Implications of Embryo Desiccation Tolerance, Seed Dormancy, and Seed Damage for Conservation of Pritchardia Palms Endemic to Hawaii

Abstract

Pritchardia remota (Kuntze) Becc. is an endemic Hawaiian palm. This species is listed as endangered due to threats such as invasive plants and animals, stochastic events, and/or reduced reproductive vigor. However, P. remota seeds are not presently stored in genebanks because it is presumed that they do not remain viable in storage. Yet, there are no studies that report the tolerance of Pritchardia species to storage conditions. Assessing the desiccation tolerance of Pritchardia is hampered by their difficult physiology. Germination is delayed in seeds of Pritchardia species and the mechanisms that control these delays are not understood. Clarifying these mechanisms can assist in forming propagation protocols for the creation of genetically diverse populations useful for recovery actions. Moreover, introduced vertebrate predators are known to damage seeds of Pritchardia. It is not known if Pritchardia seeds can tolerate damage and remain viable. The studies reported here show that developmental patterns in P. remota are intermediate to those observed for species that can and can not tolerate storage in genebanks. Embryos tolerate relatively high levels of drying and remain viable. However, they do not tolerate the extreme drying (< 0.10 g H2O/ g dry weight) necessary to maintain viability in conventional genebanks conditions. Therefore, it may be necessary to employ other techniques, such as cryo-preservation, to extend the longevity of this species in storage. Pritchardia remota seed are dormant at shedding. Emhryo growth is restricted by the operculum and endocarp. Emhryos are also underdeveloped and must reach a critical length, moisture content, and water potential for operculum displacement and subsequent radicle protrusion. Germination is hastened at warm constant temperatures {i.e., > 25°C) and if seeds are removed from the fruit coats. The combination of mechanisms suggests that P. remota seeds are morpho-physiologically dormant. Finally, moderate levels of seed damage may not be limiting in terms of germination for Pritchardia species. Damage to the endosperm caused seeds to germinate more rapidly compared to non-damaged seeds. Nevertheless, damaged seeds may succumb to fungal attack. Therefore, it is critical therefore to prevent predators from damaging Pritchardia seeds.