Identification and Observation of Infection Processes of Colletotrichum Species Associated with Persimmon Anthracnose in Guangxi, China

Persimmon originated from China where it has a long cultivation history. Anthracnose fruit rot and leaf blight caused by Colletotrichum species are major diseases of persimmon in China and cause severe economic losses. To determine the species causing anthracnose of persimmon in Guilin, Guangxi Province, diseased samples were collected from the four local counties: Gongcheng, Yangshuo, Pingle, and Lipu. Seventy-five isolates were obtained from persimmon samples with anthracnose symptoms and had similar morphological characteristics. Isolates were identified using a BLAST search and phylogenetic analysis of the internal transcribed spacer region, glyceraldehyde-3-phosphate dehydrogenase, partial actin, β-tubulin, chitin synthase genomic regions, Apn2-Mat1-2 intergenic spacer, and the partial mating type gene and calmodulin genes. Five species (C. fructicola, C. horii, C. karstii, C. cliviicola, and C. siamense) accounted for 54.7, 25.3, 12.0, 5.3, and 2.7%, respectively, of the total isolates. All five Colletotrichum species were pathogenic on attached leaves and detached fruits of persimmon (cultivar Gongcheng Yueshi) in pathogenicity assays. The infection processes of the five Colletotrichum species were observed on persimmon leaves using light microscopy. Conidia of C. fructicola germinated at 12 h post inoculation (hpi) and quickly formed acervuli at 6 days post inoculation (dpi) and were the most aggressive. By contrast, conidia of C. cliviicola germinated at 3 hpi but produced the acervuli at 8 dpi and were the least aggressive. This is the first description of C. fructicola, C. cliviicola, and C. siamense as causal agents of persimmon anthracnose in Guangxi Province, China.

First Report of Leaf Spot Caused by Colletotrichum fructicola and C. siamense on Zizyphus mauritiana in Guangxi, China

Zizyphus mauritiana Lam. is an important tropical fruit tree and has significant economic value. It is widely planted in Hainan, Guangdong, Guangxi and Fujian provinces in China (Yang et al. 2017). In March 2019, leaf spot was observed on leaves of Z. mauritiana at Bagui fields in Nanning, Guangxi, China, with incidence exceeding 50%. Symptomatic leaves developed a yellow to tan-brown sunken lesion and finally abscised. To isolate the pathogen causing the symptoms, small pieces (5 × 5 mm) of infected leaves were surface sterilized by exposure to 75% ethanol for 10 sec, 1% sodium hypochlorite for 1 min and rinsed three times in sterile water. Fifty pieces were isolated, surface sterilized, and pieces were plated onto potato dextrose agar (PDA) and grown at 28°C for 7 days. The isolation rate of Colletotrichum species was 100%. Three representative isolates (DQZ3-1, DQZ3-2 and DQZ3-3) were selected for further study. Mycelia were greyish-white for all three isolates, with isolate DQZ3-1 also appearing dark green in the center of the colony. Conidia were elliptical, aseptate and hyaline, with sizes of 13.4 ± 0.12 µm × 5.7 ± 0.1 µm, 14.8 ± 0.1 µm × 5.8 ± 0.1 µm and 15.1 ± 0.1 µm × 5.5 ± 0.1 µm for DQZ3-1, DQZ3-2 and DQZ3-3, respectively. Genomic DNA was extracted using the DNAsecure Plant Kit [Tiangen Biotech (Beijing) Co., Ltd] and the internal transcribed spacer (ITS), partial actin (ACT), calmodulin (CAL), chitin synthase (CHS-1), beta-tubulin (TUB2), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were sequenced (Weir et al. 2012). Phylogenetic analysis of the three isolates was performed with MEGA-X (Version 10.0) based on sequences of multiple loci (ITS, ACT, CAL, CHS-1, TUB2 and GAPDH) using Maximum Likelihood analysis. Isolate DQZ3-1 was identified as C. fructicola, and the other two isolates, DQZ3-2 and DQZ3-3, were identified as C. siamense (accessions MT039396 to MT039410, for ACT, CAL, CHS-1, GAPDH and TUB2 of DQZ3-1, DQZ3-2 and DQZ3-3; MT041651 to MT041653 for ITS of DQZ3-1, DQZ3-2 and DQZ3-3). Pathogenicity tests were conducted on 1-year-old plants. Young, healthy leaves were artificially wounded by gently scratching with a sterile needle and 10 µl droplets of conidial suspension (106 spores/ml) applied per wound site for each isolate. Some wounded leaves were inoculated with 10 µl droplets of water as controls. Each isolate was inoculated onto three plants, with 15 leaves at least for each plant, same as controls. All inoculated plants were sprayed with water and covered with plastic bags to maintain high humidity. Symptomatic lesions were observed on the inoculated leaves after 7 days at 28°C, whereas no symptoms were observed on the control leaves. To fulfill Koch's postulates, fungi were re-isolated from 50 symptomatic leaf pieces and fungi re-isolated from each leaf piece were morphologically identical to the inoculated isolates, for a 100% isolation frequency. To our knowledge, this is the first report of leaf spot caused by C. fructicola and C. siamense on Z. mauritiana worldwide. This research may accelerate the development of future epidemiological studies and management strategies for anthracnose caused by C. fructicola and C. siamense on Z. mauritiana.