Verticillium nonalfalfae (weed pathogen)
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Author(s): Wayne National Forest
Source: Wikimedia Commons
Verticillium nonalfalfae (weed pathogen) Inderb., H.W. Platt, Bostock, R.M. Davis & K.V. Subbarao, 2011
This fungus has been previously considered to be a strain of Verticillium alboatrum. It infects various plants and is also regarded as a pathogen of crops (see Verticillium nonalfalfae). In north-eastern North America, a strain of this fungus causes wilting, defoliation and death of the invasive tree Ailanthus altissima since 2009. Field tests with this strain resulted in almost complete eradication of A. altissima stands. The natural disease incidence on A. altissima has been reported as ~77% in two locations in Virginia (Snyder et al., 2013). The strain is now under development as a biological control agent against this weed.
Studies on the host range in an outbreak area in Pennsylvania showed that only 1% of striped maple saplings showed symptoms of Verticillium wilt and that artificial inoculations of oak, other maple species, ash and poplar did not produce disease symptoms (Schall and Davis, 2009). In addition, V. nonalfalfae isolates from hosts other than Ailanthus are not pathogenic on Ailanthus.
The conidia are hyaline, oval to cylindrical with rounded apices, smooth-walled and approximately 5-6 x 3 µm large. Microsclerotia (thick-walled, brown-pigmented resting mycelia) are formed as part of its life cycle. The species is morphologically indistinguishable from the alfalfa pathogen Verticillium alfalfae. It differs in its genetic structure and its host range. The species is also very similar to Verticillium alboatrum (which, however, does not form microsclerotia on PDA medium and has brown-pigmented conidia).
- Other images of Verticillium nonalfalfae (PLoS ONE, 2011, 6 (12) e28341 - click to enlarge)
branched conidiophore after 13 days on WA-p (scale = 20 µm)
colony after 14 days on PDA, 10a = frontal view, 10b = reverse view (scales = 2 cm)
10d) conidiophore after 13 days on WA-p (scale = 50 µm), 10e) phialide of apical whorl after 13 days on WA-p (scale = 20 µm), 10f) conidia after 31 days on WA-p (scale = 20 µm)
10g) resting mycelium after 18 days on WA-p, 10h) Intertwined hyphae of resting mycelium in the lumen of a thick-walled plant cell after 18 days on WA-p, 10i) torulose hyphal cells after 18 days on WA-p (scales = 20 µm)
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