Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops. J Exp Bot

CSIRO Plant Industry, Canberra, ACT 2601, Australia.
Journal of Experimental Botany (Impact Factor: 5.53). 05/2012; 63(9):3485-98. DOI: 10.1093/jxb/ers111
Source: PubMed


Wheat yields globally will depend increasingly on good management to conserve rainfall and new varieties that use water efficiently for grain production. Here we propose an approach for developing new varieties to make better use of deep stored water. We focus on water-limited wheat production in the summer-dominant rainfall regions of India and Australia, but the approach is generally applicable to other environments and root-based constraints. Use of stored deep water is valuable because it is more predictable than variable in-season rainfall and can be measured prior to sowing. Further, this moisture is converted into grain with twice the efficiently of in-season rainfall since it is taken up later in crop growth during the grain-filling period when the roots reach deeper layers. We propose that wheat varieties with a deeper root system, a redistribution of branch root density from the surface to depth, and with greater radial hydraulic conductivity at depth would have higher yields in rainfed systems where crops rely on deep water for grain fill. Developing selection systems for mature root system traits is challenging as there are limited high-throughput phenotyping methods for roots in the field, and there is a risk that traits selected in the lab on young plants will not translate into mature root system traits in the field. We give an example of a breeding programme that combines laboratory and field phenotyping with proof of concept evaluation of the trait at the beginning of the selection programme. This would greatly enhance confidence in a high-throughput laboratory or field screen, and avoid investment in screens without yield value. This approach requires careful selection of field sites and years that allow expression of deep roots and increased yield. It also requires careful selection and crossing of germplasm to allow comparison of root expression among genotypes that are similar for other traits, especially flowering time and disease and toxicity resistances. Such a programme with field and laboratory evaluation at the outset will speed up delivery of varieties with improved root systems for higher yield.

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Available from: Michelle Watt, May 18, 2015
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    • "Improvement of nutrient use efficiency can be achieved by enlarging root systems or modifying root function with enhanced levels of proteins directly or indirectly involved in uptake and assimilation of soil nutrients such as nitrogen and phosphorus (Mudge et al. 2003; Werner et al. 2010; Shrawat et al. 2008; Ma et al. 2012). In water-limited crop production environments , the capability of a root system to extract stored soil moisture is considered to be the most important factor determining the yield of dryland and rainfed crops such as wheat (Wasson et al. 2012). "
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    ABSTRACT: Key message: A strong, stable and root-specific expression system was developed from a rice root-specific GLYCINE - RICH PROTEIN 7 promoter for use as an enabling technology for genetic manipulation of wheat root traits. Root systems play an important role in wheat productivity. Genetic manipulation of wheat root traits often requires a root-specific or root-predominant expression system as an essential enabling technology. In this study, we investigated promoters from rice root-specific or root-predominant expressed genes for development of a root expression system in bread wheat. Transient expression analysis using a GREEN FLUORESCENT PROTEIN (GFP) reporter gene driven by rice promoters identified six promoters that were strongly expressed in wheat roots. Extensive organ specificity analysis of three rice promoters in transgenic wheat revealed that the promoter of rice GLYCINE-RICH PROTEIN 7 (OsGRP7) gene conferred a root-specific expression pattern in wheat. Strong GFP fluorescence in the seminal and branch roots of wheat expressing GFP reporter driven by the OsGRP7 promoter was detected in epidermal, cortical and endodermal cells in mature parts of the root. The GFP reporter driven by the promoter of rice METALLOTHIONEIN-LIKE PROTEIN 1 (OsMTL1) gene was mainly expressed in the roots with essentially no expression in the leaf, stem or seed. However, it was also expressed in floral organs including glume, lemma, palea and awn. In contrast, strong expression of rice RCg2 promoter-driven GFP was found in many tissues. The GFP expression driven by these three rice promoters was stable in transgenic wheat plants through three generations (T1-T3) examined. These data suggest that the OsGRP7 promoter can provide a strong, stable and root-specific expression system for use as an enabling technology for genetic manipulation of wheat root traits.
    Plant Cell Reports 11/2015; DOI:10.1007/s00299-015-1897-3 · 3.07 Impact Factor
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    • "This necessitates genotypes showing drought avoidance via uptake optimization, termed " water spenders " by Levitt (1980). In that respect, enhanced plant root systems are considered to be a promising approach (Wasson et al., 2012). WUE as target trait was critically discussed by Blum (2009) because (i) WUE defined as BM/WU is not independent of WU, and (ii) it might go along with reduced crop transpiration and hence yield under moderate stress conditions. "
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    ABSTRACT: Trait-based breeding is essential to improve wheat yield, particularly when stress adaptation is targeted. A set of modern and underutilized wheat genotypes was examined in a 2-year field experiment with distinct seasonal water supply. Yield formation and drought response strategies were analyzed in relation to components of Passioura's yield-water framework based on phenological, morphological, physiological, and root characteristics. Limited water supply resulted in 60% yield loss and substantially lower water use (37%), water use efficiency (32.6%), and harvest index (14%). Phenology and root length density were key determinants of water use. Late flowering underutilized wheat species with large root system and swift ground coverage showed greatest water use. Leaf chlorophyll concentration and stomata conductance were higher in modern cultivars, supporting their high biomass growth and superior water use efficiency. While, lower chlorophyll concentration and stomata conductance of underutilized wheats indicated a water saving strategy with an intrinsic limitation of potential growth. Harvest index was strongly dependent on phenology and yield components. Optimized flowering time, reduced tillering, and strong grain sink of modern cultivars explained higher harvest index compared to underutilized wheats. Cluster analysis revealed the consistent differentiation of underutilized and modern wheats based on traits underlying Passioura's yield-water framework. We identified physiological and root traits within modern cultivars to be targeted for trait-based crop improvement under water-limited conditions. High capacity of water use in underutilized genetic resources is related to yield-limiting phenological and morphological traits, constraining their potential role for better drought resistance. Still some genetic resources provide adaptive features for stress resistance compatible with high yield as revealed by high harvest index under drought of Khorasan wheat.
    Frontiers in Plant Science 08/2015; 6:570. DOI:10.3389/fpls.2015.00570 · 3.95 Impact Factor
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    • "Small diameter and finer roots increases surface area in contact with soil water, the volume of soil that can be explored for water and root hydraulic conductivity in addition to enhancing root growth rate (Robinson et al. 1999; Comas et al. 2012). Accordingly, breeding for decrease in root diameter has the potential to enhance plants acquisition of water and productivity under drought (Wasson et al. 2012). To achieve optimal growth of biofuel crops on marginal lands and promote carbon sequestration, their adventitious and lateral roots need to be shallow and dispersed, respectively, to forage top soils for diffusion-limited nutrients and reduce runoff on steep grades, whereas deeper roots develop to increase water and soluble nutrient uptake (Hirel et al. 2007). "
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    07/2015; DOI:10.1002/fes3.63
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