Isolation And Identification Of Pathogenic Fungi Of Rice Brown Spot And The Study Of The Biological Characteirstics

Rice was an important food crop, and occured a variety of diseases from theseedling to the harvest stage, which caused significant loss of rice yield. Rice brownspot caused by Bipolaris oryzae was one disease of them. The history of the world,India, Bangladesh, rice brown spot was out breaking; in china, the disease occurred inthe northern and southern rice was widespread and serious. Separation, identificationby morphological and molecular of rice brown spot of rice were studied; the impact ofexternal conditions on the mycelia growth, colony morphology and spore germination.The specific findings were as follows:1. The way of conventional fungal separation was used, the contaminatedmycelium of the colony edge was repeatedly picked up and a pure strain was got andthe strain was proved by the Koch’s postulates.2. The morphological characteristics colony, conidiophores and conidial wereobserved in order to conduct the morphological identification. The pathogen ofseparation firstly was white and fluffy, gradually changed into the dark grey and thecolor of medium on the back changed light yellow into black. Colonies closed to themedium, crawled and growed up. When the mycelia growed on the7th day, thecolony was clearly concentric annulation, the surface had a large of scleroderma in thePDA medium. The conidiophores of the pathogenic fungi of rice brown spot isolatedwere single, brown, not branched and their tops are geniculation. Conidia waselongated oval, spindle, pour sticks shape, straight or bent to one side, brown, the bothends of the conidia gradually narrowed, obtuse, its hilum was relatively flat,5～10replums. The result of morphological identification was Bipolaris oryzae.3. The molecular identification was used by the method of18SrDNA and ITSnucleic acid sequence homology comparison, The sequences measured werecompared with the other sequences in the Blast of NCBI; The result showed thatbetween the18S rDNA of pathogen identified and one of Cochliobolus cynodontiswas the highest homology, and their similarity was99%; between the ITS of pathogenidentified and one of Bipolaris oryzae was the highest homology, and their similaritywas99%. The result of molecular identification was Bipolaris oryzae.4. The effects of the medium, light, temperature, pH, carbon source, nitrogensource on the mycelia growth and colony morphology were studied. The resultsshowed that the optimal medium of mycelia growth was corn meal agar medium, the optimal light was light dark alternate, the optimal pH was9, the optimum temperaturewas25℃and the temperature of death was55℃for10minutes. The optimal carbonsource was the sucrose; the optimum nitrogen source was glycine. The colonymorphology in a variety of medium, light, carbon and nitrogen sources were different.5. The effects of the light, temperature, pH, carbon source, nitrogen source on thespore germination were studied. The results showed that the optimal light of sporegermination was24h full light, the optimum temperature was25℃, and the optimalpH was also9. The optimal carbon source was soluble starch; the optimum nitrogensource was potassium nitrate.These laid the foundation for further studying the pathogenesis of the disease andthe measures of prevention and control.