Creation of novel interspecific-interploid Hylocereus hybrids (Cactaceae) via embryo rescue

Abstract

In this study we developed a technique for rescuing embryos at a very early developmental stage following interspecific-interploid crosses between Hylocereus sp. Controlled hand pollinations were performed between the tetraploid H. megalanthus (Vaup.) Bauer as the female parent and either diploid H. monacanthus (Lem.) Britton et Rose or H. undatus (Haw.) Britton et Rose as the male parent. The fertilized ovules were excised from ovaries 10 or 30 days after pollination (DAP). Pollinated ovules containing the funiculi and placental tissue and immature embryos were placed on half-strength basal Murashige and Skoog (MS) medium containing 680 μM glutamine, 0.54 μM α-naphthaleneacetic acid, and 0.45 μM thidiazuron and supplemented with 0.00, 0.09, 0.17 or 0.26 M sucrose concentrations. The best ovule response was recorded at 30 DAP, and the most prolific callus formation was observed at 10 DAP. Callus formation was observed in most of the treatments using whole ovules but not in the isolated immature embryos. The calli were mucilaginous or compact, transparent and friable, but they did not form embryogenic structures. Embryo development was significantly affected by the sucrose concentration, and the best results were obtained with 0.17 M sucrose. More than 70 % of the obtained hybrids were successfully hardened off and transplanted in soil where they grew normally. Ploidy level analyses of 77 putative hybrids exposed diploid, triploid, tetraploid, and higher than tetraploid levels. Among those hybrids studied, 22 progenies were randomly chosen for amplified fragment length polymorphism analysis, and all were identified as genuine hybrids. The technology described here is an additional stage in the breeding program for Hylocereus species resulting in novel, interspecific hybrids obtained using the embryo rescue technique.