Resistance of Plasmopara viticola to multiple fungicides in vineyards of Maharashtra

Abstract

This study aims to assess the fungicide resistance status of P. viticola for developing a future guideline for downy mildew management of grapes in India. One hundred and sixty downy mildew infected grape leaf samples were collected from 16 vineyards located in Maharashtra, India during September 2015 to November 2016. Most of these vineyards had heavy incidence of downy mildew disease, even though several fungicide interventions for its control were made. The fungicide sensitivity was assessed against kresoxim methyl, dimethomorph, Cymoxanil and Metaxyl-M using leaf disc bioassay, and QoI and CAA resistance gene was detected using allele specific multiplex PCR. Based on the sensitivity response in leaf disc bio-assay, isolates of P. viticola were categorized as, sensitive (S), intermediate (I) or highly resistant (R) to four fungicides. The percentage of sensitive P. viticola isolates were 23.75, 19.37, 32.5, 12.5, intermediate were 15.0, 48.12, 48.8, 45.62 and highly resistant were 23.8, 20.6, 29.4, 12.5 to kresoxim methyl, dimethomorph, cymoxanil and metalaxyl-M, respectively. Multiplex allele-specific primer–polymerase chain reaction (ASP-PCR) confirmed G143A mutation in the cytb gene in 123 highly and intermediate resistant P. viticola isolates to quinone outside inhibitor fungicide and G1105S mutation in the PvcesA3 gene in 129 highly and intermediate resistant isolates to carboxylic acid amide fungicides. Among these, 101 isolates showed the presence of both G143A and G1005S mutations. Forty-nine isolates showed the presence of either G143A or G1005S mutation,while ten isolates were sensitive to both the fungicides and did not harbor either of the mutations.