Molecular Mechanism Of Resistance To Succinate Dehydrogenase Inhibitor In Monilinia Fructicola

Peach brown rot caused by Monilinia spp. can cause serious economic losses in the world. Currently, chemical control is still the main method, but Monilinia spp. have developed resistance to a variety of fungicides. Succinate dehydrogenase inhibitor(SDHI) is a new class of fungicides, its unique site of action makes it hard to produce cross-resistance with other chemical classes, thus has a good prospect in disease control. In this paper, the resistant isolates and sensitive isolates have been studied to clarify the resistance mechanism of Monilinia fructicola to boscalid.The succinate dehydrogenase of Monilinia spp., the target of succinate dehydrogenase inhibitors, its genes have been cloned. Alignment of the succinate dehydrogenase genes of sensitive and resistant strains, revealed that only SDHB subunit had a few synonymous mutations that did not change the amino acid sequence. By Agrobacterium-mediated genetic transformation system, SDHB gene containing synonymous mutations in resistant strains Dmap3-08and BM09-4a were transformed into the sensitive strain HG12-3a for evaluating the correlation of such mutations and boscalid resistance. As a result, the transformants did not show resistance to boscalid, indicating that synonymous mutations on the SDHB gene are unrelated to the boscalid resistance.Subsequently, the expression of some transporter genes in M. fructicola were measured by real-time quantitative PCR. Results showed that the expression of MfABC1gene, which had been cloned in previous study, did not show significant difference between resistant and sensitive strains. Whereas expression level of MfRTAl gene in resistant strain Dmap3-08increased13times compared to that in sensitive strain. Therefore, the overexpression of MfRTAl gene most likely be associated with the resistance to boscalid in M. fructicola.