Tree breeding is a slow process when compared to annual crop breeding becau
se of the long generation times typical for trees and the fact that quality
traits are only visible at maturity. Nowadays, molecular biology can signi
ficantly accelerate tree improvement by identifying genes responsible for d
esirable traits and by controlling their expression by gene engineering. Po
tential targets for tree improvement are wood quality, tl ce architecture a
nd development, sterility, and resistance to pests, diseases and herbicides
. The main achievements obtained in these different fields are presented.