First Report of Fruit Rot Caused by Calonectria canadiana on Peach ( Prunus persica ) in Korea

Abstract

In August 2025, fruit rot symptoms were observed on peach (Prunus persica) in four open-field orchards located in Chuncheon (three orchards) and Wonju (one orchard), Gangwon Province, Korea. The disease occurred at a low incidence of approximately 1% in each orchard. Initial symptoms appeared as small lesions on the fruit surface, which expanded and developed into sunken rot accompanied by grayish-white mycelial growth. Symptoms were limited to fruit, and no symptoms were observed on leaves or branches. Four symptomatic fruits were collected (three from Chuncheon and one from Wonju). Small tissue pieces were excised from the margins of lesions, surface sterilized, and plated onto potato dextrose agar (PDA). After incubation at 25°C for 3 days, morphologically similar fungi were obtained by hyphal tip isolation, yielding four representative isolates (25-484, 25-488, 25-489, and 25-502). The representative isolates were deposited in the Korean Agricultural Culture Collection(KACC) under accession numbers KACC 411323, KACC 411324, KACC 411325, and KACC 411326. Colonies on PDA were initially white, dense, and cottony, becoming ivory to pale apricot with age and gradually turning brownish in the center. Conidia were hyaline, cylindrical with rounded ends, straight, and measured 41.8–47.7 × 3.2–4.7 μm (n = 30). Sphaeropedunculate vesicles were observed, and these morphological characteristics were consistent with the current circumscription of Calonectria canadiana (Liu et al. 2020). For molecular identification, five gene regions(act, tef1, tub2, his3, and cmdA) were amplified using previously published primers (Crous et al. 2004) and sequenced. All sequences generated from the four isolates(25-484, 25-488, 25-489 and 25-502) have been deposited in GenBank database on NCBI(GenBank accession numbers PX920276, PX920278, PX920279 and PX920280 for act; PX920281, PX920282, PX920283 and PX920285 for cmdA; PX920286, PX920287, PX920288 and PX920290 for his3; PX920291, PX920292, PX920293 and PX920295 for tef1, and PX920296, PX920297, PX920298, and PX920299 for tub2). Phylogenetic analysis based on concatenated sequences was performed using the maximum likelihood method with 1,000 bootstrap replicates implemented in RAxML (Stamatakis 2014). All four isolates clustered with reference strains of C. canadiana with high bootstrap support(≥95%). Recent taxonomic studies have recognized C. montana as a synonym of C. canadiana based on multilocus sequence comparisons and overlapping morphological characteristics (Liu et al. 2020); therefore, the isolates were identified as C. canadiana in this study. Pathogenicity tests were conducted on attached peach fruits (cv. Kawanakajima Hakuto) in the field. A conidial suspension of a representative isolate, adjusted to 1 x 105 spores/ml, was sprayed onto the surfaces of 10 fruits until runoff. Each fruit was considered a biological replicate. Inoculated fruits were maintained under natural field conditions. After 5-7 days, typical fruit rot symptoms identical to those observed in the field developed on inoculated fruits, whereas non-inoculated control fruits remained symptomless. The pathogen was consistently re-isolated from symptomatic tissues. C. canadiana has previously been reported on peach in China (Zhang et al. 2022); however, to our knowledge, this is the first report of fruit rot caused by C. canadiana on peach in Korea.