First report of gray mold on Allium victorialis var. platyphyllum caused by Botrytis cinerea in Korea

Allium victorialis var. platyphyllum (Hultén) Makino (alpine leek, Liliaceae) is an edible perennial herb in East Asia and is used as a leafy vegetable (Woo and Lee 2013). In April 2016, symptoms resembling gray mold on alpine leek leaves were found in an experimental plot of Highland Agriculture Research Institute (37°40ʹ52ʺ N; 128°43ʹ50ʺ E), Pyeongchang, Korea, with approximately 2 to 5% disease incidence (percentage of leaves infected). Water-soaked, brown or gray spots, with abundant mycelium and conidia appeared on the affected leaves. Severely infected leaves were distorted and died. Diseased tissue was excised, surface-sterilized in 0.1% sodium hypochlorite for 1 min, rinsed with sterile water, placed on potato dextrose agar (PDA, Difco), and incubated at 20 ± 2°C with a 12-h photoperiod. After 3 weeks incubation, the fungus formed black, irregularly shaped sclerotia ranging from 1.2 to 4.6 × 1.1 to 3.1 mm (n = 20). Conidia (n = 50) were ellipsoidal or ovoid, 5.5 to 9.3 × 5.3 to 8.2 µm on naturally infected leaves and 5.6 to 10.2 × 5.1 to 7.3 µm on PDA. A representative isolate was deposited in the Korean Agricultural Culture Collection (KACC48119) and used for further studies. Morphological characteristics of the isolate were consistent with those of Botrytis cinerea Pers. (Ellis 1971). The internal transcribed spacer (ITS) region of rDNA of the isolate was amplified with primers ITS1/ITS4 and sequenced. BLAST analysis of the resulting 567 bp nucleotide ITS segment (GenBank KX443701) showed 100% identity with the GenBank KM016533 sequence of Botryotinia fuckeliana (perfect stage of B. cinerea). Additionally, glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60), and DNA-dependent RNA polymerase subunit II (RPB2) were sequenced (Staats et al. 2005). The G3PDH, HSP60, and RPB2 sequences (KX443702, KX443703, and KX443704) had 100, 99, and 100% identity with reference sequences of GenBank KM016535, KM016534, and KU760986, respectively. To determine pathogenicity, a conidial suspension (1 × 10⁵ conidia/ml) was collected from 2-week-old cultures on PDA and sprayed on three pot-grown, 1-year-old A. victorialis var. platyphyllum plants until run-off. Another three plants, serving as controls, were sprayed with sterile water. All the plants were incubated for 48 h in a growth chamber (20°C, 90 ± 10% RH). After 5 days, water-soaked lesions with conidia developed on inoculated leaves, whereas control plants remained symptomless. The pathogen was reisolated from symptomatic leaves, fulfilling Koch’s postulates. The pathogenicity test was repeated twice with similar results. Gray mold caused by B. cinerea has been reported on several species of Allium worldwide, but not on A. victorialis (Farr and Rossman 2016). To our knowledge, this is the first report of gray mold on A. victorialis var. platyphyllum globally as well as in Korea. Since this crop is mostly grown on organic farms in Korea and harvested in April to May while the leaves are young and tender, a management strategy to minimize gray mold should be developed.