Pilidium

Kunze, Mykol. Hefte 2: 92. 1823.

• Synonyms: Sclerotiopsis Speg., Anal. Soc. Cient. Argent. 13: 14 1882.
• Hainesia Ellis & Sacc., in Saccardo, Syll. fung. (Abellini) 3: 698. 1884.
• Discohainesia Nannf., Nova Acta Regiae Soc. Sci. Upsal., Ser. 4 8: 88. 1932.
• Classification: Leotiomycetes, Leotiomycetidae, Helotiales, Chaetomellaceae.
• Type species: Pilidium acerinum (Alb. & Schwein.) Kunze. Iconotype in Kunze & Schmidt (1823), table 2, fig. 5. Epitype and ex-epitype culture: BPI 843555, CBS 736.68. 
• DNA barcode (genus): LSU. 
• DNA barcode (species): ITS.

Ascomata apothecial, flat to funnel-shaped, short stipitate, white, pale brown to amber in the basal portion, wall pseudoparenchymatous (plectenchymatous). Paraphyses narrow, simple or branched, aseptate. Asci unitunicate, cylindrical, clavate, rounded or truncate at the apex, deliquescent. Ascospores ellipsoidal, somewhat enlarged at one side, straight to slightly curved, aseptate, smooth-walled. Conidiomata pycnidial or sporodochial; pycnidia globose, subglobose, obpyriform or oblong, sessile, pale brown when young, dark brown to black at maturity, superficial, solitary or gregarious, uniloculate, smooth; conidiomatal wall with two regions: outer region dark brown, inner region hyaline; opening by a stellate slit, rupturing irregularly, or lacking. Conidiophores hyaline, smooth, branched, cylindrical or filiform. Conidiogenous cells enteroblastic, phialidic, acropleurogenous, hyaline, smooth. Conidia mostly non-septate, hyaline, smooth, fusiform to falcate or cymbiform, with ends slightly pointed, straight to curved. Sporodochia globose becoming cupulate, discoid, with irregularly wavy margin, slimy, pale luteous, superficial, solitary, stalk pale brown near base, becoming dark brown at apex. Conidiophores hyaline, smooth, branched, cylindrical or filiform. Conidiogenous cells enteroblastic, phialidic, acropleurogenous, determinate, integrated, filiform or subcylindrical, hyaline, smooth, with minute collarette. Conidia aseptate, hyaline, smooth, fusiform to falcate or cymbiform to allantoid, with acute ends, straight to curved.

Culture characteristics:

Colonies on PDA surface and reverse white to cinnamon, buff, honey, sepia or isabelline, slimy with aerial mycelium absent or sparse, flat, granulose due to production of fruiting bodies; margin smooth and lobate.

Optimal media and cultivation conditions:

PDA, OA and MEA incubated at 25 °C for 1 wk at 25 °C under alternating fluorescent (12 h) and near ultraviolet (12 h) light are suitable to determine cultural characteristics and induce sporulation of the asexual morph. The sexual morph is not formed in vitro, and is relatively uncommon and inconspicuous.

Distribution:

Worldwide.

Hosts:

Species of this genus are mainly found on different hosts of Anacardiaceae, Hippocastanaceae, Myrtaceae and Rosaceae, and also in several other families such as Betulaceae, Ebenaceae, Fabaceae, Geraniaceae, Oleaceae, Paeoniaceae, Pinaceae, Polygonaceae, Salicaceae, Sapindaceae, Saxifragaceae and Vitaceae.

Disease symptoms:

Leaf spots, root lesions and tan-brown rot of fruits.

Notes:

Species of Pilidium are commonly found as plant-associated fungi or isolated from soil (Sutton 1980), and they are known to produce two kinds of conidiomata. Pilidium lythri (formerly known as Pi. concavum) and Pi. pseudoconcavum form sporodochia in culture. Although, the former species also produces the pycnidial morph, both species can be distinguished based on conidial shape (fusiform vs. cymbiform), sporodochial size (300–1000 μm diam vs. up to 300 μm diam) and DNA sequences (Crous et al. 2013). Both Pi. acerinum and Pi. eucalyptorum produce brown pycnidia in vitro and they are phylogenetically related. However, they differ in pycnidial size (200–1000 μm diam vs. up to 300 μm diam), conidiophore shape (cylindrical vs. filiform) and in the production of guttulate conidia, which are absent in Pi. acerinum and present in Pi. eucalyptorum (Rossman et al. 2004, Crous et al. 2015).

Discohainesia oenotherae and Hainesia lythri were considered the sexual and synasexual morphs of Pi. lythri (Rossman et al. 2004). However, after the one fungus = one name initiative the generic name Pilidium was proposed for conservation over Hainesia and Discohainesia (Johnston et al. 2014).

References:

• Sutton 1980, Shear & Dodge 1921, Palm 1991 (morphology); Sutton & Gibson 1977 (morphology and pathogenicity); Rossman et al. 2004 (morphology, pathogenicity and ecology).
• Crous PW, Wingfield MJ, Guarro J, et al. (2013). Fungal Planet description sheets: 154–213. Persoonia 31: 188–296.
• Crous PW, Wingfield MJ, le Roux JJ, et al. (2015). Fungal Planet description sheets: 371–399. Persoonia 35: 264–327.
• Johnston PR, Seifert KA, Stone JK, et al. (2014). Recommendations on generic names competing for use in Leotiomycetes (Ascomycota). IMA Fungus 5: 91–120.
• Kunze G, Schmidt JK (1817). Mykologische Hefte. 2nd vol. Leipzig, Germany.
• Palm ME (1991). Taxonomy and morphology of the synanamorphs Pilidium concavum and Hainesia lythri (coelomycetes). Mycologia 83: 787–796.
• Rossman AY, Aime MC, Farr DF, et al. (2004). The coelomycetous genera Chaetomella and Pilidium represent a newly discovered lineage of inoperculate discomycetes. Mycological Progress 3: 275–290.
• Shear CL, Dodge BO (1921). The life history and identity of Patellina fragariae, Leptothryrium macrothecium, and Peziza oenotherae.  Mycologia 13: 135–170.
• Sutton BC (1980). The Coelomycetes. Fungi imperfecti with pycnidia, acervuli and stromata. Commonwealth Mycological Institute, Kew, UK.
• Sutton BC, Gibson IAS (1977). Pezizella oenotherae. CMI Descriptions of Pathogenic Fungi and Bacteria 535: 1–2.

Table 13. DNA barcodes of accepted Pilidium spp.

¹BCC: BIOTEC Culture Collection, National Center for Genetic Engineering and Biotechnology (BIOTEC), Khlong Luang, Pathumthani, Thailand; CBS: Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands. ^T and ^ET indicate ex-type and ex-epitype strains, respectively.

²ITS: internal transcribed spacers and intervening 5.8S nrDNA; LSU: partial 28S large subunit RNA gene.

• Crous PW, Wingfield MJ, Guarro J, et al. (2013). Fungal Planet description sheets: 154–213. Persoonia 31: 188–296.
• Crous PW, Wingfield MJ, le Roux JJ, et al. (2015). Fungal Planet description sheets: 371–399. Persoonia 35: 264–327.
• Marin-Felix Y, Groenewald JZ, Cai, L, et al. (2017). Genera of phytopathogenic fungi: GOPHY 1. Studies in Mycology xxxx.
• Rossman AY, Aime MC, Farr DF, et al. (2004). The coelomycetous genera Chaetomella and Pilidium represent a newly discovered lineage of inoperculate discomycetes. Mycological Progress 3: 275–290.