Hot water treatment combined with <i>Trichoderma</i> inoculation in the nursery protects planting material against grapevine trunk disease

Grapevine trunk diseases (GTDs) cause significant losses in viticulture. To enhance the phytosanitary quality of planting material, a method was developed to control the common GTD pathogens Phaeomoniella chlamydospora, Phaeoacremonium minimum, and Diplodia seriata using hot water treatment (HWT) and inoculation with the biocontrol agent Trichoderma atroviride SC1 (Vintec®, Certis Belchim B. V.) (Ta SC1). Sensitivity of P. minimum and P. chlamydospora isolates to HWT was tested in vitro and in autoclaved wood at conidial and mycelium stages and at various time/temperature combinations (30 and 40 min at 40 °C, 45 °C, 50 °C and 55 °C). The results showed that P. minimum had greater tolerance to HWT compared to P. chlamydospora. Spore germination of all P. chlamydospora isolates was completely inhibited at 45 °C, while P. minimum isolate 117607 tolerated 50 °C. Mycelium growth of both pathogens was completely inhibited at 55 °C. In autoclaved wood, P. chlamydospora growth was inhibited after 30 min at 50 °C, while treatments for 45 min were necessary to inhibit the growth of P. minimum. In nursery experiments, cuttings were artificially inoculated and incubated with the pathogens and treated with HWT at 50 °C for 45 min under conditions of common viticultural practice. In these conditions, no recovery was recorded for P. chlamydospora and D. seriata seven days post-inoculation (dpi), but the survival rate of P. minimum was 5 %. In 2021, P. minimum recovered in 40 % of the samples six months post-inoculation, P. chlamydospora in 7 % twelve months post-inoculation, and D. seriata was eliminated. In 2022, D. seriata was detected in 10 % of samples six months post-inoculation and P. chlamydospora in 25 % of the samples twelve months post-inoculation. P. minimum recovered at all sampling time points during the assessment period. Combined applications of HWT and Ta SC1 provided protection of the planting material over the twelve months assessment period, with molecular analysis confirming 90 % recovery of Ta SC1. Field experiments carried out with naturally infected scions showed that HWT at 50 °C for 45 min significantly reduced the incidence of Diplodia spp. Overall, HWT effectively reduced GTD pathogens in grapevine planting material, and the combined treatment with Ta SC1 enhanced long-lasting protection in the nursery.