INFLUENCE OF A PLANT-GROWTH REGULATOR ON THE SINK CAPACITY OF OILSEEDRAPE (BRASSICA-NAPUS L)

A pot experiment was carried out to examine the effect of the plant gr owth regulator Triapenthenol (RSW) on the apical dominance of oilseed rape and its corresponding effect on the plant's 'sink' capacity. RSW' s influence on the number of flower primordia, flowers, pods, yield an d yield structure of the whole plant and of different fractions of the plant (main shoot, lateral shoots 1-3, lateral shoots >3; 1st, 2nd an d 3rd-order lateral shoots) and its effect on gibberellin content and shoot height was measured. RSW diminished dominance of the main shoot and of 1st-order lateral shoots: the initiation of flower primordia wa s increased to about 34% and 116%, respectively, in fraction lateral s hoots higher than 3 and 3rd-order lateral shoots. Buds developed in a more synchronized pattern leading to a significantly improved number o f flowers and pods in fraction lateral shoots higher than 3. Despite a n increased number of pods per plant, grain yield remained unchanged b ecause of a decrease in the number of seeds per pod and an unaffected thousand-kernel weight. A decreased content of gibberellin A19 (GA19), GA20, GA1 and GA8 was evident after application of RSW, and a correla tion between gibberellin-content and shoot height was found. The resul ts of this study suggest that high levels of such GAs, that primarily promote shoot elongation and strengthen the apical dominance within th e plant, limit the plant's 'sink' capacity. These effects may be due t o a gibberellin-promoted auxin-synthesis.