Effect of Row Spacing on Seed Isoflavone Contents in Soybean [Glycine max (L.) Merr.]

Soybean isoflavones components namely genistein, daidzein, and glycitein have numerous human health benefits in reducing risk of cardiovascular disease, breast and prostate cancer, and menaupose symptoms of women. Understanding the genetic and environmental control of isoflavones accumulation is of great importance for developing new cultivars with high amounts of seed isoflavones. This study was conducted to analyze the effect of row spacing (25 cm vs. 50 cm) on seed isoflavones accumulation using a recombinant inbred line (RIL) population derived from the cross of PI438489B and ‘Hamilton’ (PIxH, n=50). The two row spaces generated plant densities of 250,000 plants/ha and 90,000 plants/ha, respectively. Significant differences in soybean seed isoflavones (daidzein, genistein and glycitein) contents have been observed between plants grown in the two different plant densities. The mean daidzein content was 0.03458 µg g^-1 in plants grown at 50 cm row spaces (low plant density), which was significantly higher than its content (0.03019 µg g^-1) at 25 cm row space (high plant density). Similarly, the mean glycitein content in plants grown at 50 cm row spaces (0.01905 µg g^-1) was significantly higher than its content in plants grown at 25 cm row spaces (0.00498 µg g^-1). Also, the mean genistein content in plants grown in 50 cm row spaces (0.01466 µg g^-1) was higher than its content in plants grown in 25 cm row spaces (0.00831 µg g^-1). These preliminary results are important in guiding farmers and breeders on choosing the best row spaces to grow soybean plants in in order to have optimized isoflavones contents. Further studies are needed to understand the correlation between seed isoflavones contents and other agronomic traits such as seed yield, protein, and oil.