Defining correct dormancy class matters: morphological and morphophysiological dormancy in Arecaceae
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OPINION PAPER
Defining correct dormancy class matters: morphological and morphophysiological dormancy in Arecaceae Ganesh K. Jaganathan 1 Received: 14 August 2020 / Accepted: 5 October 2020 # INRAE and Springer-Verlag France SAS, part of Springer Nature 2020 & Key message Dormancy in Arecaceae diaspores is due to underdeveloped embryos, therefore, morphological dormancy or morphophysiological dormancy. Consequently, claims such as external seed structures inhibit germination, embryos are fully developed at maturity, and underdeveloped embryo is not a form of dormancy are rejected, because embryo size of the diaspore at the time of dispersal was not taken into consideration. The re-classification proposal for moving morphological dormancy into non-dormancy is also discouraged. This is owing to the fact that when both morphological dormancy and non-dormant seeds are placed under conditions suitable for germination, those with morphological dormancy do not germinate immediately due to time needed for growth of the embryo, whereas non-dormant seeds can germinate quickly. The implications of correctly defining dormancy class are important, for researchers working with seeds at various levels from forestry to molecular biology.
With 2600+ species, palms constitute an essential component of tropical and sub-tropical biodiversity (Kissling et al. 2019). The life cycle of long-lived palms starts with diaspores, which differ considerably in size, shape, and color (Broschat et al. 2014; Corner 1966; Mabberley 2017; Tomlinson 1990). Typically, the dispersal unit of palms is a berry or fibrous drupe, which encompasses fibrous mesocarp, a thick endocarp, a fleshy nutritious endosperm, and a small embryo (Tomlinson 1990). It is well known (or inferred) that most— perhaps all—palm diaspores have an underdeveloped embryo, c. > 10% of the overall diaspore size, at the time of dispersal (Baskin and Baskin 2014b; Martin 1946; Tomlinson 1990). This feature—termed as morphological dormancy—means that embryos require time for the embryo to differentiate and grow inside the diaspores before germination occurs, which is usually within 30 days after dispersal (Baskin and Baskin 2004; Finch-Savage and Leubner-Metzger 2006; Nikolaeva 1969; see Fig. 1). However, most Arecaceae species have been reported to have morphophysiological dormancy, wherein the underdeveloped embryos also have a physiological Handling Editor: Erwin Dreyer * Ganesh K. Jaganathan [email protected] 1
Institute of Biothermal technology, University of Shanghai for Science and Technology, Shanghai 200093, China
constraint either due to a hormonal imbalance or inability of the embryo to push through the hard endocarp, i.e., physiological dormancy, which requires both growth of embryo and alleviation of physiological dormancy before germination (Baskin and Baskin 2004; Finch-Savage and LeubnerMetzger 2006; Fig. 1). Due to decades of research, there is an abundant literature on germination ecology of palms suggesting that germination requires several months to years (Bas
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