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Risk analysis for Verticillium nonalfalfae isolate VnAa40, causal agent of Verticillium wilt of Ailanthus altissima.
M. T. KASSON (1), D. D. Davis (1). (1) The Pennsylvania State University, University Park, PA, U.S.A.

Unprecedented mortality of the invasive <i>Ailanthus altissima</i> by an indigenous <i>Verticillium nonalfalfae</i> is currently widespread in south-central Pennsylvania where >13,000 trees are dead or dying following inoculation of 65 canopy trees. Because <i>Verticillium</i> spp. cause wilt diseases of many plant species, 64 species were stem-inoculated with <i>V. nonalfalfae</i> isolate VnAa40. Seventeen species exhibited wilt and vascular discoloration following inoculation: Amur corktree, autumn olive, black locust, catalpa, corkwood, crossvine, elderberry, Japanese maple, Norway maple, poison-ivy, redbay, redbud, sassafras, staghorn sumac, striped maple, and tree-of-paradise. However, mortality varied among species with only <i>Ailanthus</i>, elderberry, poison-ivy, striped maple, and sumac exhibiting >50% mortality. Furthermore, natural spread of this fungus within diseased <i>Ailanthus</i> stands was observed only for <i>Ailanthus</i>, devil’s walkingstick, and striped maple. Vascular discoloration, but without wilt or mortality, was observed in 16 inoculated species. Although artificial inoculations provide an evaluation of potential damage to non-target hosts, the low incidence of disease and mortality of these non-target hosts among inoculated <i>Ailanthus</i> offer support that VnAa40 may be host-adapted. Pending the outcome of molecular studies, <i>V. nonalfalfae</i> should be considered as a potential biocontrol for <i>Ailanthus</i>.<p><p>Keywords: Fungus, Trees, Forest Trees

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