First Report of <i>Fusarium falciforme</i> Causing Fruit Rot in Pumpkins (<i>Cucurbita moschata</i> var. <i>sergipana</i>) in the State of Rio Grande do Norte in Brazil

Pumpkins (Cucurbita spp.) are cultivated worldwide, with a global annual production of 27 million tons (FAO, 2024). In 2024, during the rainy season (January to March), pumpkin growers from northeastern Brazil reported fruits showing small, dry, and irregular lesions with a white and rotten appearance on the fruit's peel, which gradually expanded throughout the fruit. The disease affected 30% of the fruits produced, making them unsuitable for commercialization. Symptomatic fruits were collected from five producing areas in Rio Grande do Norte state in Brazil (municipalities of Baraúna, Mossoró, and Martins). Small fragments from the edges of the lesions on the fruits were collected, superficially disinfested (30 sec in ethanol 70%, 60 sec in NaClO 2.5%, and rinsed in distilled water), placed on Petri dishes containing PDA, and incubated at 28 ± 2 °C for five days. Eight isolates were monosporic cultured and morphologically characterized on PDA, Spezieller Nährstoffarmer agar, and carnation leaf agar (Leslie & Summerell, 2006). Fungal colonies exhibited mycelium white to beige in color and circular in shape. The microconidia were hyaline, oval, or reniform-shaped, with 0-1 septum and an average size of 20.1 × 5.4 μm (n = 50), typically formed in false head-like structures on short conidiophores. The macroconidia were falcate, with a hooked apical cell shape, 3-4 septa, and an average size of 41.9 × 5.5 μm (n = 50). The chlamydospores were round to oval, intercalary, hyaline, single, or in chains. The translation elongation factor 1-alpha (EF-1α) and the second largest subunit of RNA polymerase II (RPB2) genes were partially PCR amplified from all isolates and Sanger sequenced. The sequences were deposited in GenBank (Accession Numbers; EF-1α: PQ869285 - PQ869292 and RPB2: PQ869293 - PQ869300). A phylogenetic tree was constructed in MEGA software (version 11.0.10) (Tamura et al., 2021) using the partial concatenated gene sequences. Maximum likelihood analysis revealed that the isolates are closely related to Fusarium falciforme (98 bootstrap). For the pathogenicity test, healthy pumpkins (C. moschata var. sergipana) were superficially disinfested (as described above) and wounded using a sterilized punch (5 mm) to a depth of 2 mm. Plugs from seven-day-old colonies were placed (mycelium side facing down) at each wound site, and the fruits were stored at room temperature (25°C) in a humid chamber, pumpkins with PDA plugs served as mock. Six replicates (fruits) per isolate were analyzed, with three wounds per fruit. The pathogenicity test was repeated. At 30 days after inoculation, the inoculated fruits exhibited white lesions with a brownish necrotic halo, similar to the symptoms observed in the field. No symptoms were observed in the mock. The fungi were re-isolated from the inoculated fruits to fulfill Koch's postulates and confirmed as F. falciforme through the same methods as before. Sritongkam et al. (2022) reported F. falciforme causing stem and fruit rot in pumpkins in Taiwan. This species has also been associated with rot in melon and watermelon in Brazil (Araújo et al., 2021; Nascimento et al., 2024). To the best of our knowledge, this is the first report of F. falciforme causing pumpkin rot in the state of Rio Grande do Norte in Brazil. This study paves the way for developing and implementing strategic approaches to managing this disease in Brazil.