Fungal community dynamics and anthocyanin profiling of grapevine leaves in a vineyard affected by trunk diseases.. Fungal community dynamics and anthocyanin profiling of grapevine leaves in a vineyard affected by trunk diseases.

Leaves in grapevines affected by esca may occasionally manifest a symptom known as ‘esca leaf stripe symptom’. The triggering factors that lead to symptom onset and progression are still under debate, but they seem to originate from an advanced fungal infection in perennial tissues. The esca leaf stripe symptom starts as chlorotic spots in interveinal tissue, it is followed in time by scorching, and the development of pigmentation between scorched and healthy tissue, in red-berried varieties. Such pigmentation is typically of tonalities of red, however, purple and no pigmentation are occasionally observed. Working on cultivars Cabernet Sauvignon and Touriga Nacional, we used DNA metabarcoding (i) to explore the microbial dynamics during symptoms progression in esca-affected leaves, and (ii) to reveal the fungal diversity for different symptom phenotypes, along with their qualitative and quantitative anthocyanins composition. The mycobiome profiling revealed a large fungal richness (260 taxa), and a beta diversity influenced by cultivar (p<0.01) and vintage (p=0.001). We observed significant differences in beta diversity between leaves affected by chlorotic spots and asymptomatic ones (p<0.05), revealing major shifts in fungal community composition during early stages of symptom progression. Comparing asymptomatic leaves and different symptom phenotypes, we detected cultivar and vintage-dependent alterations in alpha and beta diversity, as well as in individual taxa abundance (e.g. Botrytis caroliniana over-represented in red leaves). Total anthocyanins accumulation was influenced by cultivar (p≤0.0001) but not vintage. In Touriga Nacional, and to a lesser extent in Cabernet Sauvignon, purple leaves accumulated significantly lower amounts of tri-hydroxylated anthocyanins and acyl-derivatives, when compared to red leaves. Fungal communities significantly alter in composition during esca symptom progression, and for different symptom phenotypes, suggesting a strong correlation between microbial structure and the physiological and biochemical processes that occur in leaves.