Optimization of an indirect regeneration system for common bean (Phaseolus vulgaris L.)

The main problems associated with growing common bean (Phaseolus vulgaris L.) callus are low proliferation and differentiation, and high browning. In this study, common bean callus induced by cotyledon nodes was used as explant material to investigate the effects of different exogenous substances on callus regeneration, as well as the correlation between callus browning and the changes in superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) enzyme activities during callus culture. Adding AgNO3, CoCl2, Putrescine (Put), and 1-aminocyclopropane-1-carboxylic acid (ACC) to the callus growth medium at appropriate concentrations could significantly improve callus proliferation and differentiation efficiency, while also reducing the degree of browning, compared to controls. Callus explants were cultured in callus proliferation and differentiation medium (CPADM) containing 5 mg·L−1 AgNO3, 15 mg·L−1 Put, 5 mg·L−1 CoCl2, or 0.02 mM ACC, with optimal callus growth at these dosages. After treatment with the four exogenous substances, callus browning was inversely correlated with SOD activity but positively correlated with POD and PPO activities. The maximum rooting frequency of shoots was observed when rooting media was treated with 1 mg·L−1 Indole butyric acid (IBA) or 0.1 mg·L−1 2,4-dichlorophenoxyacetic acid (2,4-D). The average number of primary roots, root length, and root fresh weight were higher after these treatments. The indirect regeneration issue was largely resolved for common bean by the callus culture technique applied in this study, which provides a framework for genetic modification, germplasm preservation, and bean application.