Verticillium zaregamsianum

Verticillium zaregamsianum

MycoBank: MB563556

Etymology: Named after Rasoul Zare and Walter Gams who collaboratively established the modern taxonomic framework this study is based on.

Latin diagnosis.

Verticillio dahliae simile sed pigmentum croceum exsudans.

Description.

Colonies on PDA after two weeks 3–6.5 cm, white at first, later yellow, reverse orange to yellow, then darkening due to the formation of microsclerotia (Figures 13a, 13b). Aerial mycelium generally abundant, floccose, hyphae smooth-walled, 1–4 µm wide. Conidiophores erect or slanted (Figures 13c, 13d), generally determinate, branched or unbranched, formed disjointedly throughout the colonies, hyaline, 50–800 µm in length, 3–4 µm wide, narrowing towards the apex to 2–3 µm, transversely septate, septa spaced more narrowly towards the apex. Conidiogenous cells are phialides (Figure 13d), arranged in (1–) 3–7 (–11) whorls along conidiophores (Figures 13c, 13d). Whorls spaced 25–100 µm apart, closer towards the apex, consisting of (1–) 2–5 (–6) phialides, arising below transverse septum. Apical whorls consisting of one apical and one to several lateral phialides (Figures 13c, 13d). Phialides subulate, tapering from 2–3 µm at the base to 1–1.5 µm at the tip, terminal phialides 25–60 µm long, lateral phialides 20–60 µm long (Figure 13d). Conidia hyaline, smooth-walled (Figure 13e), cylindrical with rounded apices to ellipsoidal, (4.0–) 5.5 µm±1.0 µm (–12.5)×(2.0–) 3.0 µm±0.5 µm (–6.5) (l/w = (1.4–) 2.0±0.3 (–2.8), n = 88), accumulating at the tip of the phialides (Figure 13c), one-septate, constricted at septum, and brown-pigmented at times with age (Figure 13e). Microsclerotia regularly or irregularly distributed throughout the colony, rounded to variously shaped, up to 90 µm diam and consisting of rounded cells, up to 14 µm diam (Figures 13f, 13g, 13h, 13i). Structures resembling chlamydospores, possibly microsclerotia initials, present at times, up to 10 µm wide (Figures 13f, 13g). Scattered brown-pigmented hyphae present at times, thick-walled, up to 5 µm wide (Figure 13j). Yellow-pigmented hyphal cells present (Figures 13k, 13l), up to 6 µm wide, containing globules of yellow pigment (Figure 13k), at times yellow pigmented crystals present outside the cells (Figure 13l).

Types.

Holotype: Dried culture of V. zaregamsianum strain PD736 (Japan: Chiba; lettuce) deposited at UC (UC 1953899), an ex-holotype culture at CBS (CBS 130342) and NRRL (NRRL 54795).

Specimens examined.

The description was based on V. zaregamsianum strains PD586, PD739 and PD740 (Japan: Chiba; tenweeks stock), PD731, PD733 and PD734 (Japan: Hyogo; lettuce), PD735 (Japan: Kagawa; lettuce), PD736, PD737 and PD738 (Japan: Chiba; lettuce) (Table S1).

Distribution and host range.

Currently only known from Japan. Substrates include lettuce and tenweeks stock.

Commentary.

Verticillium zaregamsianum differs from all other Verticillium species by the formation of microsclerotia (Figures 13h, 13i) simultaneously with yellow-pigmented hyphae (Figures 13k, 13l). Only a few potential chlamydospores, possibly immature microsclerotia (Figure 13f, 13g), and sparse resting mycelium (Figure 13j) were observed. Verticillium tricorpus, V. isaacii and V. klebahnii differ by the formation of abundant chlamydospores (Figures 7g, 8f, 12e) and resting mycelium (Figures 7f, 8f, 12d). Verticillium zaregamsianum was described as a new species because according to Index Fungorum (www.indexfungorum, accessed on September 30, 2011), there were no synonyms available for V. tricorpus. None of the two synonyms of the morphologically similar V. dahliae listed in Index Fungorum (V. ovatum G.H. Berkeley & A.B. Jackson, V. tracheiphilum Curzi) matched the morphology of V. zaregamsianum in that no yellow-pigmented hyphae were mentioned [52], [53].