Identification Of Gibellulopsis Nigrescen From Sunflower And Study On Its Biological Characteristics

Sunflower verticillium wilt is one of the three serious diseases on sunflower. It usually occurs in the main producing areas of sunflower, resulting in huge losses. Verticillium dahliae is the main pathogen of the sunflower verticillium wilt. It is reported that the other three pathogens Gibellulopsis nigrescen, Verticillium nubilum and Verticillium tricorpus can cause the verticillium wilt as well. However, in Sunflower it is rarely reported that Gibellulopsis nigrescen causes the verticillium wilt of sunflower.We choosed the plants with typical symptoms of verticillium wilt of sunflower. Pathogen was separated from basal stem and purified. We used the microscope to observe the morphology and identified the pathogen with molecular biology techneque. Accord to Koch’s postulation, we reinoculated sunflower plants. In addition to further understanding the pathogenesis law of verticillium wilt of sunflower, we made a preliminary study on morphological and biological characteristics of Gibellulopsis nigrescen that we obtained.1. Colony morphology on PDA:the colony was white in the early, underdeveloped aerial hyphae, conidium was oval or cylindrical, transparent and single spore. Conidiophore mostly produced secondary branches.The mycelium that was white. At last it produces black chlamydospores. ITS sequence analysis showed the isolate is the Gibellulopsis nigrescen, it could induce sunflower verticillium wilt.2. Gibellulopsis nigrescen growed vigorous at the temperature24～26℃. When the temperature exceeded30℃, colony growth declined. Sporulation peaked at30℃. We put the isolate in water at50℃for10min, there were still some mycelia growing, but at55℃for10min, no mycelia growed, so we determined the isolate lethal temperature was55℃for10min.3. Gibellulopsis nigrescen could grow at pH from4to13, especially when the pH was6, it growed well. When pH was4,12,13, it could still grow. It indicated the isolate had strong acid resistance and alkali resistance. In sporulation experiments, pH was7, sporulation was the maximum.4. We used PDA medium to cultivate Gibellulopsis nigrescen, when the starch as carbon source and sodium nitrate as nitrogen source, it grows the best. When the starch and the urea were chosen as carbon source and nitrogen source, sporulation was the maximum.5. When we used the inoculation methods of injection, root dipping, pouring the wound root and soil mixed with inoculum, the leaves showed verticillium wilt treated with the method injection and soil mixed with inoculum. And the basal stem becomes black90days after we used injection inoculation method. But no this sign appeared with the inoculation methods root dipping and pouring the wound root. We reisolated pathogen from the basal stem.6. We tested the resistance of54different varieties of sunflower which were planted in the soil mixed with the inoculum. Only injection and soil mixed with inoculum showed symptoms. According to the grading standard of Verticillium wilt,21varieties showed immune (I),25highly resistant (HR),8resistant (R). Different varieties had different disease resistance level. Due to the disease index was below30, Gibellulopsis nigrescen was weakly pathogenic to the sunflower varieties.