Fusarium transvaalense 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 transvaalense Sandoval-Denis, Crous & W.J. Swart sp. nov. Fig. 7

Diagnosis.

Different from most species in FSAMSC by its slender sporodochial conidia with tapered and somewhat rounded apex; its smooth- to tuberculate, often pigmented chlamydospores and the formation of large mycelial tufts on OA.

Type.

South Africa, Kruger National Park, Skukuza, Granite Supersite, 25°06'45.5"S, 31°34'35.0"E, from rhizosphere soil of Sida cordifolia , 23 Mar 2015, W.J. Swart, holotype CBS H-23497, dried culture on SNA, culture ex-holotype CBS 144211 = CPC 30923.

Description.

Colonies on PDA growing in the dark with an average radial growth rate of 8.5-9.3 mm/d, reaching 34-37 mm diam. in 7 d at 24 °C, filling an entire 9 cm Petri dish in 7 d at 27-33 °C. Minimum temperature for growth 12 °C, maximum 36 °C, optimal 27-30 °C. Colony surface at first white, turning coral to dark vinaceous with white periphery and abundant yellow hyphae at the centre; flat, velvety to woolly, with abundant aerial mycelium and erect hyphal strings reaching several mm tall; colony margins regular and filiform. Reverse with yellow, coral or dark vinaceous patches, coral diffusible pigments strongly produced between 15-30 °C, turning scarlet to orange at 33-36 °C. Colonies on CMA and OA incubated at 24 °C in the dark occupying an entire 9 cm Petri dish in 7 d. Colony surface coral, rust to chestnut coloured in irregular patches, flat, felty to woolly, aerial mycelium scarce on CMA, mostly as radially dispersed white patches, on OA aerial mycelium abundant, especially on the periphery of the colony, forming dense, pustule-like, white mycelial tufts, formed by abundant intermingled hyphae and chlamydospores, 1-1.5 cm tall, with flesh to coral coloured stipes; margins on CMA and OA regular. Reverse pale luteous with red to coral periphery. Sporulation abundant from conidiophores formed on the aerial mycelium, at the agar level and from sporodochia. Conidiophores on the aerial mycelium straight or flexuous, septate, smooth- and thin-walled, up to 150 μm tall, sometimes emerging from irregular, swollen, pigmented and rough-walled cells on the hyphae; simple or sparingly and irregularly branched, branches bearing terminal, rarely lateral monophialides or reduced to conidiogenous cells borne laterally on hyphae; phialides on the aerial conidiophores short ampulliform, subulate to subcylindrical, smooth- and thin-walled, (7 –)9–14(– 15) μm long, (3 –)4– 5 μm at the widest point, without periclinal thickening and with a minute, inconspicuous collarette; conidia formed on aerial conidiophores of two types: a) hyaline, obovoid, ellipsoidal to clavate, smooth- and thin-walled, 0-1-septate, 2-14 × 2-4 μm; b) lunate to short falcate with a pointed apex and a somewhat flattened base, smooth- and thin-walled, 3-5-septate. Three-septate conidia: (16 –)18–27(– 29) × 5-6 μm; four-septate conidia: 21 –24(– 25) × 5-6 μm; five-septate conidia: (25 –)27– 33 × 5-6 μm. Sporodochia cream to orange coloured, formed abundantly on the surface of carnation leaves and rarely on the agar surface, at first very small and sparse later becoming aggregated. Conidiophores in sporodochia 22-31 μm tall, irregularly branched, bearing clusters of 3-6 monophialides; sporodochial phialides doliiform to ampulliform, (5 –)9–14(– 18) × (3 –)4– 5 μm, smooth- and thin-walled, with periclinal thickening and a short apical collarette. Sporodochial conidia falcate, wedge-shaped, tapering towards both ends, markedly curved and robust; apical cell longer than the adjacent cell, pointed; basal cell distinctly notched, sometimes somewhat extended (1 –)3–5(– 6)-septate, hyaline, smooth- and thick-walled. One-septate conidia: 19 × 4 μm; three-septate conidia: 20 –27(– 28) × 5-7 μm; four-septate conidia: (29 –)30– 32 × 5-7 μm; five-septate conidia: (26 –)29–41(– 53) × 4 –5(– 6) μm; six-septate conidia: 36 × 7 μm; overall (19 –)25.9–40(– 53) × (3.5 –)4–6(– 7) μm. Chlamydospores abundant, hyaline or pigmented, smooth- to rough-walled or tuberculate, 7-8 μm diam., terminal or intercalary, solitary, in chains or in clusters.

