MORPHO-ANATOMICAL STRUCTURE AND PHYSICAL DORMANCY BREAKING OF MALVASTRUM COROMANDELIANUM SSP. COROMANDELIANUM (MALVACEAE) SEEDS

Background and aims: The occurrence of seeds with physical dormancy is an obstacle for the use and management of many plant species. Here, we studied the presence of physical dormancy in mericarps (seed-dispersal units) and seeds, the morpho-anatomical structures responsible for physical dormancy, and the effects of possible methods for breaking dormancy in seeds of Malvastrum coromandelianum (Malvaceae). M&M: Imbibition essays were used to confirm the presence of physical dormancy in mericarps and seeds, and the morpho-anatomical seed structure was described by using a scanning electron microscopy. The effects of mechanical, chemical and thermal scarifications on seed germination and seed structure were also evaluated. Results: Mericarps and scarified seeds increased > 160% of their initial weight, whereas intact seeds increased < 40% of their initial weight. The presence of a palisade cell layer in seed coat and a water-gaps complex in the chalazal region were observed. Higher germination percentages and lower t(50) were registered after mechanical scarification, followed by chemical and thermal scarifications (dry heat). Chemical and thermal scarifications caused the chalazal cap elimination and the contiguous cracks to form around the chalazal region; whereas the formation of a chalazal blister and its elimination were only observed after chemical scarification. Conclusions: Seeds of M. coromandelianum have physical dormancy. Water enters the seeds through a water-gap complex (Type III compound) located in the chalazal region. Mechanical, chemical and thermal scarifications are effective methods for breaking physical dormancy and increase germination.