The effect of a single inbreeding on the growth and development of fast-growing tree species, Betula pendula and Betula pubescens

The aim of the research is to study parameters of seed reproduction systems in Betula pendula and B. pubescens , find possibilities for producing viable inbred plants, and analyze their growth and development and hybrid heterosis at crossing the selected forms in generations F1 and I1. Differentiation in deciduous trees by self-fertility level was established. By this feature the progeny of different tree groups have different genetic and selection value depending on pollination method of parent trees: at open pollination the progeny of self-sterile and transitional forms (cross-pollinating) are the most fast-growing and resistant to unfavorable environmental factors, whereas at self-pollination – the progeny of self-fertile forms. Accordingly parent trees were classified into three groups: self-fertile, self-sterile and transitional forms. Frequency of self-fertile forms and preservation of inbred plants in downy birch are higher than the similar indicators in silver birch. Thus an ambiguous effect of closely related crossing in tree species on the growth and development of their seed progeny was revealed. The effect of inbreeding on some trees is positive, on other negative, and there is the third group, in which the growth deflections caused by inbreeding are inessential. Such trees are suggested for use in various selection programs.