Fungal Communities Within Pitaya Fruit Peel Shift During Ripening and Early Canker Onset

Canker is a major fungal disease that causes substantial yield losses in pitaya (Selenicereus monacanthus (Lemaire) D.R.Hunt, syn. Hylocereus polyrhizus (F.A.C. Weber) Britton and Rose; red-fleshed pitaya). However, how fruit ripening and pathogenesis interactively shape fungal communities in fruit peels remains unclear. Here, we investigated the diversity, assembly mechanisms, co-occurrence networks, and functional guilds of fungal communities in healthy and diseased fruit peels at immature (green) and mature (red) stages of 'Jindu No. 1' pitaya using ITS1 amplicon sequencing. Our results revealed that fruit maturity exerted stronger effects on fungal community structure than disease status, with ripening reducing diversity and increasing dominance. Notably, disease-induced stage-dependent responses: immature communities shifted from stochastic to deterministic assembly under pathogen selection, whereas mature communities maintained stochastic processes despite infection. Co-occurrence network analysis revealed that healthy mature peels formed highly complex, cooperative networks with dense positive interactions, while healthy immature peels exhibited fragmented, modular structures vulnerable to invasion. Diseased immature peels displayed intermediate network topology, and diseased mature peels showed disrupted connectivity. Functionally, healthy fruits maintained balanced pathotroph-saprotroph-symbiotroph guilds, whereas diseased fruits exhibited higher relative abundance of pathotrophs and saprotrophs, reflecting a shift from symbiotic nutrient cycling toward necrotrophic pathogenicity and decomposition. These findings challenge the single-pathogen paradigm by revealing canker as an ecological process involving community-wide restructuring. They provide a theoretical basis for stage-specific microbiome-targeted disease management in tropical fruits, emphasizing the preservation of stochastic assembly and cooperative network structures to enhance disease resistance.