Abstract
Photosynthesis (A) and intrinsic water use efficiency (WUE) are physiological traits directly influencing biomass production, conversion efficiency, and grain yield. Though the influence of physiological process on yield is widely known, studies assessing improvement strategies are rare due to laborious phenotyping and specialized equipment needs. This is one of the first studies to assess the genetic architecture underlying A and intrinsic WUE, as well as to evaluate the feasibility of implementing genomic prediction. A panel of 383 soybean recombinant inbred lines were evaluated in a multi-environment yield trial that included measurements of A and intrinsic WUE, using an infrared gas analyzer during R4–R5 growth stages. Genetic variability was found to support the possibility of genetic improvement through breeding. High genetic correlation between grain yield (GY) and A (0.80) was observed, suggesting increases in GY can be achieved through the improvement of A. Genome-wide association analysis revealed quantitative trait loci (QTLs) for these physiological traits. Cross-validation studies indicated high predictive ability (>0.65) for the implementation of genomic prediction as a viable strategy to improve physiological efficiency while reducing field phenotyping. This work provides core knowledge to develop new soybean cultivars with enhanced photosynthesis and water use efficiency through conventional breeding and genomic techniques.
Highlights
Since the early 1900s, soybean yields have increased steadily (Hartwig, 1973; Specht et al, 1999; Suhre et al, 2014) and the rate of annual increases is estimated as 22–27 kg ha−1 yr−1 (Specht et al, 1999; USDA-ERS, 2011; Fox et al, 2013; Koester, 2014)
Selection of the recombinant inbred lines (RIL) was based on Best Linear Unbiased predictors (BLUP) for maturity, measured as the number of days from planting to physiological maturity, corresponding to soybean growth stage R8 (Fehr and Caviness, 1977), and grain yield calculated from field experiments from Indiana and Illinois during the years 2011 and 2014 (Xavier, 2016)
A study in china using materials of 82 year of soybean breeding found an unbalance improvement between E and A with increases in transpiration rate of ∼58% while photosynthesis barely reached ∼18% (Liu et al, 2012). Though these authors conclude that the biggest cost of producing high yielding soybean cultivars is the augmented water consume, our results show that doubling the intrinsic water use efficiency (WUE) (A/gs) might be possible
Summary
Since the early 1900s, soybean yields have increased steadily (Hartwig, 1973; Specht et al, 1999; Suhre et al, 2014) and the rate of annual increases is estimated as 22–27 kg ha−1 yr−1 (Specht et al, 1999; USDA-ERS, 2011; Fox et al, 2013; Koester, 2014). Soybean Photosynthesis and Water Use Efficiency loss, CO2 uptake – water lost relationship, and nitrogen assimilation. Some of these correspond to the gas exchange dynamic, photosynthesis (A) and water use efficiency (WUE). A positive relationship between photosynthesis and yield is not always observed (Long et al, 2006), a positive correlation between yield and photosynthesis has been found in soybean (Ainsworth et al, 2012) This positive association is documented for other crops like rice, where Ohsumi et al (2007) and Peng et al (2008) reported higher photosynthetic rates and improved physiological traits as significant contributors for high yielding cultivars. Similar results were presented by Tollenaar (1991) and Duvick (2005) in maize, and Fischer et al (1998) and Xiao et al (2012) in wheat
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