AN IMPROVED METHOD FOR SOMATIC PLANTLET PRODUCTION IN HYBRID LARCH (LARIX X LEPTOEUROPAEA) .1. SOMATIC EMBRYO MATURATION

Somatic embryogenesis was induced from full-sib immature zygotic embry os of hybrid larch (Larix x leptoeuropaea) that were collected at thre e different dates. Analysis of variance showed interaction between the collection date and the induction medium. The highest response (55%) was observed from embryos that were at the precotyledonary stage. Twel ve media containing various concentrations of abscisic acid and sucros e were used to promote the development of 'high quality' mature somati c embryos that would undergo a1 period of developmental arrest. Only m edia supplemented with abscisic acid (20, 40, and 60 muM), indolebutyr ic acid (1 muM), and 0.1 or 0.2 M sucrose supported such a1 developmen t. The number of mature somatic embryos produced per gram fresh weight of embryonal mass was significantly affected by the three factors tes ted: embryogenic line, sucrose concentration, and abscisic acid concen tration. Moreover, strong interaction effects among these factors exis ted, complicating the formulation of a1 universal maturation medium th at would be optimal for all embryogenic lines.