Pepper (Capsicum annuum L.) is an important solanaceous vegetable crop, with high nutritional and economic value. However, it is susceptible to Colletotrichum spp. infection during its growth and development, which seriously affects production yield and quality. Chili anthracnose, caused by Colletotrichum spp., is one of the most destructive diseases of pepper. In August 2020, chili anthracnose was observed with widespread distribution in the horticulture field of Northwest A&F University (34.16° N, 108.04° E) in Shaanxi Province, China. Approximately 60% of the pepper plants had disease symptoms typical of anthracnose. Lesions on pepper fruits were dark, circular, sunken, and necrotic, with the presence of orange to pink conidial masses (Figure S1A). To perform fungal isolation, the tissue at the lesion margin was cut from eight symptomatic fruits, surface disinfested with 75% ethanol for 30 s, and 2% NaClO for 1 min, then rinsed three times with sterile distilled water and dried on sterile filter paper. The tissues were placed on potato dextrose agar (PDA) and incubated at 28 ºC in the dark. After 3 days, hyphae growing from tissue of each lesion were recultured on PDA (Liu et al. 2016). A representative single-spore isolate (NWAFU2) was used for morphological characterization, molecular analysis, phylogenetic analysis, and pathogenicity tests. NWAFU2 colonies had gray-white aerial mycelium, and the reverse side of the colonies was dark gray to light yellow after 10-days growth on PDA (Figure S1B-C). Conidia were cylindrical, aseptate, with obtuse to slightly rounded ends, and measured 10.1 to 16.9 (length) × 4.7 to 7.0 (width) μm (n=50) (Figure S1D). Based on morphological features, the isolate was consistent with the description of C. gloeosporioides species complex (Weir et al. 2012). For molecular identification, genomic DNA was extracted using a CTAB method and the internal transcribed spacer (ITS) region, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and partial sequences of actin (ACT) genes were amplified and sequenced using primers ITS1F/ITS4, GDF1/GDR1 and ACT-512F/ACT-783R, respectively (Dowling et al. 2020). Using the BLAST, ITS, ACT, GAPDH gene sequences (GenBank accession nos. MW258690, MW258691 and MW258692, respectively) were 100%, 100% and 98.19% identical to ZJL-4 of C. gloeosporioides (GenBank accession nos. MN075757, MN058142 and MN075666, respectively). Phylogenetic analysis was conducted using MEGA-X (Version 10.0) based on the concatenated sequences of published ITS, ACT and GAPDH for Colletotrichum species using Neighbor-Joining algorithm. The identified isolate (NWAFU2) was closely related to C. gloeosporioides (Figure S2). To confirm the pathogenicity, ten healthy pepper fruits were surface-sterilized and 2 μL of conidial suspension (1×106 conidia/mL) was injected the surface of pepper. Five fruits were inoculated with 2μL sterile distilled water as controls. After inoculation, the fruits were kept in a moist chamber at 28°C in the dark. The experiment was repeated three times. Anthracnose symptoms similar to those observed in the field, were observed 7 days after inoculation (Figure S1F) and control fruits remained healthy. A similarly inoculated detached leaf assay resulted in water-soaked lesions 3 days after inoculation. C. gloeosporioides was reisolated from the infected pepper fruits, fulfilling Koch’s postulates. C. gloeosporioides has been reported to cause chili anthracnose in Sichuan Province, China (de Silva et al. 2019; Liu et al. 2016). However, Shaanxi is one of the main pepper producing areas in china and it is geographically distinct from Sichuan; its climate and environmental conditions are different from Sichuan. Knowledge that C. gloeosporioides causes chili anthracnose of pepper in Shaanxi province, China may aid in the selection of appropriate management tactics for this disease. Reference: de Silva, D. D., Groenewald, J. Z., Crous, P. W., Ades, P. K., Nasruddin, A., Mongkolporn, O., and Taylor, P. W. J. 2019. Identification, prevalence and pathogenicity of Colletotrichum species causing anthracnose of Capsicum annuum in Asia. IMA Fungus 10:8. Dowling, M., Peres, N., Villani, S., and Schnabel, G. 2020. Managing Colletotrichum on Fruit Crops: A "Complex" Challenge. Plant Dis 104:2301-2316. Liu, F. L., Tang, G. T., Zheng, X. J., Li, Y., Sun, X. F., Qi, X. B., Zhou, Y., Xu, J., Chen, H. B., Chang, X. L., Zhang, S. R., and Gong, G. S. 2016. Molecular and phenotypic characterization of Colletotrichum species associated with anthracnose disease in peppers from Sichuan Province, China. Sci Rep 6. Weir, B. S., Johnston, P. R., and Damm, U. 2012. The Colletotrichum gloeosporioides species complex. Stud Mycol 73:115-180.
Differential Reactions on Mature Green and Ripe Chili Fruit Infected by Three Colletotrichum spp.
