Verticillium zaregamsianum

General information about Verticillium zaregamsianum 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 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).

Morphologically similar species

Verticillium zaregamsianum differs from all other Verticillium species by the formation of microsclerotia (Figures 13h, 13i) simultaneously with yellow-pigmented hyphae (Figures 13k, 13l).

Figure 13. Morphological features of Verticillium zaregamsianum.

13a. Colony of strain PD736 after 10 days on PDA, frontal view. 13b. Colony of strain PD736 after 10 days on PDA, reverse view. 13c. Conidiophore of strain PD736 after 32 days on WA-p. 13d. Solitary phialide of strain PD733 after 31 days on WA-p. 13e. Conidia of strain PD736 after 44 days on PDA; Inset: Brown, septate and constricted conidium of strain PD733 after 44 days on WA-p. 13f–13i. Microsclerotia of strain PD586 after 31 days on WA-p. 13f. Microsclerotium initial resembling chlamydospores. 13g. Microsclerotium initial with cells that originated by lateral cell divisions. 13h. Small microsclerotium. 13i. Microsclerotium. 13j. Hypha of resting mycelium in strain PD586 after 31 days on WA-p. 13k. Hyphal cells of strain PD733 containing yellow pigment after 44 days on PDA. 13l. Hyphal cells of strain PD736 encrusted by yellow crystals after 10 days on PDA. Scale bar: 13a, 13b = 2 cm; 13c = 50 µm; 13d–13l = 20 µm. Imaging method: 13a, 13b = DS; 13c, 13f–13l = BF; 13d, 13e = DIC.

Phylogenetic position

Verticillium nonalfalfae belongs to the group of Verticillium that does not produce yellow-pigmented hyphae (group Flavnonexudans), and is closely related to V. alfalfae. For a phylogenetic tree, see Figure 1 in Inderbitzin et al. (2011).

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. longisporum. Sugar beet is currently the only known non-Brassicaceae host of V. longisporum confirmed by DNA sequence data.

SubstratesGeographic distribution# plant hosts / # countries
Tomato (Solanum lycopersicum), Potato (Solanum tuberosum), Lettuce (Lactuca sativa), Tenweeks stock (Matthiola incana) Israel, Japan, Middle Asia 4 / 3