Role of mucilage in germination of Dillenia indica (Dilleniaceae) seeds

Dillenia indica Linn. is a nearly evergreen tree widely distributed in South-east Asia. Regeneration is by seeds borne within large indehiscent fruits. When extracted fresh, seeds are glued together by the sticky mucilage on the seedcoat. Mucilage anchors seeds during rains, thus preventing them from escaping the fruit. Mucilage does not promote or inhibit germination, but it does restrict the inflow of water into seeds during the initial stages of imbibition. In nature, seeds germinate (within fruits) in July-August following heavy rains that wash off most of the mucilage. Light had a significant effect on germination: a 12/12h light/dark regime resulted in more and faster germination than when seeds were incubated in total darkness. Seeds exhibited one flush of germination within fruits and another flush in the laboratory following extraction, drying and rehydration, suggesting the occurrence of two physiological types of seeds with regard to light requirement for germination. The embryo of D. indica is underdeveloped, and seeds take ∼30 days to germinate under appropriate conditions. Thus, the seeds have morphological dormancy (MD). The possible roles of seed-coat mucilage and light in the germination biology of D. indica seeds in nature are discussed.