Diversity in the morphology of clones of witches’ broom in Siberian stone pine

Abstract

Mutational witches’ broom (WB) is a fragment of a tree crown with abnormally dense branching and slow shoot growth compared with those of a normal crown. All WBs have thicker and denser crown compared to the normal crown part of their parental tree, but the crown density differs significantly among WBs. There are both relatively loose WBs, whose crown density differ from normal crown part not very strong, and WBs with a very dense crown. The aim of this study was to conduct a comparative analysis of morphological traits in Pinus sibirica WB clones with different crown densities and to determine which traits contribute most to their differences. The object of the study was clones from 11 mutational WB with different crown density. The density of WB was considered low if it exceeded the density of a normal crown by less than 2 times, medium - by 2-3 times, high - by more than 3 times. Morphological characteristics of crown and shoots were measured in 12-year-old clones. It was found that the higher the WB clone crown density the smaller and less elongated its crown shape, as well as less crown continuity. The basis of this phenotype formation was primarily the shorter length of annual shoots, the reduced level of apical dominance compared to other clone groups, and advanced branching. An additional factor that increased crown density was the significantly shorter internodes compared to the other clone groups. The needle length did not contribute to the differences in crown density of the clones.