Fusarium avenaceum causes core rot of apple (Malus × domestica Borkh.) in the North-Western Himalayan region of India

Abstract

Apple is widely cultivated in the North-Western Himalayan region of India. In 2023, wet core rot of apple fruit was recorded at moderate to high severity, leading to excessive pre-harvest fruit drop. The rot was detected in the core areas of the dropped fruit, which appeared healthy with no external signs of disease. Upon cutting the fruit, light brown or straw colour spongy lesions were observed. Following fungal isolation, pure culture of isolates TH8F2 and TH8F3 showed whitish mycelium, which later turned to a greyish rose colour. Pathogenicity assays with both isolates (TH8F2 and TH8F3) reproduced core rot symptoms similar to those observed in field-collected fruit after two-week incubation. Two types of conidia, i.e. macroconidia (30.15 × 3.9 μm) and microconidia (12.64 × 3.11 μm), were observed after 7 days of incubation. Molecular characterization was performed by amplifying two isolates using ITS, TEF1 alpha, and Beta tubulin genes. ITS, Tef1 alpha, and Beta tubulin gene sequences of TH8F2 and TH8F3 isolates showed 99–100% similarity to F. avenaceum. This study marks the first documented case of Fusarium avenaceum causing wet core rot of apples in India.