Studies On Resistance Of Sclerotinia Sclerotiorum To Dimethachlon

Sclerolinia sclerotiorum (causal agent of rapeseed stem rot) is one of worldwide disease, seriously affecting production and quality of rapeseed. At present, chemical control is still the main method for the control of S. sclerotiorum. Carbendazim and other benzimidazole fungicides have always been the main fungicides to control S. sclerotiorum. However, due to single site of action, wide spread control failures were reported due to development of carbandazim resistance in S. selerotiorum. The sensitivity of S. sclerotiorum to dimethachlon was determined for isolates from Sichuan, Qinghai, Gansu, Hunan, Jiangsu and Anhui Province by the method of minimum inhibition concentration (MIC) and EC50.The results of MIC indicated that there was no resistant isolates detected. The proportions of the Sichuan, Qinghai, Hunan, Gansu, Jiangsu and Anhui isolates having mycelial halo in the plate containing 5μg/mL dimethachlon were 76.42%,90%,62.84%, 95.97%,23.01% and 9.68%, respectively.The results of mycelial growth test indicated that the EC50 values of dimethachlon ranged from 0.3 mg/1-1.8 mg/1 in Gansu, Sichuan, Qinghai, Jiangsu and Anhui Province.We obtained the dimethachlon-resistant mutants by UV induction. The resistance factors for the isolates ranged from 86.0 to 201.2, with the mean value of 129.3. We obtained the dimethachlon-resistant mutants by dimethachlon induction. The resistance factors for the isolates ranged from 39.7 to 234.8, with the mean value of 136.4. The stability of resistance results indicated that the resistance of the UV-induced mutants was stable after they were subcultured for twenty generations on PDA.Differences in mycelial growth, pathogenicity and scelerotial production were detected between the sensitive and the resistant isolates. The laboratory-induced dimethachlon-resistant isolates appeared to have slower speed of mycelial growth, lower scelerotial pathogenicity compared with the field dimethachion-sensitive isolates. Results of osmotic tests showed that compared with the sensitive isolates, the resistant mutants were more sensitive to high osmotic stress, which suggested that the dimethachlon-resistant isolates might have lower fitness than the sensitive isolates in the field.