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| Microstrobilinia castrans Beenken & Andr. Gross, in Beenken, Stroheker, Dubach, ... et Gross, 2023. |
Abstract
The fungal pathogens of spruce are well known in Europe and elsewhere. Therefore, it was surprising to discover a new fungal species and genus in Central Europe that attacks the pollen cones of three spruce species. The new ascomycete forms apothecia on stromatized pollen cones of Norway spruce (Picea abies) and Serbian spruce (Picea omorika) in mountain areas and on West Himalayan spruce (Picea smithiana) planted in urban lowland regions of Switzerland, Germany, and Italy. It was also detected in France, based on metabarcode sequences deposited in the GlobalFungi database. Its sudden appearance and the different origins of the host trees in Europe and Asia leave the origin of the fungus unclear. The new fungus might be a neomycete for Europe. A phylogenetic analysis using SSU, LSU, ITS, RPB2, and TEF1 sequences classified the fungus as a member of Sclerotiniaceae (Helotiales, Leotiomycetes). However, it differs morphologically from the other genera of this family in having an ascus without apical apparatus containing four mainly citriform spores with 16 nuclei each. Furthermore, it is the only known cup fungus that parasitizes pollen cones of conifers by stromatizing their tissue and infecting pollen grains. The fungus does not seem to cause major damage to the spruce populations, as only a few pollen cones per tree are affected. All this leads us to describe the newly discovered fungus as the new species and new genus Microstrobilinia castrans, the fungus that castrates pollen cones of spruce.
Keywords: GlobalFungi database, Helotiales, Multinucleate ascospores, Neomycete, New genus, New species, Phenology, Pollen parasite
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| Microstrobilinia castrans: a–e On Picea smithiana: a P. smithiana tree at type location, two P. omorika trees in the background; b fresh infected pollen cone showing first symptoms like deformation and brown discoloration; c infected pollen cone with apothecia in the first year after infection; d, e several years old pollen cones overgrown with mosses and lichens with fresh apothecia and remnants of last year’s apothecia. f–i On Picea abies: f P. abies at a typical habitat in the Swiss Alps; g infested pollen cones on twigs; h pollen cone with small immature apothecia; i pollen cone with mature apothecia. j Pollen cones of P. omorika with dry, mature apothecia |
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| Microstrobilinia castrans, ontogeny of apothecia: a Black primordium in center of a cone scale in early summer; b immature apothecium in summer; c mature apothecia in autumn with gray velvet outer surface; d dehydrated mature apothecia with black smooth outer surface in next spring; e, f hydrated mature apothecia in next spring; g apothecium in side-view showing the stipe; h dissected pollen cone scales with apothecium. a–d from P. abies; e, f, h from P. smithiana; g from P. omorika. Scale bars: a, b = 0.25 mm; c, d, g = 0.5 mm; e, f, h = 1 mm |
Microstrobilinia Beenken & Andr. Gross, gen. nov.
Etymology: The genus name refers to the substrate: “microstrobilus” means “small cone” in Greek and is the botanical term for the male pollen cone of conifers.
Diagnosis: Member of Sclerotiniaceae Whetzel (1945) emend. Holst-Jensen et al. (1997) (Helotiales, Leotiomycetes), different from all other members of the Sclerotiniaceae in 4-spored, cylindrical asci with a short stipe and an iodine negative apex without apical apparatus, mature ascospores containing 16 nuclei, parasitizing pollen cones of Picea spp.
Microstrobilinia castrans Beenken & Andr. Gross, spec. nov.
Etymology: The species name refers to the fact that the fungus prevents the male reproduction of its host: “castrans” is Latin for castrating/emasculating.
Short diagnosis: Apothecia brown, short stipitate, desiccation-tolerant, 1–5 mm in diameter, growing on stromatized pollen cones of Picea spp.; ectal excipulum of brown textura globulosa-angularis; asci cylindric, av. 108 × 14.6 µm when alive, iodine negative without visible apical apparatus, 4-spored, ascospores citriform, and almond-shaped, av. 25 × 13 µm when alive, containing 16 nuclei when mature.
Ludwig Beenken, Sophie Stroheker, Vivanne Dubach, Markus Schlegel, Valentin Queloz and Andrin Gross. 2023. Microstrobilinia castrans, A New Genus and Species of the Sclerotiniaceae parasitizing Pollen Cones of Picea spp. Mycological Progress. 22, 14. DOI: 10.1007/s11557-023-01865-w
