Abstract
Genetic selection for whole-plant water use efficiency (yield per transpiration; WUEplant ) in any crop-breeding programme requires high-throughput phenotyping of component traits of WUEplant such as intrinsic water use efficiency (WUEi ; CO2 assimilation rate per stomatal conductance). Measuring WUEi by gas exchange measurements is laborious and time consuming and may not reflect an integrated WUEi over the life of the leaf. Alternatively, leaf carbon stable isotope composition (δ13 Cleaf ) has been suggested as a potential time-integrated proxy for WUEi that may provide a tool to screen for WUEplant . However, a genetic link between δ13 Cleaf and WUEplant in a C4 species has not been well established. Therefore, to determine if there is a genetic relationship in a C4 plant between δ13 Cleaf and WUEplant under well watered and water-limited growth conditions, a high-throughput phenotyping facility was used to measure WUEplant in a recombinant inbred line (RIL) population created between the C4 grasses Setaria viridis and S. italica. Three quantitative trait loci (QTL) for δ13 Cleaf were found and co-localized with transpiration, biomass accumulation, and WUEplant . Additionally, WUEplant for each of the δ13 Cleaf QTL allele classes was negatively correlated with δ13 Cleaf , as would be predicted when WUEi influences WUEplant . These results demonstrate that δ13 Cleaf is genetically linked to WUEplant , likely to be through their relationship with WUEi , and can be used as a high-throughput proxy to screen for WUEplant in these C4 species.
Highlights
Water availability constrains agricultural production and threatens food security in many drought-prone regions (Morison et al, 2008)
In this C4 grass recombinant inbred line (RIL) population, δ13Cleaf showed a significant and consistent response to water limitation and significant genotypic variation and heritability. “dditionally, δ13Cleaf correlated with WUEplant and its components, suggesting a physiological relationship between these traits
This is further supported by the fact that there were even stronger negative correlations between δ13Cleaf and WUEplant within the allele classes defined by QTL of δ13Cleaf
Summary
Water availability constrains agricultural production and threatens food security in many drought-prone regions (Morison et al, 2008). Improving the harvestable yield relative to water supplied to crop systems (agronomic water use efficiency; WUEag) has long received attention from researchers and government agencies (Bierhuizen and Slatyer, 1965, Passioura, 1977, Sinclair et al, 1984, Vadez et al, 2014). It has been proposed by Passioura (1977) that yield could be improved relative to available water by increasing (1) the ratio of transpiration (T) to evapotranspiration (ET), (2) whole plant water use efficiency (ratio of biomass production to total transpiration; WUEplant) and (3) harvest index (HI). As improvements in WUEag through management practices reach their theoretical maximum, the continued increases in WUEag will likely be through improved WUEplant, which have so far been minimal (Condon et al, 2004, Deng et al, 2006, Medrano et al, 2015a)
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