Regeneration from Rhizome Fragments of Agropyron repens (L.) Beauv. III. Effects of Nitrogen and Temperature on the Development of Dominance Amongst Shoots on Multi-node Fragments
Not all buds developed equally when 7-node rhizome fragments of Agropyron repens (L.) Beauv. were incubated in the dark at 23 °C. Instead, after an initial flush of several shoots, buds were inhibited in a highly ordered sequence to leave only one dominant shoot growing. Applying an exogenous supply of nitrogen KNO3) early during this sequence increased the mean shoot lengths and delayed the onset of dominance. Additionally, the application of nitrogen after eight days incubation altered the sequence of shoot growth such that, in some instances, small rapidly-growing basal shoots ‘dominated’ larger and more slowly-growing apical ones. Dominance (correlative inhibition) was maintained in untreated fragments for up to 383 days Numbers of active budsand shoot extensionrate weremaximal in therange 13°to 23 °C where dominance was established within 30 days. Incontrast only 6 per cent of rhizome fragments kept at 33 °C had dominant shoots after 65 days. At 3 °C shoot growth was so slow that dominance was not permanently established within 150 days. Numbers ofactive budsand shoot extensionrate weremaximal in therange 13° to 23°C where dominance was established within 30 days. Incontrast only 6 per cent of rhizome fragments kept at 33 °C had dominant shoots after 65 days. At 3 °C shoot growth was so slow that dominance was not permanently established within 150 days It is suggested that the effects of nitrogenand temperature on dominance in multi-noderhizome fragments can be interpreted in terms of competition for nutrients between shoots, and the antagonistic effects of nitrogen on an auxin-mediated inhibition by the dominant shoot.