The Cultural Characteristics And Pathogenic Differentiation Of Verticillium Dahliae From Cotton In Shandong Province

Shandong is the most important cotton production area in China. Cotton verticillium wilt (VW) that caused by Verticillium dahliae Kleb is one of the most improtant disease of cotton in Shandong, also in China. The pathogenicity of V. dahliae had been differentiated in China for many years, but at present which still was not clear in Shandong province. In order to identify the pathogenicity of V. dahliae in Shandong province, the occurrence of VW was carried out in 2007, 2008 respectively, and 30 strains of V. dahliae were isolated, purification and identification from diseased cottons collected from main cotton production areas in Shandong province. The culture characters pathogenicity of 30 strains and their crude toxin were also studied.The result of investigation of two years showed that the cotton verticillium wilt occured widely in cotton-growing regions of Shandong and harm heavily, with 4.26-96.7% disease plant rate and 2.66-76.7% disease index, which had distinct difference in different production area.According to the study of culture characteristics, 30 strains of V. dahliae in Shandong province has some difference in colony colour, and it could be divided into two types: sclerotium type and filamentous type. The most strains belonging to the filamentous type, accounting for 71.9%。The production of micro-sclerotium also have some difference in 30 strains, about more than 50% strains could produce many micro-sclerotium afrer culturing 2 weeks. There are only about 32% of strains looks have radialization pleat in colony bottom.The result of temperature and pH indicat that, there are no diffience in the colony diameter of 30 strains in the same temperature and pH, but colony diameter of the same strain has big difference in the different temperature and pH (p<0.05). The optimum temperature is between 20℃and 25℃and pH is ranged from 5 to 8.The virulence of 30 strains of V. dahliae and 2 standard strains (T9 and VD18) on four cotton varieties were determined respectively by root inoculation injury in greenhouse. The results showed that the virulence variation of strains from different regions was significant. According to the results of pathogenicity, 30 strains of V. dahliae in Shandong province could be divided into three pathogenic tyes: severe virulent type, intermediate virulent type and mild virulent type, and accounting for 21.9%, 16.8% and 59.4 respectively.The further research of virulence found that, there are significant difference in the height and fresh weight of cotton after inoculated by three pathogenic tyes strains. The infection from high to low is intermediate virulent type, mild virulent type, and severe virulent type, respectively. There are also some different infection on the height and fresh weight of different cotton varieties after inoculated by the same pathogenic tyes strains.The virulence of crude toxin from different strains on Lumianyan-27 was tested. The results showed that the crude toxin of 30 strains of V. dahliae had strong pathogenic ability. The pathogenic ability increased with the time and reached a stable value after 96 hours. The pathogenicity of V. dahliae had significant correlation with the capacity of wilting of crude toxin. The higher of the wiltiing index, the stronger of the virulence.But the result of protein cotent of crude toxin indicated that, there no cottelation between the wilting index and protein cotent of crude toxin. Therefore, the protein content of crude toxin has no impact on the pathogenicity of V. dahliae.