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 greenhousegrown 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-1 sugar, 0.1 gl-1 α-cysteine , 10 mgl-1 calcium pantothenic acid, 2.0 mgl-1 asparagine, 2.0 mgl-1 arginine, 80.0 mgl-1 adenine sulfate (AdSO4) and 0.1 mgl-1 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-1 benzylamino purine (BAP) or, MSA medium. Callus was effectively induced from the vegetative tissues in MS medium added with 1.0 mgl-1 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 mgl1 2,4-D and 0.5 mgl-1 BAP, or in 1.0 mgl-1 picloram and 0.5 mgl-1 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-1 ABA and 100 mgl-1 glutamine. This step improved the germination of somatic embryos in one-half strength PGR-free MS medium containing 100 mgl-1 glutamine (regeneration medium). All somatic embryoderived plantlets were morphologically normal and established well in soil.