EMBRYO RESCUE CULTURE-MEDIUM FOR IMPROVED SYNTHESIS OF 4X WHEAT X RYEHYBRIDS

The cross-incompatibility barrier between 4x wheat and rye has limited the genetic base for triticale breeding. Experiments designed to impr ove the synthesis of wheat-rye amphihaploids were conducted. The effec ts of 2,4-D on crossability and 3x hybrid embryo differentiation, and the influence of one-step and two-step media on the culture of immatur e 3x embryos in vitro, were investigated. Application of 10 mg L(-1) 2 ,4-D slightly improved seed set but significantly reduced the frequenc y of normal embryos. In contrast to the reported favourable effect of 2,4-D on haploid embryo formation in wheat x maize crosses, the applic ation of 2,4-D in the present study offers no real advantage on amphih aploid embryo formation from 4x wheat x rye crosses. For small and imm ature wheat-rye hybrid (3x) embryos, optimum recovery in vitro was obt ained via a two-step procedure consisting of a semi-solid MN medium fo llowed by MS medium supplemented with IAA (1 mg L(-1)) and BAP (1 mg L (-1)). For bigger and well-differentiated embryos, the use of a one-st ep Gamborg's B5 medium was sufficient.