Seed morphology and germination of Willd. ex Schult. emulating environmental conditions within ant nest

Damiana (Turnera diffusa Willd. ex Schult.) is a species of plant used in traditional Mexican medicine for its aphrodisiac properties. Although it has a high commercial demand, both nationally and internationally, its sexual propagation is not usual due to the low percentage of seed germination. It has been proposed that ants play an important role in germination, due to the presence of elaiosomes. Therefore, the objectives of this study were to characterize the seed morphology of T. diffusa for agronomic purposes, analyze their viability, and evaluate their germination by simulating environmental conditions of an ant nest. For the morphological characterization, 30 seeds were selected and evaluated for the variables of color, size, and weight. Viability was evaluated with a tetrazolium test using two lots of seeds collected in 2016 and 2017, with different concentrations and three exposure times at 40°C. The germination of T. diffusa was evaluated under three pre-germination treatments and nine germination treatments. The results of the study showed that the seeds of T. diffusa have an average size of 0.725 mm long and 0.182 mm wide; the color of the seeds varies from brown to black when ripe and yellowish white when immature. There are no significant differences in the viability percentage (60%) for seeds collected in 2016 and 2017 (p = 0.20). On the other hand, there are significant differences between all the pre-germination and germination tests analyzed. Seeds of T. diffusa have the highest percentage of germination (36%) with the presence of elaiosome and 500 ppm of GA3. The germination interval of the seeds occurs over a period of six to 39 days. The application of GA3 in the germination of the seeds indicates that they present a physiological latency which was inhibited at concentrations of 500 and 300 ppm.