Microbotryum polycnemoides T. Denchev, Denchev, Kemler & Begerow, sp. nov.
Index Fungorum number: IF 557222; MycoBank number: MB 557222; Facesoffungi number: FoF 07517; Fig. 1
Etymology – The specific epithet refers to the host species.
Holotype – SOMF 30200
Parasitic on Polygonum polycnemoides. Infection systemic, all flowers of an inflorescence affected. Sori in perianth tube, hypanthium, and filaments of each flower, and in achenes, swelling considerably the affected organs and filling them with pulverulent, blackish brown spore mass. Ovaries, anthers, and perianth lobes remain intact. Spores subglobose, broadly ellipsoidal, ovoid, globose, slightly irregular or sometimes ellipsoidal, (14–)15–19(–21)×(12.5–)13.5–17(–18.5) (16.6±1.1×15.2±0.9) μm (n=300), medium reddish brown; wall reticulate, (1.7–)2–2.7(–3) μm thick (including reticulum), meshes (8–)9–12(–13) per spore diameter, 0.4–2.5(–3.5) μm wide, muri 1–1.9(–2.3) μm high. In SEM meshes mostly rounded, interspaces often perforate with up to 4(–6) holes per interspace, sometimes with 2(–4) warts.
Material examined – TURKEY, the Anti-Taurus Mts (Aladağlar), Niğde Province, near Çamardı, Mt. Küçük Denizli, alt. 2300–2500 mls, on Polygonum polycnemoides Jaub. & Spach (Polygonaceae), 11 August 1992, V. Vašák s.n. (SOMF 30200, holotype).
GenBank numbers – ITS=MN989380, LSU=MN989381.
Additional material examined – Microbotryum aviculare (Liro) Vánky—SWEDEN, Uppland, near Uppsala, on Polygonum aviculare L., 10 August 1978, Sz., T. & K. Vánky (as ‘Ustilago avicularis’, H.U.V. 7439, kept at BRIP); M. shastense (Zundel) Vánky—USA, California, Siskiyou Co., Mt. Shasta, 41°22ʹN 122°12ʹW, ca 2700 msl, on Polygonum shastense W.H. Brewer, 8 August 1988, F. Oberwinkler et al., 3207 (Vánky, Ustilag. 717, in SOMF 19825; topotype).
Notes – Polygonum polycnemoides is an Irano-Turanian species, distributed in Armenia, Nakhichevan, Turkey, Syria, Lebanon, Israel, North Iraq, Iran, the Central Asian Republics, Xinjiang, Mongolia, Afghanistan, and West Himalaya (Davis 1967; Li et al. 2003; Uotila 2017). Microbotryum polycnemoides is known only from the type collection.
Microbotryum contains species that parasitize plants from many different lineages of euasterids, with host-specificity of individual parasite species in general being exceptionally high (Kemler et al. 2020). On hosts in Polygonum, only two species of Microbotryum have been previously known: M. aviculare on Polygonum aviculare, P. norvegicum and P. oxyspermum subsp. raii (from Europe, Asia, and North America), and M. shastense on Polygonum shastense (from North America) (Vánky 2011). Microbotryum polycnemoides (Fig. 1) can be easily distinguished from M. aviculare and M. shastense in having a different colour of the spore mass, larger spores, higher number of meshes per spore diameter, and higher spore wall muri. Microbotryum polycnemoides is closely related to M. parlatorei (97% MLBS support) and does not form a monophylum with M. shastense. The topology of our phylogenetic tree additionally indicates that M. polycnemoides is not closely related to M. shastense, but there is no statistical support for this relationship. Further analyses are warranted to understand the relationship between the clade of M. polycnemoides/M. parlatorei and M. shastense (Fig. 2).
Figure 1 – Microbotryum polycnemoides (SOMF 30200, holotype). a Habit. b, c Spores in LM (in median and surface view, respectively). d–h Spores in SEM. Scale bars: a=0.5 cm, b, c=10 μm, d–g=5 μm, h=1 μm
Figure 2 – Most likely tree inferred by maximum likelihood analysis via RAxML version 8.2.11 (Stamatakis 2014) based on concatenated MAFFT v7.450 (Katoh and Standley 2013) alignments of ITS and LSU dataset for Microbotryum species and several closely related genera in Microbotryales. The tree is based on the same dataset as in Kemler et al. (2009), but was pruned to only show one specimen per fungal species. Values at nodes indicate bootstrap values inferred by 100 replicates; only values greater than 50% are shown. The newly generated sequence is in blue bold