Sensitivityof<italic>Rhizoctoniasolani</italic>tothifluzamideinShandongProvinceandthebiologicalcharacteristicsofresistantmutants

In order to clarify the sensitivity and resistance risk of Rhizoctonia solani to thifluzamide in Shandong Province, 102 isolates of R. solani in 6 areas in Shandong, including Tai’an, Linyi, Weifang, Laiwu, Rizhao and Qingdao, were investigated using the mycelial growth rate method. The EC₅₀ values of thifluzamide against different isolates of the pathogen ranged from 0.010 to 0.194 μg/mL, with an average EC₅₀ value of (0.086 ± 0.004) μg/mL, which showed a single-peak curve distribution. Five drug-resistant isolates were obtained by UV induction and one resistant mutant was obtained by drug domestication. Their resistance levels ranged from 6.46 to 20.08. The mutation frequencies were 0.87% and 0.52%, respectively. Five drug-resistant isolates obtained by UV induction could not be stably inherited. While one mutant QD2-Y4 obtained by acclimation of the drug could be stably inherited. Studies on the biological traits of antagonistic mutants showed that the mycelial growth rate of TA3-X2 isolate was higher than that of the parent isolates, and no other obvious difference was detected. The dry weight of mycelium and the dry weight of sclerotia of the five resistant isolates and one resistant mutant were all lower than the parent isolates. The pathogenicity of TA3-X2, WF6-A2 and QD2-Y4 was lower than that of the parent isolates. However, the pathogenicity of TA17-X6, LY8-3 and QD14-Y7 was not significantly different from that of the parental isolates. There was no cross-resistance between thifluzamide and some other fungicides, including tebuconazole, propiconazole, fludioxonil, validamycin, difenoconazole and carbendazim. However, the cross-resistance among thifluzamide, boscalid and penflufen was observed. Overall, R. solani is sensitive to thiafuramide in 6 areas of Shandong Province. It is speculated that thiafidamide can be used as an ideal candidate for controlling banded leaf sheath blight in corn.