In vitro evaluation of grapevine endophytes, epiphytes and sap micro-organisms for potential use to control grapevine trunk disease pathogens

Abstract

Grapevine trunk diseases (GTDs) threaten the economic sustainability of viticulture, causing reductions of yield and quality of grapes. Biological control is a promising sustainable alternative to cultural and chemical methods to mitigate the effects of pathogens causing GTDs, including Botryosphaeria dieback, Eutypa dieback and Esca. This study aimed to identify naturally occurring potential biological control agents from grapevine sap, cane and pith tissues, and evaluate their in vitro antagonistic activity against selected fungal GTD pathogens. Bacterial and fungal isolates were preliminarily screened in dual culture assays to determine their antifungal activity against Neofusicoccum parvum and Eutypa lata. Among the fungal isolates, Trichoderma spp. inhibited mycelium growth of E. lata by up to 64% and of N. parvum by up to 73%, with overgrowth and growth cessation being the likely antagonistic mechanisms. Among the bacterial isolates, Bacillus spp. inhibited mycelium growth of E. lata by up to 20% and of N. parvum by up to 40%. Selected antagonistic isolates of Trichoderma, Bacillus and Aureobasidium spp. were subjected to further dual culture antifungal analyses against Diplodia seriata and Diaporthe ampelina, with Trichoderma isolates consistently causing the greatest inhibition. Volatile organic compound antifungal analyses showed that these Trichoderma isolates inhibited mycelium growth of N. parvum (20% inhibition), E. lata (61% inhibition) and Dia. ampelina (71% inhibition). Multilocus sequence analyses revealed that the Trichoderma isolates were most closely related to Trichoderma asperellum and Trichoderma hamatum. This study had identified grapevine sap as a novel source of potential biological control agents for control of GTDs. Further testing will be necessary to fully characterize modes of antagonism of these microorganisms, and assess their efficacy for pruning wound protection in planta.