Studies On Populational Structrures Of Sclerotinia Sclerotiorum On Rape In The Western Sichuan Province

373 isolates of S. sclerotiorum were obtained from sclerotia that were collected from infected rape stems in four areas of the Western Sichuan Province in May, 2002. The four areas are Daxing County of Pujiang City, Wolong County of Qionglai City, Huangshui County of Shuangliu City and Guyi County of Qionglai City. The main results of studies on populational Structrures of S. sclerotiorum were reported at the present paper.1. The test of resistance to carbendazim (MBC) of 373 S. sclerotiorum isolates from rape in four areas of the western Sichuan Province indicated no resistance in the fungal population. The EC50 of the 8 measured isolates was from 0.12660ug/ml to 0.2817ug/ml. The average EC50 was 0.1773 ug/ml. The average inhibition rate of mycelial growth of 373 isolates by carbendazim at 1 ug/ml and 5 ug/ml were respectively 94.31% and 97.99%, while the minimum inhibition rate by carbendazim at these two concentrate were respectively 55.30% and 90.43%. No significant mycelial growth was observed on PDA plates amended with carbeadazim. All these results suggested that S. sclerotiorum isolates from rape in the western Sichuan Province were prevalently sensitive to carbendazim.2. The results of measurement for mycelial growth rate showed there were distinct differences in S. sclerotiorum isolates. The mycelial growth rate was from lmm/48h to 85mm/48h. The average mycelial growth rate was 60.47mm/48h.3. The studies on the production of sclerotia indicated there were distinct differences among four areas. The proportion of isolates that could producted sclerotia in Wolong County of Qionglai City was 59.00%. It was the lowest among the four areas. The proportion in Daxing Conty of Pujiang City was 94.74% that was the highest. Some isolates producted a few and big selerotia, even there were two sclerotia per Petril dish. While 48 small sclerotia were producted by some isolates in each Petril dish.4. 30 mycelial compatibility groups (MCGs) (within each of which all isolates were incompatible) were distinguished among 40 S. sclerotiorum isolates. Of the 30 MCGs, 7 MCGs, each consisting of two or more isolates, were identified. The largest MCGs including 4 isolates observed in Daxing County of Pujiang Ctiy. The other 23 MCGs were each made up of one isolate, only compatible with itself. The isolates of each areas belonged to specific MCGs, but MCGs4 could consisted of two isolates( 9 and86) coming from two different areas.5. 30 S. sclerotiorum isolates were analysed with RAPD markers, 9 random primers generated a total of 53 polymorphic bands, with an average of 5.89 per primer. The genetic similarity coefficient based on RAPD data was estimated with Nei's method. Cluster analysis using the program of UPGMA divided 30 isolates into 2 groups. The first group could be further divided into 7 sub-groups that indicated distinct area differences. It was detected by RAPD markers that various MCGs, various area and various isolates in the same area had a little different genetic bases and indicated some genetic diversity. But the genetic distance between isolates was not far (GD 0.333). So RAPD markers were showing the genetic difference and also showing genetic similarity among isolates at the same time.