Multiple Mutations and Overexpression in the CYP51A and B Genes Lead to Decreased Sensitivity of Venturia effusa to Tebuconazole

Abstract

Multiple demethylation-inhibiting (DMI) fungicides are used to control pecan scab, caused by Venturia effusa. To compare the efficacy of various DMI fungicides on V. effusa, field trials were conducted at multiple locations applying fungicides to individual pecan terminals. In vitro assays were conducted to test the sensitivity of V. effusa isolates from multiple locations to various concentrations of tebuconazole. Both studies confirmed high levels of resistance to tebuconazole. To investigate the mechanism of resistance, two copies of the CYP51 gene, CYP51A and CYP51B, of resistant and sensitive isolates were sequenced and scanned for mutations. In the CYP51A gene, mutation at codon 444 (G444D), and in the CYP51B gene, mutations at codon 357 (G357H) and 177 (I77T/I77L) were found in resistant isolates. Expression analysis of CYP51A and CYP51B revealed enhanced expression in the resistant isolates compared to the sensitive isolates. There were 3.0- and 1.9-fold increases in gene expression in the resistant isolates compared to the sensitive isolates for the CYP51A and CYP51B genes, respectively. Therefore, two potential mechanisms—multiple point mutations and gene over expression in the CYP51 gene of V. effusa isolates—were revealed as likely reasons for the observed resistance in isolates of V. effusa to tebuconazole.

The APSES Transcription Factor SsStuA Regulating Cell Wall Integrity Is Essential for Sclerotia Formation and Pathogenicity in Sclerotinia sclerotiorum

“…The inhibition rate of tebuconazole, myclobutanil and propiconazole was all increased in ΔSsStuA (Figure 3A,B), and the expression level of SsStuA also increased under tebuconazole treatment (Figure 3C). CYP51 is the target of tebuconazole [38,39], therefore, the expression of SsCYP51 was measured in WT and ΔSsStuA. The results showed that SsCYP51 was upregulated in ΔSsStuA, which indicate that SsCYP51 is not the only target of tebuconazole in S. sclerotiorum (Figure 3D).…”