Genotype, environment, and genotype by environment interaction for seed isoflavone concentration in soybean grown in soybean cyst nematode infested and non-Infested environments

Soybean (Glycine max [L.] Merr.) is a major isoflavone producing legume. Isoflavones and their derivatives function as phytoalexins that may function in protecting plants against pathogens. They are also known as phytoestrogens in the human diet, which have putative positive human health effects such as reduced risk of breast and prostate cancers, cardiovascular disease, and high blood cholesterol levels. Therefore, increasing isoflavone concentration could be a desirable target for developing added value for food-grade soybean cultivars. Soybean cyst nematode (SCN; Heterodera glycines) is the most yield-limiting pathogen for soybean world-wide. The objectives of this study were to: 1) determine genotype (G) and genotype-by-environment (GE) interaction variation for seed isoflavone concentration and, 2) determine the effects that SCN resistance may have on seed isoflavone concentration in SCN infested and non-infested environments. A population of 109 recombinant inbred lines (RILs), derived from a cross between DH4202 and RCAT1004, along with 11 commercial check cultivars were grown in two SCN infested and two non-infested fields in southern Ontario, Canada, in 2015 and 2016. The genotypes were categorized into resistant, moderately resistant, and susceptible lines based on SCN female indices calculated from SCN infested environments. Significant G, environment (E), and GE interaction effects were observed for total isoflavone concentration as well as for yield. Higher isoflavone concentrations were observed in non-infested environments when compared with SCN infested environments for all three levels of resistance. Within SCN infested environments, resistant genotypes had significantly higher isoflavone concentrations than susceptible genotypes, indicating a potential role of isoflavones in plant defense from SCN in resistant genotypes. SCN infested environments were found to be more reliable for genotype evaluation of isoflavone concentration than non-infested environments due to similar relative performance of genotypes in all SCN infested environments. A strong relationship between the level of SCN resistance and relative yield among the genotypes was observed in SCN environments. When evaluating genotypes, soybean breeders should consider the negative impact SCN has on seed isoflavone concentration, the positive relationship between SCN resistance and isoflavone concentration in SCN environments, as well as the greater stability in isoflavone concentration across genotypes within SCN environments compared to the non-infested ones.