Trichoderma atroviride SC1 can prevent infections of Phaeoacremonium aleophilum and Phaeomoniella chlamydospora on grapevine in nurseries

Esca is a destructive wood disease of grapevine (Vitis vinifera L.) worldwide. Several microorganisms are associated with the disease. However Phaeoacremonium aleophilum (Pal) and Phaeomoniella chlamydospora (Pch) are frequently isolated from wood of plants showing esca symptoms and are responsible for the vascular disorder. Esca is commonly a major problem in old vineyards, even if young esca can be increasingly noticed on young newly planted vineyards. In this case infection may take place already during propagation of the plants in nurseries. Plant colonization by these two microorganisms is supposed to take place from the wounds, which are created during the preparation of the new plants. Chemical treatments are ineffective against the disease and the efficacy of hot water treatments of dormant cuttings to eradicate or even reduce populations of the pathogens is debated and in many case can result in reduced plant quality. Therefore protection of wound could be of extreme importance to prevent infection by these two microorganisms. Biocontrol microorganisms colonizing wood can offer a solution. The strain Trichoderma atroviride SC1 was isolated from decayed wood and has been shown a good capacity of colonizing wounds in established vines. When applied in the nursery process it successfully colonizes almost all parts of the plants (rootstocks and scions). It fully controls infections of Pal and Pch during grafting and the level of colonization is stable during the entire process, showing a percentage of colonization of plants close to 100% at the time of commercialization. Applications at different stages of the nursery process indicated that crucial times for the application are just after the collection plant material from mother plants and before grafting, while treatments during stratification or rooting did not fully control the disease. Increasing time of dipping in the solution and increasing concentration of the conidia did not result in any further increase of the efficacy. In contrast a chemical disinfectant commonly applied by growers resulted in increased incidence of Pal and Pch. T. atroviride SC1 also controlled grey mould, which commonly developed during stratification. The trials were carried out for three years in two sites in Italy indicating a good adaptability to different environmental conditions and consistency of results. T. atroviride SC1 may represent an interesting strain for further developments in the protection of grapevine wounds from esca-associated microorganisms.