Abstract:
Flower bud influence on rootability of Rhododendron shoots was
assayed by rooting leaf-petiole cuttings. Monthly samples of an easy-and
an intermediate-to-root cultivar showed periods of poor rooting
in the latter during flower development, although both rooted similarly
during bud dormancy. The decrease in rooting-potential following
flower initiation and development was avoided by preventing flowering
with heavy shading (90 percent). The decreased rooting accompanying
flowering was attributed to specific stages of flower development
that were intensely competitive for growth substances needed in
root regeneration.
Leaves from the lower portions of flowering shoots were larger
and rooted less readily than those from similar positions on vegetative
shoots. Shading experiments revealed that the association of
large leaves with poor rooting is valid only in flowering shoots.
Responses to early terminal bud excision suggested that the increased
leaf size and decreased rootability associated with flowering commences
at time of initiation. Later excision of the terminal flower bud
had less effect on leaf size, but enhanced rootability possibly as a
result of eliminating this strong growth center from competing for
growth substances needed in rooting.
Defoliation experiments revealed a quantitative aspect to the
flowering hormone stimulus from leaves, while establishing a minimum
leaf complement for continued flower development. Partial
defoliation demonstrated the importance of leaves in flowering and
rooting relationships; for example, removal of terminal leaves inhibited
flowering, but enhanced rootability. Labelled auxin transport
studies revealed a positive correlation between transport in leaf-petiole
tissue and lamina rootability. However, there was an inverse
relationship between the amount of auxin transported and that absorbed
by petiole tissue. It was concluded that developing flowers mobilize
auxins from subtending leaves, thereby depleting these tissues of
such materials needed in root regeneration. The extent of the
flower's influence on rooting of shoots in rhododendron depends on
the cultivar and the stage of flower bud development at the time of
sampling.
