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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #390641
Research Project: Healthy, Sustainable Pecan Nut Production

Location: Fruit and Tree Nut Research

Title: Multiple mutations and overexpression in the CYP51A and B genes lead to decreased sensitivity of Venturia effusa to tebuconazole

Author
item MOORE, LOGAN - University Of Georgia
item BRENNEMAN, TIMOTHY - University Of Georgia
item WALIULLAH, SUMYYA - University Of Georgia
item Bock, Clive
item ALI, MD EMRAN - University Of Georgia

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2021
Publication Date: 1/11/2022
Citation: Moore, L.C., Brenneman, T.B., Waliullah, S., Bock, C.H., Ali, M. 2022. Multiple mutations and overexpression in the CYP51A and B genes lead to decreased sensitivity of Venturia effusa to tebuconazole. International Journal of Molecular Sciences. Vol 47: 43-57. https://doi.org/10.1007/s40858-021-00479-5.
DOI: https://doi.org/10.1007/s40858-021-00479-5

Interpretive Summary: Several different fungicides in the demethylation inhibiting (DMI) class are used to control pecan scab (caused by the plant pathogenic fungus Venturia effusa). The efficacy of several of these DMI fungicides against V. effusa was tested in field trials in several pecan orchards by applying fungicide to individual terminals. Lab assays were conducted to test the sensitivity of V. effusa isolates from each locations to tebuconazole, a common DMI. Both studies confirmed high levels of resistance to tebuconazole. The CYP51 genes are known to be involved in resistance to the DMIs. The mechanism of resistance was investigated by sequencing the CYP51A and CYP51B genes of resistant and sensitive isolates. Mutations were found in resistant isolates which indicates two potential resistance mechanisms: multiple point mutations and gene over expression occurring in DMI resistant isolates of V. effusa.

Technical 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 fungicide 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.