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Seed Dormancy in Avena fatua. IV. Further Observations on the Effect of Mechanical Injury on Water Uptake and Germination in Different Pure Lines

A comparative study of the effect of mechanical injury on water uptake and germination in different inbred lines of Avena fatua showed that the initial rate of water uptake by the embryo in the intact caryopses was inversely related to genetically determined differences in their degree of dormancy. When germination was induced by cutting or localized abrasion of the dry or imbibed caryopsis and by supplying water to the site of injury, the rate of germination was again inversely related to the degree of dormancy of each genetic line. Mechanical injury of the seed coat resulted in a rapid increase in the water content of the embryo prior to emergence of the radicle. Releasing the embryo from physical restraint by removing the covering layers caused a transient increase in size and water content of the embryo of dormant caryopses but failed to induce germination. The same treatment delayed germination of a nondormant line and also of dormant caryopses induced to germinate by mechanical injury but promoted the germination of injured caryopses imbibed for 10 days prior to treatment. When embryos were excised to eliminate effects of the seed coat, their rate of germination, as measured by the rate of radicle elongation, was still inversely related to genetic differences in their degree of dormancy. These results are consistent with the hypothesis that the supply of water to the embryo, as determined by the hydraulic conductivity of the covering tissues, plays a major role in the mechanism of dormancy in wild oats. They also provide evidence, however, that certain characteristics of the embryo itself are at least partly responsible for differences in the degree of dormancy between different genetic lines.