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 gr owth of the bud into a shoot was studied in roses. Age of the buds occ upying a similar position on the plant varied from 'subtending leaf ju st unfolded' up to 1 year later. With increasing age of the axillary b ud its dry mass, dry-matter percentage and number of leaves, including leaf primordia, increased. The apical meristem of the axillary bud re mained 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 th e bud in vitro. When the correlative inhibition (i.e. domination of th e apical region over the axillary buds) was released, additional leave s and eventually a flower formed. The number of additional leaves decr eased with increasing bud age and became more or less constant for axi llary buds of shoots beyond the harvestable stage, while the total num ber of leaves preceding the flower increased. An increase in bud age w as reflected in a greater number of scales, including transitional lea ves, and in a greater number of non-elongated internodes of the subseq uent shoot. Time until bud break slightly decreased with increasing bu d age; it was long, relatively, for 1 year old buds, when they sproute d 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 sho ot. 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.