Enhanced biological control of powdery mildew in vineyards by integrating a strain of Trichoderma afroharzianum with sulphur

Abstract

Identifying a superior bio-control strain is the first step in developing a successful bio-control strategy for any disease. Field trials were conducted to systematically screen six potential Trichoderma isolates for control of powdery mildew disease during 2013–2016. Treatments were applied as foliar sprays with a simple liquid formulation of Trichoderma containing 5 ×106 spores ml−1. The preliminary scale, small scale, and field scale trials showed that isolates NAIMCC-F-01938 and NAIMCC-F-01965 were superior to the other four Trichoderma isolates reducing disease by 43.67–50.36% and 35.71–53.40% respectively. Analysis of ITS, act, rpb2 and tef1 genes showed homology of strains NAIMCC-F-01938 and NAIMCC-F-01965 to T. afroharzianum and T. asperelloides respectively. Both isolates produced an array of enzymes implicated in bio-control activities. In coculture studies on grape leaves, Trichoderma hyphae grew towards and coiled around Erysiphe necator conidia, caused distortion of conidial structure and overgrew the powdery mildew colonies. T. afroharzianum showed higher tolerance to fungicides commonly used in powdery mildew management. In the large scale demonstration trial it showed 43% reduction in disease severity as compared to the untreated control. Furthermore, introducing two late season T. afroharzianum applications in a fungicide spray schedule, as replacement for sulphur, enhanced powdery mildew control by 31% as compared to the only fungicide schedule. The study shows that the T. afroharzianum strain NAIMCC-F-01938 can be positioned with safe fungicides for enhanced control of powdery mildew in vineyards.