Use of plant extracts and biocontrol agents for the management of brown spot disease in rice

Fifty plant extracts, four oil cakes and eight antagonistic organisms were tested against Bipolaris oryzae (Cochliobolus miyabeanus), the causal agent of brown spot disease of rice. In vitro studies indicated that two leaf extracts, Nerium oleander and Pithecolobium dulce exerted the higher percent inhibition to mycelial growth (77.4, 75.1%) and spore germination (80.3, 80.0%) of B. oryzae. Among the four oil cake extracts tested in vitro against B. oryzae, neem cake extract showed the maximum inhibition percent to mycelial growth (80.18%) and spore germination (81.13%) of the pathogen followed by mahua cake extract, castor and gingelly cake extract. Trichoderma viride (Tv2) was significantly effective in inhibiting the mycelial growth (62.92%) and spore germination (77.03%) of the pathogen followed by Trichoderma harzianum (Th5) and Trichoderma reesei (Tr3). The promising leaf extracts, oil cake extracts and antagonistic microorganisms were further evaluated for their efficacies in disease management under glasshouse and field conditions. In glasshouse studies, post-infectional spraying of rice plants with neem cake extract, N. oleander leaf extract and T. viride (Tv2) was significantly effective in reducing the incidence of brown spot of rice by 66, 52 and 45 percent respectively. Two rounds of spraying of rice plants with neem cake extract, N. oleander leaf extract and T. viride (Tv2) in the field at initial appearance of disease and 15 days later reduced the incidence of brown spot (70, 53 and 48% disease reduction respectively) and increased the yield by 23, 18 and 15 percent respectively.