Dynamics of oil and fatty acid accumulation during seed development in historical soybean varieties

Soybean seed oil concentration and fatty acid (FA) composition are relevant traits defining oil quality and economic value for industry. In spite of the importance of FA composition for soybean value, a detailed description of FA profile and accumulation during seed filling in contrasting soybean varieties and management conditions is currently lacking. This study aims to: i) evaluate whether genetic progress in soybean yield indirectly affected FA profile, ii) assess the influence of N fertilization on FA profile, iii) characterize the temporal dynamics of FA accumulation during seed filling, and iv) evaluate the relative contribution of FA accumulation rate vs. duration on final FA seed content. Seven soybean varieties released between 1980 and 2013 were field grown under control (0 kg N ha(-1)) and fertilized (670 kg N ha(-1) added) treatments. In addition to seed yield, total seed oil and FA contents during seed filling were recorded by sampling seeds from the beginning of seed formation to maturity. Genetic progress was evident in seed yield with an increase of 31.3 kg ha year(-1). Total oil concentration (g oil kg(-1)) slightly decreased across year of release for the control. Fatty acid concentration (g FA 100 g oil(-1)) profile was not associated with year of release but affected by varieties. Variation in total oil and FA contents (mg seed(-1)) across varieties and N treatments was mostly associated to longer filling but was also affected by accumulation rates. Interestingly, individual FA concentration at maturity was independent from FA content. Our results indicate past breeding efforts have not modified soybean FA profile. The fact that changes in FA contents were not translated in changes in FA concentration indicates that seed control of FA profile is narrow. Disentangling the physiological mechanism associated with FA homeostasis warrants further examination.