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Mechanisms of Seed Contamination by Verticillium albo-atrum in Alfalfa. H. C. Huang, Plant pathologist, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1; M. R. Hanna(2), and E. G. Kokko(3). (2)(3)Alfalfa breeder, and electron microscopist, respectively, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1. Phytopathology 75:482-488. Accepted for publication 18 October 1984. Copyright 1985. Department of Agriculture, Government of Canada. DOI: 10.1094/Phyto-75-482.

Infection of alfalfa tissue and contamination of seeds by Verticillium albo-atrum were investigated in a growth room with root-inoculated plants of cultivars Anchor, Vela, and Vernal, and progeny of Beaver x Lutèce. The frequency of contamination of seeds by V. albo-atrum ranged from 0% in Vela to 5% in Anchor following hand pollination of plants showing disease symptoms. Although the pathogen was present throughout the stems, it occurred only sporadically in peduncles, pedicels, pods, and seeds. When the stigmas of healthy plants of Vernal were surface inoculated with spores of V. albo-atrum at the time of flower-tripping, infection occurred readily and resulted in a discoloration of the stigma and upper style. The fungus appeared to be latent in the style during all stages of seed development. It was not detected in seeds from pods with infected styles. Under humid conditions, however, the fungus in the remnant style tissue of a mature seed pod was able to colonize the pod and seed coat.

Additional keywords: Medicago sativa.