Enhancing grapevine viability and pathogen control through optimised hot water treatment

Petri disease is a Grapevine Trunk Disease (GTD) primarily associated with the ascomycete species Phaeomoniella chlamydospora, which leads to 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 potential risk for future vineyards. Nurseries need tailor-made and effective methods for guaranteeing the supply of GTD-free material. This study evaluated Hot Water Treatment (HWT), a widely used method to reduce or eliminate GTD-associated fungi in grapevine propagation materials, in one of the most common scion-rootstock combinations in Portuguese grapevines. The assessment focused on the elimination of P. chlamydospora and plant viability in plants of cv. Touriga Nacional grafted onto 1103 P rootstock. Treatments included non-HWT and HWT plant parts at 46 °C, 50 °C and 54 °C for 45 min, 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 measured after stratification and three months in a nursery. HWT effectively eliminated P. chlamydospora; however, inoculated plants exhibited reduced quality traits compared to non-inoculated plants. The 46 °C treatment produced the highest-quality plants, enhancing the callogenesis process of the grafting union. Mathematical modelling of the pathosystem comprising the pathogen P. chlamydospora and hosts Vitis vinifera as scion and V. rupestris × V. berlandieri as rootstock suggests a better resilience of the symbiont plants to higher temperatures when compared to P. chlamydospora. Optimised HWT protocols are recommended to reduce GTD pathogens while maintaining plant viability.