First Report of Fusarium redolens Causing Root and Bulb Rot Disease on Lanzhou Lily (Lilium davidii var. unicolor) in China

Lanzhou lily (Lilium davidii var. unicolor), a famous edible lily with large, white, and sweet bulb scales, is mostly planted in the middle areas of Gansu Province in China. In recent years, severe wilt symptoms, including root, bulb, and stem rots, with a progressive yellowing and wilting of leaves from the base, were observed on Lanzhou lily in Qilihe District, Lanzhou. The disease has resulted in serious loss of bulb production, especially in continuous cropping fields or soil with high moisture content. Here we report our finding that Fusarium redolens is a causal agent of root and bulb rot in Lanzhou lily. Small pieces of symptomatic root (0.5 cm in length) and bulb (0.5 × 0.5 cm in size) were surface sterilized with 75% ethanol for 30 s, followed by 2.5% sodium hypochlorite for 1 min, and then rinsed three times with sterile water. The surface-sterilized tissues were placed on potato dextrose agar (PDA) medium and incubated at 25°C. Subcultures of the mycelia grown out of the diseased tissues yielded fungal colonies on PDA that formed dense white aerial mycelium and produced orange-yellow or red pigmentations. Macroconidia were fusiform or sickle-shaped, 16.6 to 38.3 × 3.4 to 6.0 μm (n = 50), and three to five septate. Microconidia were oval or kidney-shaped, 5.5 to 12.4 × 2.2 to 3.5 μm (n = 50), and zero to one septate. These morphological characteristics of the causal pathogen were similar to those of Fusarium spp. (Leslie and Summerell 2006). For further identification of the fungus, the internal transcribed spacer region of the ribosomal DNA (ITS) and the translation elongation factor 1α (TEF-1α) gene were amplified and sequenced using primer set ITS1 (TCCGTAGGTGAACCTGCGG)/ITS4 (TCCTCCGCTTATTGATATG) and EF1 (ATGGGTAAGGAAGACAAGAC)/EF2 (GGAAGTACCAGTGATCATGTT), respectively. The sequences amplified from the ITS region (GenBank MK312593) showed 100% identity with those of F. redolens in GenBank (KC924920 and HQ703404) and displayed 100% similarity with accession SH219673.07FU of F. redolens in the Fusarium MLST database. The partial sequence of TEF-1α gene (MK353340) exhibited 100% homology to 10 accessions of F. redolens (e.g., FD_01081 and FD_01080) in the FUSARIUM-ID database. The isolate was further identified as F. redolens based on PCR using the F. redolens-specific PCR assay of Bogale et al. (2007). Pathogenicity tests were performed to fulfill Koch’s postulates. Two seedlings of Lanzhou lily cultivated in a plastic pot in a sterile mixture of sphagnum peat and sand at 3:2 (v/v) were inoculated with 200 ml of the conidial suspension (10⁵ spores/ml) on the roots. Control plants were treated with sterile water. Each treatment included three replicates, and four pots served as one replicate. The seedlings were incubated in a climate chamber at 25°C with 16 h of light per day and irrigated with sterile water. The pathogen-inoculated plants exhibited root and bulb rot and typical wilt symptoms after 60 days, whereas no typical wilt symptoms were observed in the control plants, and F. redolens was reisolated from the infected tissues. The pathogen has been reported previously in ornamental lily in Ukraine (Zerova 1940), tulip in Scotland (Pitt 1966), and onion in Turkey and Iran (Bayraktar and Dolar 2011; Ghanbarzadeh et al. 2014). However, to the best of our knowledge, this is the first report of F. redolens causing root and bulb rot on edible Lanzhou lily in China. F. redolens as a plant pathogen was often mixed with F. oxysporum. The root rot disease in asparagus, chickpea, and sugar beet caused by F. oxysporum had actually been caused by F. redolens (Baayen et al. 2000; Cao et al. 2018; Tekeoglu et al. 2017).