Development and growth potential of axillary buds in roses as affected by bud age

The effect of axillary bud age on the development and potential for growth of the bud into a shoot was studied in roses. Age of the buds occupying a similar position on the plant varied from 'subtending leaf just unfolded' up to 1 year later. With increasing age of the axillary bud its dry mass, dry-matter percentage and number of leaves, including leaf primordia, increased. The apical meristem of the axillary bud remained vegetative as long as subjected to apical dominance, even for 1 year. The potential for growth of buds was studied either by pruning the parent shoot above the bud, by grafting the bud or by culturing the bud in vitro. When the correlative inhibition (i.e. domination of the apical region over the axillary buds) was released, additional leaves and eventually a flower formed. The number of additional leaves decreased with increasing bud age and became more or less constant for axillary buds of shoots beyond the harvestable stage, while the total number of leaves preceding the flower increased. An increase in bud age was reflected in a greater number of scales, including transitional leaves, and in a greater number of non-elongated internodes of the subsequent shoot. Time until bud break slightly decreased with increasing bud age; it was long, relatively, for 1 year old buds, when they sprouted attached to the parent shoot. Shoot length, mass and leaf area were not clearly affected by the age of the bud that developed into the shoot. With increasing bud age the number of pith cells in the subsequent shoot increased, indicating a greater potential diameter of the shoot. However, final diameter was dependent on the assimilate supply after bud break. Axillary buds obviously need a certain developmental stage to be able to break. When released from correlative inhibition at an earlier stage, increased leaf initiation occurs before bud break.