In VitroPhenotypic Variation in Larch Cotyledon Number

Somatic embryos of hybrid larch (Larix × leptoeuropaea) have significantly fewer cotyledons per embryo than embryos of zygotic origin. They also have a much greater variance and range in cotyledon number (zero to 15) than do seed embryos (four to seven), as well as a greater number of phenotypes. Somatic embryos were matured on modified Murashige and Skoog’s (1962) medium supplemented with one of the following combinations of growth‐regulating substances: (1) 60 μM abscisic acid (ABA), (2) 2.2 μM benzyladenine (BA), (3) 60 μM ABA and 2.2 μM BA, or (4) a control medium containing neither plant growth regulator. Of these treatments, BA caused the greatest reduction in cotyledons per embryo. Embryos produced on different BA concentrations (0, 0.04, 0.4, 4.4, 44, and 444 μM) showed significant differences in cotyledon number per embryo as well as percentage of embryos with cotyledons. At higher concentrations, BA‐treated embryos had shorter hypocotyls and longer cotyledons than embryos produced at lower concentrations. At concentrations >4.4 μM, BA reduced the percentage of embryos able to initiate cotyledons. Precocious germination was reduced by concentrations of BA above 0.44 μM BA.