Integrated hot water treatment: A tool for strengthening grapevine viability and reducing pathogen load

Abstract: Petri disease, a Grapevine Trunk Disease (GTD) primarily associated with the
ascomycete species Phaeomoniella chlamydospora, causes substantial losses in young vineyards, particularly during the first years after planting. Contamination of plant material before and during nursery procedures with this species represents a significant risk to future vineyards. Nurseries are increasingly demanding effective, tailor-made methods to ensure the supply of GTD-free material to customers. This study evaluated Hot Water Treatment (HWT) – a widely used method to reduce or eliminate GTD-associated fungi in grapevine propagation material – in one of the most common scion-rootstock combinations in Portuguese viticulture. The assessment focused on the elimination of P. chlamydospora and plant viability in cv.’Touriga Nacional’ grafted onto ‘1103 P’ rootstock. Treatments included non-HWT and HWT applications at 46 °C, 50 °C, and 54 °C for 45 minutes, applied to both non-inoculated and P. chlamydospora-inoculated scions and rootstocks. Fungal presence was assessed before and after HWT, and growth parameters of grafted plants were recorded after stratification and three months in the nursery.
HWT effectively eliminated P. chlamydospora; however, inoculated plants exhibited
reduced quality traits compared to non-inoculated ones. The 46 °C treatment produced the
highest-quality plants, enhancing callus formation at the graft union. The grafted plants’ resilience to temperature was higher than that of P. chlamydospora, as predicted through mathematical modelling of the pathosystem. These promising results, demonstrating effective elimination of P. chlamydospora without harming young plants, are being incorporated into ongoing studies aiming to define post-nursery protocols involving biocontrol agents active against GTDs (e. g., Trichoderma spp.). This will support Portuguese nurseries in supplying high quality, Petri disease-free plants during the critical early years after planting.