From induction to embryo proliferation: improved somatic embryogenesis protocol in grapevine for Italian cultivars and hybrid Vitis rootstocks

Somatic embryogenesis is the most common regeneration method for the application of new genomic techniques like cisgenesis/intragenesis, genome editing, and RNAi. However, some local important genotypes show recalcitrance to this morphogenetic strategy, which represents an obstacle for the application of genetic engineering techniques. Whole flowers, stamens, and pistils of three different Italian Vitis vinifera L. cultivars (Ancellotta, Glera, and Lambrusco Salamino), and four hybrid rootstocks (110 Richter, 17.37, SO4, Star 50) have been tested in several culture media with changing basal salts (NN and MS), different combinations of growth regulators (BAP, 2,4-D, NOA, PIC, and NAA), and gelling agents, to initiate somatic embryogenesis. The formation of embryogenic calli was observed mainly from whole flowers cultured on PIV medium (NN salts, B5 vitamins, 3 g L −1 gelrite, 60 g L −1 sucrose, 8.9 µM BAP, and 4.5 µM 2,4-D), and stamens on MS1 medium (MS salts and vitamins, 7 g L −1 plant agar, 20 g L −1 sucrose, 4.5 µM BAP, and 5 µM 2,4-D), in the cv. Ancellotta, Lambrusco Salamino, and all the rootstocks, except for Star 50, which showed the best embryogenetic response from pistils placed on MS1. In a recalcitrant cv. as Glera, pistils placed on MS medium supplemented with 1 µM BAP, 5 µM 2,4-D, and gelrite as gelling agent, showed the highest percentage of embryogenesis. In addition, a two-step protocol was efficiently optimized for further induction of secondary embryo production for the above-listed grapevine genotypes, which guaranteed the long-term maintenance of embryogenic cultures from clusters or single somatic embryos.