First report of Fusarium commune Causing Bulb Rot on Lily (Lilium brownii var. Viridulum Baker) in Hunan Province of China.

Lily (Lilium brownii var. Viridulum Baker) is a well-known edible plant with large, white and sweet bulb scales that has important medicinal value (Zhou et al. 2021) and is grown mainly in the Hebei, Shanxi and Henan provinces of China. In May 2021, a case of bulb rot was discovered in a 3.33 hm2 plantation in Huaihua, Hunan Province, affecting 20% of the area (27°59'30″N, 110°32'20″E). The disease is most severe during the rainy season in May and June. In the early stage, irregular brown spots appeared on the lily scales, the necrosis was depressed and gradually enlarges, and in the later stage, the scales were scattered from the base of the disc and slough off. Ten samples were taken randomly from different plants in the plantation area to isolate the pathogens. After washing with sterile water, they were cut into small pieces and sterilised with 3% hydrogen peroxide for 30 s, 75% ethanol for 90 s, rinsed three times with sterile water and dried on sterile filter paper, then placed on a water agar plate and incubated in the dark in a constant temperature incubator at 28℃ for 3 to 5 days. After 2 days, the mycelium at the edge of the colony was transferred to a PDA plate and incubated for 3-5 days at 28°C in the dark to obtain pure fungal isolates. Eighteen purified fungal isolates were obtained, of which sixteen looked like Fusarium (88.9% isolation rate) and three representative isolates (BHBR2, BHBR3 and BHBR5) were selected for further study. The surface of this fungus was white with dense aerial mycelium. Some had an orange centre in the medium. Microconidia were oval in shape and appeared either straight or slightly curved. These microconidia were colourless, had 0-1 septa and measured 3.334 to 14.724 × 2.216 to 5.385 µm (n=100). Macroconidia were predominantly three-septate, crescent-shaped structures that were thin-walled and slightly curved. Cells at the apex and base were similarly curved. Macroconidia measured 17.956 to 32.150 × 2.788 to 4.492 µm (n=100). The mitochondrial small subunit (mtSSU) and translation elongation factor 1-α (TEF1) genes were amplified and sequenced using the NMS1/NMS2 and TEF-R/TEF-F primers to verify the identity of the pathogens (Stewart et al. 2006). The sequences were submitted to GenBank (BHBR2: mtSSU, PP273435; TEF, OR900976; BHBR3: mtSSU, PP277729; TEF, OR900977; BHBR5: mtSSU, PP277728; TEF, OR900978). A concatenated phylogenetic tree of the two genes was constructed and analysis showed that BHBR2, BHBR3 and BHBR5 were significantly clustered with Fusarium commune. Based on the results of morphological identification and phylogenetic tree analysis, the three isolates were identified as Fusarium commune. We carried out pathogenicity tests using two methods, one in which 6 × 6 mm fungal blocks were inoculated on lily (L. brownie var. viridulum Baker) scales and controls inoculated with sterile blocks, and the other in which strain BHBR2 was selected to carry out pathogenicity tests on bulbs of live plants soaked with 50 ml of a 1 × 106 conidial suspension and bulbs of control plants soaked with sterile water, all in three replicates. They were placed in a growth chamber at 28°C and 80% relative humidity, and the scales were moistened with moistened sterile filter paper. After 3 days of rearing treated scales, lesions appeared on lily scales inoculated with mycelial blocks and expanded with time, whereas no lesions appeared on lily scales inoculated with sterile blocks. One month later, whole plants soaked in the spore suspension wilted, while the control plants grew well. The pathogens re-isolated from the diseased tissues had the same morphological characteristics as representative isolates. This confirms Koch's hypothesis. Fusarium commune has been shown to be the most important pathogenic fungus causing root rot in Alfalfa (Medicago sativa) (Yang et al. 2022) and blueberry (Vaccinium uliginosum L.) (Li et al. 2023) in China. To our knowledge, this is the first report of Fusarium commune causing lily bulb rot in the world, which will lay the foundation for future control of lily bulb rot.

First Report of Leaf Spot of Atractylodes macrocephala Caused by Fusarium commune in Zhejiang province, China.

Atractylodes macrocephala Koidz is a very common herbs in China, also famous for its high medicinal value (Lee et al., 2007). In summer of 2019, in Fuyang county of Zhejiang province, the main production area of China, 74 plants of A. macrocephala from a total of about 300 plants, showed black leaf spots . The incidence of the disease was 25% and increased under high temperature and humidity conditions. Initial leaf symptoms appeared as black or tan spots surrounded by brown margins and expanded irregularly. Finally, large blackish brown spots appeared on the leaves, elliptical or irregular, 1.0 to 1.5 cm in diameter, and then lesions turned necrotic. To isolate the pathogen, small pieces (5×5 mm) from the margin of symptomatic leaves were surface-sterilized with 75% ethanol for 30 s and 2% sodium hypochlorite for 2 min, rinsed five times with sterile water, and incubated on potato dextrose agar (PDA) at 28°C in darkness. Purified colonies were white to pink with densely floccose to fluffy aerial mycelium and peach-orange pigmentation. Macroconidia, usually three-septate, were 26.7 to 43.3×3.1 to 5.3µm (n=50), thin-walled, slightly curved, with apical and basal cells curved when cultured in continuous darkness. Microconidia were mostly aseptate, ovate-oblong, straight to slightly curved, and measuring 5.9 to 14.3×2.3 to 3.9µm in size (n=50). Spherical chlamydospores were produced singly or in pairs from mycelium and spores. These characteristics were consistent with the description of Fusarium spp. (Leslie and Summerell, 2006). To identify the species, the translation elongation factor-1 alpha regions (TEF-1α) and the mitochondrial small subunit (mtSSU) were amplified using primers EF-3/ EF-22 (Palmore et al.,2010 and O'Donnell et al., 1998) and MS3F/ MS3R (Stenglein et al., 2010), respectively. Sequences were deposited in GenBank (MT263720, OM203177, OM203178, OM203179, OM203180, OM203181 and MN853662, MZ028170.1, MZ028171.1, MZ028172.1, MZ028173.1, MZ028174.1). These six isolates clustered in the Fusarium commune clade with 100% and 98% similarity, respectively. To test pathogenicity of every isolate, five 8-week-old potted A. macrocephalae plants were wound-inoculated and mycelial discs of 5-mm diameter were used to inoculate. As a control, five plants were inoculated with 5-mm PDA plugs. All plants were individually covered with a plastic bag and kept in a greenhouse at 25 ± 2°C with a 12-h photoperiod at 70 to 80% relative humidity. Typical symptoms similar to those of the field appeared only in inoculated plants after five days. In addition, a conidial suspension (1×105 spores/ml) was sprayed onto young leaves of three potted healthy plants. Three plants sprayed with sterile distilled water served as controls. After 7 days, typical symptoms were observed on all inoculated leaves. Experiments were replicated three times. F. commune was successfully re-isolated from diseased plants. Based on morphological and molecular identification, the pathogen was identified as F. commune. In China, Alternaria alternata (Zhuang, 2005), A. longipes (Tan et al., 2012), Phyllosticta commonsii (Sang et al., 2006) and Phoma exigua (Zhang et al., 2018) were reported as causal agents of the leaf spot disease of A. macrocephalae. To our knowledge, this is the first report of leaf spot disease on A. macrocephalae caused by F. commune in China. Effective control strategies need to be established to reduce the losses.