Embryo rescue and plant regeneration following interspecific crosses in the genus Hylocereus (Cactaceae)

The aim of this study was to develop an efficient methodology to rescue embryos following interspecific crosses in the genus Hylocereus. Crosses between the diploids Hylocereus polyrhizus and H. undatus in both directions were performed. Fertilized ovules carrying embryos at very early pro-embryonic stages were excised from ovaries 5 days after pollination (DAP) and placed on half-strength basal MS medium containing 680 μM glutamine, 0.55 μM α-naphthaleneacetic acid (NAA), 0.45 μM thidiazuron (TDZ) and various concentrations of sucrose. After 30 days in culture, ovules were isolated from the surrounding tissue and transferred to the same fresh medium. Significant differences were found between the main effects (cross and sucrose concentration) in ovule response, i.e., increased ovule size and callus formation. The best responses were obtained in the cross: H. polyrhizus × H. undatus; and sucrose concentration of 0.09 M. In terms of embryo conversion, polyembryony and number of regenerated plants, the highest responses were observed on the culture medium supplemented with 0.17 M sucrose in both interspecific crosses. All tested plants were found to be diploid by flow cytometric analyses. Fluorescent amplified-fragment length polymorphism (fAFLP) confirmed the hybrid origin of the regenerated plants. This study reports on the success of a three-step embryo rescue procedure for Hylocereus species. The procedure developed here provides the means for producing plants from very-early embryo stage, thus expanding the prospects for vine-cactus breeding programs.