Production of somatic embryos and plantlets from root cells of the Greater Yam

Abstract

Morphogenically competent cell clusters were induced from 3–4 mm-long root segments excised from in vitro shoot cultures of the greater yam (Dioscorea alata L. ‘Oriental Lisbon’)plated in a liquid modified Murashige and Skoog (1962) medium (PMS) supplemented with 1 mg l⁻¹ 2,4-dichlorophenoxy-acetic acid and 3% sucrose at 25°C in the light. Embryogenic cell clusters released from subcortical regions of the root explants proliferated further into proembryonic cell masses which, when transferred to auxin-free medium, differentiated into somatic embryos. A proportion of the somatic embryos (as high as 80% in some experiments) converted to plantlets within two months after initial root segment culture. A description of the different stages of yam somatic embryogenesis is presented. Cultural factors which affected somatic embryo maturation in liquid medium to the greatest extent were embryogenic cell cluster density and gibberellic acid (GA₃) level present in the medium. Optimal somatic embryo maturation occurred when the density of embryogenic clusters was adjusted to 2–4 per 5 ml PMS and when GA₃ was present in conditioned PMS medium at a concentration of 1.5 mg l⁻¹