First report of Penicillium georgiense as a fungal pathogen of onion (Allium cepa L.)

Previously, we identified Aspergillus awamori, Fusarium oxysporum, Penicillium brasilianum, and Rhizopus oryzae as the predominant fungal species in onion bulbs in Korea. In that study, we also observed other minor Penicillium spp., among which a specific species was often isolated from yellowish sunken lesions of the bulbs and usually appeared with A. awamori. Hence, in this study, we identified this unknown Penicillium sp. GR-68 by molecular and morphological characteristics and tested its pathogenicity against onion bulbs. As a result, isolate GR-68 was identified as Penicillium georgiense by phylogenetic analyses using neighbor-joining and maximum-likelihood methods with internal transcribed spacer (ITS) and β-tubulin region sequences. When the micro- and macro-morphological characteristics of isolate GR-68 were compared with those of the reference isolate NRRL 35509T of P. georgiense, isolate GR-68 was similar to the reference isolate. In the pathogenicity tests, isolates GR-68 and NRRL 35509T were found to be pathogenic to onion bulbs, where hole-inoculated bulbs showed symptoms of weak yellow halos or yellowish sunken lesions. In addition, the fungal isolates were re-isolated from the symptomatic lesions on the inoculated bulbs and re-confirmed as P. georgiense by the ITS and β-tubulin region sequence analyses. To the best of our knowledge, this is the first report of P. georgiense as a fungal pathogen of onion bulbs.