Fungal community dynamics and anthocyanin profiling of grapevine leaves in a vineyard affected by esca

Leaves in grapevines affected by esca, a grapevine trunk disease, may occasionally manifest a symptom known as the ‘esca leaf stripe symptom.’ Most frequently, this symptom appears as scorching in the interveinal tissue, with red pigmentation observed between scorched and healthy tissue. However, purple pigmentation or an absence of pigmentation is occasionally reported. The synthesis and accumulation of anthocyanins may drive these different symptom phenotypes. Recent evidence also implicates fungal endophytes in host manipulation, potentially influencing grapevine metabolic profiles, including anthocyanins. In this study, working on cultivars Cabernet Sauvignon and Touriga Nacional, we used DNA metabarcoding (i) to explore the microbial dynamics of endophytes during symptom 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 endophytic 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 esca 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 anthocyanin accumulation was influenced by cultivar (P ≤ 0.0001) but not by vintage. In Touriga Nacional, and to a lesser extent in Cabernet Sauvignon, purple leaves accumulated significantly lower amounts of trihydroxylated 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.