A Review of Blast Disease of Rice in Nepal

Blast disease is caused by Magnaporthe grisea (syn. Pyricularia oryzae) firstly reported in 1637 from China. In Nepal it was firstly reported from Thimi, Bhaktapur in 1964. Symptoms of this disease appear in all stages from seedling in nursery to heading in main field, however, the most devastating stages are seedling stage, tillering stage and panicle initiation stage. Typical symptoms of blast appear on leaves, node, neck, collar, panicles, rachis and even the glumes are also affected. Globally, blast of rice is responsible for 10-30% of yield losses every year. In susceptible varieties the disease causes 10-20% yield reduction but in severe condition it went upto 80% in Nepal. Cloudy weather, high relative humidity (93-99%), low night temperature between 15-20°C, longer duration of dew are the most favorable condition for the outbreak of blast fungus. The most usual approaches for the management of rice blast disease are management in fertilizers and irrigations, plantation of resistant varieties and application of fungicides. Higher dose of nitrogen increase susceptibility so, it should be applied in split doses. Use of resistant cultivars such as Khumal-1, Khumal-2, Khumal-3, Radha-12, Chandannath-1, Chandannath-3, Sabitri and Palung-2 for the management of rice blast is sustainable and ecofriendly approach. Seed treatment with Trichoderma viridae at  4 g/kg or Pseudomonas fluorescens at  10 g/kg help to inhibit growth of blast fungus. Use of chemical named Kasugamycin used to control blast fungus is most commonly used and popular among Nepalese farmers.