First Report of Colletotrichum siamense Causing Anthracnose on Jasminum mesnyi in China

Jasminum mesnyi Hance is one of the most popular ornamental species in the world and is often used as a Chinese traditional medicine in China (Li et al. 2017). In October 2018, anthracnose disease symptoms were observed on this cultivar in the Luzhou Park (31°53′29″N; 117°14′10″E) in Hefei City, Anhui Province, China. The disease incidence was about 60%. Symptoms began as chlorotic spots and then coalesced into larger irregular or circular lesions. The centers of typical diseased leaves were gray with a brown border surrounded by a yellow halo. To determine the pathogen, symptomatic leaves were collected from plants in October 2018 and cut into small pieces. Leaf pieces from the margin of the necrotic tissue were surface sterilized in 75% alcohol for 0.5 min, followed by 2% sodium hypochlorite solution for 3 min, and then rinsed three times in sterile distilled water. The tissues were plated on potato dextrose agar (PDA) medium and incubated at 28°C for 4 days in the dark. Five-day-old isolates had white aerial mycelium with olivaceous gray mycelium below. Hyphae were multinucleated and septate. Conidia were hyaline, cylindrical, straight or slightly curved, nonseptate, 11.8 to 26.1 × 2.6 to 7.1 μm (n = 50) (average 15.4 × 4.5 μm), and obtuse at both ends. The mycelial appressoria were ovoid to slightly irregular, brown, and ranged from 5.9 to 11.6 μm (mean 9.6 μm) × 5.4 to 7.8 μm (mean 6.5 μm) (n = 50). The morphological characteristics of the present isolate were similar to those of the species of Colletotrichum siamense (Chang et al. 2018; Liu et al. 2017). For accurate identification, the genomic DNA sequences were obtained from internal transcribed spacer (ITS), actin, CAL, CHS-1, β-tubulin, and ApMat genes deposited in GenBank under accession numbers MK248636, MK341539, MK341540, MK341541, MK341542, and MK585074, respectively. BLAST analysis revealed that the ITS, actin, β-tubulin, CAL, and ApMat sequences were 99 to 100% identical to those of C. siamense ICMP 18578. A maximum likelihood phylogenetic tree was generated based on the concatenated data from sequences of ITS, CAL, actin, and ApMat using MEGA5.1, which clustered the present isolate with C. siamense strain ICMP 18578 with high bootstrap support (99%). Based on cultural characteristics and phylogenetic analysis, the current isolate associated with anthracnose disease of J. mesnyi was identified as C. siamense. The representative isolate was deposited at the China Center for Type Culture Collection (CCTCC) as CCTCC AF 2018032 SX02. To confirm the pathogenicity, the detached twigs of wild J. mesnyi were put into Erlenmeyer flasks with water. Ten healthy leaves were inoculated with either spore suspension (1.5 × 10⁵/ml) or 5-mm-diameter mycelial plugs using sterile water or sterile PDA plugs as a control. All inoculated plants and controls were placed under high humidity conditions and kept in a light incubator (12 h light/dark) at 28°C. The experiments were performed in triplicate. Ten days after inoculation, typical symptoms appeared on all inoculated leaves, whereas the controls remained symptomless. The pathogen was reisolated from inoculated leaves and matched the molecular and morphological characteristics of the original isolates, as previously described. To our knowledge, this is the first report of anthracnose caused by C. siamense on J. mesnyi in China. The identification of this pathogen will establish a foundation for managing the disease in China.