Somatic embryogenesis and plant regeneration in purple food yam (Dioscorea alata L

A study was conducted to establish a reliable procedure for somatic embryogenesis and plant regeneration from callus cultures of purple food yam (Dioscorea alata L.). The procedure involved three steps; (1) culture of nodal stem segments from greenhouse-grown plants to generate in vitro plantlets; (2) induction of callus from the leaf, petiole and nodal stem tissues; and (3) initiation of somatic embryo from callus. Results showed that the agar-solidified Murashige and Skoog (MS) medium containing 30 gl sugar, 0.1 gl d-cysteine , 10 mgl calcium pantothenic acid, 2.0 mgl asparagine, 2.0 mgl arginine, 80.0 mgl adenine sulfate (AdSO4) and 0.1 mgl naphthalene acetic acid(NAA) effectively broke dormancy of lateral buds of nodal stem cultures from both VU-2' and 'Kinampay' varieties. Production of multiple adventitious shoots occurred after transfer of in vitro nodal pieces to the same medium added with 1.0 mgl benzylamino purine (BAP) or, MSA medium. Callus was effectively induced from the vegetative tissues in MS medium added with 1.0 mgl 2,4-Dichlorophenoxy acetic acid (2,4-D) or, with picloram. Among the three types of explants, the nodal stem was the most suitable which produced purplish nodular embryogenic callus. A higher percentage of nodal stem-derived calli produced globular embryos in MS medium containing 1.0 mgl 2,4-D and 0.5 mgl BAP, or in 1.0 mgl picloram and 0.5 mgl BAP than, in the plant growth regulator-free medium (control). The maturation of embryos was facilitated by one-month culture in MS medium containing 0.1 mgl ABA and 100 mgl glutamine. This step improved the germination of somatic embryos in one-half strength PGR-free MS medium containing 100 mgl glutamine (regeneration medium). All somatic embryo-derived plantlets were morphologically normal and established well in soil.