Sensitivity to prochloraz and main biological characteristics of resistant mutants of Fusarium oxysporum from cucurbitaceous crops in North China

The present study was performed to explicit sensitivity of Fusarium oxysporum Schl. on cucurbitaceous crops from North China and clarify the biological characteristics of the resistant mutants. The sensitivities of 112 isolates of Fusarium oxysporum on cucurbitaceous crops to prochloraz were determined by mycelial growth rate method. And the isolates were collected mainly from areas in Beijing, Shandong and Hebei provinces where no azoles fungicides had been used before. Resistant mutants to prochloraz were acquired by fungicide adaptation test. The results showed that the frequency of isolates with different sensitivity to prochloraz distributed as a unimodal curve, and there was no subgroup with declining sensitivity. The mean EC50 value was (0.030 1±0.030 4) μg/mL and it could be considered as the sensitivity baseline. Seven resistant mutants of F. oxysporum to prochloraz were obtained with the resistance factors ranging from 6.2-26.8 fold. The growth rate of mycelium on PDA between the mutants and the parent isolates, the dry weight of mycelium, and the virulence of 7 resistant mutants were significantly lower than that of the parent isolates. Only the resistance of mutant HG13052701-R1 could be stably inherited, while the other 6 mutants could not be inherited stably. Cross-resistance existed only between prochloraz and tebuconazole, and there is no cross-resistance found among prochloraz, carbendazim and hymexazol. The results suggested that resistant mutant of F. oxysporum on cucurbitaceous crops can be developed under the selection of prochloraz, and the resistance risk is low.