EMBRYOGENIC COMPETENCE OF IMMATURE WHEAT EMBRYOS - GENOTYPE, DONOR PLANT ENVIRONMENT, AND ENDOGENOUS HORMONE LEVELS

The genotype and the environment in which donor plants grow influence embryogenic competence of immature wheat (Triticum aestivum L,) embryo s and levels of endogenous hormones in kernels. We studied relationshi ps between embryogenic competence and hormone levels in kernels and ca lli of PCYT 10 (highly competent) and Yaqui 50 (nearly incompetent) wh eat grown at 15 and 25 degrees C, Endogenous levels of abscisic acid ( ABA), indole-3-acetic acid (IAA), and six cytokinins were determined f or kernels at 0, 4, 8, and 12 d past anthesis (DPA). Immature embryos were cultured at 12 DPA and hormone content of calli was determined at 7, 14, 21, and 28 d past culture initiation (DPI), Somatic embryos we re counted at 28 DPI, Embryogenic competence was associated with low I AA and ABA levels in kernels from 0 to 12 DPA, high zeatin to IAA rati os in kernels at 4 DPA, and high cytokinin to auxin ratios in calli, I ncompetence in Yaqui 50 may be due to low cytokinin to auxin ratios in kernels at 4 DPA and sharp increases in kernel IAA and/or ABA levels prior to embryo excision (12 DPA). Low temperatures during donor plant growth delayed the rise in IAA and ABA in Yaqui 50 kernels and signif icantly increased the embryogenic response from both Yaqui 50 and PCYT 10 embryos. It may be possible to increase competence of nearly nonem bryogenic wheat lines by growing donor plants in cool conditions,,whic h appear to delay the accumulation of IAA and ABA in kernels.