16 isolates), black with fluffy growth (12 isolates) and white with cottony growth (1 isolate). The frequency of the black and suppressed type was the highest (42%) with maximum aggressiveness (mean spore count of 1854/cm2), whereas the white and cottony growth isolate had lowest frequency (2%) and aggressiveness (548/cm2). Thirteen B. oryzae isolates (four isolates from Groups I, II and III and one isolate from Group IV) were further tested for their variability with random amplified polymorphic DNA (RAPD) primers. Twenty RAPD primers were screened, of which 10 gave amplification; however, only six primers gave reproducible results. Based on the molecular similarity of the RAPD profiles, the isolates were grouped in to three major clusters and maximum linkage distance between them was determined as 0.29 units. This study establishes the variability among B. oryzae isolates.