Effect of Physical Restraint on Seed Growth in Soybean1

The growth and development of an individual soybean [Glycine max(L.) Merr.l seed is an important part of the yield production process; however, the effect of fruit size on the physiological processes controlling seed growth and final seed size are not completely understood. Thus, two experiments were conducted in a greenhouse to evaluate the effect of physical restriction of the fruit on seed growth. The plastic pod restriction device (PPRD) was constructed from a 6.35‐mm diam. plastic drinking straw cut into 4‐cm lengths. The PPRD's were placed over the fruit when the fruit fit tightly into the PPRD. All of the fruits on the treated plants (cv. McCall) were placed in the PPRD's and samples were taken at frequent intervals to determine seed fresh and dry mass. Application of the PPRD's had no effect on the number of fruits or seeds per plant at maturity in either experiment. Final size (mg seed−1) of seeds from the PPRD's was decreased relative to control plants by 30 and 15% in Exp. 1 and 2, respectively. Mature seeds from the PPRD's were cylindrical in shape and had a higher N concentration. The initial seed growth rate (SGR) of seeds in the PPRD's was similar to the control seeds, however, when the seed mass reached 80 (Exp. 1) or 65 (Exp. 2) mg seed−1, the SGR was drastically decreased and there was no further increase in seed water content. However, seed maturation (seeds turning yellow and moisture level reaching 550 g kg−1) did not occur in the PPRD treatments until after the control seeds matured. The PPRD's provide a useful technique to study the effects of physical restraint on seed growth. The data demonstrate that physical restraint has a direct effect on the ability of the seed to accumulate dry matter.