Abstract
Aim of study: We studied the germination ecology of a threatened daffodil in order to develop a protocol to produce plants ex-situ from seeds, a key tool for population reinforcement.Area of study: Experiments were carried out both outdoors and in the laboratory in Albacete (Spain).Material and methods: Embryo length, radicle and shoot emergence were analyzed to determine the level of morphophysiological dormancy (MPD). Effects on germination of cold stratification or desiccation in late stages of embryo growth were also studied.Main results: Mean embryo length in fresh seeds was 1.36 mm, needing to grow up to 2.20 mm to be able to germinate. In the laboratory, embryo growth occurred during warm stratification (28/14, 25/10ºC), and then radicle emerged when temperatures went down (15/4ºC in darkness). Phenology study in outdoors conditions revealed that embryo grew during summer-early autumn, short time after seed dispersal in nature (i.e., May); radicle emerged in autumn. The shoot however did not emerge until late winter-early spring, because it was physiologically dormant and required a cold (5ºC) period of 30 days to break dormancy. Early cold temperatures interrupted the embryo growth and induced dormancy in seeds whose embryo had grown 30% with respect to the initial length. Desiccation in seeds whose embryo had grown 30% did not induce dormancy, but did it when the embryo growth reached 70%.Research highlights: Seeds of Narcissus radinganorum have deep simple epicotyl MPD.Key words: dormancy break; radicle emergence; shoot emergence; epicotyl MPD; phenology; secondary dormancy.
Highlights
The genus Narcissus L. belongs to the monocotyledon family Amaryllidaceae, which includes about 900 species in 60 genera (Mabberley, 2008)
Seeds with underdeveloped embryos can have morphological dormancy (MD), if embryo growth and radicle emergence are completed in about 30 days under suitable conditions, or morphophysiological dormancy (MPD) when an additional physiological mechanism preventing embryo growth and germination occurs (Nikolaeva, 1977; Baskin & Baskin, 2004)
We aimed to confirm this hypothesis by analysing several germination traits of N. radinganorum, such as the effect of environmental conditions on embryo growth, phenology of embryo growth and germination, dormancy break in buried seeds and influence of warm or cold stratification on germination, whose study is essential in species with MPD (Baskin & Baskin, 1998; 2004; 2005; Herranz et al, 2010; Kondo et al, 2004; Vandelook et al, 2007)
Summary
The genus Narcissus L. belongs to the monocotyledon family Amaryllidaceae, which includes about 900 species in 60 genera (Mabberley, 2008). Many species of this family at seed-dispersal time have seeds with underdeveloped, fully differentiated, linear embryos, which need to grow before the seed germinates (Baskin & Baskin, 1998). Seeds with underdeveloped embryos can have morphological dormancy (MD), if embryo growth and radicle emergence are completed in about 30 days under suitable conditions, or morphophysiological dormancy (MPD) when an additional physiological mechanism preventing embryo growth and germination occurs (Nikolaeva, 1977; Baskin & Baskin, 2004). In this study special attention was given to the analysis of environmental conditions that promote embryo growth and subsequent germination in Narcissus radinganorum Fdez.
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