Seed dry weight response to source-sink manipulations in wheat, maize and soybean:: a quantitative reappraisal

Determining to what degree seed weight differences are due to competition among seeds for insufficient source is critical for the rational design of breeding and management strategies aimed at maximizing crop yields. While the crop physiology literature cites many examples of source and/or sink yield limitations during seed filling, interpretation of these data has usually been qualitative in nature, biasing our view of the source-sink yield limitations during this period. In the present review, we applied a quantitative approach for determining the magnitude of seed dry weight changes in response to manipulations in assimilate availability during seed filling for previously published articles in wheat (Triticum aestivum), maize (Zea mays L.) and soybean (Glycine max L.). This quantitative approach demonstrates that yield is usually more sink than source limited during seed filling in the three crops, though: (i) interspecific variation exists in the magnitude of limitation, and (ii) intraspecific variability is larger in soybean than in cereals. Seeds of wheat appeared to grow mostly at saturated assimilate availability, so yield is mainly sink limited in all growing conditions x cultivar combinations explored in the analysis. Soybeans seem to experience a large degree of co-limitation by the source and the sink, as seeds greatly respond to source-sink modifications. Maize displayed a consistent trend to dramatic reductions in seed dry weight when assimilates produced during seed filling are reduced, but a virtual lack of responsiveness to improvements in potential availability of assimilates per growing seed. This results in a sink-limited crop in most growing conditions, but a source-limited crop if resource availability is strongly reduced during seed filling. (C) 2003 Elsevier B.V. All rights reserved.