Verticillium albo-atrum

General information about Verticillium albo-atrum 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 DA after two weeks 4.5–5.5 cm diam, white at first, later turning yellow to orange due to the formation of yellow-pigmented hyphae, then darkening due to formation of resting mycelium immersed in the agar medium (Figures 4a, 4b). Aerial mycelium generally abundant, floccose to pruinose, hyphae smooth-walled, (1–) 1.5–4 µm wide. Conidiophores erect or slanted, generally determinate (Figure 4c), branched or unbranched (Figure 4d), formed disjointedly throughout the colonies, hyaline, base brown-pigmented at times, 80–480 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, arranged in 1–4 (–6) whorls along conidiophores (Figures 4c, 4d), arising below transverse septum (Figure 4e). Whorls spaced 20–140 µm apart, closer towards the apex, consisting of (1–) 2–4 (–6) phialides (Figures 4c, 4d, 4e). Apical whorls consisting of one apical and one to several lateral phialides (Figures 4c, 4d, 4e). Phialides subulate, tapering from 1.5–3 µm at the base to 1–1.5 µm at the tip, terminal phialides 40–80 µm long, lateral phialides 20–50 µm long (Figure 4e). Conidia hyaline, smooth-walled, cylindrical with rounded apices to oval (Figure 4f), tapering at times, (3.0–) 6.0 µm±1.5 µm (–10.5)×(2.0–) 3.0 µm±0.5 µm (–6.0) (l/w = (1.1–) 2.0±0.4 (–3.0), n = 86), accumulating at the tip of the phialides (Figures 4c, 4d). After 4 wks, a small number of conidia (generally <1%) with central septum, constricted at the septum at times (Figure 4f). Budding conidia and conidia germinating by formation of a phialide observed (Figure 4f). Resting mycelium present, consisting of brown-pigmented hyphae, up to 7 µm wide, thick-walled, straight or curved, solitary or aggregated, up to 25 µm wide (Figures 4g, 4h). Microsclerotia present, composed of tightly interwoven, torulose brown-pigmented hyphae, rounded or variously shaped, up to 230 µm diam and consisting of rounded to elongate cells, up to 10 µm diam (Figures 4i, 4j, 4k). Yellow-pigmented hyphal cells present at times, up to 5 µm wide (Figure 4l).

Morphologically similar species

Verticillium albo-atrum produces resting mycelium, as do V. alfalfae and V. nonalfalfae. But Verticillium albo-atrum differs by the formation of microsclerotia and yellow-pigmented hyphae. However, microsclerotia are not formed on PDA, and yellow-pigmented hyphae disappear after multiple transfers in the lab.

Figure 4. Morphological features of Verticillium albo-atrum.

4a. Colony of strain D747 after 10 days on PDA, frontal view. 4b. Colony of strain PD747 after 10 days on PDA, reverse view. 4c. Conidiophore of strain PD748 after 29 days on WA-p. 4d. Branched conidiophore of strain PD670 after 29 days on WA-p. 4e. Phialide of strain PD670 after 29 days on PDA. 4f. Conidia of strain PD670 after 29 days on PDA; Insets: Pigmented, septate and constricted conidium of strain PD670 after 29 days on PDA, budding conidium and conidium germinating by formation of a phialide, both of strain PD748 after 29 days on WA-p. 4g. Resting mycelium of strain PD747 after 33 days on WA-p. 4h. Aggregated hyphae of resting mycelium in strain PD670 after 28 on WA-p. 4i. Microsclerotium of strain PD670 after 47 days on PLYA. 4j. Microsclerotium of strain PD670 after 28 on WA-p. 4k. Microsclerotium of strain PD747 formed in the lumen of a thick-walled plant cell after 32 days on WA-p. 4l. Hypha of strain PD747 containing yellow pigment after 10 days on PDA. Scale bar: 4a, 4b = 2 cm; 4c, 4d = 50 µm; 4e–4h, 4j–4l = 20 µm; 4i = 100 µm. Imaging method: 4a, 4b = DS; 4c, 4d, 4g–4l = BF; 4e, 4f = DIC.

doi:10.1371/journal.pone.0028341.g004

MycoBank: MB199278 (as V. alboatrum)

Phylogenetic position

Verticillium albo-atrum belongs to the group of Verticillium that produces yellow-pigmented hyphae (group Flavexudans). For a phylogenetic tree, see Figure 1 in Inderbitzin et al. (2011). This tree, based on the combined partial sequences of the protein coding genes actin (ACT), elongation factor 1-alpha (EF), glyceraldehyde-3-phosphate dehydrogenase (GPD) and tryptophan synthase (TS), was adopted from Inderbitzin et al. (PLoS One, 2011, 6(12): e28341).

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. albo-atrum.

SubstratesGeographic distribution# plant hosts / # countries
Pestilence wort (Petasites hybridus), Potato (Solanum tuberosum), Stinging nettle (Urtica dioica), soil Australia, Canada, Netherlands, UK, USA (WI)3 / 5