Encapsulation in Calcium Alginate of Nodes from Stolons of <i>Mentha spicata</i> L.

It is well known that the products of encapsulation (multifunctional beads and synthetic seeds) can be used as innovative technological tools to integrate micropropagation both for plant germplasm conservation and to simplify the management of propagation materials in nurseries. Nevertheless, the usual concept of encapsulation concerns the use of initial in vitro derived explants. In this study, for the first time, in vivo derived organs of Mentha spicata L., obtained through the excision of fragments (nodes) from stolons of cultivated mother plants, were employed. The artificial endosperm had a tenfold reduced concentration of Murashige and Skoog (MS) substrate, with the addition of sucrose (5 g L−1), 6-benzyl-aminopurine (BAP) (0.1 mg L−1) and 1-naphthalene acetic acid (NAA) (0.01 mg L−1). Moreover, the calcium alginate matrix was enriched with different thiophanate-methyl (TM) concentrations (0, 10, 50, 100 and 200 mg L−1) in order to prevent possible contamination during the conversion in nonsterile conditions. Interesting results were obtained encapsulating every single node of fresh stolon as a bipolar propagule able to develop a whole plantlet (conversion), as the coated seed in other species. The synthetic seeds of spearmint without TM in the artificial endosperm showed a satisfactory ability to convert (56.7%) into plantlets after sowing in soil under nonsterile conditions. TM at 100 and 200 mg L−1 negatively affected the total emergence, which decreased to 30.0 and 33.3%, respectively. In general, in the artificial seeds without TM, higher values for most of the aboveground and belowground plants parameters were recorded compared to naked nodes