ABSTRACT
Duration of primary and secondary seed dormancy in field populations of wild oats (Avena fatua L.) is controlled by several genes which are expressed as different physiological and biochemical traits. Mechanisms producing variation in levels of primary and secondary dormancy include hormonal and environmental control of biochemical pathways which can interact with components of seed structure. Water is undoubtedly the one environmental factor with greatest capacity for germination control, and it has been suggested that seed dormancy in A. fatua is due to factors that prevent, the uptake of imbibed water by the embryo in the amount reguired for the induction of germination. Light inhibits germination in seeds of genetically nondormant populations. This light-induced germination inhibition is intensity-dependent: the higher the light intensity, the greater the inhibition. Germination inhibition by light is accentuated by higher incubation temperatures. Temperature can not only administer its effect directly on seed metabolism, but can also mediate its effect either through maternal tissues or on the immature ovule. Thus temperature can regulate germination behaviour by its effect on three stages of the life cycle of A. fatua plants, i.e., vegetative growth, seed maturation, and the incubation period following seed maturation. The total effect of genetic and environmental factors at these stages of the life cycle may provide flexible strategies for their survival. However, in spite of numerous studies on factors that influence the degree of dormancy of seeds, there is still no general agreement about the nature of the conttol mechanism(s) involved.
