Genotypic response of cowpea Vigna unguiculata (L.) to in vitro regeneration from cotyledon explants

A plant regeneration system applicable to 17 cowpea genotypes was developed. Cotyledons were initiated on 173 MS medium containing 15 to 35 mg N6-benzyladenine (BA) per 1 (66.6 to 155.3 μM) for 5 to 15 d. For shoot regeneration, the explants were transferred to a medium containing 1 mg BA per 1 (4.4 μM). Within 1 wk, shoot formation was visible at the proximal end of the cotyledons. Regeneration percentages (1% to 11%) and the numbers of shoots (4 to 12 per explant were significantly influenced by genotype. Culture duration and BA concentration in the initiation stage significantly affected regeneration capacity. Explants initiated on media containing 15 mg BA per 1 for 5 d resulted in the highest percentage of explants capable of regeneration. Conversely, the highest number of shoots was obtained from explants initiated on media supplemented with 35 mg BA per 1. Whole plants were obtained on a plant growth regulator-free medium. To our knowledge, this is the first report of plant regeneration from U.S. commercial cowpea cultivars and breeding lines. This system is adaptable to diverse cowpea genotypes and will facilitate cowpea genetic transformation.