Methods and role of embryo rescue technique in alien gene transfer

Abstract

Embryo abortion occurs frequently in wide crosses, and thus embryo rescue is required for survival of the next generation. Rescues are performed by either directly transferring the excised embryo to an artificial medium or indirectly through flower (ovary), immature seed (fertilized ovule), or pod (silique) culture. Varioustechniques used for oil crops, cereals, legumes, and horticultural crops are presented. Altering medium components were the major routes for developing protocols for each species with adaptations to the base medium, sucrose concentration, or vitamin and growth regulator content. Monocot culture tended to be more direct than dicot culture, where many protocols required a multi-step approach from pod to ovule culture to embryo rescue, shoot regeneration, and root induction. Each step required a specific medium and growth conditions. Hybrid embryos as young as 2 days after pollination have been recovered. However, many species such as soybean and chickpea still needprocedures for rescue of very young embryos. In other species hurdles such as poor rooting have been overcome byusing grafting techniques. Embryo rescue remains a useful component in any breeding program where wide or interspecific crosses are preformed, where rapid cycling through generations is used, and where germplasm preservation is required.