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 explants. The optimum tissue culture conditions were: 1/2GDbasal medium gelled with agar-Gelrite during shoot formation and with agar during rooting, inclusion of 5.0μM benzylaminopurine (BAP) and 0.05 μM naphthaleneacetic acid (NAA) for 2 weeks for shoot induction, and repeated 2.7 μM 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 conserve seedlings from which cotyledons have been cultured give new possibilities for accelerated tree breeding.