| The conformity and resistance mechanism of Rhizoctonia solani isolates against LH-2010 A were determined to evaluate the resistance risk. The materials applied in this study including sensitive LH-S and isolates with induced resistance which was named LH-RM and LH-RH. The cross-resistance of resistant isolates to other fungicides was investigated; the differences of physiological and biochemical characteristics of sensitive and resistant isolates were also clarified. The mixture of LH-2010 A and hexaconazole showed favorable toxicity to R. solani, and then the optimum proportion of the mixed fungicides was determined. The results were shown as follows:1. Six fungicides showed different toxicity to R. solani. Hexaconazole had the highest inhibition activity against R. solani, with the EC50 of 0.0185μg/m L; that of LH-2010 A,carbendazim, flusilazole, azoxystrobin, thiram were 0.7646, 0.4240, 1.0200, 1.9922 and6.4620μg/m L, respectively. The joint toxicity measurement was also conducted for LH-2010 A and hexaconazole. When the ratios ranged from 5:5 to 9:1, the co-toxicity coefficients were 104.12-215.03; the optimum mixture ratio was 5:5(with the highest value).2. The two resistant strains were obtained through indoor UV-irradiating and fungicide selection, with the resistant level of 61.12 and 172.26. After being cultivated without fungicide for 10 times, the resistance of two resistant mutants could be inherited stably. No significant cross-resistances were observed for hexaconazole, flusilazole, carbendazim,azoxystrobin, thiram and LH-2010A+ hexaconazole(1:1), of which the resistant level ranged from 0.85 to 3.76. The mycelia growth rate, mycelium dry weight, sclerotium output,pathogenicity and osmolarity sensitivity of resistant mutants did not exhibit significant influence when compare with parent mutants. This suggested that the fitness of the resistant strain had slightly improved. R. solani had a medium or high resistance risk to LH-2010 A.Therefore, we should do well in resistance management strategy to delay the development of resistance before the large-scale application of LH-2010 A.3. The defense enzyme activities of sensitive and resistant strains were tested. The results showed that a higher activity of phenylalanine ammonialyase and peroxidase was observed for resistant strains compared with that of sensitive strains. When R. solani was treated withLH-2010 A for 24 h, the POD activity of all strains increased continuously; besides, the POD activity of resistant strains was obviously higher than that of sensitive strains. The PAL activity shot up at first and then exhibited a decline trend; the PAL activity arrived the top point 1.5h after LH-2010 A, and then it decreased with time extending.4. The activities of succinate dehydrogenase(SD) were also measured. With the increase of treatment dosage, the SD activity of sensitive strains was apparently inhibited. When LH-2010 A was applied at the dosage of 25 mg/L, the inhibition ratio of SD activity in sensitive strains was as high as 72.10%, however, that of resistant strains showed no significant variation. Therefore, we deduced that the function target of LH-2010 A against R.solani may be the SD in the respiratory chain. |
PDF Full Text Request