Colletotrichum karsti You L. Yang, Zuo Y. Liu, K. D. Hyde & L. Cai

Colletotrichum karsti You L. Yang, Zuo Y. Liu, K. D. Hyde & L. Cai, Cryptog. Mycol. 32 (3): 241 (2011) Fig. 6 = Colletotrichum wuxuhaiense Z. F. Yu & Hua Zheng, J. Fungi 8 (1, no. 87): 20 (2022). Description. Isolated from a leaf spot of Rosa chinensis Jacq. Sexual morph: undetermined. Asexual morph: Conidiomata pycnidial, globose, dark brown, superficial on PDA, releasing conidia in a yellow mass, slimy, globose. Conidiophores produce conidiogenous cells, either directly formed from hyphae or from a cushion of spherical hyaline cells, septate, and branched. Conidiogenous cells hyaline, cylindrical to clavate, straight to flask-shaped, (17.4 –) 18–50 (– 53.2) × (3.2 –) 4–5 (– 5.8) μm (mean ± SD = 33 ± 0.9 × 4 ± 0.2 μm). Setae not observed. Conidia (12.6 –) 13–14.8 (– 15) × (6.2 –) 6.3–7.9 (– 8.4) μm (mean ± SD = 14 ± 0.8 × 7 ± 0.2 μm), n = 30, L / W ratio = 2.1, hyaline, aseptate, smooth-walled, ellipsoidal to cylindrical, one end rounded and one end acute or both ends rounded, sometimes the base slightly pointed with a prominent scar, guttulate, granular. Appressoria single in short chains, pale brown, thick-walled, entire edge, rarely lobate, smooth-walled. Culture characteristics. Colonies on PDA reach 5 cm in diameter after 7 days at room temperature (± 25 ° C), exposed to 12 hours of light and 12 hours of darkness. The colonies are rhizoid to filamentous, dense, with a filamentous margin. After 14 days, the colony appears white to pale-yellow from above, producing grouped dark brown pycnidia and a white to yellow reverse (Fig. 5 a, b). Material examined. China • Yunnan province, Kunming, Kunming Botanical Garden, Symptomatic leaves of Rosa chinensis Jacq., 2023.10. 29, Wang Xingchang, KM 004-1 / GZ 25-1 / GZ 25-2 (dried culture, HGUP 25-0042), living culture GUCC 25-0060, GUCC 25-0037. Notes. Based on multi-locus phylogenetic analyses (Fig. 1), Colletotrichum wuxuhaiense was found to cluster within the Colletotrichum karsti species clade, with strong statistical support (82 % BSML, 74 % BSMP, and 1.00 BYPP). Morphologically, both species exhibit similar features, including cylindrical to clavate, hyaline conidiophores and ellipsoidal to cylindrical, one-celled, smooth-walled, hyaline conidia that are straight, truncate at the base, and obtuse at the apex. Despite their overall similarity, minor differences were observed in conidial size: C. wuxuhaiense (YMF 1.04951) measured 10.3–15.8 × 4.7–8.9 µm, whereas C. karsti (CBS 132134) ranged from 12.5–19.5 × 6.0–8.5 µm. Additionally, C. wuxuhaiense was characterized by a prominent basal scar and conidiogenous cells with distinct periclinal thickening (Yang et al. 2011; Zheng et al. 2022). Pairwise comparisons between the type strains of C. wuxuhaiense (YMF 1.04951) and C. karsti (CBS 132134) revealed very low genetic divergence across five gene regions: ITS = 0.2 % (1 / 503 bp, including one gap), gapdh = 2 % (4 / 198 bp, including one gap), chs- 1 = 0.4 % (1 / 234 bp, including one gap), act = 2 % (5 / 241 bp, including two gaps), and tub 2 = 0.4 % (2 / 470 bp, zero gaps). The strong phylogenetic affinity and low sequence variation across multiple loci indicate that these taxa represent the same species. Therefore, based on both molecular and morphological evidence, C. wuxuhaiense (Zheng et al. 2022) is regarded as a later synonym of C. karsti (Yang et al. 2011), in accordance with the International Code of Nomenclature for algae, fungi, and plants (ICN). In this study, Strains GUCC 25-0060 and GUCC 25-0037, isolated from symptomatic leaves of Rosa chinensis (Rosaceae) in Kunming, Yunnan Province, China, were identified as Colletotrichum karsti based on multi-locus phylogenetic analyses. These strains clustered within the C. karsti clade with moderate to strong statistical support (86 % BSML, 75 % BSMP, and 1.00 BYPP) (Fig. 1). Their morphological features are consistent with the original description of C. karsti, further supporting their identification (Yang et al. 2011). Colletotrichum karsti was initially described from a leaf of Vanda sp. collected in Guizhou Province, China (Yang et al. 2011), and is now recognized as both an endophyte and a pathogen across a wide range of plant hosts (Damm et al. 2012; Zheng et al. 2022). The present study represents the first record of C. karsti associated with Rosa chinensis, thus expanding the known host range of this species.