Genetic variability affecting duration of primary dormancy is demonstrated in natural populations of wild oats. Marked differences were found among local populations in germination behavior. The evidence suggests that these differences result in part from genetic adaptation to agronomic practices.

Natural inhibition of germination in A. fatua L. involves restriction of both sugar accumulation and utilization of sugar in growth. Both these metabolic blocks are independently overcome by exogenous gibberellic acid (GA). Evidence has been found for the presence of a natural gibberellin in seeds of A. fatua L. The control of dormancy is probably by a gibberellin-inhibitor antagonism since at least one inhibitor has been shown to intervene specifically in sugar production and this latter effect can be reversed by GA. The evidence presented here supports the view that control of germination during the period of after-ripening is through changes in inhibitor content rather than in endogenous gibberellin.

Plants of genetically dormant (D) and nondormant (ND) pure lines of Avena fatua were exposed to water stress during seed development. In comparison with normally well-watered controls, seeds produced by water-stressed plants exhibited shorter duration of primary dormancy. The magnitude of the effect varied among D families, but was consistently greater than in ND families.It is concluded that the dormancy phenotype of D lines is highly plastic and that the responses to high temperature and water stress are similar in a given pure line.

Evidence is presented that genetic variability affecting duration of seed dormancy and seed viability exists in field populations of Avena fatua L. and that this variability is an important factor in the persistence of this weed species in allowing populations to adapt to particular cultural weed-control practices. Duration of seed dormancy is controlled by several or many genes, the effects of which are manifested in at least two physiologically distinct physiological blocks. Expression of genotypes which confer long-term seed dormancy is highly sensitive to temperature and drought stress experienced by maternal plants during seed development. Naturally inbreeding families characterized by long-term dormancy also exhibit rigorous hormonal control of the synthesis of at least one hydrolase in endosperm (α-amylase). This association of physiological traits apparently is not due to pleiotropy but rather to coadaptive multilocus organization.

Sodium nitrate and nitrite (50–100 mM) induced germination in three out of four genetically pure dormant lines of Avena fatua L. The sensitivity to these treatments was low immediately ater harvest and increased markedly after six months of dry after‐ripening. The observation that a fourth dormant line failed to respond suggests at least two metabolic blocks may be involved in expression of dormancy. An inhibitor of gibberellin biosynthesis, 2‐chloroethyl trimethylammonium chloride, completely inhibited the dormancy‐breaking effect by nitrate and nitrite, indicating a requirement for gibberellin biosynthesis. Among reduced nitrogenous compounds, ammonium chloride and urea failed to break dormancy in all partly after‐ripened lines, suggesting that nitrate and nitrite may induce germination through their ability to act as electron acceptors. The sensitivity to all nitrogenous compounds tested increased with the length of after‐ripening indicating that the depth of the second dormancy block amy decrease with the time of after‐ripening. Other reduced nitrogenous compounds, thiourea and hydroxylamine hydrochloride, promoted some germination in the least dormant, partially after‐ripened lines. The function of these compounds as electron acceptors and their similarity in activity to the cytochrome oxidase inhibitor, sodium azide, is discussed with reference to dormancy and the possible involvement of the alternative pathway of respiration.