First Report of Aspergillus niger Causing Stem Rot of Dragon Fruit in China

Dragon fruit ( Hylocereus polyrhizus ) is an economically important horticultural crop in Guangxi Province, contributing approximately one-third of the country’s total dragon fruit production. In December 2025, stem rot symptoms were observed in a commercial dragon fruit orchard (~10 ha) located in Long’an County, Guangxi Province, China (23°07′07″N, 107°57′35″E), with an estimated disease incidence of 24%. Under artificial inoculation, stems initially developed circular to subcircular, light-brown lesions at the inoculation sites. As the disease progressed, lesions enlarged, developed dark-brown necrotic centers, and caused tissue depression, softening, and decay. Notably, lesions remained sharply demarcated from the surrounding healthy tissue (Tang et al. 2026). To identify the causal pathogen, six symptomatic stem samples were collected from two severely affected orchards. Diseased tissues were surface-sterilized by immersion in 75% (v/v) ethanol for 30 s, rinsed three times with sterile distilled water, treated with 1% (v/v) sodium hypochlorite (NaClO) for 2 min, rinsed again three times with sterile distilled water, and air-dried under aseptic conditions. Small tissue pieces (5×5 mm) excised from the lesion margins were placed on potato dextrose agar (PDA) and incubated at 28 ℃ for 5–7 days (Yang et al. 2024). A total of 14 fungal isolates were recovered. Among these, isolate Rong 6 was consistently obtained from symptomatic tissues across all samples. Colonies of this isolate were initially white and gradually darkened to dark brown or black upon conidiation. Colony surfaces appeared velvety to powdery, with well-defined, regular margins; the reverse side ranged from pale yellow to dark brown. Black, spherical sclerotia formed during later stages of colony development (Bustamante et al. 2024). For molecular identification, the internal transcribed spacer (ITS) region and the β-tubulin ( TUB ) gene were amplified using primer pairs ITS1/ITS4 and Bt2a/Bt2b, respectively. BLASTn analysis revealed that the ITS (accession no. PZ516039) and TUB sequence (accession no. SUB16247651) of isolate Rong 6 exhibited 92% nucleotide identity with Aspergillus niger strain CBS 121.28 (Hess and Stocks 1969). Pathogenicity was assessed by inoculating wounded, healthy dragon fruit stems with 5-mm-diameter mycelial plugs excised from 5–7-day-old cultures grown on PDA. Sterile PDA plugs of equivalent age served as a negative control and were inoculated onto wounded stems in parallel. All plants were incubated in a greenhouse maintained at 28 ℃ (Huaman-Pilco et al. 2024). Typical stem rot symptoms, including water-soaking, necrosis, and tissue collapse, developed on inoculated stems within 10–14 days; no symptoms were observed on control plants. The pathogenicity assay was conducted in triplicate, with consistent results across all replicates (Carrillo-Fasio et al. 2022). To our knowledge, this is the first report of Aspergillus niger causing stem rot of dragon fruit in China. Given the high susceptibility of dragon fruit to this pathogen and its widespread occurrence in major production regions, particularly Guangxi Province, the disease poses a potential threat to yield stability and fruit quality. These findings provide a foundation basis for future research into disease epidemiology, host–pathogen interactions, and the development of integrated management strategies for dragon fruit stem rot.