First Report of Fusarium Dry Rot of Garlic Caused by Fusarium proliferatum in Korea

Garlic ( Allium sativum L.) is a bulbous crop belonging to the family Amaryllidaceae, widely cultivated and consumed worldwide for its culinary and medicinal value (Tesfaye 2021). In September 2021, rot symptoms were observed on stored seed garlic bulbs in Gimpo, the Republic of Korea (37.70° N, 126.60° E). The average incidence was approximately 60-70%. Symptoms were classified into three types: (i) basal rot without internal decay, (ii) basal rot with internal decay, and (iii) decay of cloves. Fungal isolates were obtained from symptomatic tissues. Tissue pieces from lesion margins were surface-sterilized with 1% sodium hypochlorite (NaOCl) for 1 min, rinsed twice with sterile distilled water, and plated on 2% water agar (WA). After incubation at 25°C for 5 days, single-spore isolation was performed, and 10 isolates were obtained. Based on morphological characteristics, the isolates were preliminarily identified as Fusarium spp. Colonies grown on potato dextrose agar (PDA) at 25°C for 7 days showed rapid mycelial growth (9.1–10.6 mm/day) with white to pale violet aerial mycelia. Microscopic observations of cultures grown on carnation leaf agar (CLA) at 25°C for 2 weeks under near-ultraviolet (NUV) light revealed that sporodochia were rarely produced and chlamydospores were absent. Macroconidia were falcate but relatively straight, with blunt apical cells and poorly developed, foot-shaped basal cells; they were mostly 3–4 septate, measuring 24.7-49.9 × 4.0-7.2 μm (n = 50). Microconidia, which formed in chains from polyphialides, were clavate, mostly aseptate (rarely 1-septate), and measured 5.2-9.5× 1.9-3.1 μm (n = 50). These cultural and morphological characteristics were consistent with those of previously reported Fusarium proliferatum (Nirenberg 1976). For molecular identification, the translation elongation factor 1-alpha (EF1-α), RNA polymerase II largest subunit (RPB1), and second largest subunit (RPB2) genes were amplified and sequenced using primer pairs EF1/EF2 (O’Donnell et al. 1998), RPB1-F5/RPB1-R8 (O’Donnell et al. 2010), and RPB2-5F/RPB2-7cR (Liu et al. 1999), respectively. The sequences were deposited in GenBank under accession numbers PZ381872-PZ381881 for EF1-α, PZ367562-PZ367571 for RPB1, and PZ367572-PZ367581 for RPB2. Phylogenetic analysis based on the concatenated sequences using IQ-TREE identified the isolates as F. proliferatum . Pathogenicity was tested on healthy garlic bulbs using mycelial plugs. For wound inoculation, a hole (Ø 5mm) was made in the clove tissue, and a 5-mm-diameter PDA plug colonized by the isolate was inserted into the wound. For non-wound inoculation, mycelial plugs were placed on the surface of garlic bulbs. Control bulbs were treated with sterile PDA plugs. All bulbs were incubated in a moist chamber at 25°C. The experiment was conducted with three replicates. After 7 days, mycelial growth was observed on both wound-inoculated and non-wound-inoculated bulbs, and infected tissues exhibited brown to pink discoloration. No symptoms were observed in control bulbs. The fungus was reisolated from symptomatic tissues and molecularly characterized, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of Fusarium dry rot of garlic caused by Fusarium proliferatum in Korea. Given the important role of Korea as one of the most important garlic producing countries worldwide (FAOSTAT, 2024), this first report has important implications for garlic production, disease surveillance, and management. Furthermore, our findings highlight the critical need for early detection and preventive management of stored seed garlic bulbs, as infected bulbs may serve as a source of primary inoculum, facilitating disease spread during storage and subsequent cultivation.