Relation of source and sink during grain filling period in wheat and some aspects of its regulation

Abstract

The effects of changes in source‐sink relation and of cytokinin applications were examined with regard to the development of flag leaves and grain growth in two contrasting spring wheats, Triticum aestivum L., cv. Kolibri and Solo, grown in hydroculture at mean day/night temperatures of 21/19°C. Lowering temperatures during the phase of ear differentiation decreased the ratio of source and sink size (flag leaf area/grains per ear) but hardly affected maximum chlorophyll content of the flag leaf (source activity), maximum rates of grain growth (sink activity), or final grain weight. Nevertheless, considerable differences were produced with regard to the duration of grain filling, the development and coordination of source and sink activities after maxima had been attained. Changing the ratio of source and sink size during grain filling by spikelet removal affected final grain weight the less, the later the treatments began. Comparing, plants with identical source activities demonstrated that differences in grain weight were mainly due to different growth rates between day 16 and 40. Source activities were raised only temporarily (day 23) by spikelet removal done at day 2 or 14. From this it may be concluded that changing the ratio of source and sink size influenced grain weight by creating different intrinsic growth potentials in the grains. These potentials might be estimated 3 weeks after ear emergence by DNA and RNA content per grain. The effects of exogenous cytokinins were consistent with those due to spikelet removal suggesting that this hormone participates in a joint regulation of source and sink activity during grain filling.