Plant regeneration via direct shoot organogenesis from cotyledon explants of Bambara groundnut, Vigna subterranea (L.) Verdc.

Bambara groundnut (Vigna subterranea [L.] Verdc.) is mainly grown for human consumption. However, several factors limit a wider adoption of the crop including the presence of antinutritional factors in the seeds that lower product quality and protein availability but also the plant susceptibility to pests and diseases. Tissue culture techniques are very scanty in Bambara groundnut and should be developed before carrying out genetic transformation for the crop improvement. Therefore, here, an efficient system for in vitro shoot induction from cotyledons derived from mature seeds has been established. Different types and concentrations of plant growth regulators were used to induce buds in embryo-free cotyledon explants. Cotyledons were cut transversally or longitudinally into three segments: proximal, middle and distal part. The influence of explant orientation on the medium, the type of segment and landrace has then been studied. Benzylaminopurine (3 mg.l(-1)) alone or combined with a-naphthaleneacetic acid (0.05 mg.l(-1)) induced multiple shoot formations. The organogenic potential was restricted to the proximal segment of cotyledons. Frequency of bud induction (30%) and average number of buds per explant (12) were higher when the adaxial side of the proximal segment was in contact with the medium. Shoot regeneration from cotyledon explants of ten Bambara landraces revealed that the response is genotype-dependent with varieties Ci6, Ci2, Ci4 and Ci15 exhibiting 20 to 30% shoot regeneration and six to ten buds per explant. Regenerated shoot buds excised from explants were elongated and rooted on MS basal medium devoid of plant growth regulators. All rooted plantlets survived to the transfer on a sand soil mixture, and morphologically normal plants were hardened and transferred to greenhouse for further growth to maturity and seed set.