Fusarium convolutans Sandoval-Denis, Crous & W.J. Swart

Sandoval-Denis, Marcelo, Swart, Wijnand J. & Crous, Pedro W., 2018, New Fusarium species from the Kruger National Park, South Africa, MycoKeys 34, pp. 63-92 : 63

Fusarium convolutans Sandoval-Denis, Crous & W.J. Swart sp. nov. Fig. 5

Diagnosis.

Different from F. circinatum , F. pseudocircinatum O’Donnell & Nirenberg and F. sterilihyphosum Britz, Marasas & M.J. Wingf. by the absence of aerial conidia (microconidia) and the presence of chlamydospores. Different from F. buharicum Jacz. ex Babajan & Teterevn.-Babajan and F. sublunatum by its shorter, less septate and less curved conidia and by the presence of sterile hyphal coils.

Type.

South Africa, Kruger National Park, Skukuza, Granite Supersite, 25°06'33.9"S, 31°34' 40.9E, from rhizosphere soil of Kyphocarpa angustifolia , 23 Mar 2015, W.J. Swart, holotype CBS H-23495, dried culture on OA, ex-holotype strain CBS 144207 = CPC 33733.

Description.

Colonies on PDA growing in the dark with an average radial growth rate of 2.1-4.8 mm/d, 4.4-5.8 mm/d and 4.6-6.3 mm/d at 24, 27 and 30 °C, respectively; reaching 11-28 mm diam. in 7 d at 24 °C and a maximum of 23-37 mm diam. in 7 d at 30 °C. Minimum temperature for growth 12 °C, maximum 36 °C, optimal 27-33 °C. Colony surface white to cream coloured, flat and highly irregular in shape, velvety to felty, with scant and short aerial mycelium; colony margins highly irregular to rhizoid, with abundant white to grey submerged mycelium. Reverse white, straw to yellow diffusible pigment produced between 21-33 °C, scarcely produced and turning luteous to orange at 36 °C. Colonies on CMA and OA incubated in the dark reaching 40-48 mm diam. in 7 d at 24 °C. Colony surface white to cream coloured, flat or slightly elevated at the centre, velvety to dusty; aerial mycelium abundant, short and dense, concentrated on the colony centre; margins membranous and regular, buff to honey coloured, without aerial mycelium. Reverse ochreous without diffusible pigments. Sporulation scant from conidiophores formed on the aerial mycelium, sporodochia not formed. Conidiophores on the aerial mycelium straight or flexuous, smooth- and thin-walled, simple, mostly reduced to conidiogenous cells borne laterally on hyphae or up to 50 μm tall, bearing terminal single or paired monophialides; phialides subulate to subcylindrical, smooth- and thin-walled, 15.5-22 μm long, (3.5 –)4– 5 μm at the widest point, with inconspicuous periclinal thickening and a short- flared collarette; conidia clustering in discrete false heads at the tip of monophialides, lunate to falcate, curved or somewhat straight, tapering gently toward the basal part, robust; apical cell often equal in length or slightly shorter than the adjacent cell, blunt to conical; basal cell papillate to distinctly notched, (1 –2–)3-septate, hyaline, thin- and smooth-walled. One-septate conidia: 24 × 4.5 μm; two-septate conidia: 24.5 × 6 μm; three-septate conidia: (25.5 –)29–36.5(– 38.5) × (4 –)5–6.5(– 7.5) μm. Chlamydospores abundantly formed, globose to subglobose, smooth- and thick-walled, (9.5 –)11–13.5(– 14) μm diam.; terminal or intercalary in the hyphae or conidia, often borne laterally at the tip of elongated, cylindrical, stalk-like projections, solitary or in small clusters. Sterile, coiled, sometimes branched hyphal projections abundantly formed laterally from the substrate and aerial mycelium.

Distribution.

South Africa.

Etymology.

From Latin, " convolutans ", participle of convolutare, coiling, in reference to the abundant sterile, coiled lateral hyphal projections.

Additional isolate examined.

South Africa, Kruger National Park, Skukuza, Granite Supersite, 25°06'33.9"S, 31°34' 40.9E, from rhizosphere soil of Kyphocarpa angustifolia , 23 Mar 2015, W.J. Swart, CBS 144208 = CPC 33732.

Notes.

The main morphological feature of F. convolutans , namely the production of sterile, coiled hyphal projections, grossly resembles other Fusarium species producing similar structures i.e. F. circinatum , F. pseudocircinatum and F. sterilihyphosum . The three latter species, however, are genetically unrelated to F. convolutans , being allocated in the FFSC; and are also easily differentiable by the characteristics of the aerial conidia (typical Fusarium microconidia are absent in the new species) and the lack of chlamydospores (present in the new species) ( Leslie and Summerell 2006). Fusarium convolutans can be easily differentiated morphologically from their phylogenetically closely related species, F. buharicum and F. sublunatum. It has relative simple conidiophores and shorter, less septate and markedly less curved conidia (up to 38.5 μm long and 1-3-septate vs. up to 87 and 81 μm long, 0-8-septate in F. buharicum and F. sublunatum , respectively) ( Gerlach and Nirenberg 1982). Fusarium buharicum and F. sublunatum also lack sterile hyphal coils.