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

Dillenia 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 similar to 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 thy-storage (confirmation of PD). Seeds disperse with similar to 12% moisture and retain high viability even after ultradrying 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.

Automated summary

This study investigated the role of mucilage in seed dispersal, chemical defense, and germination of Dillenia indica seeds. The results showed that mucilage helps seeds float on water and acts as an antimicrobial agent without affecting seed germination. The study also revealed the presence of morphological and physiological dormancy in the seeds, as well as orthodox seed storage physiology.