Seed ecophysiology of Elephant Apple (Dillenia indica)—An important tree species of the Indomalayan realm

Abstract

AbstractDillenia indica produces mucilaginous seeds embedded in hard, fibrous, megafaunal fruits, and little is known about the ecological function of mucilage in its regeneration. Using standard laboratory protocols, we investigated the role of mucilage on seed dispersal (buoyancy), chemical defense (antibiotic, antifungal, antioxidant, and allelopathic activities), and seed germination. Further, we characterized seed germination, dormancy, and storage physiology of D. indica. Results revealed that mucilage associated with seed‐coat assists seeds in floating on water for a longer duration, acts as an antimicrobial agent without hampering the overall seed germination. It was noticed that fresh mature seeds possess an underdeveloped embryo that grows within the seed before radicle emergence (a sign of morphological dormancy; MD), and seeds took ~70 days to achieve 95% germination (a sign of physiological dormancy; PD). However, the rate of germination increased when seeds were treated with gibberellin or subjected to 1‐month dry‐storage (confirmation of PD). Seeds disperse with ~12% moisture and retain high viability even after ultra‐drying over silica gel, indicating an orthodox seed storage physiology. Study concludes that mucilage plays a crucial ecophysiological function in dispersal‐defense mechanism of D. indica seeds, by enhancing seed buoyancy, helping seeds to disperse long‐distance, and protecting the seeds from soil pathogens through antimicrobial activity. Our study confirmed that seeds of D. indica possess morphophysiological dormancy (MPD), unlike the MD reported in an earlier study from North India. Possible ecophysiological function of mucilage on seed dispersal‐defense mechanism and production of morphophysiological dormant and orthodox seeds in D. indica are discussed.