Physiology, morphology and phenology of seed dormancy break and germination in the endemic Iberian species Narcissus hispanicus (Amaryllidaceae)

Abstract

Seeds of N. hispanicus have deep simple epicotyl morphophysiological dormancy (MPD), with the dormancy formula C(1b)B(root) - C(3)(epicotyl). This is the first study on seeds with simple MPD to show that embryos in advanced stages of growth can re-enter dormancy (secondary dormancy).

Germination ecology of the endemic Iberian daffodil Narcissus radinganorum (Amaryllidaceae). Dormancy induction by cold stratification or desiccation in late stages of embryo growth

“…In N. pseudonarcissus (Vandelook & Van Assche, 2008), N. eugeniae (Copete et al, 2014) and N. hispanicus (Copete et al, 2011), growth of the embryo is continuous throughout summer, radicle emergence occurs in early autumn and shoot emergence is delayed up to late winter-early spring, so corresponding to deep simple epicotyl MPD pattern. In N. alcaracensis (Herranz et al, 2013b), dormancy break and embryo growth require only cold stratification and seeds have intermediate complex MPD, while in N. longispathus (Herranz et al, 2013a) dormancy break, embryo growth and radicle emergence require warm stratification followed by cold one, corresponding to non-deep complex MPD pattern (Baskin & Baskin, 1998).…”

“…The critical "embryo length : seed length" (E:S) ratio, calculated by averaging the E:S ratios of those 20 seeds, was 0.78 (s.e.=0.01, n=20, range=0.69-0.90). The minimum individual E:S ratio ( i.e., 0.69 in our study), was considered the "threshold E:S ratio", a reliable indicator that dormancy is being overcome (Copete et al, 2011).…”

“…On the other hand, it is known that in imbibed non-dormant seeds of some species, unfavourable environmental conditions for germination, such as extreme temperatures, hypoxia, and water stress, can induce secondary dormancy (Hilhorst, 1998;Baker et al, 2005). In this sense, we also analyzed the next hypotheses: i) exposure to low temperatures induces dormancy, as in N. hispanicus (Copete et al, 2011) and N. eugeniae (Copete et al, 2014); ii) desiccation after embryo growth induces secondary dormancy, as in Lomatium dissectum (Scholten et al, 2009) and Anemone nemorosa (Ali et al, 2007).…”

“…These data indicate that low temperatures induced non-dormant seeds into secondary dormancy. That fact has been detected only in seeds of N. hispanicus with deep simple epicotyl MPD (Copete et al, 2011). On the other hand, cold stratification also induced secondary dormancy in seeds of the winter annuals Papaver rhoeas (Baskin et al, 2002) and Chaerophyllum tainturieri (Baskin & Baskin, 1990), which have non-deep simple MPD.…”

“…However, under soil the winter temperatures are damped and the root can continue growing, and so the seedlings have a well-developed root system when the shoot expands in spring (Kondo et al, 2004;Copete et al, 2011).…”