Verticillium nonalfalfae

General information about Verticillium nonalfalfae 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 3.5–5.5 cm, white at first, later darkening due to the formation of resting mycelium immersed in the agar (Figures 10a, 10b). Aerial mycelium generally abundant, floccose to pruinose, hyphae smooth-walled, 1.5–3 µm wide. Conidiophores erect or slanted (Figures 10c, 10d), generally determinate, branched or unbranched (Figure 10c, 10d), formed disjointedly throughout the colonies, hyaline, 30–710 µm in length, 4.5–6 µm wide, narrowing towards the apex to 2–3 µm, transversely septate, septa spaced more narrowly towards the apex. Conidiogenous cells are phialides (Figure 10e), arranged in (1–) 2–6 whorls along conidiophores (Figures 10d 10e). Whorls spaced 50–160 µm apart, closer towards the apex, consisting of (1–) 2–5 (–7) phialides (Figure 10e), arising below transverse septum. Apical whorls consisting of one apical and one to several lateral phialides (Figures 10d, 10e). Phialides subulate, tapering from 2–3 µm at the base to 1–1.5 µm at the tip, terminal phialides 40–60 µm long, lateral phialides 30–45 µm long (Figure 10e). Conidia hyaline, smooth-walled, cylindrical with rounded apices to oval (Figure 10f), allantoid at times, (4.0–) 6.0 µm±1.0 µm (–10.5)×(2.5–) 3.0 µm±0.5 µm (–3.5) (l/w = (1.3–) 2.0±0.2 (–2.7), n = 80), accumulating at the tip of the phialides (Figure 10d). Resting mycelium present (Figures 10g, 10h, 10i), consisting of brown-pigmented hyphae, up to 9 µm wide, thick-walled, straight or curved, solitary or aggregated (Figures 10g, 10h), torulose at times (Figure 10i).

Morphologically similar species

Verticillium nonalfalfae produces resting mycelium, as do V. albo-atrum and V. alfalfae. Whereas V. alfalfae is morphologically indistinguishable from V. nonalfalfae, V. 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 10. Morphological features of Verticillium nonalfalfae.

10a. Colony of strain PD592 after 14 days on PDA, frontal view. 10b. Colony of strain PD592 after 14 days on PDA, reverse view. 10c. Branched conidiophore of strain PD616 after 13 days on WA-p. 10d. Conidiophore of strain PD616 after 13 days on WA-p. 10e. Phialide of apical whorl of strain PD616 after 13 days on WA-p. 10f. Conidia of strain PD808 after 31 days on WA-p. 10g. Resting mycelium of strain PD811 after 18 days on WA-p. 10h. Intertwined hyphae of resting mycelium in strain PD810 in the lumen of a thick-walled plant cell after 18 days on WA-p. 10i. Torulose hyphal cells of resting mycelium in strain PD592 after 18 days on WA-p. Scale bar: 10a, 10b = 2 cm; 10c, 10e–10i = 20 µm; 10d = 50 µm. Imaging method: 10a, 10b = DS; 10c, 10e, 10f = DIC; 10d, 10g–10i = BF.

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
Alfalfa (Medicago sativa), Cotton (Gossypium hirsutum), Hop (Humulus lupulus), Petunia (Petunia sp.), Potato (Solanum tuberosum), Soil, Spinach (Spinacia oleracea), Tomato (Solanum lycopersicum), Tree of heaven (Ailanthus altissima), Wild celery (Apium graveolens) Belgium, Canada, China, Cuba, Japan, Middle Asia, Netherlands, Slovenia,
UK, USA (IL, PA) 9 / 10