Cytochrome b Gene Analysis for Pyraclostrobin-Resistant Colletotrichum asianum in Mango Unveils Unanticipated F129L Mutation Caused by TTA SNP

Fungal resistance against Quinone outside inhibitors (QoI) fungicides has been a long-standing concern amidst numerous efforts to protect agricultural production. An allele-specific cytochrome b gene-based polymerase chain reaction (PCR) using cDNA has been developed to unveil G143A mutation leading to QoI resistance in Colletotrichum gloeosporioides but the possibility of detecting the mutation in other members of Cg species complex yet to be clarified. Bioassay assessments including mycelial growth, conidial germination, and germ tube length inhibition tests on four mango-isolated C. asianum and four citrus-isolated C. gloeosporioides showed partial resistance only on the C. asianum HM_IJB isolate. Direct sequencing on the cytochrome b region determined all eight isolates lacked G143A mutation. However, HM_IJB isolate demonstrated F129L mutation that had been reported to confine a low-level resistance to QOI fungicides. Moreover, the F129L substitution was caused by a TTA SNP, which has never been observed in Colletotrichum asianum. The allele-specific PCR and restriction fragment length polymorphism PCR were further deployed to confirm that there was no G143A mutation in the eight tested isolates thus indicated that these approaches also applicable to detect resistance profile of C. asianum.