Enhanced sporulation by different light and nutritional sources in Bipolaris oryzae causing brown spot disease of rice

Aim: The present study aimed to investigate the inter-relation of different light and nutritional sources on the sporulation of fungus. Methodology: Two isolates of Bipolaris oryzae collected from IIRR, Hyderabad and Lonavala were used in the present study. These isolates were cultured on routine culture media-potato dextrose agar for five days and irradiated with different regimes of near ultraviolet (NUV), ultraviolet and visible light to assess their ability to induce sporulation in fungus. With standardized light source (exposure of fungus to NUV 12hr and 12 hr of darkness), different stresses such as nutrient stress, cold and heat stresses were assessed for its ability to support the abundant sporulation. Results: The enhanced sporulation in B. oryzae (55.9x104 and 36.2x104 spores ml-1, respectively, in IIRR and Lonavala isolates) was obtained by culturing fungus on rabbit food agar media for five days under darkness and later 12 hr alternate exposure of near ultraviolet light and darkness. Interpretation: The maximum sporulation obtained in the present study used in pathogenesis test can be employed in screening programme for identification of resistant genotype for brown spot disease. Key words: Brown spot, Bipolaris oryzae, Nutrition, Rice, Sporulation