Stagonosporopsis rhizophilae, Wei & He & Riccardo & Yang & Yuan, 2021

Wei, Huanshen, He, Xinghua, Riccardo, Baroncelli, Yang, Yuzhan & Yuan, Zhilin, 2021, Stagonosporopsis rhizophilae sp. nov. (Didymellaceae, Pleosporales), a new rhizospheric soil fungus associated with Populus deltoides Marsh, Phytotaxa 491 (1), pp. 23-34 : 28-29

Taxonomy Stagonosporopsis rhizophilae sp. nov. Z. L. Yuan and H. S. Wei ( Fig. 2 )

MycoBank: MB833389

Etymology: The name reflects that the fungus was isolated from rhizosphere soils.

Conidiomata pycnidial, globose to sub-globose, glabrous, superficial on immersed into the agar, without obvious ostioles. Pycnidia ranged from 140 to 280 μm in diameter (x = 195.6 μm, n = 15), solitary or (2–7) confluent and irregularity-shaped. Pycnidial wall pseudoparenchymatous, 3–6 layers, with an outer wall composed of 1–3 layers of brown olivaceous cells. Conidiogenous cells phialidic, hyaline, smooth, ampulliform to doliiform, 3.0–6.8×5.5–10.0 μm (x = 7.1±1.3×4.3±1.0 μm, n = 10). Conidia majority aseptate, hyaline, ellipsoidal, oblong or rod-like, thin-walled, smooth, measuring 4.2–6.8×1.0–2.6 μm (x = 5.6±0.8×1.7±0.5 μm, n = 30), with usually 2 distinct polar guttules. Sexual morph unknown.

Culture characteristics: colonies on PDA reaching 53–74 mm diameter after 7 days at 22 ° C in darkness, with regular edge, white to black with grey olivaceous, aerial mycelium was villous on the surface, abundant, aseptate, black in the center with a white margin. Colony reverse was olivaceous to dark in the central with white edge. Hyphae are little submerged in the medium. After 7 days, colonies on OA had a diameter of 55 to 66 mm, Mycelium was dark brown in the center, with white floss-shaped aerial mycelium at the periphery; colonies were not visible on the reverse of the plate in cultures grown on agar at 22 ° C. After 7 days colonies on MEA were 65 to 70 mm of diameter, regular, with loose; colony were pale white to olivaceous grey with greenish olivaceous in the center; pale white aerial mycelium; reverse similar. After 7 days colonies on CA had a 53 to 63 mm diameter, regular, with well-developed, compact, and floccose, white aerial mycelium; colony white to olivaceous grey in the center, staining the agar due to the release of a pigment; reverse citrine margin to greenish olivaceous with pale brown. NaOH spot test: negative, no change in color on MEA.

Specimen examined: CHINA. Zhejiang Province, Hangzhou, XinDeng town, from rhizosphere soils of P. deltoides (Salicaceae) , 10 August 2016, Z. L. Yuan (holotype HMAS 248285 , Herbarium of Microbiology, Academia Sinica). Ex-type living culture (CGMCC 3.19852 = XDPOP-RS-9, China General Microbiological Culture Collection Center) . ibid. XDPOP-RS-16B (CGMCC 3.19851, HMAS 248284 ) ; ibid. XDPOP-RS-16W (CGMCC 1813., HMAS 248283 ) .

Notes:— Stagonosporopsis rhizophilae is placed in the genus Stagonosporopsis (Didymellaceae) based on molecular evidence and morphological characteristics. Morphological characteristics of S. rhizophilae are closely related to those described for S. ajacis and S. adonidicola ( Li et al. 2006, 2013). Phylogenetically, S. rhizophilae sp. nov. is also close but distinct to S. nemophilae ( Fig. 1 ) a plant pathogens causing leaf spot and stem rot in Nemophila spp. ( Boerema et al. 2004). The size of S. rhizophilae conidia (4.2–6.8×1.0–2.6 μm) are different from those of S. nemophilae , which produced two different kinds of conidia (mainly aseptate, 4–9.5 μm×1.5–2.5 μm; 1-septate conidia up to 12 μm×3.5 μm). Moreover, pycnidia of S. nemophilae are characterized by 1–5 usually papillate ostioles in pycnidia ( Boerema et al. 2004), while those from S. rhizophilae are absent or not papillate ostioles. In addition, S. rhizophilae sp. nov. also differs from S. nemophila due to its negative response to NaOH spot test, indication of no production of diffusible antibiotic metabolite E ( Boerema et al. 2004, Hou et al. 2020b). A full comparison of morphological characters between S. rhizophilae and closely related species is reported in Table 2 .

Figures

FIGURE 1. Phylogenetic tree generated from a maximum likelihood analysis based on the combined ITS, LSU, TUB, and RPB2 sequence alignment. Bayesian posterior probabilities (left, BI PP ≥ 0.50) and maximum likelihood bootstrap (right, ML BP ≥ 50) values are given at the nodes. The strains of the new fungus are highlighted in orange. Bold lines indicate BI PP = 1 and ML BP = 100. The tree is rooted with Allophoma labilis CBS 124.93, All. minor CBS 325.82, and Heterophoma adonidis CBS 114309 in gray.

FIGURE 2. Stagonosporopsis rhizophilae sp. nov. (CGMCC3.19852). A–D. Colonies on PDA, MEA, CA, and OA, respectively (front and reverse); E. Pycnidia forming on OA. F. Section of pycnidium. G. Section of pycnidial wall. H. Conidiogenous cells. I. Conidia. Scale bars: 800 μm (E), 20 μm (F), 10 μm (G–I). PDA: potato dextrose agar, MEA: malt extract agar, CA: cherry-decoction agar, and OA: oatmeal agar.