شناسايي قارچ هاي ايجادكننده بيماري لكه قهوه اي برنج دراستان گيلان

Indentification of the causal agent fungi of rice Brown Spot disease in Guilan 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, species and the rate of damage. Therefore, this study carried out in order to identify the genus and species of the rice brown spot agent in Guilan.To do so, at first some samples were collected from 91 paddy fields in Guilan. In order to isolate the fungus from disease tissues the gathered samples were cultured on PDA and filter paper, and by this, 120 isolates were isolated. Isolates were cultured for sporulation on culture medium of TWA+wheat straw. In order to identify the taxonomy, conidium and conidiophore morphology and the process of conidium formation and pattern of its germination were studied. According to the results, the present isolates were belonged Bipolaris, which was divided into 3 species: Bipolaris oryzae, Bipolaris victoriae Nelson and Bipolaris sp. The total isolates were consisted of 15% Bipolaris oryzae, 75% Bipolaris victoriae and 10% Bipolaris sp. Pathogenicity test of isolates in these three species was applied on cultivar Khazar seedlings in desicator, which revealed the pathogenicity of the species and their ability to cause brown spot on rice.