Intraspecific variability for soybean cotyledon isoflavones in different cropping and soil conditions

Abstract

Cotyledon isoflavones, such as genistein, daidzein and their glucosyl and malonyl forms, were detected by HPLC–UV in 18 0- and 1-maturity class soybean varieties, cultivated under organic and conventional farming (3 years) and various soils (2 years) at Legnaro, NE Italy. Among varieties, the overall coefficient of variation for total cotyledon isoflavone concentration (TCIC) was 22%, and cluster analysis revealed three variety groups. Group L had 1.22 mg g −1 TCIC (low) and 40.3% proteins; group H, mainly including black-hilum varieties, 2.10 mg g −1 (high) and 39.2%, and group I 1.77 mg g −1 (intermediate) and 39.4%. Isoflavone profiles were similar in groups L and H (55% genistein and 45% daidzein aglycone equivalents), whereas group I had increased genistein (61%), which is recognised to have lower intestinal bioavailability (nutraceutics). Under organic management, a 2% protein increase (all groups) was associated with a 5–15% variety-dependent decrease – in groups H and I – and stable TCIC in group L. Isoflavone accumulation was positively affected by rainfall and limited daily range temperature regimes during pod filling, and hail damage (year 2005). In the Nikir variety (maturity class 1), grown in four lysimeter soils, TCIC was negatively correlated with soil C/N ratio, partially explaining the worse TCIC in organic cultivation. Based on this relationship, TCIC followed the order clay-loam > silty-loam >organic > sandy, with a 64% difference between extremes.