Embryo Culture and Embryo Rescue for Wide Cross Hybrids

Abstract

Embryo culture is a well-established branch of plant tissue culture (see Hu and Wang 1986 for review). Embryos excised from the developing seed at or near the mature stage are completely autotrophic. They germinate and grow on a simple inorganic medium with a supplemental energy source. The most important aspect in culturing immature embryos is to define a culture medium that can sustain their growth and development. In less than optimum medium, the im­mature embryos may fail to survive, turn into undifferentiated callus, or germi­nate prematurely (precocious germination). Such germination results in weak seedlings displaying only those morphological structures already present at the time of embryo excision. Factors recommended to suppress precocious germi­nation are high osmotic pressure, elevated potassium level, ample nitrogen in the form of the ammonium salt of an organic acid, abscisic acid, and/or reduced oxygen tension (see Norstog 1979). When heart stage and younger embryos are excised (see Figs. 1 and 2), it is best to keep the suspensors intact (Yeung and Sussex 1979). The suspensor is the nutrient uptake site during early stages of embryo development.