First Report of Postharvest Longan ( <i>Dimocarpus longan</i> Lour.) Fruit Rot Caused by <i>Aspergillus westerdijkiae</i> in China

Longan (Dimocarpus longan Lour.; Sapindaceae) is an economically important fruit crop (Xu et al. 2025). On 28 June 2025, 5 kg of longan were obtained from Qujing fruit market, China (25°07′ N, 103°29′ E). Within three days, 34% of the fruits developed rot symptoms, characterized by white granular spots on the peel, pulp softening and white flocculent growth. Tissue samples (5 × 5 mm) from the lesion margins of symptomatic fruits (n=5) were surface-sterilized by immersion in 75% ethanol for 3 min and 2% sodium hypochlorite for 3 min, rinsed five times with sterile distilled water, and then placed on potato dextrose agar (PDA) plates and incubated at 28°C in the dark. After two days, yellowish-brown aerial hyphae emerged from the inoculated tissues. Hyphal tips from five colonies were subcultured onto fresh PDA plates. Three days later, single hyphal tips were transferred again from the edges of these five new colonies onto separate fresh PDA plates. After a seven-day incubation, five morphologically identical colonies (JJL-1 to JJL-5) with concentric yellowish-brown mycelia covered the plates. JJL-1 was selected for further morphological and molecular study. Morphologically, the conidiophores were transparent, smooth, and slender, measuring 272.7-446.1 μm × 3.1-10.0 μm (n=50). The vesicles were spherical, measuring 50.5-76.6 μm × 50.5-78.1 μm (n=50). The conidia were spherical to subspherical, rough, and measured 0.8-2.7 μm × 1.0-2.8 μm (n=50). Based on morphological characteristics, the strain was consistent with the genus Aspergillus (Visagie et al. 2014). The internal transcribed spacer (ITS) and β-tubulin (TUB) gene regions were amplified using the primers ITS1/ITS4 and BT2a/BT2b (Glass and Donaldson 1995), respectively. The ITS (PX423620) and TUB (PX505057) sequences exhibited 99.82% and 100% nucleotide identity, respectively, to those of A. westerdijkiae ( PV984153.1 and FN185740.1). Phylogenetic analysis of the concatenated ITS and TUB sequences using maximum-likelihood and Bayesian methods in PhyloSuite placed isolate JJL-1 within the A. westerdijkiae clade, confirming its identity as Aspergillus westerdijkiae based on both molecular and morphological data. Pathogenicity was tested on twenty surface-disinfected longan fruits, each wounded at four symmetrical points. The fruits were divided into four groups (n=5) and treated as follows: inoculation with 100 μL of a JJL-1 conidial suspension (10⁶ spores/mL); sterile water as a control; a 5-mm mycelial plug from an active JJL-1 colony; or a plain PDA plug as a control. All fruits were incubated at 28°C. Within three days, white granular spots developed on fruits inoculated with either JJL-1 conidia or mycelial plugs, which softened significantly by day seven. Internal pulp rot with white flocculent material, matching original disease symptoms, was observed upon dissection. All control fruits remained healthy. The experiment was repeated five times with consistent results. Fungal isolates reisolated from the symptomatic tissues were confirmed to be morphologically and molecularly identical to JJL-1, thus fulfilling Koch's postulates. To our knowledge, this is the first report of A. westerdijkiae causing postharvest fruit rot on longan (Dimocarpus longan Lour.). This finding provides a scientific basis for managing the storage of postharvest longan fruits.