Isolation,production and in vitro effects of the major secondary metabolite produced by Trichoderma species used for the control of grapevine trunk diseases

Antibiosis has been shown to be an important mode of action by Trichoderma species used in the protection of grapevine pruning wounds from infection by trunk pathogens. The major active compound from Trichoderma isolates known to protect grapevine pruning wounds from trunk pathogen infection was isolated and identified. The compound, a 6‐pentyl‐α‐pyrone (6PP), was found to be the major secondary metabolite, by quantity, which accumulated in the culture filtrate of T. harzianum isolate T77 and the two T. atroviride isolates UST1 and UST2. Benzimidazole resistant mutants generated from these isolates also produced 6PP as their main secondary metabolite, except for a mutant of T77 that had lost its ability to produce 6PP. The isolates UST1 and UST2 were co‐cultured with the grapevine trunk pathogens Eutypa lata and Neofusicoccum parvum in a minimal defined medium and a grapevine cane‐based medium (GCBM). Co‐culturing UST1 with N. parvum induced 6PP production in the minimal defined medium and the GCBM. The production of 6PP by UST2 was induced in the GCBM, while co‐culturing with the two trunk pathogens either reduced or had no effect on 6PP production. Mycelial growth and ascospore/conidia germination of E. lata, N. australe, N. parvum and Phaeomoniella chlamydospora were inhibited by 6PP in a concentration‐dependent manner. The results show that the presence of N. parvum and grapevine wood elicits the production of 6PP, suggesting that this metabolite is involved in Trichoderma–pathogen interactions on grapevine pruning wounds.