BRANCH AND ROOT-FORMATION IN TRIFOLIUM-REPENS IS INFLUENCED BY THE LIGHT ENVIRONMENT OF UNFOLDED LEAVES

In plagiotropic plants, axillary buds on the stolen can be exposed to low red:far-red (R:FR) ratios, while the leaves may be positioned in t he uppermost layer of the sward where they are exposed to a high R:FR ratio. We tested whether the light environment of unfolded leaves infl uences outgrowth of the axillary buds and the formation of nodal roots of Trifolium repens. Single plants were grown in a growth cabinet wit h high photosynthetic photon flux rate (PPFR) and a high R:FR ratio (F HRH, control), low PPFR and high R:FR (FLRH) or low PPFR and low R:FR (FLRL) In an additional treatment (SS), only stolons were shaded so th at developing leaves grew into light conditions similar to the control treatment. Neutral shading (FLRH) had a minor effect on branching and did not influence root formation. A reduction in the R:FR ratio (FLRL ) significantly delayed the outgrowth of axillary buds so that, compar ed to the control plants, the percentage of branched phytomers was red uced by 43% on the parent axis and by 75% on primary branches. Further more, the number of nodal roots per plant was reduced by about 30%. Wh en only the stolons were shaded (SS), the percentage of branched and r ooted phytomers was similar to that of the control plants. Extension o f petioles and leaves was very variable, increasing the values in the FLRL treatment at least 2.5-fold compared with the control plants. It was concluded that the light environment of the unfolded leaves had a significant influence on the regulation of the outgrowth of axillary b uds and that the high plasticity in petiole growth allows the position ing of the leaves in a light environment conducive to the stimulation of branch outgrowth.