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,) embryos and levels of endogenous hormones in kernels. We studied relationships between embryogenic competence and hormone levels in kernels and calli of PCYT 10 (highly competent) and Yaqui 50 (nearly incompetent) wheat grown at 15 and 25 degrees C, Endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), and six cytokinins were determined for 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 were counted at 28 DPI, Embryogenic competence was associated with low IAA and ABA levels in kernels from 0 to 12 DPA, high zeatin to IAA ratios in kernels at 4 DPA, and high cytokinin to auxin ratios in calli, Incompetence 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 significantly increased the embryogenic response from both Yaqui 50 and PCYT 10 embryos. It may be possible to increase competence of nearly nonembryogenic wheat lines by growing donor plants in cool conditions,,which appear to delay the accumulation of IAA and ABA in kernels.