The differences between clones of witches' brooms and their seed progeny are determined by the age status of maternal plants

Key messageClones originating from the young seed progeny of mutational witches' broom have a compact crown and no flowering phenotype caused by the combined effect of the mutation and biological age of the source plant material.AbstractMutational witches' broom (WB), which is formed on trees, is a bud sport that has a modified crown structure. Phenotypically, it differs from the normal crown part in its high density, abundant branching and usually shorter needles. Grafted WBs have a high ornamental value and are propagated for landscaping purposes. WB seed progeny and their clones have also been successfully used in breeding for a long time. However, it is still unknown how the two types of clones differ from each other. To reveal the differences, a comparative analysis of clones from the original mature 170-200-year-old trees of Pinus sibirica with cone-bearing WBs and clones from the 9-year-old mutant seed progeny was carried out in the uniform environment of a common garden. Unlike the initial WB clones, the derivative clones did not flower, which was the most pronounced influence of the age of the source plant material. The growth of derivative WB clones was also affected by the age of the source plant material, which reduced linear growth in addition to the mutation. They were 1.5 times less than in the initial clones, and their crowns were even more compact due to the decreased branching threshold and apical dominance. Significant variation was observed amongst groups of derivative clones derived from different saplings in the progeny of an original WB. The obvious source of the variation was the effect of recombination in the WB seed progeny, which gave rise to the clones. Thus, the influence of the age of the source plant material is fully manifested in the WB of Pinus sibirica, just as it occurs in normal trees. Together with great variation in morphological traits, this made the WB seed progeny an almost inexhaustible source of material for ornamental breeding.