First Report of <i>Fusarium citri</i> Infecting Chayote ( <i>Sechium edule</i> ) Postharvest in Indonesia

Chayote (Sechium edule) is one of the important vegetable commodities in Indonesia with a total production volume of 453,263 tonnes in 2023 (Badan Pusat Statistik 2024). Tropical postharvest vegetables and fruits are often challenged by pathogen infections such as Fusarium spp. (Zakaria 2023). In July 2025, a postharvest fungal infection with a 7% incidence was recorded among 58 chayote fruits in Tangerang Selatan, Banten Province, Indonesia. Fungal hyphae were observed growing on almost the entire fruit surface (Figure 1). The fungus was cultured on potato dextrose agar, yielding a pure culture from a single-spore colony designated isolate LS725, which appeared white on the obverse and yellowish on the reverse (Figure 2). Microscopic examination of lactophenol blue-stained samples showed septate hyphae, sporodochial conidiophores and monophialides (Figure 3a–d). Macroconidia were abundant, typically straight to slightly curved, with two to five septa measuring 17–32 × 2–4 µm (Figure 3h). Microconidia were moderately present, exhibiting an oval to slightly curved shape with zero to one septum, measuring 4–12 × 1.5–3 µm (Figure 3g). Chlamydospores were rarely observed, globose to obovoid in shape, and measured 8–12 µm in diameter (Figure 3e,f). DNA was extracted from isolate LS725 and three DNA regions, the internal transcribed spacer (ITS), elongation factor 1-alpha (EF1-α) and RNA polymerase II—second largest subunit (RPB2), were used as a molecular barcode to identify the isolate (White et al. 1990; O'Donnell et al. 1998; Parihar et al. 2025). The sequences of these regions were deposited in GenBank with Accession Nos. PX362657 (ITS), PX372838 (EF1-α) and PX372837 (RPB2). A nucleotide homology search using BLAST revealed 99.79%, 97.09% and 99.68% identity with Fusarium citri for ITS, EF1-α and RPB2, respectively. The phylogenetic tree constructed from concatenated ITS, EF1-α and RPB2 gene sequences, using the Maximum-Likelihood method, placed isolate LS725 within the F. citri clade (Figure 4), supporting the BLAST result. The pathogenicity of isolate LS725 was evaluated on 10 chayote fruits. All fruits were surface disinfected with 1% NaOCl for 5 min before spraying with 5 mL of a 1 × 106 spore suspension, while 10 control fruits received sterile distilled water. After 7 days’ incubation at 25°C, all inoculated fruits exhibited mycelial growth and rot symptoms, whereas controls remained symptomless (Figure 5), thereby fulfilling Koch's postulates. F. citri has been reported as the causal pathogen of postharvest chayote disease in Mexico (Montecinos-Pedro et al. 2023). This is the first report of F. citri infecting postharvest chayote in Indonesia.