การศึกษาปัจจัยที่ทำให้เกิดโรคใบจุดสีน้ำตาลและการป้องกันกำจัด

Abstract

Brown spot of rice is caused by a fungus, Bipolaris oryzae (Breda de Haan) Shoemaker. In the past few years, it has been found widespread more frequently in the areas where continuous cultivation together with a high rate of chemical fertilizer, nitrogen in particular, are practiced. In addition, the disease symptom is more diverse than it used to be. Since the research and information on disease control of Brown spot in Thailand is limited, this work was carried out aiming to identified the causal agent of various symptoms of Brown spot, to study the correlation between disease severity and nutrients both in the soil and plant and to find out the best chemical for controlling Brown spot of various symptoms. Results revealed that the causal agents of all 5 symptoms of Brown spot have been primarily identified as fungi having conidia similar to those of Bipolaris oryzae despite a small difference in the shape, size, thickness and number of cells. In general, the 2 most effective chemicals for all 5 pathogenic fungi from the culture test in the laboratory were mancozeb and propiconazole. Disease and soil samplings showed that Brown spot was found in sandy, sandy-loam and clay-loam soil. Despite the availability of N, P and K in the soil. The amount of N and P in the root of diseased plants were lower than those of normal plants while the amount of K in both plant and root were similar. The information obtained would be of beneficial for further study on effective integrated disease management.