Severe Isolate of Alfalfa Mosaic Virus and Its Impact on Alfalfa Cultivars Grown in Alberta

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Abstract
Five isolates of alfalfa mosaic virus (AMV) occurring in Canada were classified as one mild, three moderate, and one severe type by host range and symptomatology on seven species, but they were indistinguishable by serology and morphology. Four alfalfa cultivars commonly grown in Alberta, Canada, along with a breeding line were tested in the greenhouse and growth chamber for their responses to inoculation with the severe isolate, A-515, both in the seedling stage and during repeated cuttings and regrowth. Their responses to sap inoculation in the seedling stage were not necessarily reflected in their capabilities to support AMV spread to previously noninfected plants by repeated cuttings. In cultivar Apica, which was the most resistant cultivar in the seedling stage, repeated cuttings progressively increased the number of infected plants. After the ninth cutting, only 7% of these plants remained noninfected. Cultivar Anchor was four times as susceptible to sap inoculation as Apica in the seedling stage; however, 33% of the inoculated Anchor plants remained virus-free after receiving the same treatment. The cultivars also differed in their ability to sustain AMV multiplication during reqrowth as measured by enzyme-linked immunosorbent assay.