First Report of Penicillium expansum (Link) Thom. Causing Postharvest Fruit Rot of Kiwifruit in Northern Greece

Actinidia deliciosa, the dominant kiwifruit species, is an important crop in northern Greece. In 2016, the total kiwifruit production was 182,589 metric tons, and the total harvested area was 7,710 ha (FAOSTAT 2018). In March 2017, a survey was conducted to evaluate the postharvest losses of cold-stored kiwifruits in Chrysoupoli, Prefecture of Kavala, Greece. Most of the diseased fruit had obvious signs of injury. Diseased fruits showed soft, watery, pale yellow to light brown lesions on the surface with masses of blue-green sporulation. Fungal isolations were performed on potato dextrose agar. The plates were incubated at 23°C for 7 days, and colonies rapidly grew that were velvety to powdery and were green on the surface. Microscopic morphology showed septate and hyaline hyphae. Conidiophores were simple or branched, and phialides were grouped in brush-like clusters at the ends of the conidiophores. Conidia were unicellular, round to ovoid, hyaline or pigmented, rough walled or smooth, in chains with average size 2.90 to 3.85 μm. Based on morphological characteristics the pathogen was identified as Penicillium expansum (Kong 2007). Species identification was confirmed by isolating genomic DNA from five isolates followed by amplification of both their partial ribosomal internal transcribed spacer regions and β-tubulin loci according to the methods of White et al. (1990) and Sholberg et al. (2005), respectively. The corresponding nucleotide sequences were deposited in GenBank (accession nos. MH010968 to MH010972 and MH040781 to MH040785), and BLASTn analysis revealed a 100% identity with P. expansum (GenBank MG770360 and LT898269, respectively). Koch’s postulates were completed in the laboratory by inoculating mature kiwi fruits (cultivar Hayward). Kiwi fruits were surface sterilized by dipping in 0.1% chlorine solution for 10 min, allowed to dry in a laminar flow hood, and wounded with a flamed knife of 6 mm in diameter; a 6-mm-diameter mycelial disk of fungus was placed over each wound. There were 10 inoculated and 10 control fruits (similarly wounded and inoculated with an agar disk without mycelium) in a randomized design and incubated at room temperatures (20 to 23°C) for 7 days. Koch’s postulates were satisfied after reisolating the fungus from inoculated fruit that developed symptoms similar to those observed on fruit collected from cold storage. To our knowledge, this is the first report of the occurrence of P. expansum causing postharvest fruit rot of kiwifruit in Greece. Previously, P. expansum has been reported causing postharvest kiwifruit rot in China (Wang et al. 2015) and South Korea (Hur et al. 2005). The percentage of diseased fruits was about 12% of the rotted fruits, reflecting the economic importance of P. expansum for the kiwifruit industry.