Sunflower (Helianthus annuus L.) achenes often display pericarp‐imposed dormancy, which is long‐lasting and causes serious problems to crop production and the seed industry. For this study we assessed an extensively used sunflower inbred line that has this type of dormancy. Our goals were (i) to determine the effect of pericarp on germination and to evaluate its impact on crop field emergence, (ii) to provide insight into the physiological basis of pericarp‐imposed dormancy by determining the effects of abscisic acid (ABA) accumulation in the embryo and the embryo sensitivity to ABA during incubation at different temperatures, (iii) to assess the effect of oxidant agents and other compounds on dormancy termination, and (iv) to evaluate the feasibility of using oxidants to remove dormancy at an industrial scale. Incubation at high temperatures (i.e., 25 to 30°C) allowed the expression of dormancy, which was imposed by the pericarp and was accompanied by an increase in embryo sensitivity to ABA, but not in ABA concentration. Treated achenes with sodium hypochlorite, or their incubation in presence of an ethylene precursor or gibberellins overcame dormancy. ABA concentration decreased during incubation when treated with sodium hypochlorite. Application of sodium hypochlorite on a commercial seed lot (i.e., washing with 3 and 7%, after additional chemicals used by the industry were applied) resulted in higher germination compared with dormant non‐treated controls. Field trials showed that pericarp‐imposed dormancy reduced crop emergence in the inbred line tested herein. However, treating achenes with sodium hypochlorite using described industrial procedures improved field emergence.

We used two sunflower genotypes displaying pericarp-imposed dormancy at high incubation temperatures (i.e. 30°C) to investigate the role of the pericarp as a limitation to oxygen availability to the embryo (hypoxia), and its impact on embryo abscisic acid (ABA) content and sensitivity to ABA. Results showed that both genotypes displayed very different oxygen threshold values for inhibition of embryo germination when incubation was performed at 30°C. Expression of dormancy in one genotype was therefore related to exacerbated embryo sensitivity to hypoxia, whereas in the other genotype, the pericarp appeared to act as a more severe restraint to oxygen entry. Increased sensitivity to hypoxia was, in part, related to increased sensitivity to ABA, but not to alterations in ABA metabolism. The activity of pericarp-microbial communities (bacteria and fungi) at high temperatures was also assessed as a potential determinant of hypoxia to the embryo. Oxygen consumption in pericarps incubated at 30°C was attenuated with antibiotics, which concomitantly promoted achene germination. In agreement with the observed more severe oxygen deprivation to the embryo exerted by the pericarp, the bacterial load in the pericarp was significantly higher in the commercial hybrid than in the inbred line; however, the application of antibiotics strongly reduced the bacterial colony counts for each genotype. Different bacterial and fungal communities, assessed through their profiles of carbon-source utilization, were determined between genotypes and after treatment with antibiotics. This work highlights the relationship between enhancement of sensitivity to hypoxia with incubation temperature and seed dormancy expression, and suggests that microbial activity might be part of the mechanism through which hypoxia is imposed.