Optimization of somatic embryogenesis in suspension cultures of horsegram [Macrotyloma uniflorum (Lam.) Verdc.]-A hardy grain legume

Cell suspension cultures were established from immature cotyledon derived calli from drought tolerant legume horsegram [Macrotyloma uniflorum (Lam.) Verdc.]. Embryogenic callus could be originated from cut slices of the immature cotyledons on MS solid medium [Murashige, T. Skoog, K., 1962. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiol. Plant. 15, 473-497] augmented with 1.0 μM zeatin and 4.5 μM NAA. Numerous somatic embryoids (26.4%) appeared on MS liquid basal nutrient medium with 5.6 μM NAA and with absence of zeatin during 3 weeks culture. Sustained cell division resulted in the formation of cell aggregates, and then progressed to globular, heart and further if they differentiate properly to torpedo and cotyledonary stages within 5 weeks. Transfer of individual embryos on to a fresh MS basal medium with no plant growth regulators was able to achieve complete maturation. Only a relatively few number of embryos developed into root/shoot when transferred to 0.9 μM GA3, 15 g/l−1 sucrose and 2.4 g/l−1 gelrite containing medium. Substitution of sucrose associated with the use of l-glutamine gave, in the range of concentrations tested, the strongest enhancement of the embryo growth and development. About 5% of somatic embryos were converted into true-to-type fertile plants.