Susceptibility Screening of Winterberry Cultivars Against Latent Fruit Rot, and Identification of Metabolites Correlated with Rot-resistant Phenotypes

Abstract Winterberry [Ilex verticillata (L.) A. Gray] is a species of deciduous holly bearing colorful fruit, and is popularly used in landscape design and as specialty woody cuts for fall and winter seasonal decoration. Latent fruit rot of winterberry, caused by the fungus Diaporthe ilicicola, has recently afflicted nurseries in the Northeastern and Midwestern United States. Trials conducted in 2021 and 2022 screened eight commercially available winterberry cultivars for their susceptibility to the disease. Results showed that not all cultivars are equally susceptible, and that ‘Maryland Beauty’ and ‘Winter Red’ consistently had the lowest disease ratings. UHPLC-MS/MS metabolomic analysis was used to determine whether differences in susceptibility are reflected in the fruit metabolome. Principal components analysis of whole metabolome data showed a distinct separation of the less susceptible cultivars from the more susceptible cultivars, and univariate analysis comparing these two groups of cultivars at three phenological timepoints (corresponding with fruit set, fruit color change, and fruit maturation) found 89 features present at a significantly higher relative abundance in the less susceptible cultivars. Some compounds identified in less susceptible cultivars with reported antifungal bioactivity are derivatives of terpenes, cinnamic acids, and stilbenes. These results suggest that differences in susceptibility could be based on the presence of antifungal compounds within winterberry fruit. Future research to further identify unknown features and assess compound bioactivity against winterberry fruit rot pathogens should be done to inform both resistance breeding efforts and chemical or biological control programs. Species used in this study: Common winterberry [Ilex verticillata (L.) A. Gray]; Diaporthe ilicicola S. Lin, Taylor & Peduto Hand, 2018.