Cracking the woody endocarp of Santalum spicatum nuts by wetting and rapid drying improves germination

Abstract

Seeds of many plant species, including those of sandalwood (Santalum spicatum (R.Br.) A.DC., Santalaceae), are surrounded by a fruit endocarp that is hard and woody (this structure hereafter referred to as a 'nut'). The woody endocarp of S. spicatum provides a physical barrier to germination. This study investigated how this barrier is removed and the mechanism(s) controlling it. Field trials demonstrated that the endocarp cracked naturally and that the time of harvest and the presence of the epicarp affected the percentage of endocarps that were cracked. An investigation of the influence of wetting period and rate of drying on endocarp cracking showed that the rate of drying was most critical in inducing cracking and that the process was not heat-dependent. Field and pot studies showed that germination of sown nuts was improved when the woody endocarp was fractured. Results suggest that a simple wetting and rapid drying procedure can be used to crack large amounts of sandalwood nuts prior to sowing in the field. Results are discussed in relation to S. spicatum seed ecology. The relevance of weakening the woody endocarp of other non-Santalum species through endocarp wetting and rapid drying is discussed.