Chili pepper (Capsicum annuum) is an economically important crop that contains vitamins, minerals, flavonoids, carotenoids, and antioxidant properties (Zhong et al., 2021). In September 2025, a fruit rot disease was observed in greenhouse-grown chili peppers in Sacheon, Korea (E:35.1058, N:128.1300), with an incidence rate of approximately 15%. While early symptoms were nearly indistinguishable from Black rot (Alternaria spp.) or Anthracnose (Colletotrichum spp.), distinct symptomatic progression was noted in 4% of the affected fruits. These atypical lesions allowed for the differentiation of the causal agent from common pathogens during the advanced stages of infection. Fragments of the symptomatic tissue (n= 10) were surface sterilized with 70% ethanol for 30 sec, 1% sodium hypochlorite (NaOCl) for 30 sec, and then rinsed twice with sterile distilled water. The sterilized fragments were placed on water agar containing 100 µg/mL of streptomycin and incubated at 25°C for 2 days. Four hyphae representing the same type were selected from 10 isolated fragments. The tip of the hyphae was collected with a sterile tip and sub-cultured in 1/5 Potato Dextrose Agar (PDA) and incubated at 25°C for 7 days. Morphological identification revealed that the macroconidia (n = 30) were typically slender, straight to slightly curved, and were moderately to strongly septate (usually three to five septate). They exhibited a pointed apical cell and distinctly foot-shaped basal cells, with thin walls. For species identification of Fusarium spp., DNA was extracted using the cetyltrimethylammonium bromide buffer (CTAB) method (Wilson 2001). ITS, EF-1α, CAM, RPB2 were amplified by PCR using the specific primers (Wang et al., 2019). Recent studies have shown that robust species delimitation within the Fusarium incarnatum-equiseti species complex (FIESC) can be achieved using fewer but highly informative loci, particularly EF-1α and RPB2, often in combination with CAM. These sequences of PK showed 99.78% (446/447 bp) in ITS region (MK280807), 99.66% (590/592 bp) in EF-1α region (MK289601), 99.21% (628/633 bp) in CAM region (MK289698), and 99.52% (833/837 bp) in RPB2 region (MK289754) identity to the sequences of F. luffae strain LC12167. The PK sequences of the four genetic regions (ITS, EF-1α, CAM, RPB2) were also enrolled in NCBI (PX900841, PX909995, PX909996, PX909997). To test pathogenicity, F. luffae was cultured on 1/5 PDA medium at 25°C for 7 days. The conidial suspension (105 conidia/mL, 100 µL) was inoculated onto the surface of the sterilized peppers using a syringe. Three peppers served as a control (SDW), and three fruits were inoculated with the isolated strain as the treatment group. After inoculation, the pathogenicity was confirmed by incubation at 25°C for 19 days under 16 hr light conditions and 8 hr dark conditions. The pathogenicity assay was conducted with three independent biological replicates. Inoculated peppers developed fruit browning and internal decay, whereas no symptoms were observed in the control treatment. Although the disease progression differed slightly from field observations-likely due to the longer development period in the field compared to the shorter incubation. The fungus was reisolated from the infected peppers. No fungal growth was observed in the control. The reisolated fungus was morphologically identical to the original isolate, thereby fulfilling Koch’s postulates and confirming its pathogenicity. To our knowledge, this is the first report of chili pepper fruit rot caused by F. luffae in the Republic of Korea. This finding suggests the potential for F. luffae to potentially pose a threat to chili pepper production grown in South Korea, and an understanding of F. luffae may provide important information about pepper fruit rot management.
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