First Report of Postharvest Fruit Rot on Korla Fragrant Pear ( <i>Pyrus sinkiangensis</i> ) Caused by <i>Fusarium incarnatum</i> in China

Korla fragrant pear (Pyrus sinkiangensis) is one of the most valuable fruits in Xinjiang Province, China (Gao et al., 2005). In September 2024, brown lesions were observed in approximately 7% of Korla fragrant pears from a market in Aral City, Xinjiang. Initially, the lesions are light brown, gradually expanding to form depressions and necrotic areas where the tissue softens and rots. To isolate the causal agent, tissue samples were collected from the margins of nine symptomatic fruit lesions. These tissues were surface-disinfected with 75% ethanol and 1% sodium hypochlorite for 1 min and 30s, respectively. Pieces were then rinsed with sterile water and air-dried. The samples were inoculated onto potato dextrose agar (PDA) and incubated at 28°C for seven days. Colonies were round with aerial mycelium gradually changing from white to light yellow; the reverse side of the medium exhibited a light brown colouration. The macroconidia were sickle-shaped, possessing 3-7 distinct septa, and measured 38-55 × 4-5 μm; the microconidia measured 4.25-9.98 × 1.56-3.13 μm, exhibiting a pyriform to obovate shape with one or no septa, while the chlamydospores were either oval or pyriform in shape, measuring 7-9 × 2.5-3 μm. A representative strain (Fr 03-1) was selected, and DNA was extracted from the aerial mycelium after seven days of incubation. The ribosomal DNA internal transcribed spacer region (ITS) and the translation elongation factor-1α (TEF) gene were amplified using the primers ITS1/ITS4 and EF1-728/EF1-986R, respectively, and subsequently sequenced (White et al., 1990; Carbone & Kohn, 1999). The nucleotide sequences have been submitted to GenBank (PV416814 and PV423520). BLAST showed 99.61% identity of the ITS sequence and 99.56% identity of the TEF sequence with the strain Fusarium incarnatum NRRL 13379 (GQ505680 and GQ505591) originating from the FUSARIOID-ID database. Phylogenetic analyses were performed with Iqtree v.1.6.12 for maximum likelihood (ML). The results showed that the strain clustered with others of the same species. Consequently, based on both morphological and molecular characteristics, this fungus has been identified as F. incarnatum (Balamurugan et al., 2024). To evaluate its pathogenicity, F. incarnatum was inoculated onto wound sites of Korla fragrant pears, agar blocks as a control, repeated three times. After seven days of incubation at 28°C, the fruits inoculated with F. incarnatum displayed identical symptoms of rot, while the control fruits remained healthy. F. incarnatum was subsequently isolated from the infected fruits, and both morphological and molecular data confirmed the infection, thereby fulfilling Koch's postulates. Previous studies have indicated that F. incarnatum can act as either a saprophyte or a pathogen, causing black spot disease in Chinese jujube (Ziziphus jujuba) (Guo et al., 2016), walnut canker (Juglans regia) (B. Singh et al., 2011), and postharvest fruit rot in muskmelon (Cucumis melo) (Wonglom and Sunpapao, 2020). However, to our knowledge, this is the first report of F. incarnatum causing postharvest fruit rot in Korla fragrant pears in China. This study broadens the host range of F. incarnatum and contributes to the development of effective management strategies for postharvest fruit rot in Korla fragrant pears.