First report of Fusarium fujikuroi causing bulb rot on Lilium lancifolium in China

Lilium lancifolium Thunb., commonly known as Juandan lily and tiger lily, is widely cultivated in China for its edible bulbs and medicinal properties, with a commercial value worth of ~RMB 6 billion Yuan per year. Bulb rot is an increasingly common disease on L. lancifolium, significantly impacting both the quantity and quality of the main product, the scaled bulbs. Typically, the causal pathogens invade the plant through wounds in the root or the ends of the bulb, causing the roots and bulb to brown and rot, which can eventually lead to stem wilt and death of the whole plants. During pathogenesis, the infected bulbs typically turn from white to brown, with sunken lesions and later the scales flaking off from the base of the bulb (Figure 1A and 1B). Plants growing from infected bulbs are generally short, with discolored leaves, wilting, and death at an early stage. Bulb rot is commonly observed in fields with excess water and a history of continuous Juandan lily cultivation. For this study, wilted L. lancifolium plants with rotted bulbs were collected from Longshan in Hunan, Enshi in Hubei, Yixing in Jiangsu, and Lu'an in Anhui in 2018 and 2019. Infected bulbs were surface sterilized with 75% ethanol for 30 seconds, followed by disinfection with 2% sodium hypochlorite for 5 minutes, and then rinsing with sterile water three times. The surface-sterilized tissue was divided into small pieces of 0.5 × 0.5 cm in size, placed on potato dextrose agar (PDA) medium containing 50 mg/l streptomycin sulfate, and incubated at 25℃. Mycelia growing from diseased tissues were sub-cultured onto fresh PDA medium to obtain pure culture, which formed dense white hyphae after a few days (Figure 1C and 1D). Colonies on PDA produced abundant condia about 15 days after subculturing. Microconidia were abundant, solitary, thin walled, hyaline, ovoid, 0 to 1 septate, with an average size of 6.1 × 2.6 μm (n=50) (Figure 1E). Macroconidia had a curved apical cell and foot-like basal cell with 3 to 5 septa, with an average size of 35.4 × 4.3 μm (n=30) (Figure 1E). No chlamydospore was observed. These morphological characteristics of the causal pathogen were similar to those of Fusarium spp. (Leslie et al., 2006). To identify the Fusarium isolates to species level, DNA fragments of the internal transcribed spacer (ITS) regions of the ribosomal RNA gene cluster, translation elongation factor subunit 1-alpha (TEF1-α), and RNA polymerase II subunit 2 (RPB2) genes were amplified using prime