Verticillium isaacii

General information about Verticillium isaacii is provided below. Included are a morphological description, comments about morphologically similar species and phylogenetic affiliation. The data is from Inderbitzin et al. (2011) where additional information can be found. Host range data is from Inderbitzin and Subbarao (2014).

Species 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).

Morphologically similar species

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

Figure 7. Morphological features of Verticillium isaacii.

7a. Colony of strain PD619 after 10 days on PDA, frontal view. 7b. Colony of strain PD619 after 10 days on PDA, reverse view. 7c. Conidiophore of strain PD618 after 21 days on WA-p. 7d. Phialides of strain PD660 as part of an apical whorl after 21 days on WA-p. 7e. Conidia of strain PD611 after 22 days on WA-p; Insets: One-septate, constricted conidium and two septate conidium of strain PD660 after 21 days on WA-p. 7f. Hypha of resting mycelium and yellow crystal of strain PD752 after 35 days on PDA. 7g. Chlamydospores of strain PD752 after 35 days on PDA. 7h. Microsclerotium of strain PD752 after 35 days on PDA. 7i. Hyphal cell of strain PD660 encrusted with yellow pigment after 20 days on PDA. Scale bar: 7a, 7b = 2 cm; 37c = 50 µm; 7d–7i = 20 µm. Imaging method: 7a, 7b = DS; 7c, 7f–7i = BF; 7d, 7e = DIC.

Phylogenetic position

Verticillium isaacii belongs to the group of Verticillium that produces yellow-pigmented hyphae (group Flavexudans). For a phylogenetic tree, see Figure 1 in Inderbitzin et al

Host range and geographic distribution

These are inferred from GenBank ITS records, and most likely underestimate the current host range and geographic distribution of V. isaacii.

SubstratesGeographic distribution# plant hosts / # countries
Artichoke (Cynara scolymus), Bear’s breech (Acanthus mollis subsp. mollis), Brassica sp., Florist’s daisy (Chrysanthemum x morifolium), Hairy nightshade (Solanum physalifolium), Lettuce (Lactuca sativa), Potato (Solanum tubero- sum), Soil, Spinach (Spinacia oleracea), Tomato (Solanum lycopersicum) Australia, Belgium, Canada, Israel, Italy, UK,
USA (CA, WA)9 / 7