Verticillium wilt of alfalfa: epidemiology and control strategies

Verticillium wilt caused by Verticillium albo-atrum is an important disease of alfalfa (Medicago sativa) in Europe, North America, and northern Japan. The pathogen can spread by various means, including on infected alfalfa seeds and debris, through contact between roots, on farm implements, and through air and water. Recent studies in Canada reveal that V. albo-atrum can also be spread by insect pests, predators, and pollinators, as well as alfalfa pollen. Certain insects, such as the pea aphid (Acyrthosiphon pisum), alfalfa weevil (Hypera postica), migratory grasshopper (Melanoplus sanguinipes), two-striped grasshopper (Melanoplus bivittatus), and alfalfa leafcutting bee (Megachile rotundata) can serve as vectors for effective transmission of the pathogen. Therefore, management of insect vectors should be a part of the strategy for control of this disease. Breeding for disease resistance is thus far the most effective means for control of verticillium wilt of alfalfa. Aspects of breeding efforts for development and commercialization of new alfalfa cultivars in regions of high risk in Canada and approaches to control insect vectors are discussed.