Grapevine cultivar variation to pruning wound protection by Trichoderma species against trunk pathogens
Using Trichoderma species to protect grapevine pruning wounds from trunk disease pathogens is one of the options available for managing grapevine trunk diseases. The growth and persistence of Trichoderma species in the pruning wound and the resulting control effect may depend on intrinsic wound factors and hence may vary between cultivars. Cultivar variability to pruning wound protection by Trichoderma species was evaluated in eight wine grape (Cabernet Sauvignon, Chardonnay, Chenin blanc, Colombar, Merlot, Pinotage, Sauvignon blanc and Shiraz) and four table grape (Prime, Red Globe, Thompson Seedless and Victoria) cultivars. Two strains of Trichoderma atroviride (USPP-T1 and USPP-T2) separately or in combination and Eco 77® a registered pruning wound biocontrol agent based on T. harzianum, were applied to fresh pruning wounds of spur-pruned wine grapevines and cane-pruned table grapevines. Trichoderma spp. and a variety of trunk pathogens, Phaeomoniella chlamydospora and species of Phaeoacremonium, Phomopsis, Botryosphaeriaceae and Diatrypaceae, were isolated from the pruning wounds eight months after treatment. Significant treatment × cultivar interactions (P<0.01) were found in the incidence of Trichoderma spp. in table and wine grapes. Trichoderma incidence varied greatly between cultivars and was less between Trichoderma treatments within the same cultivar. The highest Trichoderma incidence in wine grapes was found in Chenin blanc (71.4-82.5%) and in table grapes in Thompson Seedless (43.5-76.7%). In the remaining wine grape cultivars Trichoderma incidence varied between 20-50% while with all treatments in Chardonnay Trichoderma incidence was less than 24%. In table grapes Trichoderma incidence varied from 20-67% in the other cultivars. Trichoderma reduced the pathogen by between 10.3% in Chardonnay to 66.7% in Chenin blanc. Trichoderma incidence and pathogen reduction were significantly correlated in most cultivars (r> 0.50; P<0.05) though not in Chardonnay (r=0.37; P=0.11), Pinotage (r=-0.12; P=0.62), Sauvignon blanc (r=0.26; P=0.26) and Victoria (r=0.29; P=0.22). It was concluded that the wound protection effect of Trichoderma spp. is also dependent on the Trichoderma-grapevine interaction and is not only due to the suppressive effect of Trichoderma spp. on the pathogens.