First report of blue-green mold caused by Penicillium crustosum on lulo fruit ( Solanum quitoense Lamarck) in Mexico

Lulo (Solanum quitoense Lam. var. septentrionale), is a perennial, spiny plant reaching up to 3 m tall. Leaves are alternate, pubescent, measuring up to 60 × 45 cm, with purple veins. Inflorescences are short-peduncled lateral cymes bearing few flowers. Their fruit also known as naranjilla, is a highly valued, and widely cultivated in Colombia and Peru, commonly used to prepare juices and desserts. In Mexico, it is considered a promising crop with a growing area of production (Olguín-Hernández et al. 2023). On June, 17th, 2025, moldy lulo fruits were observed in an orchard in the municipality of Huatusco, Veracruz, Mexico (19.134722 N -96.951389 W, altitude 1344 m) with 30% of incidence. Initial symptoms on fruits collected in the field and postharvest consisted of small, circular, water-soaked lesions around the pedicel scar. Lesions rapidly enlarged, became soft and sunken, and eventually developed abundant blue-green sporulation after 8 days at room temperature (23 ± 2°C). The sporulated material was taken from symptomatic fruit and cultured on potato dextrose agar (PDA). The isolates obtained were purified before growing on different media by the single conidial isolation: PDA, malt extract agar (MEA) and yeast extract sucrose agar (YES) (Pitt and Hocking 2009). Colonies growing on PDA and MEA exhibited a blue-green sporulation; on YES colonies produced exudates. After 14 days of incubation, colony diameters were in average 23.62 ± 4.98 mm on PDA, 28.36 ± 5.25 mm and 37.40 ± 10.33 mm on MEA and YES, respectively. On PDA and MEA, colonies exhibited similar morphology, characterized by abundant conidial masses, a dry powdery texture, an opaque blue-green surface, and a yellowish-brown coloration on the reverse side of the colony. On YES the colony had a white-beige appearance, slightly wrinkled, sulcate, superficial mycelium and yellow exudates, yellowish-brown on plate reverse view. Conidiophores were terverticillate and conidia were spherical to subglobose, on PDA conidia measured 2.75–4.25 µm in diameter (mean = 3.18 µm, n = 50). The morphometric data were consistent with those described for Penicillium crustosum (Frisvad and Samson 2004; Pitt and Hocking 2009). Molecular identification was performed in Lulo25 isolate using the primers ITS1-ITS4 (White et al., 1990), and RPB2-5F2/fRPB2-7cR (Liu et al. 1999), to amplify the internal transcribed spacer (ITS) and RNA polymerase II subunit II (RPB2) regions. The ITS and RPB2 resulting consensus gene sequences were deposited in GenBank with acc. nos. PZ321505, and PZ337120, respectively. BLASTn analysis showed that the ITS and RPB2 sequences shared 98.12% and 100% identity, respectively, with Penicillium crustosum strain CMW:61304 (acc. PP356479) in NCBI GenBank database. Maximum Likelihood analysis of concatenated ITS and RPB2 sequences placed the lulo isolate within the Penicillium crustosum group. Forty fruits were washed with tap water to remove surface trichomes and debris, and disinfested with 70% ethanol for 30 s followed by 1.5% sodium hypochlorite for 2 min; 20 fruits were inoculated and 20 were used as controls. Secondly, a conidial suspension in water of 50 µL (1×106 conidia/mL) was inoculated without wounding on the scar of the pedicel-fruit junction of healthy and sanitized fruit, then fruits were placed in a wet chamber (23 ± 2°C, RH >90%) and observed daily for 8 days. The signs of disease, identical to those of the initial isolates, appeared on day 3 and were evaluated on day 8, then all inoculated fruits developed symptoms. The fungus reisolated from symptomatic inoculated fruit and its morphological characteristics were identical to those of the original isolate, thereby fulfilling Koch’s postulates. This species is well-known as a postharvest pathogen in apple, nectarine, and sugar beet (Vico et al. 2014; Duduk et al. 2021; Bhuiyan et al. 2025). To our knowledge, this is the first report of P. crustosum causing blue-green mold and fruit rot on lulo in Mexico, and it has not been previously documented. This finding indicates that P. crustosum may represent a potential postharvest threat to lulo fruit during storage.