PHYSICAL RESTRICTION OF POD GROWTH ALTERS DEVELOPMENT OF SOYBEAN PLANTS

Efforts to determine the mechanistic relationships between fruit and canopy development are complicated by difficulties in designing nondestructive 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 determine how decreases in pod growth influenced whole-plant growth and development. Both the rate and final accumulation of seed dry matter were decreased by restricting pod growth. Conversely, restricting pod growth increased seed number due to increased production and decreased abscission of fruits. Plant dry matter and N accumulations during the linear seed-fill period were not affected by restricting pod growth. This resulted from proportional increases in partitioning of assimilates into stems and leaves. Thus, decreases in reproductive growth apparently did not cause feedback inhibition of photosynthesis. Although leaf abscission was delayed by restricting pod growth, dry matter and N accmulation late in development were affected only slightly. In general, restricting pod growth influenced plant develop ment and assimilate allocation in a similar manner as physical removal of fruits. The inverse relationship between the rate of dry matter accumulation in seed and pod and seed number per plant indicated that assimilate availability limited seed number. The delay in leaf yellowing and abscission induced 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.