Improvement of plant regeneration and <i>Agrobacterium</i>-mediated genetic transformation of <i>Stylosanthes guianensis</i>

As a pioneer tropical pasture legume, stylo (Stylosanthes guianensis) is well adapted to growth-limiting factors in acid soils. Considering the importance of stylo, there is a need to improve Agrobacterium-mediated genetic transformation to enable development of elite cultivars. In this study, S. guianensis cv. RY5 was used to systematically optimize Agrobacterium-mediated transformation based on its plant regeneration. Results showed that Murashige and Skoog (MS) medium containing 0.2 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) and 2 mg/L 6-benzylaminopurine (6-BA) was the optimal callus induction medium. MS medium supplemented with 2 mg/L 6-BA was suitable for shoot regeneration from cotyledon-derived calluses, and 0.5 mg/L indole-3-acetic acid (IAA) and 0.5 mg/L indole-3-butyric acid (IBA) applications were beneficial for rooting. The highest transformation efficiency (67%) was obtained at an Agrobacterium concentration of optical density = 0.6 combined with an infection time of 15 min and 3 days of co-cultivation. Furthermore, 200 mg/mL carbenicillin (Carb) and 0.6 mg/L Basta® supplements were effective in eliminating excess bacterial growth and selecting transgenic plants, respectively. Subsequent polymerase chain reaction (PCR) analysis confirmed that the β-glucuronidase (GUS) and BAR genes were successfully integrated into the stylo genome. Wider testing of this improved protocol as a means of enhancing genetic improvement and gene function analysis of stylo seems warranted.