Verticillium nubilum

General information about Verticillium nubilum 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 darkening due to the chlamydospores immersed in the agar (Figures 11a, 11b). Aerial mycelium generally abundant, floccose to pruinose, hyphae smooth-walled, (1–) 2–4 µm wide. Conidiophores present (Figure 11c). Conidiogenous cells are phialides (Figure 11d) arranged in whorls along conidiophores (Figure 11c), arising below transverse septum. Whorls consisting of one or more phialides (Figures 11c, 11d). Phialides subulate (Figure 11d). Conidia hyaline, smooth-walled, cylindrical with rounded apices to oval (Figure 11e), allantoid at times, rarely with central septum, (4.5–) 7.5 µm±2.0– µm (–14.5)×(2.0–) 2.5 µm±0.5 µm (–3.5) (l/w = (2.0–) 3.0±0.5 (–5.0), n = 50) (Figure 11e). Chlamydospores present, rounded to elongate, 6–14 µm diam, solitary or in chains of up to 6, straight or curved (Figures 11f, 11g, 11h). Brown-pigmented hyphae present at times (Figures 11h, 11i), generally attached to chlamydospores (Figure 11h).

Morphologically similar species

Verticillium nubilum can be differentiated from other Verticillium species by the near exclusive formation of chlamydospores as resting structure (Figures 11f, 11g, 11h), in combination with the relatively large conidia (Figure 11c). But V. nubilum can be confused with Gibellulopsis nigrescens, the former V. nigrescens, but G. nigrescens forms distinctly smaller chlamydospores (Isaac, 1953; Zare, Gams, Starink-Willemse, & Summerbell, 2007).

Figure 11. Morphological features of Verticillium nubilum.

11. Colony of strain P742 after 13 days on PDA, frontal view. 1b. Colony of strain PD742 after 13 days on PDA, reverse view. 11c. Conidiophore of strain PD621 after 17 days on WA-p. 11d. Apical phialide of strain PD621 after 17 days on WA-p. 11e. Conidia of strain PD621 after 17 days on WA-p. 11f. Solitary chlamydospore of strain PD742 after 17 days on WA-p. 11g. Linear chain of chlamydospores of strain PD742 after 17 days on WA-p. 11h. Angular chain of chlamydospores of strain PD621 after 25 days on PDA. 11i. Brown-pigmented hyphae of strain PD621 after 25 days on PDA. Scale bar: 11a, 11b = 1 cm; 11c–11i = 20 µm; Imaging method: 11a, 11b, = DS; 11c = PC; 11d, 11e = DIC; 11f–11i = BF.

doi:10.1371/journal.pone.0028341.g011

MycoBank: MB225664

Phylogenetic position

Verticillium nubilum belongs to the group of Verticillium that does not produce yellow-pigmented hyphae (group Flavnonexudans). 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
Potato (Solanum tuberosum), Soil UK 1 / 1