Physiological processes associated with soybean genetic progress in Argentina

Abstract

The main physiological processes associated with soybean [Glycine max (L.) Merr.] genetic yield progress in central temperate Argentina are largely unknown. This knowledge is critical to identify opportunities to accelerate yield gains via trait-based hybridization. Our objectives were to: (a) evaluate the influence of biomass accumulation vs. harvest index (HI) in explaining genetic progress, and (b) assess the role of radiation and/or N capture and use efficiency (RUE and NUE, respectively) as drivers of biomass accumulation. We tested 173 cultivars released from 1980 to 2014 in two high-yielding environments. Additionally, a crop modeling exercise was performed to demonstrate the physiological perception that any genetic increase in RUE would only translate into more yield if there is enough water for the realization of that RUE. Observed genetic progress was 42 kg ha−1 yr−1, or ∼1% yr−1, and was mostly explained by increased aboveground biomass accumulation. This higher biomass of modern cultivars was associated with increased RUE and total N uptake. This suggests that, if residual genetic variation is still present in current soybean cultivars, future genetic improvements should focus on further improving N uptake to increase RUE. Increases in RUE are associated with increased stomatal conductance and water use. Therefore, it would be expected that genetic progress is faster in environments with increased rainfall. Our modeling exercise was consistent with this hypothesis and showed that soybean genetic progress simulated in different locations within a rainfall gradient was positively associated with cumulative seasonal precipitation.