Wilsonomyces

Adask. et al., Mycotaxon 37: 283. 1990.

• Classification: Dothideomycetes, Pleosporomycetidae, Pleosporales, Dothidotthiaceae.
• Type species: Wilsonomyces carpophilus (Lév.) Adask. et al. Lectotype: plate 7, fig. 5 in Léveillé JH. 1843. Ann. Sci. Nat., Bot., sér. 2 19: 215. Epitype and ex-epitype culture designated here: CBS H-23113, CBS 231.89.
• DNA barcode (genus): LSU.
• DNA barcodes (species): ITS, tef1.

Sexual morph unknown. Conidiomata sporodochial, usually punctiform, tan to olivaceous brown, finally becoming black. Stroma present in host tissue, compact, immersed, erumpent, discoid on leaves, fusoid on twigs. Conidiophores macronematous, mononematous, densely compacted, straight or flexuous, branched or not, subcylindrical, geniculate, smooth, subhyaline to pale brown, cicatrised, 1–4-septate. Conidiogenous cells terminal and intercalary, subcylindrical, subhyaline, smooth, proliferating sympodially at apex, scars unthickened. Conidia holoblastic, solitary, dry, acrogenous, simple, thick-walled, cylindrical, clavate, ellipsoidal or fusiform, occasionally forked, rounded to acute at the apex, truncate at the base, generally (2–)3–5(–10) transverse with occasionally 1–2 oblique septa, rarely with 1 longitudinal septum, subhyaline, becoming medium brown to golden-brown, dark olivaceous to black in mass, conidia in vivo are larger (adapted from Adaskaveg et al. 1990).

Culture characteristics:

Growth moderate, PDA plates covered in 4 wk, mostly consisting of submerged hyphae with sparse aerial mycelium. In cultures grown in the dark, aerial mycelium sub-felty to felty, initially white becoming pale olive-grey to greyish olive, occasionally olive-ochre. In cultures grown exposed to light, submerged light brownish olive to olive-brown hyphae radiate outward from mycelial mat; aerial hyphae buffy-brown; olivaceous black to black conidia produced in mass (more details in Adaskaveg et al. 1990).

Optimal media and cultivation conditions:

PDA at 20 °C on the laboratory bench.

Distribution:

Worldwide.

Hosts:

Pathogens mainly of Prunus spp., particularly peaches and apricots, but also of other members of the family Rosaceae, i.e. Pyrus communis, Malus domestica, Sorbus aucuparia and Cydonia oblonga. Also reported in Cleome sp. (Cleomaceae) and Quercus ilex (Fagaceae).

Disease symptoms:

Wilsonomyces causes a disease known as shot-hole disease because of the symptoms on the host leaves: small circular purple lesions with pale centres that gradually enlarge and become necrotic in the centre until the centre falls out. This genus also produces necrotic spots on the twigs and necrotic lesions on fruit.

Notes:

Wilsonomyces is a monotypic genus. Wilsonomyces carpophilus was initially described as a new species of Helminthosporium, and was subsequently transferred to different genera until Adaskaveg et al. (1990) introduced Wilsonomyces to accommodate it. The taxonomy of the genus was controversial, and Sutton (1997) regarded it as synonym of Thyrostroma. However, all the strains of Wilsonomyces carpophilus included in the phylogenetic analysis based on LSU, ITS and tef1 (Fig. 49, 64) sequences were located in a clade separate from the rest of the taxa incorporated in the tree including the type species of Thyrostroma, T. compactum. Therefore, it is herewith confirmed that Wilsonomyces represents a distinct genus. Finally, its location in the Dothidotthiaceae is also confirmed.

References:

• Ellis 1959, Adaskaveg et al. 1990 (morphology); Ahmadpour et al. 2012 (morphology and pathogenicity).
• Adaskaveg JE, Ogawa JM, Butler EE (1990). Morphology and ontogeny of conidia in Wilsonomyces carpophilus, gen. nov. and comb. nov., causal pathogen of shot hole disease of Prunus species. Mycotaxon 37: 275–290.
• Ahmadpour A, Ghosta Y, Javan-Nikkhah M, et al. (2012a). Study on morphology, pathogenicity and genetic diversity of Wilsonomyces carpophilus isolates, the causal agent of shot hole of stone fruit trees based on RAPD-PCR in Iran. Archives of Phytopathology and Plant Protection 45: 1–11.
• Ellis MB (1959). Clasterosporium and some allied Dematiaceae - Phragmosporae. II. Mycological Papers 72: 1–72.
• Sutton BC (1997). On Stigmina, Wilsonomyces and Thyrostroma (Hyphomycetes). Arnoldia 14: 33–35.

Table 22. DNA barcodes of accepted Wilsonomyces sp.

¹CBS: Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands. ^ET indicates ex-epitype strain.

²ITS: internal transcribed spacers and intervening 5.8S nrDNA; tef1: partial translation elongation factor 1-alpha gene.

• Marin-Felix Y, Groenewald JZ, Cai, L, et al. (2017). Genera of phytopathogenic fungi: GOPHY 1. Studies in Mycology xxxx.