Effect of 22(S),23(S)-homobrassinolide on somatic embryogenesis in plumule explants of Cocos nucifera (L.) cultured in vitro

Abstract

SummaryThe increasing demand for coconut palms resistant to diseases requires massive multiplication of improved or selected palms. This could be achieved through micropropagation. A reproducible regeneration protocol via somatic embryogenesis from plumule explants has already been reported, but its efficiency is still low. The protocol is based on the use of an auxin to induce embryogenic callus. Since brassinosteroids are known to act synergistically with auxins and might be involved in the control of plant embryogenesis, the effect of the brassinosteroid 22(S),23(S)-homobrassinolide on initial callus, embryogenic callus and somatic embryo formation in coconut plumule explants was tested. The explants were exposed (during a 3 or 7 d pre-culture) to different concentrations (0.01, 0.1, 1, 2 and 4 μM) of the brassinosteroid. The explants responded favourably to the brassinosteroid increasing their capacity to form initial callus, embryogenic callus and somatic embryos. The largest amount of somatic embryos formed, 10.8 somatic embryos per explant, was obtained exposing the explants for 3 d to the brassinosteroid at 0.01 or 0.1 μM, whereas 3.8 somatic embryos per explant were obtained from untreated explants. This is a very promising result considering the very slow progress of micropropagation research for this very recalcitrant species, that has taken now three decades since it started. This effect of a brassinosteroid on somatic embryogenesis of coconut (or of any other plant species) is as far as we know the first report.