Effects of year, site, genotype and their interactions on various soybean isoflavones

The popularity of soybeans is increasing as soybean products are now regarded as healthy foods, partly due to the isoflavones contained in their seeds. This study was initiated to study the isoflavone content in soybean seeds as influenced by genotype, year, site and their interactions. Fifteen cultivars were grown at three sites (Seoul, Suwon and Kyongsan) in Korea in 1998–2000, and harvested seeds were measured to determine the content of nine different isoflavones. This study led to the following conclusions. The main environmental effects (year and year-by-site interactions) and genotype-by-environment interactions (genotype-by-year and genotype-by-year-by-site interactions) were the most important sources of variation for the content of various isoflavones in soybean seeds. Significant differences among genotypes in isoflavone content exist that can only be reliably detected through multi-site and multi-year tests. The genotype 'Geomjeong 1' had consistently higher total isoflavone content. While the genotype 'Jangyeob' also had high total isoflavone content, it was less stable than 'Geomjeong 1'. There were no major genetically determined negative associations among the isoflavones, except for that between glycitin (GLY) and malonylgenistin (MGIN). On the contrary, a strong negative environmental association was observed between genistein (GEIN) (along with glycitein (GLIEN)) and daidzin (DIN) (along with genistin (GIN)). Both genetically and environmentally, total isoflavone content was most closely associated with malonylgenistin (MGIN).