Geotropic Responses and Pod Development in Gynophore Explants of Peanut (Arachis hypogaea L.) Cultured In Vitro

Abstract

Peanut gynophore explants cultured in vitro on a defined medium show a positive geotropic response in both light and dark when planted either horizontally, or vertically with the tip pointing upwards. The growth following the initial curvature depended on age of the gynophores and on the levels of growth substances in the medium. In the dark and in presence of 0·01–0·1 p.p.m. kinetin, naphthalene acetic acid at concentrations of 0·1 p.p.m. and lower promoted gynophore elongation. At higher concentrations elongation was promoted to a lesser extent in younger explants, caused enlargement of the ovary and formation of pods. Young explants generally elongated more than older ones and pod formation took place inside the medium, while in older ones it took place above the medium. In the light, the initial positive geotropic response was followed by elongation but without any enlargement of the ovary. Decapitation of gynophores 1·5–2·0 mm below their tip, removing the ovary but leaving most of the intercalary meristem, had no effect on the geotropic response and elongation. The initial geotropic response and elongations of explants in vitro was not dependent on the presence of the ovary but on the meristem proximal to it. Changes in growth substances balance during gynophore development seem to affect geotropic response, elongation and pod formation in the peanut.