EFFECTS OF SOYBEAN RACEME-ORDER ON POD SE T AND SEED GROWTH IN 3 CULTIVARS

The characteristics of pod see and seed growth as affected by raceme o rder were investigated to determine the yield-determining process of s oybean. Observations of racemes were made on the 4th, 7th, 10th, 13th and terminal nodes of the main stem of three cultivars (Indeterminate type: Harosoy; Determinate types: Enrei, Tamahomare). Pod-setting rati o and dry seed weight reduced in higher-order racemes, while the numbe r of seeds in a pod did not vary among raceme orders. The lower seed w eight of higher-order racemes was due to the short seed growth period. Compound leaves of secondary racemes enhanced the seed growth but not the pod-setting. With the highest node of determinate types, seed dry weight and rate of dry matter accumulation (RDA) of primary racemes e xceeded those of terminal racemes, suggesting that more competition fo r assimilates among racemes occurred in terminal racemes. The results indicate that, regardless of growth habits, the lower the raceme order , the higher the number of pods and the pod-setting ratio. Seeds deriv ed from lower-order racemes accounted for the majority of the yield. H ence, pod-setting and seed growth of lower-order racemes are more impo rtant than those of higher-order racemes in determining soybean yield.