Colletotrichum juglandis X. Wei & J.X. Deng, 2022

Wei, Xin, Yang, Shu Qi, Jiang, Zhi Gang, Cui, Meng Jiao, Deng, Jian Xin & Zhang, Yi, 2022, Colletotrichum juglandis sp. nov. (Ascomycota: Glomerellaceae) associated with walnut leaf spot in China, Phytotaxa 556 (3), pp. 256-268 : 263-264

Colletotrichum juglandis X. Wei & J.X. Deng , sp. nov. Fig. 3

MycoBank No: 843086.

Etymology: In reference to the host genus name, Juglans .

Type. China, Hubei Province, Yichang city, Xingshan county on infected leaves of Juglans regia . 11 July , 2019, J . X. Deng (ex-type culture YZU 191277 )

Description: Colonies on PDA attaining 47–52 mm diam. after 7 days at 25 °C, whitish to gray, dense, aerial mycelium with masses of conidial ooze. Conidia on SNA unicellular, hyaline, smooth-walled, aseptate, straight, subcylindrical to fusiform with one end round and one end slightly acute, 6–15×2–5 μm (av.: =10.8×4.1, n =50). Appressoria single, brown to dark brown, smooth-walled, variable in shape, irregular unlobed or slightly lobed, 6–17× 4–10 μm (av.: =9.3×6.4, n =30). Chlamydospores formed laterally on hyphae. Setae absent. Sexual morph not observed.

Materials examined: China, Hubei Province, Yichang City, Xingshan County, Walnut orchard, from the leaf of Juglans regia anthracnose 11 July, 2020, X. Wei, living cultures YZU 191277 and YZU 201192.

Note: This species belongs to C. acutatum species complex ( Fig. 1 ) and forms a mono-lineage in a clade comprising C. chrysanthemi , C. cosmi , C. guajavae , C. nymphaeae , C. scovillei , and C. walleri with 1.0/100% (PP/BS) values. It is phylogenetically close related to C. nymphaeae , C. guajavae , C. scovillei and C. chrysanthemi . Morphologically, it is readily differentiated with C. chrysanthemi by conidia shape and distinct from the other three species by producing larger appressoria ( Table 2 ). In addition, C. guajavae and C. scovillei produce conidia with acute ends (Damn et al. 2012a), which is not observed in this species.

Pathogenicity tests

Pathogenicity tests revealed that Colletotrichum juglandis sp. nov. from Juglans regia could induced necrotic symptoms on living leaves by the spore suspension of isolate YZU 191277. After 7 days, the disease symptoms caused by spore suspension were around 4.3 mm in diameter ( Fig. 3B ), while symptomless on controls. After re-isolation, the same pathogen was obtained and identified based on morphology.

Figures

FIGURE 1. Phylogenetic tree of Colletotrichum spp. associated with walnut leaf spot based on the combined gene sequences of ITS, GAPDH, CHS-1, and ACT. The Bayesian posterior probabilities ≥0.6 (PP), maximum likelihood bootstrap support values ≥60% (BS) are given at the nodes (PP/BS). Examined isolates are in bold. Isolates marked with “*” are ex-type or ex-epitype and “(*)” are ex-type or authentic culture.

FIGURE 3. Morphology of Colletotrichum juglandis sp. nov. and its pathogenicity test on walnut leaf (Juglans regia). A. Diseased samples from field; B. Pathogenicity tests on living leaf; C. Colony on PDA; D. Conidioma; E. Conidiophores; F. Chlamydospores; G–I. Appressoria; J. Conidia. D. Scale bars = 100 μm; E–J = 10 μm.