Assimilation and Distribution of Photosynthate in Winter Wheat Cultivars Differing in Harvest Index

Abstract

Yield differences among New York winter wheat (Triticum aestivum L.) are related to harvest index. This study was conducted to see how four cultivars, which differed in harvest index and plant height, differed in partitioning of photosynthate before and during grain filling. Experiments were conducted in field plots grown at Hamden, CT in 1985 and 1986 in Cheshire fine sandy loam (coarse‐loamy, mixed, mesic Typic Dystrochrept). The assimilation, distribution, and retention of radioactivity from ¹⁴CO₂‐derived photosynthate was measured. In each year, the canopy was labeled at heading and early and late in grain filling. Harvest index was inversely related to stem height. The fractional distribution of the ¹⁴C remaining at maturity varied with labeling date and cultivar. The amount in the spike was 0.35 to 0.5 when labeled at heading, with less than 0.15 in the grain. When labeled during grain filling, a greater fraction of ¹⁴C was distributed to the spike in the semidwarf than in the tall cultivars, 0.9 and 0.8, respectively, and most of the ¹⁴C in the spike was in the grain. Almost half of the radioactivity initially assimilated was lost from the plants by maturity. Tall semi‐dwarf ‘Purcell’ retained a greater fraction of radioactivity initially assimilated than did tall ‘Honor’, 0.56 and 0.51, respectively. Thus, differences in harvest index were related to differences in distribution of photosynthate and to differences in retention of photosynthate to maturity.