Dormancy attributes in Sunflower achenes (Helianthus annuus L.): I. Intraspecific variability

Cultivated sunflowers (Helianthus annuus L.) display variable degrees of achene dormancy at harvest and persistence during storage, interfering with high-quality hybrid seed production. Information on intraspecific variability for dormancy among cultivated sunflowers is scarce and was the subject of this work. A set of 21 sunflower genotypes of diverse origins (18 crop and 3 wild) was used for phenotyping dormancy traits. Experimental data included achene and embryo germination at different incubation temperatures, in water or abscisic acid (ABA), and different storage times postharvest. Multivariate analyses produced dormancy groups differing mostly in their patterns for dormancy expression along the thermal range and their dormancy release rate. The observed variability was interpreted as resulting from the overlap of two mechanisms: low temperature-expressed dormancy (LTED), common to all genotypes; and thermo-inhibition (TI) at high incubation temperatures, exclusive to some genotypes. Embryo responsiveness to ABA varied among genotypes and was positively related to LTED and TI, supporting that both responses share a common regulatory pathway operating in the embryo. We show that there is considerable intraspecific variability for dormancy attributes among cultivated sunflowers.