Etiology of Moldy Core, Core Browning, and Core Rot of Fuji Apple in China.
'Fuji' apple fruit were collected in Shaanxi Province, China, and 186 fungal isolates were obtained from the fruit core region. Fungi were isolated from fruit with symptomless core regions, as well as from the core regions of fruit showing browning, typical moldy core, or core rot. Based on phylogenetic and morphological analysis, all fungi were identified to species. Pathogenicity was determined by cutting apple fruit into halves and daubing spore suspensions containing 1 × 104 up to 1 × 108 spores/ml on the carpel in the core region. Pathogenicity varied significantly among genera, with Alternaria and Cladosporium spp. causing core browning at lower spore concentrations and moldy core at higher spore concentrations. Combinations of pathogens initiated more browning and moldy core than the pathogens applied alone. Epicoccum and Phoma spp. predominated in dry core rot, whereas primarily Trichothecium but also Fusarium and Penicillium spp. caused wet core rot. Core browning was introduced as a new type of core symptom, along with moldy core, dry core rot, and wet core rot. Alternaria alternata, A. tenuissima, A. arborescens, Cladosporium cladosporioides, and C. tenuissimum were the main pathogens causing core browning and moldy core.