Callus induction and proliferation from cotyledon explants in Bambara groundnut.
Bambara groundnut [Vigna subterranea (L.) Verdc. Fabaceae] is an indigenous African crop grown across the continent. It is the third most important grain legume after groundnut and cowpea. Application of modern biotechnology methods (genetic transformation) for bambara seeds quality improvement is highly desirable, but this in turn depends on the availability of an efficient regeneration system. Callus induction from cotyledon explants was studied in indigenous grain legume Bambara groundnut on Murashige and Skoog (MS) basal medium, containing different combinations and concentrations of growth regulators. Callus formation and callus growth were recorded after four weeks of culture. Maximum frequency of callus induction (98%) and the most significant callus growth index (3) were observed on the medium supplemented with 0.5 mg l-1 2,4- dichlorophenoxyacetic acid (2,4-D) or Picloram (Pic). The combination of 2,4-D with four cytokinins [Benzylaminopurin (BAP), Kinetin (KIN), Thidiazuron (TDZ) and Zeatin (Zea)] resulted in reduction of both callus formation rate and cell proliferation. The potentiality of the cotyledon explant to induce callus formation and subsequent growth was better with the distal segment either in adaxial (59.24%; 2.51) or abaxial (52.22%; 2.60) orientation. The results also showed that 3% sucrose was a better source of carbon for callus formation (74%). Among the landraces tested, the highest rate of callus formation (70%) and maximum growth index (2.65) of callus was observed with landrace Ci7.
Keywords: 2-4D, cytokinins, Vigna subterranea