Complete Decapitation and Rootstock Culture In Vitro Are Efficient Methods for Shoot Regeneration from Eggplant Hypocotyls, Poster Board #154

The complete decapitation method (CDM), in which main and all lateral stems were removed, promoted shoot regeneration in tomato plants grown in open fields (Harada et al., 2005). Here, the CDM was applied to eggplants, which show unstable shoot regeneration in in vitro culture. Seedlings of Solanum melongena ‘Sisui’ were cultured on Murashige and Skoog (MS) medium, and were cut at the center of the hypocotyl in vitro (CDM in vitro; CDMi). Hypocotyl explants were cultured on MS medium containing 1.0 mg·L^-1 benzyladenine (BA) as the control. Calli formed at the cut end of hypocotyls 1 week after cutting in both the CDMi culture and the control hypocotyl culture. Adventitious buds regenerated 1 week earlier in the CDMi culture than in the control hypocotyl culture. The average number of adventitious buds was 10.3 in the CDMi culture and 3.1 in the control hypocotyl culture at 6 weeks after cutting. Shoots longer than 1 cm were obtained 2 weeks earlier in the CDMi culture than in the control hypocotyl culture. The average number of shoots per hypocotyl was 8.1 in the CDMi culture and 2.4 in the control hypocotyl culture at 6 weeks after cutting. These results indicated that CDMi is a simple and efficient method to obtain multiple shoots without determining optimal concentrations of plant growth regulators. We applied CDMi  to three other eggplant cultivars; ‘Senryou-2 gou’, ‘Kokuyou’, and ‘Shouya-oonaga’. The highest number of shoots was obtained from ‘Sisui’, followed by ‘Senryou-2 gou’, ‘Kokuyou’, and ‘Shouya-oonaga’. This result indicated that there were different regeneration frequencies among cultivars of eggplant in the CDMi. To increase the number of shoots from ‘Shouya-oonaga’, hypocotyl explants of ‘Shouya-oonaga’ were grafted onto ‘Sisui’ rootstocks before CDMi. This method, i.e., rootstock culture of hypocotyl segments, increased the number of shoots obtained from hypocotyls of ‘Shouya-oonaga’ compared with direct application of CDMi. In contrast, when the hypocotyls of ‘Sisui’ were grafted on ‘Shouya-oonaga’ rootstocks before CDMi, we obtained fewer shoots from hypocotyls of ‘Sisui’ compared with direct application of CDMi. These results show that well-regenerated rootstock is the optimal material to obtain multiple shoots via CDMi. Rootstock cultures may be useful to regenerate plant material following genetic transformation.