Correlations among lateral shoots in young apple trees

Abstract

Growth correlations among axillary buds and young shoots in one-year-old apple trees were investigated. Darkening of every second bud for 3-5 days during bursting time resulted in the formation of mainly short shoots. Thinning of part of the buds caused a higher percentage of the remaining ones to form long shoots. High nutrition level favored the formation of long shoots. When no special treatment was given to the trees, the initial size of the buds played an important role in the determination of future shoot vigor. The medium-size and large buds, in most cases, showed an ability to accumulate more <sup>32</sup>PO<sup>3-</sup><sub>4</sub> per unit of dry weight than did the smaller ones. This indicates that the initial differences among the buds are amplified by a positive feedback mechanism. In horizontally placed trees, the buds on the lower side showed inhibited phosphate uptake. Different growth regulators applied in very small amounts, in a droplet of water to every second bud or shoot tip, markedly changed the correlative interrelations among the developing shoots. The development of vascular connections between the main axis and the lateral buds and shoots of different sizes was investigated.