P-001 - Fungal Population Dynamics in Cranberry Fruit Rot: A Stage-Specific Analysis from Bloom to Harvest Maturity from Massachusetts

Abstract Text: Cranberry fruit rot (CFR) remains a major challenge, reducing fruit quality and yield. Coleophoma empetri, Allantophomopsis cytisporea, Colletotrichum spp., Botryosphaeria vaccinii and Physalospora vaccinii are consistently isolated from rotten fruit in Massachusetts. Infections are hypothesized to begin at bloom, guiding fungicide applications from bloom to early fruit set. Understanding CFR fungal dynamics across bloom, pinhead, blush, and harvest maturity will improve management strategies. To investigate this, we sampled ‘Stevens’ and ‘Mullica Queens’ from three fields each in 2023 and 2024 seasons. CFR incidence was significantly higher in 2024 than in 2023; and increased from blush to harvest in both years. While no significant cultivar differences were observed, cultivar-stage interactions were significant in 2024. Early-season was dominated by Alternaria spp. (27%), Epicoccum spp. (22%), and Cladosporium spp. (13%), while Colletotrichum spp. (35%), C. empetri (21%), and P. vaccinii (9%) became predominant at later stages. Network co-occurrence analysis revealed strong correlations (ρ > 0.6) between early-season and late-season fungi, suggesting early microbial interactions may predispose fruit to rot. Pathogen abundance varied between seasons, indicating environmental influences. Phyllosticta vaccinii and Botryosphaeria were found in similar abundance in healthy and rotten fruit, suggesting a limited role in causing rot. These findings raise critical questions about CFR disease dynamics, infection timing, fungal roles as infection progresses and fungicide efficacy.