An allele-specific PCR assay for detecting azoxystrobin-resistant Alternaria isolates from pistachio in California

Alternaria late blight caused by Alternaria spp. in the alternata, tenuissima and arborescens species-groups is one of the most common fungal diseases of pistachio in California. A single point mutation resulting in the replacement of a glycine by an alanine at codon 143 (G143A) in the mitochondrial cytochrome b (cyt b) has been found in all azoxystrobin-resistant isolates of these three species from California pistachio. In this study, a pair of allele-specific polymerase chain reaction (PCR) primers was developed to detect this point mutation. The allele-specific PCR assay coupled with a rapid DNA extraction method could detect azoxystrobin-resistant Alternaria isolates in a few hours. The allele-specific PCR method was also reliable for detecting azoxystrobin-resistant Alternaria directly in both laboratory-inoculated and naturally infected pistachio leaves.