First Report of Blue Mold on Postharvest Fig Fruit Caused by Penicillium sumatraense in Japan

In November 2024, postharvest fruits of common fig (F. carica cv. San Piero) harvested from an orchard at the Toyo Institute of Food Technology (34.81926°N, 135.40315°E), Japan, developed gray-green mold during storage at room temperature. The incidence of symptomatic fruits was approximately 40%. Initial symptoms appeared as small, water-soaked lesions on the fruit surface. Lesions rapidly became sunken, brown, and soft, and were covered with velvety mycelia within 3 days. To isolate the causal agent, small tissue pieces were excised from the margins of lesions on symptomatic fruits, surface sterilized in 70% ethanol for 30 s, rinsed three times with sterile water, placed onto potato dextrose agar (PDA), and incubated at 25°C for 3 days. Five single-spore isolates were obtained by repeated purification, and their cultural characteristics were examined on PDA, Czapek yeast extract agar (CYA), and malt extract agar (MEA), with all media incubated at 25 and 37°C. Colonies reached 26 to 29 mm in diameter on PDA, 35 to 40 mm on CYA, and 35 to 37 mm on MEA after 7 days at 25°C, whereas no growth was observed at 37°C. On MEA, colonies were gray-green with a white margin, a pale yellowish reverse, and a velvety texture. Exudate and soluble pigments were absent. Conidiophores were predominantly biverticillate, occasionally with an additional branch, having smooth-walled stipes (1.7 to 2.8 μm wide). Phialides were ampulliform, smooth, with dimensions of 6.4 to 8.2 × 1.4 to 2.7 μm. Conidia were spheroidal or subspheroidal, finely roughened, thin-walled, borne in chains, measuring 1.7 to 2.5 μm. Based on these morphological characteristics, the fungus was identified as Penicillium sumatraense (Houbraken et al. 2011). For molecular identification, genomic DNA was extracted from two representative isolates, SHK1200 and SHK1210. The internal transcribed spacer region (ITS), β-tubulin gene (BenA), and calmodulin gene (CaM) were amplified using primers ITS4/ITS5, Bt2a/Bt2b, and CF1/CF4 (Visagie et al. 2014). The nucleotide sequences of ITS, BenA, and CaM (LC940789–LC940794) showed 100% (MK910053.1), 100% (JX141030.1), and 99.48% (ON637884.1) identity to the sequences of P. sumatraense, respectively. A combined phylogenetic tree revealed that the isolates clustered with reference strains of P. sumatraense. Pathogenicity was assessed in three independent experiments using F. carica cv. San Piero fruits surface-sterilized with 70% ethanol. In each experiment, six wounded and six unwounded fruits were spray-inoculated with a conidial suspension (1.0 × 106 conidia/ml) or sterile water as a negative control. After 3 days of incubation at 25°C under 80 to 90% relative humidity, all wounded sites inoculated with the conidial suspension developed water-soaked lesions that rapidly expanded and were covered with gray-green velvety mycelia. No symptoms developed on unwounded fruits inoculated with the conidial suspension or on any of the water-inoculated fruits, suggesting P. sumatraense requires wounds to infect fig fruit. The reisolated fungi from the symptomatic fruits were confirmed as P. sumatraense by morphological and molecular analyses, fulfilling Koch’s postulates. P. sumatraense has been reported as the causal agent of blue mold on table grape (Mahdian and Zafari 2017), cauliflower mushroom (Liu et al. 2018), and apple (Smiri et al. 2021). To our knowledge, this is the first report of blue mold on postharvest fig fruit caused by P. sumatraense in Japan.