Studies On Resistance To Carbendazim And Pathogencity Of Sclerotinia Sclerotirum In Sichuan

The sclerotinia stem rot caused by Sclerotinia.sclerotiorum is a serious fungal disease on rape and economic crops.To determine the resistance to MBC and the pathogenic mechanism and the dsRNA of S.sclerotiorum in Sichuan,the 110 isolates from different region and host in Sichuan province were selected to test.The results of the research showed as follows:Taking 0.42μg/mL as the test standards,out of the total 110 tested isolates of S.sclerotiorum,31 isolates from 11 regions of Sichuan were MBC resistant with the proportion of 28.18%.The EC₅₀ were identified by measuring mycelial growth in fungicide-amended media.Average EC₅₀ of 79 sensitive isolates were 0.1234μg/ml and those of 39 resistant isolates were 0.1720μg/ml.All of the resistant isolates were low-resistant to MBC.The MBC-resistant isolates showed positive cross-resistance to thiabendazole and thiophante-methyl.Pathogenicity to dedetached rape leaves was not different between MBC-resistant and sensitive isolates of S.sclerotiorum.Resistant isolates could infect rape leaves soaked in MBC of 50μg/ml concentration,while sensitive isolates did not infect these leaves.The assay of the ability for producing oxalic acid and pathogenicity in different isolates indicated that the ability for producing oxalic acid of each isolates was correlated positively with its pathogenicity with the correlated coefficient being 0.9856.The production ability of cell wall-degrading enzymes was evidently different among the isolates.There was a positive correlation between the production ability of cellulose enzyme(Cx) and the pathogenicity of the isolates with the correlated coefficient being 0.9400.But the production ability for polymethylgalacturonase(PMG) and polygalacturonase(PG) of isolates was not correlated with its pathogenicity.It indicated that oxalic acid and cellulose enzymes(Cx) played an important role in the infection.A total of 65 isolates of from different regions of Sichuan were collected to extract dsRNA,there were 21 dsRNA-positive isolates with the proportion of 32.31%. Among the 21 isolates,there were 13 less virulent strains and 8 mild virulent strains contained dsRNA,but all the tested virulent isolates contained few dsRNA.There were 9 distinct dsRNA electrophoretic patterns in the 21 isolates.Almost all less virulent isolates contained about a 6.0kb segent.It indicated that the 6.0kb dsRNA segment would be involved with the hpovirulence directly.The types of dsRNA were not relate to the geographic distribution and host origin and fungicide-resistance.