Axillary bud development in rose.

Axillary buds form the basis of flower production of a rose crop. Within a rose crop there exists an undesired large variation in shoot number and size, which affects flower yield. Part of this variation may be traced back to early variation in axillary buds. The aim of the research reported in this thesis was to enlarge the knowledge and insight in the development of axillary buds. It was investigated to what extent the growth of an axillary bud into a shoot can be influenced during axillary bud formation and to what extent during actual outgrowth into a shoot. Factors studied were bud age, bud position, assimilate supply and temperature. Growth potential of the buds was studied both in situ and in isolation (grafted or in vitro), enabling to distinguish between direct effects on the buds and indirect effects via the parent plant.An axillary bud contains the lower part of the future shoot. The axillary buds which are most likely to form the first basal shoots are already present as secondary buds in the bud which is used for propagation. Later formed basal shoots usually develop from basal axillary buds of the basal shoots. Each basal shoot was shown to be connected to only a segment of the root xylem. Later formed basal shoots may restrict the growth of the older basal shoots by limiting the xylem serving the older basal shoots.Axillary buds needed a certain developmental stage to be able to break. Bud break also required release from correlative inhibition. As long as axillary buds were correlatively inhibited, they remained in the vegetative stage. They were not dormant, but continued to grow although at a low rate. When released from inhibition their developmental programme (bud break, leaf initiation and flower initiation) was already set to a large extent. However, they displayed a high degree of plasticity in their development into a shoot, in response to ambient conditions in which they were growing. Number of leaves preceding the flower appeared to be determined during axillary bud formation and increased with increasing bud age, decreasing position along the shoot, increasing assimilate supply and decreasing temperature. Rate of bud break increased with increasing position, increasing temperature during bud formation and increasing temperature after release from inhibition. Shoot diameter correlated with pith diameter. Number of pith cells in the axillary bud reflects the potential diameter of the subsequent shoot. Final pith diameter was dependent on cell expansion after bud break and was reached soon after start of shoot growth. Increased assimilate supply and decreasing temperature positively affected expansion of the pith cells and as a result the pith diameter. Length and weight of the shoot at harvest and growth period were largely dependent on the assimilate supply and the temperature after release from inhibition