First Report of Anthracnose on Kadsura coccinea Fruit Caused by Colletotrichum fructicola in China

The aggregate fruit of Kadsura coccinea (Lem.) A.C. Smith is rich in trace elements and holds significant economic value. However, in September 2024, a new fruit rot disease was observed in a plantation in Jinxiu County, Guangxi, China (24°7′N, 110°11′E). The disease is widespread in orchards across Guangdong, Guangxi, Yunnan and other regions of China, with particularly severe outbreaks occurring during the rainy season. The diseased fruits exhibited dark brown circular lesions (2-3mm in diameter) with salmon-colored conidial masses. In advanced stages, the infection progressed to complete fruit maceration, characterized by tissue softening and browning. Based on these classic symptoms and signs, the causal agent was suspected to be a Colletotrichum species. To identify the pathogen, fifteen symptomatic fruits were systematically collected. Tissue sampling (6 × 6 mm) was conducted at the lesion-marginal interface, followed by sequential sterilization: 0.1% HgCl₂ for 60s, then 70% ethanol for an additional 60s. After rinsing with sterile water, surface-sterilized tissue fragments were cultured on PDA at 28°C for 3-4 days. Hyphal tips were subcultured for purification, yielding four isolates from 15 samples (excessive degradation of certain samples prevented successful pathogenic bacteria isolation). Colonies exhibited white mycelium with light-yellow reverse pigmentation after 5 days. Microscopic examination revealed conidia that were oval to cylindrical in shape, with blunt ends, unicellular, and colorless, measuring approximately 12-16 × 3-4 μm. These morphological features were distinct from C. gloeosporioides, which typically possesses pointed ends, further supporting the preliminary identification. For molecular confirmation, genomic DNA was amplified using ITS (ITS1/ITS4), GAPDH (GDF1/GDR1), ACT (ACT-512F/ ACT-783R) and TUB2 (T1/Bt2b) primers for sequencing (Weir et al., 2012). All sixteen sequences were deposited in GenBank (ITS: PQ655449-PQ655452, GAPDH: PX245443-PX245446, ACT: PX523498-PX523501, TUB2: PX245447-PX245450). These sequences exhibited ≥ 99% identity and 100% coverage with reference isolates of C. fructicola CNUCC 711-1-2 (PP843301, PP849801, PP922881, PP870971) in the Nr database. Phylogenetic analysis, using the Maximum Likelihood algorithm with NCBI Colletotrichum ITS/GAPDH/ACT/TUB2 datasets, confirmed the four strains as C. fructicola. Pathogenicity tests were subsequently performed on Kadsura coccinea fruits. A 1mL spore suspension (1×106 spores/mL) from four rot-derived strains (JX-08, JX-10, JX-12, JX-13) was syringe-injected into fruits (2-3 mm beneath the epidermis). Sterile water served as control and all assays were repeated three times. After 3 days at 28°C, inoculated fruits developed black rot lesions matching field symptoms, while controls remained unaffected. C. fructicola was reisolated from all inoculated fruits but not controls. The isolates exhibited consistent PDA colony morphology and 100% sequence identity (ITS/GAPDH/ACT/TUB2) with original strains. While C. fructicola was previously reported to infect only leaves of this host (Jiang et al., 2022), this study represents confirming C. fructicola identification via morphological, cultural, and molecular analyses-thus fulfilling Koch’s postulates. This represents the first documented occurrence of this pathogen on Kadsura coccinea fruits in China, highlighting the necessity for targeted disease control strategies and phytosanitary measures.