USE OF EXOGENOUS GROWTH SUBSTANCES IN PROMOTING POLLEN TUBE GROWTH AND FERTILIZATION IN BARLEY-RYE CROSSES

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Abstract
Exogenous growth substances applied to the seed bearing parent during the reproductive stage, promoted pollen tube growth and embryo initiation in otherwise incompatible matings between auto-tetraploid barley and diploid rye. Gibberellic acid (GA) and indole - 3 - acetic acid (IAA) continuously during the reproductive stage at a concentration of 25 ppm and 1. 0 ppm respectively were found to be most effective for promoting pollen tube growth. The frequency of embryo formation however, was increased over controls only with the use of relatively high rates of application of GA (eg. 100 ppm). Treatments used in this study were not effective in sustaining embryo development in vivo past the pro-embryo stage. Attempts to culture these embryos on artificial media failed. The results indicate that although exogenous GA and IAA were effective in overcoming an initial barrier to hybridization of the 2 species used in this study (viz. retarded pollen germination and growth of pollen tubes), the nutritional requirements for sustained development of hybrid embryos were still lacking.

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