Grain filling and dry matter translocation responses to source-sink modifications in a historical series of durum wheat

To understand yield limitations imposed by the source-sink relationship and the effects that breeding had on it, the source-sink ratio was modified on 24 durum wheat cultivars released in different periods. Field experiments were conducted during 3 yr, with treatments consisting of removing the flag-leaf blade, degraining half of the spike, and intact checks. Grains from near-basal spikelets tended to be the most sensitive to source-sink modifications. Degraining increased grain weight up to 15% in modern cultivars, which were more source limited and more responsive to source-sink modifications than the old ones. Our results suggest a source-sink colimitation for grain filling in Mediterranean environments. Translocation of preanthesis assimilates was responsible for 25, 27, and 33% of grain weight in old, intermediate, and modern cultivars, respectively. Defoliation did not alter dry matter translocation (DMT) from the main stem, as the reduction in translocation of leaf blades was compensated with translocation increases from the chaff. Sink demand determined DMT that was mostly regulated by the stem. Our results indicate that future yield improvements may be achieved by strengthening the source capacity.