Maternal environment and dormancy in sunflower: The effect of temperature during fruit development

A rapid and uniform germination in the field is an important requirement for commercial hybrid sunflower seed. Persistence of dormancy after harvest can negatively affect this aspect of seed quality, and seed lots with some degree of dormancy cannot be commercialized. Seed dormancy intensity and duration can vary greatly among sunflower genotypes, but it is also subject to strong interactions with the maternal environment. In this paper we report results of investigations into the effect of temperature during sunflower fruit development on the level of dormancy after harvest. After conducting controlled (greenhouse) and field experiments (sowing dates and plastic tents), we found that higher temperatures during later stages of achene development significantly increased the level of dormancy at harvest and its persistence during storage. The impact of the maternal (thermal) environment on embryo and coat-imposed dormancy was also investigated. Results showed that although maturation under warmer environments reduced embryo dormancy, this effect was overcompensated for by the enhancement of inhibition imposed by the pericarp and the seed coat. In addition, the results obtained suggest that observed changes in dormancy in response to the maternal environment could be at least partially explained by changes in achene and/or embryo sensitivity to ABA. Results presented here should be useful when choosing a proper environment for the production of hybrid sunflower seed of high quality, avoiding high temperatures during later stages of fruit development.