The Resistance Monitoring Of Rhizoctonia Solani To Jinggangmycin And Its Resistance Risk Assessment

Rice sheath blight, which is caused by Rhizoctonia solani, is considered to be the most destructive disease among the three serious rice diseases in China. Jinggangmycin is the most primary fungicide controlling rice sheath blight, the fungicide has been applied to agricultural production for more than 30 years, but very little was known about study of resistance risk assessment of R. solani to Jinggangmycin. So the objectives of the study is about the resistance of R. solani to Jinggangmycin and its resistance risk assessment. Jinggangmycin-resistance(JR) mutant was obtained by induction and its biological characters were studied; the resistance to Jinggangmycin of 161 isolates of R. solani .which is from Fujian Province, was detected, and the resistance risk of R. solani to fungicide was evaluated.Laboratory JR mutant was obtained by induction 24 generations on PSA medium with Jinggangmycin. Its resistance level was over 36.77 times in comparison with that of the parent isolate. The JR mutant could maintain its resistance after 10 generations successive transfers on the fungicide free PSA medium. The result showed that the resistance of mutant was stably inherited after continuously transfers.The fitness of JR mutant was decreased compared with its parent isolate, because of its lower mycelium growth rate, mycelium dry weight and pathogenicity, but the germination rate and pathogenicity of JR mutant sclerotium were similar with its parent isolate. The results showed that JR mutant have some competitive ability compared with sensitive isolate in natural condition. JR mutant didn't express cross-resistance to carbendazim and thiophanate-methyl.161 wild isolates of R. solani, which were collected from rice paddy fields in 11 prefectures including 27 counties/cities of Fujian Province, had been detected for their sensitivity to Jinggangmycin by the method of minimum inhibitory concentration (MIC), The results showed that 4 isolates were resisitant to Jinggangmycin and other isolates were sensitive.The frequency of Jinggangmycin-resistance isolates have certain differences in the different area of Fujian Province. EC50 average value of sensitivity isolates was 0.3589 μg·mL^-1, which was regarded as sensitivity baseline of R. solani to Jinggangmycin.EC₅₀ value of the resistance isolates were between 2.429⁴.1668 μg·mL^-1. Resistance level was 6.78-11.61 times in comparison with sensitivity baseline. The inhibition growth rate of 161 wild isolates was detected on WA medium with 0.5 μg·mL^-1 Jinggangmycin, the results showed that the inhibition rate of wild sensitivity isolates was 66.56 % (95 % confidence limits was 60.23 %⁷2.89 %). The inhibition rate of wild resistent isolates was under 50 % and exceeded 95 % confidence limits of wild sensitivity isolates. The monitoring result...