First Report of Colletotrichum jiangxiense Causing Anthracnose on Rosa hybrida in Yunnan Province, China

Rosa hybrida, a deciduous Rosa shrub (Rosaceae), serves as a key global ornamental for cut blooms and landscaping, with petals used for food, fragrance and medicine. Large field and greenhouse plantations exist in Yunnan, Sichuan and Jiangsu, China. (Cao et al. 2019). In March 2026, severe anthracnose was observed on Rosa hybrida in the rural courtyard of Gejiu, Honghe Hani and Yi Autonomous Prefecture, Yunnan Province (103.046890 E, 23.144789 N). Disease symptoms were observed on 40-60% of leaves in planting plots (~ 0.02 ha) across 50-80 mature Rosa hybrida shrubs. On Rosa hybrida, tiny water-soaked pinpoint lesions expand into round dark brown necrotic spots encircled by broad yellow halos (1.1×0.9 - 4.7×4.0 cm) with sunken tan cores and faint concentric rings. Lesions initiate along veins and spread vasularly under high humidity; dense black Colletotrichum jiangxiense acervuli produce orange conidial masses in wet conditions. Coalesced spots cause severe blight, leaf chlorosis and premature defoliation in field-grown roses. To isolate the fungus, 10 symptomatic leaves were randomly sampled from five rose shrubs for isolation. ~5 mm² infected tissues underwent surface sterilization: 75% ethanol (30 s), 3% hypochlorous acid (3 min), triple sterile water rinses, then cultured on PDA. Plates incubated at 28 ℃ under a 12-h photoperiod yielded 8 morphologically identical strains; 2 isolates MGTJ1 and MGTJ2 were purified. Purified colonies initially had sparse edges on PDA, becoming dense fluffy white aerial hyphae after 5 days, covering the dish by 12 days, with circular colonies bear entire smooth flat edges. Microscopically, Conidia were short cylindrical with obtuse, hyaline, rounded apices and aseptate, measuring (11.12-17.13) × (4.07-6.13) μm (n = 50). These morphological characteristics resembled C. jiangxiense. To confirm identification, genomic DNA from mycelium of these 2 isolates was extracted, and the sequences of internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), chitin synthase (CHS1), β-tubulin (TUB2) and calmodulin (CAL) were amplified (Carbone and Kohn 1999), with GenBank accessions: ITS (PZ716124, PZ716125), GAPDH (PZ797211, PZ797212), ACT (PZ797213, PZ797214), CHS1 (PZ797215, PZ797216), TUB2(PZ797217, PZ797218), CAL (PZ797223, PZ797224). Pathogenicity tests for isolates MGTJ1 and MGTJ2 were conducted on needle-wounded healthy 1-year-old rose leaves using 5-mm mycelial plugs, with three biological replicates. Leaves were incubated at 25-30 ℃, 85-95% RH and a 12-h photoperiod. All inoculated leaves produced typical anthracnose lesions at 5 dpi, while sterile PDA and water controls had no symptoms. The pathogen recovered from lesions was verified as C. jiangxiense, fulfilling Koch’s postulates. The pathogen was re-isolated from inoculated diseased rose leaves and identified as C. jiangxiense, fulfilling Koch’s postulates (Ji et al. 2019). C. jiangxiense has previously been documented as the causal agent of severe anthracnose on chili in China and avocado in Mexico (Zhang et al. 2023; Ayvar-Serna et al. 2021). To our knowledge, this study represents the first record of C. jiangxiense associated leaf anthracnose on Rosa hybrida in Yunnan, verified by multilocus phylogeny. The pathogen damages rose ornamental quality, and this finding guides targeted management for commercial rose farms, while motivating research on host-pathogen interactions and resistant rose breeding.