Root and Shoot Initiation in Sweet Potato Explants as Related to Polarity and Nutrient Media Variations

Abstract

Ipomoea batatas explants were cultured on White's basal salt medium, with or without supplements, and grown under 500 ft-c, with a 12-hr photoperiod, at 25 C The amount of callus or number of roots formed depended upon tissue polarity, explant orientation, cultivar response, and culture medium A slight callus formed on the upper surface of explant cylinders, normally oriented and taken from the apical portions of the root Inverted cylinders and those from the median portion of the root formed heavy callus on the upper surface and relatively less on the lower surface The cultivar Centennial produced the most callus when grown on basal medium + indoleacetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), while Jersey Orange produced only slightly less on the same medium Jersey Orange produced the most abundant callus on basal medium + IAA and adenine, more callus than Centennial Yellow Jersey produced the most abundant callus of the three cultivars studied when grown on basal medium + IAA and kinetin. The number of roots formed correlated well with the total amount of callus formed. Root formation also depended upon the cultivar and the medium-supplemented with CM, GA3, kinetin, adenine, and IAA or 2,4-D In strongly polar Yellow Jersey and Jersey Orange, roots grew best on normally oriented or inverted cylinders In the weakly polar Centennial cultivar, roots grew best on cylinders in a lateral position. Root-induction experiments suggested that naphthaleneacetic acid (NAA) did not substitute for IAA, and adenine did not substitute for kinetin Polarity may reflect an IAA-kinetin gradient, and sophisticated media may nullify inherent tissue polarity Shoots formed from Yellow Jersey callus on basal medium + coconut milk (CM), adenine, kinetin, gibberellic acid (GA3), and IAA, or even rarely from basal medium + IAA Centennial explants formed shoots on media with kinetin, GA3, IAA, or 2,4-D, and either CM or adenine Jersey Orange callus formed no shoots Shoots originated from apical callus or from the phloem-pericycle region of primary or lateral roots treated with 2,4-D