Study On The Biological Characteristics Of The Weakly Pathogenic Strains Of Sclerotinia Sclerotiorum

Sclerotinia sclerotiorum is a kind of destructive plant pathogenic fungi.The disease which is infected by S.sclerotiorum occurs rapeseed-producing region in china.Especially,it is a serious threat to the Yangtze River and the southeast coastal areas,but also impacts the yield and quality of rapeseed.In order to study the pathogenicity differentiation and the formation mechanism of weakly pathogenicity of S.sclerotiorum,the biological characters of weakly pathogenic strains were studied.The main results are as follows:The isolates from different areas of Anhui Province were selected as the study subject.The different rapeseed varieties were inoculated by applying isolated leaf inoculation,evaluating the pathogenicity among different strains.The results showed that the pathogenicity of S.sclerotiorum to four different rapeseed cultivars varies with the same strain.The pathogenicity of 25 different strains varies with the same rapeseed cultivars,which indicated that there was significant differentiation in the pathogenicity of S.sclerotiorum strains to rapeseed among isolates.According to the results,6 representative strains of S.sclerotiorum(WJB-4,TC-7,SX-2,LA3,WW2,SX-6-1)were selected as the tested strains.The molecular identification of weakly pathogenicity strains(LA3,WW2 SX-6-1)were carried out.The sequence of the weakly pathogenic strains were closest relative to that of S.sclerotiorum published with 100% identity by ITS sequence analysis It can be seen that the weakly pathogenic strains were S.sclerotiorum and there were no other organisms.Six representative strains,which were strongly pathogenic strains WJB-4,TC-7,SX-2 and weakly pathogenic strains LA3,WW2,SX-6-1,were screened for identification further,compared whether there is a significant biological properties.The results showed that WJB-4 was fastly growth type,the growth rate was 4.20 cm/d,the colony expanded evenly and the biomass was high.SX-6-1 was a slowly growth type,the growth rate was only 2.43 cm/d,the colonies were unevenly expanded,the aerial mycelium was not developed and the biomass was low.In order to analyze the biochemical mechanism of weakly pathogenic strains,by comparing whether there is a significant difference in pathogenic factors,the pectinase and cellulase activities,oxalic acid production,and the number of infection cushion,were investigated respectively,with the tested isolates of S.sclerotiorum.The results showed that the ability of weakly pathogenic strains were significantly lower than those of strongpathogenic strains in producing oxalic acid,cellulase,pectinase,and the number of infection cushions.Further more,the the possible cause of the formation of the weakly pathogenic strains was explored from the endogenous bacterial identification and the detection of dsRNA virus.The results showed that no endophytic bacteria were detected in the weakly pathogenic strains,which suggesting the formation of the weakly pathogenic strains were not caused by endophytic bacteria.At the same time,the dsRNA virus was not detected in the weakly pathogenic strains,which indicated that the dsRNA virus was not the cause of the formation of weakly pathogenic strains.Therefore,there are other reasons to further explore the formation of the weakly pathogenic strains.