Improved efficiency of callus induction, bud differentiation, and plant regeneration in radish (Raphanus sativus L.)

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ABSTRACT Radish (Raphanus sativus L.) is a recalcitrant variety for embryogenic callus induction that does not result in an efficient genetic transformation system. In this study, a highly efficient system for callus induction and bud differentiation in radish was established using orthogonal design tests with combinations of several synthetic auxins and cytokinins. Thirteen types of explants were tested; among them, cotyledon had the highest callus induction rate (91.01%) and was the most suitable explant. The optimal medium for callus induction was improved Murashige and Skoog medium (MS-1) supplemented with 0.2 mg/L 2,4-dichlorophenoxyacetic acid, 0.2 mg/L α-naphthalene acetic acid, 0.5 mg/L thidiazuron (TDZ), 4 mg/L 6-benzylaminopurine (BA), 0.1 mg/L kinetin, with a callus induction rate of 94.77%. The optimal medium for shoot regeneration was MS-1 medium supplemented with 1 mg/L TDZ, 1 mg/L BA, with a bud regeneration rate of 15.54%. The most suitable medium of rooting was 1/2 MS-1 medium supplemented with 0.2 mg/L NAA, 0.2 mg/L 3-indolebutyric acid, and 0.1% activated carbon, achieving a rooting ratio of 89.05% and transplant survival rate of 94.92%. This study lays a good foundation for future breeding and molecular studies on radishes. HIGHLIGHTS Cotyledon had the highest callus induction rate (91.01%) and were the optimal explants. Optimal medium for callus induction was MS-1 medium supplemented with 0.2 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D), 0.5 mg/L thidiazuron (TDZ), 0.2 mg/L α-naphthalene acetic acid (NAA), 4 mg/L 6-benzylaminopurine (BA), 0.1 mg/L kinetin, 8 g/L agar, and 3 g/L sugar, with a callus induction rate of 94.77%; Optimal medium for shoot regeneration was MS-1 medium supplemented with 1 mg/L TDZ, 1 mg/L BA, 8 g/L agar, and 3 g/L sugar, with a bud regeneration rate of 15.54%. An efficient regeneration system for callus induction and bud differentiation in radish has been established.