First Report of Root Rot Caused by Fusarium oxysporum on Aralia elata in China.

Abstract

Aralia elata (Miq.) Seem., is grown for its medicinal and nutritional properties in northeastern China. The tender shoots are used as wild vegetables. The plant saponin components have antioxidant and neuroprotective activities, and are used for the treatment of chronic disease (Xia et al. 2021). In July 2021, root rot disease was observed in five-year-old A. elata plants in Qingyuan County (41°91' N, 124°59' E), Liaoning Province, China. The incidence of roots rot was approximately 50% in old fields, with the leaves of the infected plants appearing chlorotic and wilting. The lesions on the taproots were dark brown and soft, with degraded internal organization. Leading edge of necrotic tissue from symptomatic roots was cut 5×5×3 mm, placed in 75% ethanol for 30 s, and then in 3% sodium hypochlorite for 2 min. After three rinses in sterile distilled water, the samples were dried on sterile filter paper before plating on potato dextrose agar (PDA) and incubation at 25℃. Monosporic cultures were obtained by the collection of single spores from individual isolates. After 7 days on PDA, mycelia in the colonies appeared cottony and pink, white, or purple in color, while their undersides were pink and white. Spore characteristics were evaluated after transfer to carnation leaf agar (CLA) and incubation for 20 days (Zhang et al. 2021). The macroconidia were falciform, slightly curved or straight, two to five septate, and 20.57 to 33.75 × 3.62 to 6.11 μm (n=40). The microconidia were ovoid or oval, zero to one septate, and 5.12 to 13.53 × 3.04 to 4.79 μm (n=40). Chlamydospores were globose to subglobose, intercalary or terminal, with an average diameter of 13.76 μm (n=40).To identify the pathogen, the internal transcribed spacer (ITS) region, large subunit (LSU) ribosomal DNA, and translation elongation factor 1 alpha (TEF-1α) gene were amplified using the respective primer pairs ITS1/ITS4, LR0R/LR7, and EF1-728F/EF1-986R (Cheng et al. 2020; Fu et al. 2019). Comparisons with GenBank, the sequences of ITS, LSU, and TEF-1 had 99 to 100% homology with Fusarium oxysporum (accessions numbers- MH707084, OQ380519, and GU250609, respectively). The sequences were deposited in GenBank: OP482273 (ITS), OP491955 (LSU), and OP503498 (TEF-1α). Maximum likelihood phylogeny of the identified sequences using MEGA-X software indicated that the isolate represented F. oxysporum. The taproots of 30 one-year-old A. elata were washed and inoculated with 1×106/ml of the conidial suspension for two hours, and another 30 used as controls with sterile water. After planting in sterilized forest soil in flowerpots (36×30 cm), the plants were grown in a greenhouse for two weeks at 25℃ with 14 h of light. It was found that 50% of the roots showed typical root rot symptoms, while the controls were asymptomatic. The pathogenicity test was repeated three times, and reisolation of F. oxysporum from the roots fulfilled Koch's postulates. This is the first report of root rot in A. elata caused by F. oxysporum in China and indicates the necessity for suitable management strategies to protect A. elata production.