Detection of G143A mutation in Erysiphe necator and its implications for powdery mildew management in grapes

Abstract

Quinone outside inhibitor (QoI) fungicides are used worldwide for the management of Erysiphe necator but with associated problem of resistance development in the pathogen. Twenty nine E. necator isolates were collected during 2015-2016 from different geographical regions of India. In leaf disc bioassay using azoxystrobin, the EC50 of four isolates from research farms was less than 1 μg/ml, while 25 isolates from commercial vineyards had EC50 more than 115 μg/ml. The 256 fold resistance factor indicated G143A mutation. All the resistant isolates produced a 100 bp PCR product with G143A mutant allele specific primer which was not produced by the four sensitive isolates. A primer pair was designed for partial amplification of cytochrome b gene (Cyt b) and used for amplification of the gene from two resistant and two sensitive isolates. Alignment of amino acid sequences showed that the QoI resistant isolates harboured a G143A mutation, which was absent in the sensitive isolates. The two haplotypes of Cyt b gene from a resistant isolate, SAA2, and a sensitive isolate, HP1, have been deposited in GenBank under accession numbers KY418049 and KY418048, respectively. This is the first report of presence of QoI resistant isolates of E. necator from India. Studies point out the need for developing resistance management strategies by interspersing bio-control agents with judicious use of fungicides.