First Report of Postharvest Fruit Rot of Yellow Dragon Fruit ( Selenicereus megalanthus ) Caused by Fusarium sulawesiense in China

Yellow dragon fruit (Selenicereus megalanthus) is a high-value tropical cactus fruit crop. In September 2025, postharvest fruit rot was observed on yellow dragon fruits at a fruit market in Kunming, Yunnan Province, China (102.76°E, 25.03°N), where approximately 38 % (38/100) of inspected fruits were symptomatic. Initial symptoms appeared as small, light brown spots on the fruit surface. The lesions rapidly enlarged, and the affected tissues subsequently softened and rotted. Tissue fragments (5 × 5 mm) were excised from lesion margins of symptomatic fruits, surface-sterilized sequentially in 75 % ethanol for 30 s and 1 % sodium hypochlorite for 1 min. Pieces were then rinsed with sterile water and air-dried. The colonies were inoculated onto potato dextrose agar (PDA) and incubated at 25 °C in the dark for 7 days. Representative isolate YWG was selected for further morphological and molecular characterization. On PDA, colonies were initially white and cottony, later becoming yellowish brown, with a yellowish-brown reverse. Macroconidia were falcate to slightly curved, mostly 3 to 4-septate, 13.4 to 37.2 × 3.2 to 6.6 μm (mean = 25.3 × 4.4 μm), with curved apical cells and foot-shaped basal cells. Microconidia were not observed. Based on these morphological and cultural characteristics, isolate YWG was preliminarily identified as Fusarium sp. For molecular identification, partial sequences of the translation elongation factor 1-alpha gene (TEF1) were amplified using primer pair EF1/EF2, and RNA polymerase II second largest subunit gene (RPB2) sequences were amplified in two overlapping fragments using primer pairs 5f2/7cr and 7cf/11ar (O’Donnell et al. 1998; O’Donnell et al. 2022). The TEF1 and RPB2 sequences of isolate YWG were deposited in GenBank under accession numbers PZ527890 and PZ527891, respectively. BLASTn searches against the FUSARIOID-ID database using TEF1 and RPB2 sequences revealed that isolate YWG shared 100% sequence similarity with reference strains of Fusarium sulawesiense (e.g., CBS 122439, CBS 163.57). Phylogenetic analysis based on concatenated TEF1 and RPB2 sequences was conducted in MEGA 11 using the NJ method with 1,000 bootstrap replications (Tamura et al. 2021). Isolate YWG clustered with F. sulawesiense reference strains, with 97 % bootstrap support, supporting its identification as F. sulawesiense. To confirm pathogenicity, surface disinfested fruits were wounded and inoculated with mycelial plugs or injected with 10 μL of 1×10⁶ conidia/mL suspension, with sterile PDA plugs and sterile water as respective controls (five fruits per treatment). Inoculated fruits were incubated in plastic containers at 25 °C under high relative humidity and a 12 h light/12 h dark photoperiod. After 7 days, typical rot lesions developed on inoculated fruits, while controls remained asymptomatic. The reisolated fungus was verified as F. sulawesiense via morphological and phylogenetic analyses, fulfilling Koch’s postulates. The assay was independently repeated three times with consistent results. F. sulawesiense has been reported to cause fruit rot on muskmelon and chili in China (Liu et al. 2023; Wang et al. 2023). To our knowledge, this is the first report of F. sulawesiense causing postharvest fruit rot of yellow dragon fruit in China. This finding provides important information for the diagnosis and management of postharvest fruit rot of yellow dragon fruit.