Seed Germination of the Herbaceous Vine Tropaeolum pentaphyllum Lam. (Tropaeolaceae): A Neglected Geophyte with High Agricultural Potential

The objective of this study was to evaluate the seed germination of Tropaeolum pentaphyllum Lam., an endangered geophyte native of southern Brazil with agriculture potential due its edible tubers. Two experiments were carried out in 2017: germination of T. pentaphyllum under natural conditions and under controlled conditions. In the experiments under natural and controlled conditions, the germination of 1,100 and 100 seeds was evaluated, respectively. In the experiment under controlled conditions, two treatments (natural light and dark) were evaluated and each treatment contained 50 seeds. In the natural conditions experiment, in 2018 (first year), of the 1,100 seeds, 5.6% germinated and 76.5% persisted in the soil; and in 2019 (second year), 5.3% of the seeds germinated and no seeds remained in the soil. In natural conditions experiment, 10.9% of seeds germinated over two years. In controlled conditions experiment, in 2018 the germination in dark was higher (48%) compared to natural light (18%); and in 2019, despite the absence of statistical differences, the dark showed a higher value of germination (12%) in relation to natural light (6%). Over two years, dark treatment showed higher germination (60%) compared to natural light (24%) and no seeds remained in the substrate. The production of tubers in plants obtained by seed germination was 98.4% and 100%, in natural and controlled conditions, respectively. The highest germination rates occurred under dark conditions indicating that the species is preferential negative photoblastic. In addition, this species forms a seed bank in the soil, in which the seeds remained for a maximum of two years. The seed germination can contribute to the genetic diversity of crops and the production of seed-tubers, decreasing the collection of tubers in situ, contributing to the conservation and agricultural use of T. pentaphyllum.