Colletotrichum actinidicola Norph. & J. P. Wang 2025, sp. nov.

Colletotrichum actinidicola Norph. & J. P. Wang sp. nov. Figs 2, 3 Etymology. The epithet refers to “dweller on Actinidia,” utilizing the Latin suffix - cola, meaning “inhabitant” or “dweller.” Type. China • Guizhou Province, Tongren, Symptomatic leaves of Actinidia chinensis (Actinidiaceae), 2024.03. 02, coll. Wang Jiaping, TRM 2-1 / GZ 24 / GZ 24 - 2 (dried culture, HGUP 25-0043, holotype), ex-type living culture GUCC 25-0036. Description. Isolated from leaf spot of Actinidia chinensis L. 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 from hyphae or from a cushion of spherical hyaline cells, septate, branched. Conidiogenous cells hyaline, cylindrical to clavate, straight to flask-shaped, (13.5 –) 14–40 (– 41) × (3 –) 3.3–5 (– 5.2) μm (mean ± SD = 22 ± 0.7 × 4 ± 0.4 μm). Setae not observed. Conidia (10 –) 14–16 (– 18) × (5 –) 5.5–6 (– 7.2) μm (mean ± SD = 16 ± 1 × 6 ± 1 μm), n = 35, L / W ratio = 2.1, hyaline, aseptate, smooth-walled, ellipsoidal to cylindrical, one end rounded and one end acute or both ends rounded, guttulate, granular. Appressoria single in short chains, pale brown, thick-walled, entire edge, rarely lobate, smooth-walled. Culture characteristics. Colonies on MEA reach 7–9 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 flat or raised surface and a filiform margin. After 14 days, the colony appears white from above, producing grouped pycnidia with an orange ring conidial mass in the center and a white to yellow reverse (Fig. 3 a, b). Material examined. China • Guizhou Province, Tongren, Symptomatic leaves of Actinidia chinensis (Actinidiaceae), 22024.03. 02, coll. Wang Jiaping, TRM 2-1 / GZ 24 / GZ 24-2 (dried culture, HGUP 25-0043, holotype), ex-type living culture GUCC 25-0036, GUCC 25-0058. Notes. Based on a multi-locus phylogenetic analysis, Colletotrichum actinidicola is placed within the C. boninense species complex, forming a well-supported and distinct lineage closely related to C. celtidis and C. spicati (Fig. 1). This placement is strongly supported by high bootstrap and posterior probability values (99 % BSML, 94 % BSMP, and 1.00 PPBI). Morphologically, C. actinidicola exhibits key diagnostic features typical of the C. boninense complex, including hyaline, smooth-walled conidia with a prominent basal scar and conidiogenous cells exhibiting distinct periclinal thickening (Damm et al. 2012). Despite these similarities, C. actinidicola can be distinguished from its closest relatives by conidial morphology and genetic divergence. It produces hyaline, ellipsoidal to cylindrical conidia, measuring (10 –) 14–16 (– 18) × (5 –) 5.5–6 (– 7.2) µm, whereas C. celtidis produces pale brown, straight to slightly curved, broadly ellipsoidal to ovoid conidia with both ends acute, measuring 13–17 × 5–6.5 μm (Tennakoon et al. 2021). In comparison, C. spicati possesses wider conidia, measuring 10.9–15.7 × 5.0–8.2 µm (Zheng et al. 2022). Furthermore, pairwise comparisons of nucleotide sequences between C. actinidicola and the type strains of C. celtidis and C. spicati revealed consistent genetic differences: ITS = 0 / 553 (0), 1 / 553 (0.18 %); gapdh = n / a, 0 / 238 (0); chs- 1 = 9 / 264 (3.4 %), 1 / 271 (0.39 %); act = 5 / 269 (1.86 %), 4 / 269 (1.49 %); β-tubulin = 2 / 400 (0.5 %), 0 / 423 (0); his 3 = n / a, n / a; and cal = n / a, n / a, respectively. These molecular differences, particularly the high variation, further support the separation of C. actinidicola from closely related taxa. Moreover, the PHI test showed no significant evidence of recombination between C. actinidicola and its closest relatives, C. celtidis and C. spicati (Φw = 1.0; Fig. 2), further supporting its status as a distinct lineage. In conclusion, the combination of strong phylogenetic support, clear morphological differentiation, and genetic divergence justifies the recognition of Colletotrichum actinidicola as a novel species within the C. boninense species complex.