Distribution.

Australia and South Africa

Etymology.

After Transvaal, the name of a former colony and Republic located between the Limpopo and Vaal rivers, currently a province of South Africa and where this species was found. From Latin trans meaning "on the other side of" and Vaal a South African river.

Additional isolates examined.

South Africa, Kruger National Park, Skukuza, Granite Supersite, 25°06'48.6"S, 31°34'36.5"E, from rhizosphere soil of Melhania acuminata , 23 Mar 2015, W.J. Swart, CBS 144224 = CPC 30928, CBS 144212 = CPC 30929); 25°06'45.6"S, 31°34'37.7"E, CBS 144496 = CPC 33750, CBS 144213 = CPC 33751; 25°06'48.8"S, 031°34'36.6"E, from rhizosphere soil of Sida cordifolia , 23 Mar 2015, W.J. Swart, CBS 144214 = CPC 30946; 25°06'45.7"S, 31°34'35.1"E, CBS 144215 = CPC 33723; 25°06'45.5"S, 31°34'35.0"E, CBS 144216 = CPC 30918, CBS 144217 = CPC 30919, CBS 144218 = CPC 30922,, CBS 144219 = CPC 30926, CBS 144220 = CPC 30927); 25°06'51.4"S, 31°34'37.5"E, from rhizosphere soil of Kyphocarpa angustifolia , 23 Mar 2015, W.J. Swart, CBS 144221 = CPC 33740; 25°06'51.8"S, 31°34'38.1"E, CBS 144222 = CPC 30939, CBS 144223 = CPC 30941.

Notes.

Fusarium transvaalense exhibits a sporodochial conidial morphology typical of members of FSAMSC with marked dorsiventral curvature and tapered ends. Several species in FSAMSC form comparable conidia in culture i.e. F. crookwellense L.W. Burgess, P.E. Nelson & Toussoun, F. sambucinum , F. sporotrichioides Sherb., F. venenatum Nirenberg and F. culmorum (Wm.G. Sm.) Sacc. However, with the exception of F. sporotrichioides , the conidia of most species above-mentioned, differ by being more robust and often more pointed apically. Fusarium transvaalense differs from F. sporotrichioides by the absence of pyriform aerial conidia.

Two strains NRRL 13829 and NRRL 31008, previously identified as F. brachygibbosum Padwick showed different degrees of genetic similitude with the new species. While NRRL 31008 clustered within F. transvaalense , NRRL 13829 formed a clearly delimited sister linage. Morphologically, F. transvaalense exhibits significant differences allowing its separation from F. brachygibbosum . Both species produce sporodochial conidia with similar septation and sizes; however, F. brachygibbosum commonly exhibits a bulge in the middle portion of the conidia ( Padwick 1945), a feature not present in F. transvaalense . In addition, the latter species produces comparatively larger sporodochial conidia, when elements with the same degree of septation are compared; its chlamydospores are smaller, smooth-walled to markedly tuberculate and pigmented (7-8 μm vs. 10.7-15.3 μm, smooth-walled and hyaline in F. brachygibbosum ) and has a distinctive colonial growth on OA, forming large, pustule-like hyphal tufts, a feature not reported for F. brachygibbosum ( Padwick 1945).