Investigating the durable effect of the hot water treatment used in nurseries on pathogenic fungi inhabiting grapevine wood and involved in grapevine trunk diseases

Hot water treatment (HWT) is used in nurseries to control pathogenic fungi involved in Grapevine Trunk Diseases (GTDs), as well as other pathogens, such as phytoplasmas. The long-term impact of this treatment on the entire microflora, especially on the general fungal microbiota living inside plants, still remains however unknown. In this study, the fungal microflora of vineyard plants, treated or not by HWT 14 and 15 years earlier were compared at different plant part levels. The fungal microflora was relatively abundant in the different types of wood tissues. Certain fungal genera were first isolated and then identified on the basis of their treatment or not by HWT. A significant change between 2010 and 2011, the two sampling years, was detected. Although the HWT may have affected the cuttings microflora at the nursery stage, this had not persisted after several years of HWT treatment for the fungi, especially the pathogenic ones. As HWT does not have a significant long-term control effect on GTD pathogens in mature plants in the vineyards, applying other sanitary methods as soon as HWT-young vines are planted in the vineyards is recommended.