Early.flowering Scots pines through tissue culture for accelerating tree breeding

Scots pine plantlets were produced via tissue culture using cotyledons excised from germinated embryos as ~xplants. The optimum tissue culture conditions were: ~4GD basal medium gelled with agar-Gelrite during shoot formation and with agar during rooting, inclusion of 5.0 btM benzylaminopurine (BAP)and 0.05 pM naphthaleneacetic acid (NAA)for 2 weeks for shoot induction, and repeated 2.7 pM NAA pulses of 1 week for rooting. Micropropagation success was genotype-dependent. Average multiplication rates varied among experiments from 3 to 15 shoots per embryo. The maximum shoot production from a single embryo was 35. Rooting was the most difficult phase in the propagation process. Most of the plantlets had a plagiotrophic and highly branched growth habit when growing in the greenhouse. Some individuals produced megasporangiate strobili at the age of 3 years and microsporangiate strobili with viable pollen at the age of 4 years. Early-flowering clones and the ability to onserve seedlings from which cotyledons have been cultured give new possibilities for accelerated tree breeding.