Fusarium tuberculatum Tiendreb., Decock, Somda & Legrève, in Cao et al., Fungal Diversity 132: 482 (2025)

Index Fungorum number: IF 856637; MycoBank number: MB 856637; Facesoffungi number: FoF 17100; Figs. 1, 2

Etymology – refers to chlamydospores ornamented with tubercules.

Holotype – MUCL58421.

Culture characteristics – On PDA in the dark at 27 °C, average growth of 7.2 mm/day, for 7 days of incubation; aerial mycelium cottony and often grazing, the colony surface grayish brown to dark Ruby with whitish features above, cottony some time dotted with floccose aerial mycelium; reverse violet brown to ruby, lacking diffusible pigment; odor absent. On synthetic nutrient agar (SNA), aerial mycelium absents, colony translucid, with abundant sporulation on the medium surface. On CLA, aerial mycelium sparse with bright orange sporodochia forming on the carnation leaves.

Microscopic characteristics – On carnations leaf agar (CLA). Aerial mycelia made of unbranched or sparingly branched hyphae; conidiophores bearing intercalary or terminal phialides, monophialidic, subulate to subcylindrical, smooth- and thin-walled; microconidia, with 0–2 septate (uni or bicellular): 0-septate 4.7–7 × 1.5–2.3 (av. 5.3 × 1.7 µm); 1-septate 6–8 × 1.6–2.3 (av. 7.2 × 2.2 µm); 2-septate, 8–10 × 2–3.2 (av. 8.8 × 2.8 µm); macroconidia conidia born on conidiogenous cells solitary or densely gathered into sporodochia; sporodochia on carnation leaves globulose, with conidia accumulating into a pale orange mucilaginous drop; sporodochial conidiophores verticillately branched and densely packed, consisting of a smooth- and thin-walled stipe, bearing apical whorls of monophialides, subulate to subcylindrical; sporodochial macroconidia smooth- and thin-walled, hyaline, falcate, curved dorsiventrally with almost parallel sides tapering slightly towards both ends, a blunt to foot-like basal cell and a blunt to papillate, curved apical cell, 3–5 sep tate: 3-septate 32–38 × 4–4.6 µm (av. 35.8 × 4.2 µm); 4-septate 37–40 × 4–5.5 µm (av. 38 × 4.5 µm); 5-septate 41.3–43 × 4–5.6 µm (av. 41.5 × 4.5 µm); chlamydospores terminal or intercalary, single or bicellular, averaging 7.3 × 6.3 µm, thick-walled, the wall tuberculate, with blunt tubercles (Fig. 1).

Material examined – BURKINA FASO, Boucle du Mouhoun region, 11°51’21”N 4°17’55”W, isolated from the root of Solanum lycopersicum (Solanaceae) with wilt symptoms, March 2019, A. Tiendrebeogo, 100/19BF4 (MUCL58421, holotype); Mouhoun region, 13°7’27”N 3°25’31”W, isolated from Solanum lycopersicum (Solanaceae) root with wilt symptoms, Avril 2019, 124/19BF4 (MUCL58422); South-West region, 10°53’18”N 3°16’36”W, root of Solanum lycopersicum (Solanaceae) with wilt symptoms, March 2019, 096/19BF8 (MUCL58423); Cascades region, 10°41’20″N 4°45’31″W, isolated from Solanum lycopersicum (Solanaceae) root with wilt symptoms, March 2019, 087/19BF7 (MUCL58424); Central Plateau region, 12°30’27″N 1°22’14″W, isolated from Solanum lycopersicum (Solanaceae) root with wilt symptoms, December 2019, 164/19BF2 (MUCL58425).

GenBank – MUCL58421: OP272543 (tef1), OQ221746 (IGS), PP938436 (cmdA), PQ036167 (rpb2).

Notes – Fusarium tuberculatum is phylogenetically closely related to F. triseptatum L. Lombard & Crous, described from the USA, and which is known to infect Ipomoea batatas (Lombard et al. 2019). It is also known from Ivory Coast. Fusarium tuberculatum differs in having rough-walled, tuberculate chlamydospores (Fig. 1) and abundance of macroconidia, curved, 3–5-septate, with less production of microconidia. Based on a Megablast search of NCBIs GenBank nucleotide database, the closest hits using the tef1 sequence (–700 bp long) corresponds to Fusarium oxysporum strain SEMAF0043, GenBank MN539104 (identities = 691/692, 99.72%, one gap). This strain has been isolated in Mali, a country neighboring Burkina Faso, from an unidentified host. Comparison of the sequences (tef1) of the 4 other strains of F. tuberculatum also showed a high similarity with SEMAF0043, GenBank MN539104, with an identity of 99.86 to 100%. Phylogenetic analysis based on the four loci (tef1, cmdA, rpb2, and IGS) was carried out in order to ensure the correct identification of these strains. The phylogenetic tree obtained highlighted a distinct clade (Fig. 2).

Figure 1 – Fusarium tuberculatum. a, b Colony on PDA. c Sporodochia with a drop of conidia. d Microphialides. e Conidiogenous cellular with monophialide. f Macroconidia. g Microconidia. h Tuberculate chlamydospore. Scale bars: d = 7 µm, e = 12 µm, f = 40 µm, g = 7 µm, h = 10 µm. Credit: Tiendrebeogo and Decock.

Figure 2 – Phylogenetic tree constructed by the Maximum Likelihood method with a bootstrap of 1000 replicates, representing the evolution of the relationships between a combined dataset of four-locus sequences, namely, tef1, cmdA, rpb2, and IGS from 31 strains isolated from tomatoes with 26 sequences recovered from Lombard et al. (2019).