Verticillium nonalfalfae

Verticillium nonalfalfae is a soilborne fungus in the order Hyppocreales. It causes verticillium wilt in some plant species, particularly Ailanthus altissima. It produces yellow-pigmented hyphae, while producing resting mycelium. It is most closely related to V. albo-atrum and V. alfalfae. Verticillium nonalfalfae has a wide host range including hops, kiwifruit, spinach, solanaceous plants like eggplants and potatoes, and tree of heaven (A. altissima). Systemic infections appear on most hosts showing vascular wilts caused by xylem blockage. Additional symptoms including vascular discoloration, defoliation show almost exclusively on A. altissima. V. nonalfalae tends not to infect non-target plants. V. nonalfalfae does not infect alfalfa unlike V. alfalfae which does infect alfalfa. The symptoms of V. nonalfalfae include vascular wilting due to the blockage of vascular system and defoliation and these symptoms may occur at the same time. V. nonalfalfae is a soilborne fungus whose infecting structures can be pulled up by plants’ vascular system and plug up xylem tissues of hosts. One important host of V. nonalfalfae is hop. The symptoms of hosts infected by V. nonalfalfae on hops are categorized into two pathotypes: mild and lethal. Mild pathotypes majorly cause symptoms including curling and leaf tissue death as indicated by the picture. Hops infected by V. nonalfalfae with mild pathotype mostly can recover from the infection or survive with the infection. For lethal pathotype of V. nonalfalfae on hops, hosts suffer from fast weakening that is observed that ultimately leads to death. The lethal form was discovered in hops in the 40s and in Europe widely. Two pathotypes share similar peroxidase, which are thought to be contribute to their pathogenicity. Another important host of V. nonalfalfae is Ailanthus altissima, also known as tree of heavens. This species of Ailanthus has been introduced in northeast America from 1790s, and has grown in an unexpectedly fast fashion widely across its regions of plantation. It was then considered as an invasive plant whose expansion was hard to control because of its fast pace of reproduction and sprouting. V. nonalfalfae later was found as a biological control of A. altissima. Symptoms of Verticillium wilt on tree-of-heaven show up quickly as indicated in studies that wilting of vascular system and especially plug-up in xylem tissues, and following deaths appeared as fast as 4 weeks after infection. Verticillium nonalfalfae is a fast-killing soilborn fungus native to America. Its disease cycle is similar to Verticillium spp. cycle with minor differences. V. nonalfalfae overwinters by producing resting structure of mycelium in soil, unlike V. dahliae producing microsclerotia. Conidia is the major infecting agent for Verticillium nonalfalfae. V. nonalfalfae produces conidia in the soil in the spring from conidiophores. It has been found that intraspecific grafting enhances V. nonalfalfae’s dispersal of conidia, meaning that conidia from disease root can be transported to healthy root tissues of host intraspecifically. One way of conidia transmission in V. nonalfalfae is through mechanical dispersal where the conidia attaches to cutting tools and spread to another plant grafting and transporting. For dispersal of hops, V. nonalfalfae is spread in hop yards during soil cultivation, in hop trash, in planting materials from infested yards, and in soil moved on equipment and workers. Long-range transportation of conidia involves insects including ambrosia beetles, which are thought to be critical in creating regional epidemics of wilting on Ailanthus. It is not possible to differentiate V. nonalfalfae and V. alfalfae from V. albo-atrum consistently, just using morphological features. Verticillium albo-atrum may be found in co-infections with V. nonalfalfae on some hosts. The hyphae penetrate the root epidermal cells of hosts and enter xylem and the fungus spreads by producing large amount of spores.