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

Peanut gynophore explants cultured in vitro on a defined mediumshow a positive geotropic response in both light and dark whenplanted either horizontally, or vertically with the tip pointingupwards. The growth following the initial curvature dependedon age of the gynophores and on the levels of growth substancesin the medium. In the dark and in presence of 0·01–0·1p.p.m. kinetin, naphthalene acetic acid at concentrations of0·1 p.p.m. and lower promoted gynophore elongation. Athigher concentrations elongation was promoted to a lesser extentin younger explants, caused enlargement of the ovary and formationof pods. Young explants generally elongated more than olderones and pod formation took place inside the medium, while inolder ones it took place above the medium. In the light, theinitial positive geotropic response was followed by elongationbut without any enlargement of the ovary. Decapitation of gynophores1·5–2·0 mm below their tip, removing theovary but leaving most of the intercalary meristem, had no effecton the geotropic response and elongation. The initial geotropicresponse and elongations of explants in vitro was not dependenton the presence of the ovary but on the meristem proximal toit. Changes in growth substances balance during gynophore developmentseem to affect geotropic response, elongation and pod formationin the peanut.