Non-conventional compounds against powdery mildew: profiling grapevine phyllobiome and elicited defence responses

The reduction of antimicrobial treatments and mainly the application of environmentally friendly compounds, such as resistance elicitors, is an impelling challenge for grapegrowers in the optic of a more sustainable viticulture. We addressed this research to study how non-conventional compounds reduce leaf fungal attack and influence the phyllobiome. Pathogenicity tests were conducted on potted Vitis vinifera 'Nebbiolo' and 'Moscato' infected with the powdery mildew agent (Erysiphe necatrix) and maintained in greenhouse. The efficacy of diverse resistance inducers was assessed on infected plants treated with either conventional (acibenzolar-S-methyl) or alternative (laminarin, potassium phosphonate) fungicides. In both the cultivars, the most effective products in terms of significant inhibition of the pathogen were laminarin and acibenzolar-S-methyl. The effect of the antifungal treatments in shaping the foliar microbial community of powdery-mildew infected grapevines was evaluated by: i) community-level physiological profiling (CLPP) by using Biolog EcoplatesTM; ii) high throughput sequencing of ITS and 16S regions; iii) depict of virome, viroids and phytoplasma; iiii) analysis of cuticular wax content and secondary metabolites. Cuticular waxes on leaf epidermis was overall higher in 'Nebbiolo' than in 'Moscato', pointing to distinct defense mechanisms between the two genotypes, likely induced, besides the pathogen presence, by the applied alternative compounds. This trend was confirmed by CLPP results obtained by performing sole-carbon source-utilization tests on leaf extracts. Further experiments are ongoing to integrate microorganism profiling with metabolomic data in order to gain a comprehensive picture of the alternative fungicide effects on phyllobiome and defense-related responses.