Resistance of melon powdery mildew isolates to kresoxim-methyl in Guangxi and determination of its sensitivity to three fungicides

ObjectiveThe resistance level, distribution and development of melon powdery mildew isolates to kresoxim-methyl in Guangxi were identified and effective alternative fungicides were screened to provide references for prevention and controlling of melon powdery mildew. MethodFrom 2007 to 2012, bitter gourd, wax gourd, muskmelon, cucumber and bottle gourd disease samples were collected from Nanning, Guiping, and Beihai, etc. Their isolates’ resistance to kresoxim-methyl were detected by leaf disk tests. Sensitivity of high-resistant isolates to carbendazim, trifloxystrobin and propineb were also analyzed. ResultThe results showed that 83 melon powdery mildew population produced resistance to kresoxim-methyl in varying degrees. Resistant isolates were mainly distributed in bitter gourd powdery mildew and their resistant fre-quency was the highest (63.89%), while bottle gourd isolates had the lowest resistant frequency (6.67%). The resistant level of bitter gourd powdery mildew against to kresoxim-methyl increased gradually from 2007 to 2012 in Nanning City, resulting in development of high-resistance population. Fungicide screening assay results indicated that powdery mildew isolates with highly resistant to kresoxim-methyl, were highly drug-fast to carbendazim and cross-resistant to trifloxystrobin, but was sensi-tive to propineb. ConclusionIn Guangxi, melon powdery mildew isolates were highly resistant to kresoxim-methyl and al-ternate use of propineb in the production process could be recommended.