Assessment of Rice Blast (Pyricularia Grisea) Disease Under Different Concentrations of Nitrogen on Different Rice Cultivars

Rice is a staple food contributing high calorie intake to humans. In Nepal, rice contributes 39% of GDP, among agricultural crops. Blast disease (Pyricularia grisea Sacc.) has been a continuous threat to rice production. This disease causes 10-20% yield reduction in susceptible varieties, whereas in severe case it causes upto 80%. Excessive nitrogen increases N-metabolism in plant, leading to enhanced tissue susceptibility to blast disease. Farmers’ household survey was carried out in Mangalpur V.D.C. ward no. 1, Chitwan during March, 2013, for determining the knowledge and perception of rice blast incidence and severity, their constraints in rice cultivation and their practices, knowledge on the disease management and amount of fertilization use. Similarly, a field experiment was carried out during June to September, 2013 to assess the impact of different concentrations of nitrogen on rice blast disease (caused by Pyricularia grisea Sacc.) incidence, severity and their effect on yield of Mansuli, Aekle and O.R. varieties of rice. Four treatments (0 kg/ha, 100 kg/ha, 200 kg/ha and 300 kg/ha) were used in RCBD with 3 replications in three different cultivars. In the field experiment, disease incidence and severity varied significantly (P≤0.05) among the treatments. The highest incidence was observed for higher concentration of nitrogen of Mansuli variety (42.22%) and lowest in no concentration of nitrogen of Aekle variety (25.56%) on 69 days after transplantation. Maximum disease severity was also recorded on Mansuli rice variety in highest concentration of nitrogen (53.43%) and minimum in Aekle variety in no concentration of nitrogen (24.32%) at September 9, 2013. Significantly highest yield (5.217 t/ha), number of grains per panicle (182.3) and 1000 grains weight (32.45 gm) were also obtained at no concentration of nitrogen. Among three varieties, Mansuli was the susceptible variety and Aekle was resistance variety.