This study revealed (a) the extremely narrow thermal range within which dormancy problems (either through expression or induction of dormancy) may not be encountered; and (b) the high sensitivity displayed by these seeds to water shortage. In addition, this work is the first one in which temperature effects on dormancy expression could be discriminated from those on dormancy induction using a hydrotime analysis.

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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.

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