| The damage characteristics of rice false smut, which is caused by [Villosiclavavirens (Nakata) E. Tanaka&C. Tanaka, Ustilaginoidea virens (Cooke) Takahashi]were observed. The results showed that the false smut balls were mainly distributed inthe middle and lower parts of the panicle, and the incidence rate was63.6%and24.9%, respectively. The decline of yield loss rate by rice false smut was10.8%to52.9%, and as the disease grade increasing, the yield loss rate was higher. The mainfactor of yield loss is the decline of seed setting percentage and then1000-grain.Besides, some black germ kernels caused by V. virens were found which did not showdisease symptom in the grain surface.In order to understand the biological characteristics of V. virens, the nutritionaland reproductive growth were tested in various culture conditions, including differentmedia, temperatures, pH values, carbon sources and nitrogen sources. The results ofnutritional growth tests showed that PSA was the optimal medium for pathogengrowth. The optimal temperature and pH value for mycelia were28℃and7.0,respectively. Sucrose was the best carbon source for pathogen growth. And the ofreproductive growth tests indicated that mannitol and KNO3could promote pathogento formulate chlamydospores and carbamide was suit for conidia sporulation. Therewas no spore formation in common artificial media after4isolated, except under themalnutritional condition or fungicide stress. The study found that V. virens couldextend the capability of sporulation by3-4generations in Dried Plum Potato SucroseAgar medium. The optimal temperature for conidium formation was28℃, and theconidia could not been found over35℃by shaking cultivation.Chlamydosporescould keep a germination rate of3.30%under the indoor dry storage condition after240days. The germination rate was higher in solid media than that in liquid media.Pure water was not good for germination. A low concentration of sucrose couldpromote germination. There was no sclerotium or ascospore in the overwintering ricefalse smut balls, and the ascospore could not be the primary infection source.The studies on the primary infection sources and the optimum phases of V. virensinoculated on potted planteds were done. Results showed that conidia which germinated by the overwintering chlamydospores may be the major primary infectionsource of rice false smut. The rice false smut was not systemic disease. The caseinoculated in the rice growth stages could not cause disease except in the bootingstage and the rupturing stage. Inoculated6-9days before the rupturing stage resultedin optimum diseased effect. According to the pathological and anatomical observationto the inoculated grains infected, we found that the floral organ was firstly infected,and the black germ kernels were found at the same time. The experimental ricevariteties performed different resistance or tolerance against rice false smut and somevarieties such as Lianyou3773and Jiafuzhan were resistant to rice false smut, whichhad the panicle incidence rate and the plant incidence rate with6.67%-5.82%and6.67%-4.80%, respectively.By the inhibitory tests in vitro and pot test, the Difenoconazole, Propiconazole30%EC was screened out. The results indicated that the inhibition rate of hyphaegrowth and Chlamydospores germination of V. virens were43.7%and99.4%. Thefield experiments showed that the control effect of Difenoconazole, Propiconazole30%EC on rice false smut was77.0-79.6%, and it was applicable to be taken intopractice. The optimum time for control was in the period of6-9days before therupturing stage, and spraying fungicide in the first-earing phase stage and the fullheeding stage for extra could decrease the control effect. |
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