Erysiphe salicina J. Feng, S.-Y. Liu & Y. Li, sp. nov.
Mycelium epiphyllous, effuse or in patches, sometimes confluent and covering the entire leaf surface, white, moderately thick, evanescent to persistent (Fig. 1a–c). Hyphal cells about 3–6 µm wide; hyphal appressoria solitary or in opposite pairs, lobed to multilobed, coral-like (Fig. 1d–g); conidiophores arising from the upper surface of the mother cell, erect, 48–87 µm long, foot-cells cylindrical, straight, occasionally slightly sinuous at the base, 17–59 × 4–7 µm, followed by 0–2 usually shorter cells, forming conidia singly (Fig. 1h); conidia ellipsoid-cylindrical, usually 20–29 × 8–14 µm, with a length/width ratio varying from 1.8 to 2.9 (Fig. 1i–l), germ tubes almost terminal, short, conidial appressoria multilobate, some showing longitubus pattern, produced laterally, near the middle or in perihilar position (Fig. 1m–n). Chasmothecia gregarious or scattered, 112–149 µm diam. (Fig. 1o); peridium cells irregularly polygonal to rounded, 8–16 µm diam. (Fig. 1p); appendages numerous, 22–53 per chasmothecium, rarely more, ± equatorial, straight and stiff, simple, 104–169 µm long (0.8–1.3 times as long as the chasmothecial diam.), width almost equal throughout or somewhat wider above, i.e., coiled part somewhat enlarged, width usually about 5–8 µm near the base, 13–19 µm towards the coiled tip (Fig. 1q–s), aseptate, hyaline, wall thin throughout, smooth, occasionally somewhat rough at the base, apices tightly or loosely uncinate-circinate or subhelicoid; asci 5–7, ellipsoid-obovoid, saccate, 57–79 × 29–50 µm, short-stalked, sometimes almost sessile, 4–7-spored (Fig. 1t–w); ascospores oblong ellipsoid-ovoid, 24–34 × 11–17 µm, colourless (Fig. 1x).
Diagnosis: Differs from all known Erysiphe species on hosts belonging to Salix in having hyphal appressoria in opposite pairs, shorter conidiophores, up to 87 µm, smaller conidia, 20–29 × 8–14 µm, chasmothecia with fewer and shorter appendages and larger ascospores, and by forming a monophyletic clade separate to all other Erysiphe species in phylogenetic analyses.
Type: China, Heilongjiang Province, Yichun, Jiayin Maolanggou National Forest Park, on Salix sinica, 16 Aug. 2014, Shu-Yan Liu and Feng-Yun Zhao (HMJAU-PM91918 – holotype; HMAS249775 – isotype, MycoBank, MB 840551); ex-holotype sequence – MZ474877 (ITS+28S).
Etymology: Composed of the name of the host genus, Salix, + Latin adjectival suffix -inus = belonging to.
Host range and distribution: On Salix abscondita (= S. raddeana), S. sinica and S. taraikensis (Salix subgen. Vetrix sect. Vetrix, Salicaceae), Asia (China).
Specimens examined: China, Heilongjiang Province, Tahe County, Qixia Mountain Botanical Garden, on S. sinica, 6 Oct. 2018, Feng-Yun Zhao, Zhen-Zhen Wang, Wei-Wen Yan (HMJAU-PM91919); Heilongjiang Province, Heihe City, Aihui Town, Aihui National Forest Park, 17 Sep. 2014, Feng-Yun Zhao, Jian Liu, Shu-Rong Tang, Peng-Lei Qiu (HMJAU-PM91920, HMJAU-PM91921, HMJAU-PM91963); Heilongjiang Province, Jiagedaqi, Beishan Park, 1 Sep. 2015, Wen-Tao Jiang, Jia-Ni Li, Lei Zhao, Feng-Yun Zhao (HMJAU-PM91922); Heilongjiang Province, Tahe County, Zhangling Forest Farm, 23 Sep. 2016, Feng-Yun Zhao, Guan-Xiu Guan, Jia-Ni Li, Peng-Lei Qiu (HMJAU-PM91923); Heilongjiang Province, Tahe County, Lvhai Holiday Inn, 25 Sep. 2016, Feng-Yun Zhao, Guan-Xiu Guan, Jia-Ni Li, Peng-Lei Qiu (HMJAU-PM91924); Heilongjiang Province, Harbin, Jinlongshan National Forest Park, 24 Aug. 2019, Jing Feng, Han-Xing Gao (HMJAU-PM91925). Heilongjiang Province, Heihe City, Aihui Town, Aihui National Forest Park, on S. taraikensis, 17 Sep. 2014, Feng-Yun Zhao, Jian Liu, Shu-Rong Tang, Peng-Lei Qiu (HMJAU-PM91920, HMJAU-PM91963); Beijing, Baihua Mountain, on S. abscondita (= S. raddeana), 19 Oct. 2018, Shu-Rong Tang, Li Liu, Peng-Lei Qiu (HMJAU-PM91989).
Notes: Erysiphe salicina morphologically differs from E. capreae, E. salicis var. salicis and E. salicis var. salicis-gracilistylae in having shorter conidiophore foot-cells [17–59 × 4–7 µm vs (25–)35–90(–110) × 5–9 µm in E. capreae and 15–45 × 5–9 µm in E. salicis] and smaller conidia (20–29 × 8–14 µm vs 25–45 × 10–24 µm in E. capreae and 23–40 × 10–18 µm in E. salicis). The ascospores are larger (24–34 × 11–17 µm) compared to E. salicis var. salicis (16–29 × 9–16 µm) and E. salicis var. salicis-gracilistylae (19–24 × 10–18 µm). In addition, Erysiphe salicina has chasmothecia with less appendages per chasmothecium [22–53 vs (33–)50–400 in E. capreae, and 25–95 in E. salicis], and appendages with enlarged uncinate-circinate apices (vs tightly uncinate-circinate, not enlarged apices in E. salicis). Furthermore, the appendages are regular, i.e., without constrictions and swellings, compared to E. salicis var. salicis-gracilistylae, and they arise equatorially, as in E. salicis, compared to E. capreae that are not equatorial or only somewhat in the upper half, and have a tendency to point upwards with maturity. Erysiphe adunca s. str. on Populus spp. (Salicaceae) is genetically as well as morphologically also distinguished from E. salicina by having much longer conidiophores, 70–150 µm, and foot-cells, 40–110 µm, larger conidia, 28–38 × 14–18 µm, and much longer chasmothecial appendages, 1–3 times as long as the chasmothecial diam. (Darsaraei et al. 2021).