Mechanisms by which basal branches suppress axillary bud outgrowth in pea (Pisum sativum)

Abstract

This study examined whether the strong inhibitory influences of basal branches on axillary bud outgrowth seen in Trifolium repens L. similarly occur in Pisum sativum L. Mechanisms by which basal branches in P. sativum suppress bud outgrowth were assessed using treatment combinations of main stem decapitation and excision, girdling, and (or) disbudding of basal branches. The combination of decapitation with basal branch excision provided a new avenue for the investigation of correlative suppression of bud outgrowth. The results revealed a dual suppressive action of basal branch buds: girdling of basal branches confirmed they act via export of an inhibitory influence, but also demonstrated, for the first time in P. sativum, their role as competitive sinks for bud outgrowth stimulus. Although all of the axillary buds on the main stem had similar intrinsic potential for outgrowth, sensitivity to these suppressive influences varied with position on the stem. This suppressive influence of basal branches was, like apical dominance, a major influence on the regulation of bud outgrowth. The finding in P. sativum that basal branches suppress bud outgrowth via their action as competitive sinks for an outgrowth stimulus, as they do in nodally rooting clonal herbs, suggests further investigation of this process is warranted.