PHYSICAL RESTRICTION OF POD GROWTH ALTERS DEVELOPMENT OF SOYBEAN PLANTS

Efforts to determine the mechanistic relationships between fruit and c anopy development are complicated by difficulties in designing nondest ructive treatments that modify plant-sink development. Pod growth was physically restricted by placing plastic straws, referred teas plastic pod-restriction devices, over 0, 50, or 100% of the soybean (Glycine mar L. Merr.) pods in greenhouse experiments. The objective was to det ermine how decreases in pod growth influenced whole-plant growth and d evelopment. Both the rate and final accumulation of seed dry matter we re decreased by restricting pod growth. Conversely, restricting pod gr owth increased seed number due to increased production and decreased a bscission of fruits. Plant dry matter and N accumulations during the l inear seed-fill period were not affected by restricting pod growth. Th is resulted from proportional increases in partitioning of assimilates into stems and leaves. Thus, decreases in reproductive growth apparen tly did not cause feedback inhibition of photosynthesis. Although leaf abscission was delayed by restricting pod growth, dry matter and N ac cmulation late in development were affected only slightly. In general, restricting pod growth influenced plant develop ment and assimilate a llocation in a similar manner as physical removal of fruits. The inver se relationship between the rate of dry matter accumulation in seed an d pod and seed number per plant indicated that assimilate availability limited seed number. The delay in leaf yellowing and abscission induc ed by physically restricting pod growth suggested that the completion of monocarpic senescence was directly affected by changes in the rate of seed dry matter accumulation per plant.