An appraisal of ear, leaf and stem 14CO2 assimilation, 14C-assimilate distribution and growth in a reproductive seed crop of amenity Lolium perenne

In seed crops of Lolium perenne, yield may be reduced by competition for a limited assimilate supply from sinks other than the ear. This study was undertaken to evaluate the priorities for allocation of assimilate within the crop from all photosynthetic sites on the main reproductive tiller after anthesis. Ear, stem and leaves were fed with ¹⁴CO₂ on two occasions; the assimilatory efficiency of these sources and the magnitude and pattern of ¹⁴C-assimilate export from each was determined. The growth of each part of the main tiller and subtending tillers was also measured. Stem elongation apparently dominated the current assimilate resource and the ear did not become a net importer of assimilate until this process had ceased. Assimilate allocation to the tillers was high throughout. The nature of any competition between these sinks is discussed. When crop growth was contrasted with that in a previous year, environmental factors were implicated as determinants of priority for assimilate allocation to each sink. Sources of carbon for seed filling are also discussed as is the relevance of these findings to seed crop management.