Verticillium isaacii

Verticillium isaacii

MycoBank: MB563553

Etymology: Named after Ivor Isaac (1914–1978), in recognition of significant contributions to Verticillium taxonomy.

Latin diagnosis.

Verticillio tricorpus morphologia simile, sed characteribus sequentiarum nucleidearum distinguendum. Actin positione 79 (T), 115 (T), 292 (T), 380 (T), 410 (T), 432 (A); Elongation factor 1-alpha positione 142 (C), 162 (A), 166 (T), 185 (A), 190 (T), 230 (A), 235 (G), 248 (A), 260 (A), 331 (A), 363 (T), 366 (G); Glyceraldehyde-3-phosphate dehydrogenase positione 153 (C), 278 (C); Tryptophan synthase positione 133 (A), 143 (A), 383 (G).

Description.

Colonies on PDA after two weeks 2.5–6 cm diam, white at first, later yellow, reverse orange to yellow, then darkening due to the formation of resting mycelium, chlamydospores and microsclerotia (Figures 7a, 7b). Aerial mycelium generally abundant, floccose, hyphae smooth-walled, 1–3.5 µm wide. Conidiophores erect or slanted (Figure 7c), generally determinate, branched or unbranched, formed disjointedly throughout the colonies, hyaline, verruculose surface ornamentation present at times, 105–690 µm in length, 3–6 µm wide, narrowing towards the apex to 2–2.5 µm, transversely septate, septa spaced more narrowly towards the apex. Conidiogenous cells are phialides (Figure 7d), arranged in (1–) 2–4 (–6) whorls along conidiophores (Figure 7c), arising below transverse septum. Whorls spaced 25–60 µm apart, closer towards the apex, consisting of (1–) 3–5 (–6) phialides (Figure 7c). Apical whorls consisting of one apical and one to several lateral phialides (Figures 7c, 7d). Phialides subulate, tapering from 2–3.5 µm at the base to 1–1.5 µm at the tip, terminal phialides 30–65 µm long, lateral phialides 20–40 µm long (Figure 7d). Conidia hyaline, smooth-walled, cylindrical with rounded apices to oval (Figure 7e), tapering at times, (3.5–) 6.0 µm±1.5 µm (–14.5)×(1.5–) 3.0 µm±0.5 µm (–5.0) (l/w = (1.4–) 1.9±0.3 (–3.5), n = 73), accumulating at the tip of the phialides (Figure 7c). Conidia rarely one- or two-septate, constricted at the septum at times (Figure 7e). Resting mycelium, chlamydospores and microsclerotia present. Resting mycelium consisting of brown-pigmented hyphae, up to 5 µm wide (Figure 7f), chlamydospores solitary or in chains, up to 12 µm wide (Figure 7g), microsclerotia rounded or variously shaped, up to 70 µm diam and consisting of rounded to elongate cells, up to 10 µm wide (Figure 7h). Yellow-pigmented hyphal cells present, up to 5.5 µm wide, containing globules of yellow pigment, at times pigment accumulating as crystals outside the cells, up to 21 µm diam (Figures 7f, 7i).

Types.

Holotype: Dried culture of V. isaacii strain PD660 (USA: CA; lettuce) deposited at UC (UC 1953896), an ex-holotype culture at CBS (CBS 130343) and NRRL (NRRL 54792).

Specimens examined.

The description was based on V. isaacii strains PD341, PD343, PD367, PD437, PD610, PD611, PD612, PD613, and PD660 (USA: CA; lettuce), PD618 (UK; garden tomato), PD619 (Canada; soil), PD661 (USA: WA; lettuce), PD752 and PD753 (USA, WA; spinach) (Table S1).

Distribution and host range.

Currently known from Canada, UK and USA (CA, WA). Substrates include garden tomato, globe artichoke, hairy nightshade, lettuce, spinach and soil.

Commentary.

Verticillium isaacii is morphologically indistinguishable from V. klebahnii and V. tricorpus.