Studies on Epidemiology and Management of Brown Spot Disease Caused by Bipolaris Oryzae (Breda De Haan) Shoemaker in Basmati Rice

Abstract

Rice (Oryza sativa L.) which belongs to family Poaceae (Gramineae) is one of the ‘big three’ cereals and principal food for 60 per cent of the world’s population.Brown spot disease of rice (Bipolari soryzae )is responsible for heavy infection which significantly reduces the number of tillers & grains and lowers the quality and weight of individual grains resulting in a yield loss of 30-43 per cent. The present study was undertaken to study the influence of weather factors on progress of disease, screening of basmati rice varieties for resistance against brown spot and evaluation of different management practices against brown spot disease. Physiological and biochemical characterization of seventeen basmati varieties and also those plants provided with different treatments for disease management were also performed and correlated with resistance to brown spot. In addition, evaluation of different chemical and bio-fungicides were also performed in vitro against the mycelial growth of causal pathogen. It was found that increase in the age of the crop, decrease in maximum and minimum temperatures, increase in morning and afternoon relative humidities at the end of crop seasons followed by intermittent drizzles had great impact on the progression of brown leaf spot disease in rice. It was found that none of the varieties screened were found resistant against brown spot disease. However, varieties viz.Improved Pusa basmati-1, Type-3, Pusa basmati-1612, Pusa basmati-1718, Pusa basmati-1637, Pusa basmati-1509, Basmati-370 and CSR-30 were found to be moderately resistant. Varieties Vallabh basmati-21, Taroari basmati, Pant basmati-2, Pusa basmati 1609 and Basmati 386 were found to be moderately susceptible and varieties viz. Punjab basmati-5, Pant basmati-1, Basmati -564 and Pusa Basmati 1121 were found to be susceptible against brown spot disease. Application of certain chemicals viz. foliar application of fungicides viz. NATIVO (Trifloxystrobin + Tebuconazole), SAAF (Mancozeb+ Carbendazim), Mancozeb and silicon-based fertilizer i.e., Orthosilicic acid either as foliar spray or through irrigation or in combination can be highly effective in reducing the disease under field conditions. Seedling root dip with efficient bio-agents and foliar application of neem oil were also found effective in reducing the percent disease index, grain discoloration and chaffiness besides increase in grain yield and harvest index. Integration of all the above practices as a holistic approach can help in achieving sustainable disease management. The high amounts of total chlorophyll, soluble protein, phenol, non-reducing sugars, mineral nutrients like potassium, iron and calcium present in the leaves were found to be responsible for resistance against brown spot disease. In-vitro evaluation of chemical and bio-fungicides against radial mycelia growth of the pathogen showed that highest inhibitionof radial mycelial growth was exhibited by TILT (Propiconazole) followed by NATIVO (Trifloxystrobin + Tebuconazole) which were found highly effective even at low concentrations after 6 days of inoculation in vitro. Plant based natural product i.e., Neem oil at 3 percent concentration was found highly effective in inhibiting the growth of the pathogen in-vitro.