Erysiphe ulmi-alatae M. Bradshaw sp. nov.

Fig. 7

Etymology.

Epithet referring to the name of the type host, Ulmus alata.

Diagnosis.

Erysiphe ulmi-alatae is morphologically barely distinguishable from E. macrospora, but can be distinguished by the host and the fact that it phylogenetically forms a separate, highly supported clade.

Type.

USA • North Carolina: Wake County, Beaverdam Campground, Falls Lake, in upland hardwood-pine forest, on leaves of Ulmus alata, 3 November 2008, L. F. Grand 2095 and C. A. Vernia (NCSLG 18204 – holotype). Ex-holotype sequence: PV 416510 (ITS), PV 409586 (IGS).

Description.

Mycelium in persistent, creamy-white patches, almost entirely on adaxial leaf surfaces; hyphae branched, often at right angles, septate, hyaline, 3–5 µm wide; hyphal appressoria solitary or in opposite pairs, lobed; conidia formed singly, cylindrical-doliiform, 34–40 × 11–18 µm. Chasmothecia scattered to gregarious, dark brown, subglobose to globose, 130–178 µm in diameter; peridium cells irregularly polygonal, 7–13 × 10–21 µm; appendages numerous, number variable (40 +), hyaline, aseptate, ± equatorial, 80–145 × 5–9 µm, mostly shorter than the chasmothecial diameter, width ± equal throughout, walls smooth, uniformly thickened from base to tip, apices uncinate to circinate when mature, uncinate-circinate apex not enlarged, circinate apices 10–15 µm across (appendages shorter, stiffer, and with pointed ends when immature); asci 10–25 per chasmothecium, obovoid, saccate, short-stalked, 48–70 × 23–24 µm, walls up to 3 µm thick, 2 - spored; ascospores ellipsoid-ovoid to slightly teardrop-shaped, 22–30 × 11–17 µm, hyaline.

Additional specimens examined.

(all on leaves of Ulmus alata): USA • North Carolina, Cabarrus County, Concord, 15 October 1972, R. L. Forster 63 (NCSLG 24392); • Wake County, Cary, 7 July 2008, Y. Weimin s. n. (NCSLG 17649); • NC State University campus, Raleigh, 27 September 1972, A. J. Julius s. n. (NCSLG 24393); • Miner Presbyterian Church, New Bern Avenue, Raleigh, 24 September 1978, R. Sohn s. n. and G. Emberger (NCSLG 24391).

Substrate / host.

Ulmus alata.

Distribution.

(based on specimens deposited in North American herbaria as ‘ Erysiphe macrospora ’ or ‘ Uncinula macrospora ’ on Ulmus alata): North America (USA: Alabama, Florida, Georgia, Illinois, Indiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas).

Notes.

Erysiphe (Uncinula lineage) on Ulmus alata was previously assigned to Uncinula macrospora and Erysiphe macrospora, respectively (Salmon 1900; Braun 1987; Braun and Cook 2012). However, in the first phylogenetic examinations of E. macrospora, Bradshaw et al. (2023 b) revealed the paraphyly of this species. Sequences obtained from the type host, Ulmus americana, as well as on U. rubra (= U. fulva) and U. pumila, formed a well-supported clade, with a sequence retrieved from U. alata clustering outside in sister position. Now, additional sequences are available and confirm the Erysiphe on U. alata as a distinct, cryptic, sister species. The genetic similarity between E. macrospora and E. ulmi-alatae in multiple loci is relatively low (~ 95 %), which supports the description of a separate species. The two species are morphologically barely distinguishable, i. e., they can only be differentiated by their sequence differences and different hosts. The separation of E. macrospora s. lat. into two species, based on its host species, is not surprising. According to the current phylogenetic-taxonomic division of the genus Ulmus (Whittemore et al. 2021), the type species, Ulmus americana, pertains to Ulmus subgen. Oreopteleae sect. Blepharocarpus, whereas U. alata is assigned to Ulmus subgen. Oreopteleae sect. Chaetoptelea. Ulmus crassifolia and U. thomasii (= U. racemosa) are two additional elm species known to be hosts of E. macrospora s. lat. (Braun and Cook 2012) that belong to sect. Chaetoptelea. It can be assumed that these elm species also pertain to the host range of E. ulmi-alatae, which is, yet, unproven by means of sequence analyses. Additionally, Ulmus rubra (= U. fulva), a species pertaining to Ulmus subgen. Ulmus sect. Ulmus, is a proven host of E. macrospora, suggesting a wider host range of this species. The occurrence of E. ulmi-alatae on U. alata likely follows the distribution of its host species in the Southeastern and Central USA.