Mechanisms and Inheritance of Dormancy in Sunflower (Helianthus annuus L.) Achenes

In dormant sunflower achenes, several structures -pericarp, seed coat and embryo- contribute to repress germination. Achene dormancy varies greatly among cultivated sunflowers, and how dormancy is transmitted to the hybrid progeny is relevant for hybrid seed production, but also to understand the role of these structures in achene dormancy. This work investigated how dormancy is transmitted to the F1 progeny with special focus on inhibition of germination at warm temperatures, or ther-mo-inhibition. Reciprocal crosses were performed using three oilseed inbred lines with varying dormancy phenotypes. Germination of achenes, seeds, and embryos was tested at 10 and 30°C at harvest and during postharvest, together with response to hormones (abscisic acid, ethylene and gibberellins) and measurements of endogenous ABA levels. Results show that expression of maternally inherited, pericarp-imposed ther-moinhibition is conditional to the level of dormancy displayed by the hybrid embryo, which follows a zygotic with incomplete dominance pattern. While embryo sensitivity to ABA related positively with thermo-inhibition, surprisingly, embryonic ABA content was inversely related to dormancy level across genotypes. Our results provide novel insight into physiological control of achene dormancy in sunflower while con-tributing to improve breeding for high quality hybrid seed.