The method for breeding and genetic assessment of Scotch pine clones at forest seed orchards

Fast height growth selection usually considered as the basic type of Scotch pine breeding strategy. Due to this fact height growth of pine clones usually is taken as the first key feature. In the view of good seed production there is only one indicator that could be adopted as having summarized effect reflecting the real contribution of a clone to the whole seed orchard yield. This is an average number of full seeds per tree (ramet). This trait is the second most important one after the height growth ability feature. The way of two-trait breeding program with the aforesaid features seemed to be the most suitable for Scotch pine. Main theses of 4-stages complex assessment procedure have been formulated concerning Scotch pine vegetative progenies grown at seed orchards. It was stated that this system of breeding and genetic assessment is based on correlations found for habitus and reproductive features of Scotch pine clones along with the height growth ability of their seed progenies. In the first stage pine clones meeting the criteria (≥ X + 0.5σx) regarding height growth are to be selected. In the second stage, clones with hard tapering stem and crown formed by long and thick branches have to be discarded. At this stage, such feature as «mean diameter of three thickest limbs at the height of 1.5–2.0 m» became the key factor. Its mean value for selected clones must not be by 1–2 % higher than for general clone set. In the third stage a complex of reproductive features for clones that have passed the previous stages are taken into account. The trait «average number of full seeds per ramet» is the key feature in this stage according to the criteria (≥ X ). The fourth stage implies that progeny trials with open-pollinated progenies ought to be laid down to calculate the general and specific combining ability. It has been concluded that high intensive selection of clones grown at the I-stage seed orchards promotes a substantial genetic gain expected at the subsequent breeding stages. Seven clones (10 % of the total) have been selected using the two-trait breeding approach. As a result, habitus features of the selected clones became much better. The height and stem diameter increased by 7.6 and 2.6 % and crown width along with branch diameter did the same by 2.1 and 1.2 %, respectively. At the same time seed yield increased by 43.0 %