AN IMPROVED METHOD FOR SOMATIC PLANTLET PRODUCTION IN HYBRID LARCH (LARIX X LEPTOEUROPAEA) .2. CONTROL OF GERMINATION AND PLANTLET DEVELOPMENT

Germination and plantlet development in somatic embryos of Larix X lep toeuropaea were affected by the duration of the maturation treatment a nd the concentrations of sucrose and abscisic acid in the maturation m edia. Extension of the maturation period from 3 weeks to 4 weeks resul ted in a1 significant decrease in germination and plantlet development frequencies. There was no significant effect of abscisic acid concent ration on either the number of somatic embryos germinated or the numbe r of plantlets obtained, but it affected the rapidity of the epicotyl development. Sucrose at 0.2 M, applied during maturation, was signific antly more beneficial in attaining high germination rates than at 0.1 M. High germination rates (92 and 93%) and plantlet development rates (74 and 80%) were achieved when somatic embryos were matured for a1 3- week period on media with either 40 or 60 muM abscisic acid, respectiv ely, and 0.2 M sucrose prior to transfer to the growth regulator-free germination medium. Two acclimatization methods were applied: the firs t required 10 to 12 weeks and ensured 97% plantlet survival under gree nhouse conditions; the second required 2-3 weeks and ensured 86% plant let survival. This represents the first detailed study of the effects of maturation regimes on the recovery of somatic embryo-derived plants of Larix.