First Report of <i>Fusarium luffae</i> Causing Postharvest Fruit Rot of Eggplant ( <i>Solanum melongena</i> ) in China

Eggplant (Solanum melongena L.) is an economically important solanaceous vegetable. In October 2024, an agricultural product quality and safety survey was conducted at a local market in Fengxian District, Shanghai, China. Soft rot symptoms were observed on eggplant fruits at four stalls, with an average incidence of approximately 8%. Infected fruits exhibited water-soaked lesions, and white fungal hyphae were observed on the lesion surfaces in some instances. To isolate and identify the pathogen, five representative diseased eggplants from the four affected stalls were collected from the market. Infected tissues (5 × 5 mm) were excised from the margins of necrotic lesions, surface-sterilized, and plated on potato dextrose agar (PDA) following the method described by Wang et al. (2022). After incubation at 25 °C for 3 days, fungal hyphae emerging from the tissues were transferred to fresh PDA plates to obtain pure cultures. Pure cultures of five isolates with consistent morphological characteristics were obtained for subsequent analysis. On PDA, these isolates formed dense white aerial mycelia and produced falcate conidia indicating morphological characteristics of Fusarium spp. A pink pigment was observed on the reverse side of the PDA plates. On carnation leaf agar, the isolates produced slightly curved macroconidia with 3–5 septa, featuring a tapered apical cell and a foot-shaped basal cell. The macroconidia measured 28.46 ± 5.58 μm × 2.9 ± 0.5 μm (n = 100), with morphological characteristics consistent with the members of Fusarium incarnatum-equiseti complex (Wang et al. 2019). Nucleotide sequences of the RNA polymerase second largest subunit (RPB2) and translation elongation factor-1 alpha (TEF) genes were amplified from three representative isolates (QZ-1, QZ-3, QZ-5) using primer pairs 5f2/7cr and EF1/EF2 (O’Donnell et al. 2022), respectively. The amplified fragments were bidirectionally sequenced and deposited in GenBank under accession numbers PX733149 to PX733151 (RPB2) and PX733152 to PX733154 (TEF). BLAST analysis against the Fusarioid-ID reference database (https://www.fusarium.org/) showed 100% similarity with TEF (accession nos. PQ823246, PQ823252, etc.) and RPB2 (accession nos. GQ505790, PQ822955, etc.) of Fusarium luffae. Collectively, these isolates were identified as F. luffae. To fulfill Koch's postulates, the pathogenicity of two representative isolates (QZ-1 and QZ-3) was evaluated using healthy eggplant fruits (cultivar Heibao). Ten fruits were used per isolate: each fruit was surface sterilized with 75% ethanol, and an 8-mm-diameter mycelia plug (excised from the margin of 3-day-old cultures of isolates QZ-1 or QZ-3) was placed on its sepal. Inoculated fruits were maintained at 25 ± 0.5 °C and 70% relative humidity in a climate chamber. Twenty fruits inoculated with blank PDA plugs served as controls. After 10 days, all inoculated fruits developed fruit stem rot symptoms identical to those originally observed in the market, while no symptoms occurred on the controls. Pathogenicity assay was repeated three times. The pathogen was reisolated from symptomatic tissues and confirmed as F. luffae based on morphological and molecular characterization. F. luffae has previously been reported as the causal agent of fruit rot on muskmelon and cherry tomato in China (Sun et al. 2024; Zhang et al. 2022), this is the first report of F. luffae causing postharvest rot of eggplant in the country.