Screening for Natural Variation in Water Use Efficiency Traits in a Diversity Set of Brassica napus L. Identifies Candidate Variants in Photosynthetic Assimilation

Multienvironment QTL analysis delineates a major locus associated with homoeologous exchanges for water-use efficiency and seed yield in canola

Canola varieties exhibit variation in drought avoidance and drought escape traits, reflecting adaptation to water-deficit environments. Our understanding of underlying genes and their interaction across environments in improving crop productivity is limited. A doubled haploid population was analysed to identify quantitative trait loci (QTL) associated with water-use efficiency (WUE) related traits. High WUE in the vegetative phase was associated with low seed yield. Based on the resequenced parental genome data, we developed sequence-capture-based markers and validated their linkage with carbon isotope discrimination (Δ¹³ C) in an F₂ population. RNA sequencing was performed to determine the expression of candidate genes underlying Δ¹³ C QTL. QTL contributing to main and QTL × environment interaction effects for Δ¹³ C and yield were identified. One multiple-trait QTL for Δ¹³ C, days to flower, plant height, and seed yield was identified on chromosome A09. Interestingly, this QTL region overlapped with a homoeologous exchange (HE) event, suggesting its association with the multiple traits. Transcriptome analysis revealed 121 significantly differentially expressed genes underlying Δ¹³ C QTL on A09 and C09, including in HE regions. Sorting out the negative relationship between vegetative WUE and seed yield is a priority. Genetic and genomic resources and knowledge so developed could improve canola WUE and yield.

Drying times: plant traits to improve crop water use efficiency and yield

Crop water use efficiency (WUE) has come into sharp focus as population growth and climate change place increasing strain on the water used in cropping. Rainfed crops are being challenged by an upward trend in evaporative demand as average temperatures rise and, in many regions, there is an increased irregularity and a downward trend in rainfall. In addition, irrigated cropping faces declining water availability and increased competition from other users. Crop WUE would be improved by, first, ensuring that as much water as possible is actually transpired by the crop rather than being wasted. Deeper roots and greater early crop vigour are two traits that should help achieve this. Crop WUE would also be improved by achieving greater biomass per unit water transpired. A host of traits has been proposed to address this outcome. Restricting crop transpiration through lower stomatal conductance is assessed as having limited utility compared with traits that improve carbon gain, such as enhancements to photosynthetic biochemistry and responsiveness, or greater mesophyll conductance. Ultimately, the most useful outcomes for improved crop WUE will probably be achieved by combining traits to achieve synergistic benefit. The potential utility of trait combinations is supported by the results of crop simulation modelling.

Natural genetic variation in photosynthesis: an untapped resource to increase crop yield potential?

Raising crop yield potential is a major goal to ensure food security for the growing global population. Photosynthesis is the primary determinant of crop productivity and any gain in photosynthetic CO2 assimilation per unit of leaf area (A) has the potential to increase yield. Significant intraspecific variation in A is known to exist in various autotrophic organs that represent an unexploited target for crop improvement. However, the large number of factors that influence photosynthetic rates often makes it difficult to measure or estimate A under dynamic field conditions (i.e. fluctuating light intensities or temperatures). This complexity often results in photosynthetic capacity, rather than realized photosynthetic rates being used to assess natural variation in photosynthesis. Here we review the work on natural variation in A, the different factors determining A and their interaction in yield formation. A series of drawbacks and perspectives are presented for the most common analyses generally used to estimate A. The different yield components and their determination based on different photosynthetic organs are discussed with a major focus on potential exploitation of various traits for crop improvement. To conclude, an example of different possibilities to increase yield in wheat through enhancing A is illustrated.

Abscisic Acid Receptors and Coreceptors Modulate Plant Water Use Efficiency and Water Productivity

Improving the water use efficiency (WUE) of crop plants without trade-offs in growth and yield is considered a utopic goal. However, recent studies on model plants show that partial restriction of transpiration can occur without a reduction in CO₂ uptake and photosynthesis. In this study, we analyzed the potentials and constraints of improving WUE in Arabidopsis (Arabidopsis thaliana) and in wheat (Triticum aestivum). We show that the analyzed Arabidopsis wild-type plants consume more water than is required for unrestricted growth. WUE was enhanced without a growth penalty by modulating abscisic acid (ABA) responses either by using overexpression of specific ABA receptors or deficiency of ABA coreceptors. Hence, the plants showed higher water productivity compared with the wild-type plants; that is, equal growth with less water. The high WUE trait was resilient to changes in light intensity and water availability, but it was sensitive to the ambient temperature. ABA application to plants generated a partial phenocopy of the water-productivity trait. ABA application, however, was never as effective as genetic modification in enhancing water productivity, probably because ABA indiscriminately targets all ABA receptors. ABA agonists selective for individual ABA receptors might offer an approach to phenocopy the water-productivity trait of the high WUE lines. ABA application to wheat grown under near-field conditions improved WUE without detectable growth trade-offs. Wheat yields are heavily impacted by water deficit, and our identification of this crop as a promising target for WUE improvement may help contribute to greater food security.

Components of Water Use Efficiency Have Unique Genetic Signatures in the Model C4 Grass Setaria

Plant growth and water use are interrelated processes influenced by genetically controlled morphological and biochemical characteristics. Improving plant water use efficiency (WUE) to sustain growth in different environments is an important breeding objective that can improve crop yields and enhance agricultural sustainability. However, genetic improvement of WUE using traditional methods has proven difficult due to the low throughput and environmental heterogeneity of field settings. To overcome these limitations, this study utilizes a high-throughput phenotyping platform to quantify plant size and water use of an interspecific Setaria italica × Setaria viridis recombinant inbred line population at daily intervals in both well-watered and water-limited conditions. Our findings indicate that measurements of plant size and water use are correlated strongly in this system; therefore, a linear modeling approach was used to partition this relationship into predicted values of plant size given water use and deviations from this relationship at the genotype level. The resulting traits describing plant size, water use, and WUE all were heritable and responsive to soil water availability, allowing for a genetic dissection of the components of plant WUE under different watering treatments. Linkage mapping identified major loci underlying two different pleiotropic components of WUE. This study indicates that alleles controlling WUE derived from both wild and domesticated accessions can be utilized to predictably modulate trait values given a specified precipitation regime in the model C4 genus Setaria.