Pericarp‐Imposed Dormancy in Sunflower: Physiological Basis, Impact on Crop Emergence, and Removal at an Industrial Scale

Abstract

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.

The role of domestication and maternal effects on seed traits of crop–wild sunflower hybrids (Helianthus annuus)

“…The increased seed dormancy observed at higher incubation temperatures in both wild and wild–crop hybrids (Fig. A) has been previously reported (Presotto et al ., ) and may be result of the increased pericarp‐imposed dormancy (Dominguez et al ., ). The increased seed germination with crop hybridisation was previously reported in sunflower crop–wild hybrids (Snow et al ., ; Mercer et al ., ) and other crop–wild complexes, such as oil‐seed rape (Adler et al ., ) and rice (Dong et al ., ).…”

“…A short‐lived dormancy is a desirable trait in crop production because it prevents germination on the mother plant (pre‐harvest sprouting) and allows a rapid and uniform germination in the next season (Shu et al ., ). A strong initial seed dormancy, totally or partially removed by an after ripening period was previously reported in cultivated sunflower (Brunick, ; Andrade et al ., ; Dominguez et al ., ; Roselló et al ., ) and results were similar to those reported in other crops, such as wheat, maize and rice (reviewed in Shu et al ., ). This short‐lived dormancy in crop seeds may be the result of remnant dormancy from domestication (Dominguez et al ., ), of conscious selection against pre‐harvest sprouting during modern improvement (Shu et al ., ) or a combination of both.…”

“…A strong initial seed dormancy, totally or partially removed by an after ripening period was previously reported in cultivated sunflower (Brunick, ; Andrade et al ., ; Dominguez et al ., ; Roselló et al ., ) and results were similar to those reported in other crops, such as wheat, maize and rice (reviewed in Shu et al ., ). This short‐lived dormancy in crop seeds may be the result of remnant dormancy from domestication (Dominguez et al ., ), of conscious selection against pre‐harvest sprouting during modern improvement (Shu et al ., ) or a combination of both. As the loss of dormancy is associated with the earliest stage of plant domestication (Purugganan & Fuller, ; Hancock, ; Meyer & Purugganan, ) it seems unlikely that the sunflower crop was not fully domesticated for this trait.…”

“…A). Crop seed dormancy is usually described as a short‐lived dormancy mainly imposed by the embryo with slight and variable levels of seed‐coat‐imposed dormancy (Brunick, ; Andrade et al ., ; Dominguez et al ., ; Roselló et al ., ) whereas wild seed dormancy is a long‐term dormancy mainly imposed by seed coats (Brunick, ). The increased dormancy of wild–crop seeds immediately after harvest may be explained by an additive effect of the dormant pericarp (from wild) plus the effect of crop and wild alleles in the embryo.…”

“…Therefore in crops with non‐deep PD, even when the pericarp plays a role in seed dormancy, such an effect seems to be mediated by hormonal profiles, be of short‐lived type and easily removed by an after ripening period (Andrade et al ., ; Shu et al ., ; Roselló et al ., ). Whether the increased pericarp‐imposed dormancy observed at high incubation temperatures (Dominguez et al ., ) and warmer conditions during seed development (Bodrone et al ., ) still is mediated by hormonal profiles remains elusive.…”