First report of Coniella koreana causing leaf blight on Loropetalum chinense var. rubrum (Chinese Fringe Flower) in Sichuan, China.

Abstract

Loropetalum chinense var. rubrum (Chinese Fringe Flower) is widely distributed in the middle and lower reaches of the Yangtze River, as well as northern India. It is a popular landscape plant for its red evergreen foliage and its showy red flowers in the spring. In July 2020, This leaf blight was discovered in Chengdu city (30°42＇41＂N, 103°51＇58＂E). In June 2021, the disease incidence rate at two places in Wenjiang District of Chengdu was 76% and 64%, respectively. The symptoms began to appear from May to June, worsened from July to August, and then disappeared gradually in November. Initially, brown-edged irregular necrotic patches appeared at the leaf margins. Progressively, the patches increased in number, expanded to leaf middle, and turned grayish-white. The scattered black fruiting bodies (conidia) were appeared at patches under humid conditions. Eventually, the leaves tended to dry up and fall off. Infected tissues from five samples and collected were cut into small pieces 2×2 mm, surface sterilized for 30 s in 3% sodium hypochlorite, 60 s in 75% ethanol, rinsed three times in sterile water, placed onto potato dextrose agar (PDA), and incubated at 25℃ in the dark. A total of eight isolates were collected, five isolates exhibited similar culture characteristics while two were Nigrospora sp. and one was a Fusarium sp.. The five similar isolates produced sparse, grayish-withe mycelia with a flat elevation and curled margin. Abundant globose and yellow pycnidia were formed on the PDA surface and arranged in irregular concentric zones. Conidia were 18.20 to 22.36 × 2.64 to 3.05 μm (average 20.36 × 2.82 μm, n=50) in size, fusiform, sickle-shaped, aseptate. DNA was extracted from the representative strain (HMcj B03), and the internal transcribed spacer (ITS) region, the large subunit of the nuclear ribosomal DNA (LSU), translation elongation factor 1-alpha (tef1-α), and the DNA-directed RNA polymerase II second largest subunit (rpb2), were amplified by polymerase chain reaction and sequenced with primers ITS1/ITS4 (White et al. 1990), LR0R/LR7 (Rehner and Samuels 1994; Vilaglys and Hester 1990), 728F/986R (Carbome and Kohn 1999), and 5F2/7cR (Alvarez et al. 2016), respectively. The sequences were deposited in GenBank, viz. OL468959, OL469170, OL489770, and OL855833, respectively. BLAST analysis showed >98.7% identity with several reference sequences of Coniella koreana strain CBS 143.97 and Coniella quercicola strain CBS 904.69, deposited in GenBank. A conidial suspension (1 × 107 conidia/mL) having 0.05% Tween 80 buffer was used for foliar inoculation of 6-year-old Loropetalum chinense var. rubrum plants for pathogenicity test. Ten leaves of each plant (10 pots in total) were inoculated with spore suspensions (20 μL onto the wounded sites). An equal number of control leaves were sprayed with 0.05% Tween 80 buffer to serve as a control. The experiment was repeated three times, and all plants were incubated in a growth chamber (a 12h light and 12h dark period, 25°C, RH > 80%). Twenty days later, all the inoculated leaves showed similar symptoms as the original diseased plants, however, the controls remained asymptomatic. The C. koreana was re-isolated from the infected leaves. To our knowledge, this is the first report of L. chinense var. rubrum caused by C. koreana in China. The discovery of this new disease will provide useful information for developing effective control strategies, and prove beneficial in reducing economic losses in floral product.