Study on Differential Response of Pyricularia grisea Isolates from Rice, Finger Millet and Panicum sp. with Local and Alien Media, and Their Host Range

Blast (Pyricularia grisea) is an economically important disease of rice and finger millet in Nepal. Isolates of the fungus from different hosts differed in their response in media for mycelial growth and sporulation. Radial mycelial growth (RMG) and days of sporulation (DOS) of P. grisea were studied by culturing three fungal isolates from rice, finger millet and Panicum sp. on six different media: prune agar (PA), oat meal agar (OMA), potato dextrose agar (PDA), finger millet leaf decoction agar (FLDA), finger millet polish agar (FPA) and finger millet meal agar (FMA). The highest RMG was found in the isolates from finger millet and the lowest in the isolates from rice. The shortest DOS (1 week) was found in the isolate from rice and the longest (>2 weeks) in the isolate from finger millet. Among the different media used, PA and OMA were found to be the best for mycelial growth and sporulation of the isolates both from rice and finger millet. The shape, color and compactness of the fungal colonies varied with the media and isolates used. Cross inoculation studies showed that the fungus isolates from rice were able to infect all the plant species (rice, finger millet, Panicum sp., Eleusine indica and Setaria sp.) while isolates from finger millet were only able to infect three plant species (E. coracana, Setaria sp. and E. indica). This shows that the weed management is more important in finger millet fields than in rice field to manage the blast disease; and growing of rice adjacent to finger millet field is dangerous for blast epidemics in finger millet since rice serves as the source of inoculums.