RAPID AND REPETITIVE PLANT-REGENERATION IN SWEET-POTATO VIA SOMATIC EMBRYOGENESIS

An efficient in vitro plant regeneration system characterized by rapid and continuous production of somatic embryos using leaf and petiole e xplants has been developed in sweetpotato [Ipomoea batatas L. (Lam.)]. The optimal somatic embryogenic response was obtained in the genotype PI 318846-3 with a two-step protocol: (1) stage I-incubation of expla nts in the dark for 2 weeks on Murashige-Skoog (MS) medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) (2.5 mg/l) and 6-benzylaminopur ine (0.25 mg/l) and, (2) stage II-culture in the light on MS medium wi th abscisic acid (ABA) (2.5 mg/l). The addition of ABA was critical fo r enhanced production of somatic embryos. Secondary somatic embryos we re produced from the primary embryos cultured on MS medium with 2,4-D at 0.2 mg/l. The somatic embryos were converted into normal plantlets when cultured on basal MS medium. Upon transfer to soil, plants grew w ell and appeared normal with no mortality. The system of somatic embry ogenesis described here will facilitate tissue culture, germplasm cons ervation and gene transfer research of sweetpotato due to its rapidity (6 to 10 weeks), prolific plant production by direct embryogenesis, e ase of secondary somatic embryo production and reproducibility.