Effect of Different Media, Temperature, pH and Nitrogen Sources on Growth and Development of Helminthosporium oryzae Causing Brown Leaf Spot of Rice

The pathogen Helminthosporium oryzae was subjected to different cultural conditions viz., media, temperature, pH and nitrogen sources under in vitro conditions. The supreme radial progress of Czapeck Agar, OMA & PDA was recorded highest with mean radial growth followed by Richard’s agar (88 mm), Water agar. The colony showed up as thick, leathery, slightly elevated, and abundant mycelia with brown-coloured conidia on this medium. Its colour ranged from greyish-white to dark brown. When exposed to constant light, the average mycelial growth of the fungus was measured at 58.60 mm, 51.41 mm at alternating light cycles, and 72.80 mm at total darkness. When the pathogen was assessed at various pH levels, the fungus's maximum radial growth was observed at pH 7.0 (90.00), and its least radial growth was observed at pH 4.5 (44.89 mm) and pH 5.0 (60.33 mm). Ammonium chloride showed the least growth among the various nitrogen sources, while potassium nitrate showed the greatest development.