Rice brown spot disease and indentification of the causal agent fungi in golestan province

The brown spot disease is one of the seed-borne diseases of rice, which is found in all stages of its growth from nursery to farm. It causes qualitative and quantitative damage on rice. Although the disease can be found in all parts of the country where rice is cultivated, there is no precise information about its dispersal and causal agents, the varieties of its species, and the amount of its damage in Golestan Province. Therefore, this study was carried out to identify the genus and species of the rice brown spot agent in the province. At first, samples were collected from 83 paddy fields in Golestan Province. To isolate the fungus from disease tissues, the collected samples were cultured on PDA, so 101 isolates were isolated and cultured for sporulation on PDA medium. Surveying of conidium and conidiophore morphology, the process of conidium formation and the pattern of its germination indicated that the present isolates belonged to Bipolaris which two species of it were identified, Bipolaris oryzae and Bipolaris spicifera. The total isolates contained 25% of B. oryzae and 75% of B. spicifera. Pathogenicity test of isolates in these two species was applied on seedling of Domsiah, Amol, Tarom Neda, Tarom Asgari and Sang Tarom in greenhouse, which revealed the pathogenicity of the species and their ability to cause brown spot on rice. Isolates were able to infect wheat, barley and weeds of Echinochloa crus-gali and Phalaris minor L.