Mechanisms of Seed Contamination byVerticillium albo-atrumin Alfalfa

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Abstract
Infection of alfalfa [Medicago sativa] tissue and contamination of seeds by V. albo-atrum were investigated in a growth room with root-inoculated plants of cultivars Anchor, Vela and Vernal, and progeny of Beaver .times. Lutece. The frequency of contamination of seeds by V. albo-atrium 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.