Initiation and Development of Asexual Embryos of Theobroma cacao L. in vitro

Abstract

Summary Zygotic embryos of Theobroma cacao «Amelonado» from 2.5 to 28.0 mm in length were cultured on a basal medium consisting of MURASHIGE and SKOOG salts, vitamins, glycine, casein hydrolysate, and sucrose. Asexual embryogenesis occurred only from immature white (2.5 to 10.0 mm in length) and white/pink (10.5 to 18.0 mm in length) zygotic embryos, with the highest number of asexual embryos arising from the white embryos. Although embryogenesis occurred at low frequency on basal medium alone, the combination of auxin (indole-3-acetic acid, α-naphthaleneacetic acid, or 2,4-dichlorophenoxyacetic acid) and coconut water greatly stimulated embryogenesis; the addition of each separately had little effect on the embryogenic process. A higher incidence of embryogenesis was observed with liquid than with semisolid medium. Enhanced growth of zygotic embryos was also observed in liquid medium. Microscopic examination revealed two distinct patterns of asexual embryo initiation: 1) a «budding» process in which embryos arose from glandular hair-like structures; and 2) a «nonbudding» process with differentiation from internal cotyledonary meristematic tissues. Tissues from embryogenic cultures transferred to basal medium without auxin and coconut water continued to initiate asexual embryos.