Dissecting seed dormancy and germination in Aquilegia barbaricina, through thermal kinetics of embryo growth

Threshold-based thermal time models provide insight into the physiological switchfrom the dormant to the non-dormant germinating seed.•This approach was used to quantify the different growth responses of the embryo ofseeds purported to have morphophysiological dormancy (MPD) through the complexphases of dormancy release and germination. Aquilegia barbaricina seeds were incu-bated at constant temperatures (10–25 °C) and 25/10 °C, without pre-treatment, afterwarm+cold stratification (W+C) and GA3treatment. Embryo growth was assessedand the time of testa and endosperm rupture scored. Base temperatures (Tb) and ther-mal times for 50% (h50) of embryo growth and seed germination were calculated.•W+C enabled slow embryo growth. W+C and GA3promoted rapid embryo growthand subsequent radicle emergence. The embryo internal growth base temperature(Tbe) was ca. 5 °C for W+C and GA3-treated seeds. GA3treatment also resulted insimilar Tbestimates for radicle emergence. The thermal times for embryo growth(he50) and germination (hg50) were four- to six-fold longer in the presence of GA3compared to W+C.•A. barbaricina is characterised by a multi-step seed germination. The slow embryogrowth during W+C reflects continuation of the maternal programme of develop-ment, whilst the thermal kinetics of both embryo and radicle growth after the removalof physiological dormancy are distinctly different. The effects of W+C on the multi-phasic germination response in MPD seeds are only partially mimicked by 250 mgl1GA3. The thermal time approach could be a valid tool to model thermal kinetics ofembryo growth and radicle protrusion.