Palm horticulture makes some of the most beautiful, useful, and emblematic tropical plants available to the world. Horticulture also provides a viable means of conserving palm genetic diversity (Fotinos et al., 2015) even when this was not the original intent (Asmussen-Lange et al., 2011). As few as 15 individuals grown from seed from a wild palm population can capture 80% or more of the genetic diversity in the original population (Namoff et al., 2010), though life history and breeding system should be taken into account when formulating a collecting strategy to maximize genetic capture (Griffith et al., 2015). Furthermore, horticulture can reduce collecting pressure on wild populations by making desirable plants available to the public (Kay et al., 2011). Collecting seeds is only the first step in establishing a palm in cultivation for beauty and conservation. The seeds must then be successfully germinated and the seedlings grown on.
Substrate has been found to be crucial in the germination of palm and cycad (Cycadales) seeds (Calonje et al., 2010; Murphy et al., 2013). Among the substrates that have proven most useful, aside from standard peat-based nursery mixes, are calcined clays and coarse sand. Fired ceramics of calcined montmorillonite clay have high cation exchange capacity (Warren and Bilderback, 1992). Sand is one of the most versatile inert substrates and has long been used as a stand-alone substrate in research (Hewitt, 1966), and is one of the most frequently used amendments in container substrates (Gartner, 1981). Sowing depth has also been found to significantly affect palm germination. Broschat and Donselman (1986) found that a sowing depth of 1 cm resulted in significantly increased germination percentage of golden cane palm (Dypsis lutescens) compared with either surface sowing, or depths greater that 1 cm. This result was related to the drying potential of the germination site, as differential shade treatments increased germination at shallower depths (Broschat and Donselman, 1986).
We chose to investigate germination of wild-collected seeds of two imperiled palm species native to Hispaniola. Yarey palm is imperiled by illegal extraction of mature individuals, arson, and habitat loss (Veloz et al., 2013). Buccaneer palm is confined to the far east of the Dominican Republic, where some of the populations have been extirpated for tourism development and trade (Rodríguez-Peña et al., 2014). In both cases, ex situ cultivation is an essential part of integrated conservation efforts, ensuring maintenance of genetic diversity for future introduction (Namoff et al., 2010), and also providing a germplasm source that can alleviate the need for extractive harvest (Kay et al., 2011). The first step in successful ex situ conservation is the propagation of properly collected seed. Thus, the aim of this study was to assess how different substrates of both organic and inorganic nature affect the germination and early growth of palm seedlings with different germination requirements and germination time frames. Yarey palm seeds generally do not require any scarification and germinate within a few months. In contrast, buccaneer palm seeds benefit from endocarp removal (Riffle et al., 2012) and germinate over a period of many months.
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