The nature of flower bud influence on root regeneration in the Rhododendron shoot

Graduation date: 1970Flower bud influence on rootability of Rhododendron shoots was\ud assayed by rooting leaf-petiole cuttings. Monthly samples of an easy-and\ud an intermediate-to-root cultivar showed periods of poor rooting\ud in the latter during flower development, although both rooted similarly\ud during bud dormancy. The decrease in rooting-potential following\ud flower initiation and development was avoided by preventing flowering\ud with heavy shading (90 percent). The decreased rooting accompanying\ud flowering was attributed to specific stages of flower development\ud that were intensely competitive for growth substances needed in\ud root regeneration.\ud Leaves from the lower portions of flowering shoots were larger\ud and rooted less readily than those from similar positions on vegetative\ud shoots. Shading experiments revealed that the association of\ud large leaves with poor rooting is valid only in flowering shoots.\ud Responses to early terminal bud excision suggested that the increased\ud leaf size and decreased rootability associated with flowering commences\ud at time of initiation. Later excision of the terminal flower bud\ud had less effect on leaf size, but enhanced rootability possibly as a\ud result of eliminating this strong growth center from competing for\ud growth substances needed in rooting.\ud Defoliation experiments revealed a quantitative aspect to the\ud flowering hormone stimulus from leaves, while establishing a minimum\ud leaf complement for continued flower development. Partial\ud defoliation demonstrated the importance of leaves in flowering and\ud rooting relationships; for example, removal of terminal leaves inhibited\ud flowering, but enhanced rootability. Labelled auxin transport\ud studies revealed a positive correlation between transport in leaf-petiole\ud tissue and lamina rootability. However, there was an inverse\ud relationship between the amount of auxin transported and that absorbed\ud by petiole tissue. It was concluded that developing flowers mobilize\ud auxins from subtending leaves, thereby depleting these tissues of\ud such materials needed in root regeneration. The extent of the\ud flower's influence on rooting of shoots in rhododendron depends on\ud the cultivar and the stage of flower bud development at the time of\ud sampling