First Report of <i>Cladosporium tenuissimum</i> Causing Postharvest Sooty Spot of Fig Fruit in Japan

Fig (Ficus carica L.) has been widely cultivated in temperate and subtropical regions for its nutritional and medicinal value. From October to December 2024 and June to August 2025, sooty spot disease (incidence 85%) was observed two days postharvest in fig fruits in a storage room (25°C, 80% relative humidity) at the experimental orchard of the Toyo Institute of Food Technology (34.81926°N, 135.40315°E) in Hyogo prefecture, Japan. The disease (incidence >80%) was also found in figs collected from 31 markets in major fig-producing prefectures. The symptoms appeared as necrotic lesions covered with dark-green mycelia. Tissue segments of symptomatic fruits were surface-sterilized with 70% ethanol, followed by three rinses with sterile water, and placed on potato dextrose agar (PDA). After three days of incubation at 25°C, 16 isolates were obtained from independent symptomatic fruits by hyphal-tip isolation. Each isolate colony was grayish-green to dark-green, exhibited a velvety texture with a white margin, and grew at an average rate of 2.85 mm daily at 25°C on PDA. Microscopic observations revealed that the conidiophores were solitary, erect, hyaline to light brown, straight or slightly flexuous, and septate. Ramoconidia were light brown, cylindrical to obovoid, aseptate, and 8.55 to 20.28 × 2.48 to 4.77 µm (12.01 × 3.25 µm, n = 50). Conidia were light brown, catenate in branched chains, 1 to 4 conidia in the unbranched part, obovoid to limoniform, aseptate, and 3.32 to 5.45 × 2.28 to 3.19 µm (4.36 × 2.77 µm, n = 50). The morphological characteristics corresponded to those of Cladosporium tenuissimum (Bensch et al. 2015). Three representative isolates, SHK1100 (from cv. Brunswick), SHK1110 (from cv. San Piero), and SHK1120 (from cv. Malta), were selected for molecular identification and deposited at the Research Center of Genetic Resources, National Agriculture and Food Research Organization, with accession numbers MAFF248114–MAFF248116. The internal transcribed spacer of rDNA (ITS), translation elongation factor-1α (TEF1), and actin (ACT) were amplified using the primer sets ITS4/ITS5 (White 1990), EF1-728F/EF1-986R, and ACT-512F/ACT-783R (Carbone and Kohn 1999), respectively. The nucleotide sequences of ITS (LC880265–LC880267), TEF1 (LC880268–LC880270), and ACT (LC880271–LC880273) showed 100% (NR_119855), 97.98% (KU605782), and 100% (OQ185030) identity to the sequences of C. tenuissimum in the NCBI, respectively. Phylogenetic analysis showed that the isolates could be grouped into the same clade as other C. tenuissimum strains. To assess pathogenicity, unwounded and wounded fruits were sprayed with a conidial suspension (1 × 106 conidia/ml) or sterile water. The inoculated fruits were kept in a moist chamber (25°C, 80% relative humidity) for two days. All wounded fruits inoculated with fungal conidia exhibited necrotic symptoms identical to those observed in diseased postharvest fruits. No symptoms were observed in the unwounded fruits inoculated with fungal conidia or in the wounded fruits treated with the sterile water. C. tenuissimum was reisolated from the diseased fruits based on morphological and molecular identifications, fulfilling Koch’s postulates. Fruit diseases caused by C. tenuissimum have been reported on peach (Nativitas-Lima et al. 2023), melon (Gomes et al. 2023), and dekopon citrus (Xiao et al. 2023). To the best of my knowledge, this is the first report of C. tenuissimum causing sooty spot of F. carica fruit in Japan.