Understanding the effects of moisture content and temperature on dormancy release in sunflower (Helianthus annuus L) achenes

The effects of moisture content (MC) and storage temperature (ST) on seed longevity have been modeled for many species. In contrast, our understanding on the combined effects of MC and ST on dormancy release (DR) in "dry" orthodox seeds is still insufficient to build robust predictive models. We used freshly harvested, dormant sunflower achenes to explore the effects of MC (4-10%) in combination with a wide range of ST (-18{degrees}C to +30{degrees}C) on DR dynamics, embryo responsiveness to abscisic acid (ABA) and deterioration indicators. Storage temperatures allowing full DR were inversely related to achene MC, ranging from >25{degrees}C for MC4% to sub-zero temperatures for MC10%, resembling a phase diagram. Rates of DR were plotted along a RH gradient. Combinations of MCxST optimal for DR were between ca. 40-60%RH. Increasing RH from 60 to 80% inhibited DR. Higher RH>80-85% promoted partial DR together with rapid ageing. We suggest that reactions promoting full DR are favored alongside a physical (glassy) transition and are not oxidative. We propose biophysical coordinates to guide future studies on the mechanisms involved in DR, but also to develop predictive models useful to define post-harvest conditions that maximize sunflower seed quality. Highlights{square} The effects of moisture content (MC) and storage temperature (ST) on dormancy release and deterioration were investigated in sunflower achenes using a factorial design. {square}Dormancy release was promoted by MCxST combinations in equilibrium with a RH between 40 and 60% and was delayed outside this range. {square}Storage temperatures optimal for dormancy release were inversely related to achene MC, ranging from >25{degrees}C for MC4% to sub-zero temperatures for MC10%, resembling a phase diagram. {square}Dormancy release and ageing are promoted within distinct, non-overlapping regions along the RH gradient supporting different types of reactions for each process.