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

ABSTRACT 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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    • "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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    ABSTRACT: Compared to other potential feedstocks such as sugarcane, sugar beet, maize, and watermelon, sweet sorghum possesses higher levels of directly fermentable reducing sugars within the culm and the ability to accumulate high biomass under low-input production systems. In addition, it is tolerant to drought and has more efficient utilization of solar radiation and nitrogen-based fertilizers than maize and sugar cane on marginal lands that are not optimal for food production. These collectively make sweet sorghum to be considered with huge potential as a biofuel crop. Novel phenotypes generated during plant domestication and continued crop improvements via artificial selection constitute the domestication syndrome (Am. J. Bot., 101, 2014, 1711). Here, we draw an analogy and introduce the term the biofuel syndrome to refer to a suite of sweet sorghum traits, such as plant architecture (root, leave, and stem), flowering time and maturity as well as biomass bioconversion efficiency, that are associated with biofuel production and distinguish it from grain and forage sorghum traits. We discuss the biofuel syndrome amenable for targeted genetic modulation and what is currently known about the genetics and genomics of these traits as a potential route to optimize sweet sorghum for biofuel production. Continuous availability of sweet sorghum, transport and storing much mass and minimizing the postharvest loss of fermentable sugars are fundamental to exploiting sweet sorghum as a bioenergy crop. Due to the relatively short history of sweet sorghum breeding, we consider the development of ideotypes adapting to various phenological requirements to maximize the rapid deployment of sweet sorghum for biofuel production.
    07/2015; DOI:10.1002/fes3.63
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    • "Root depth is one of the most important traits for plant resistance to WS (Wasson et al., 2012; Lynch and Wojciechowski, 2015). Modeling studies indicate that selection for deeper, more effective roots could significantly improve the capture of water and N in wheat (Manschadi et al., 2006; Asseng and Turner, 2007; Lilley and Kirkegaard, 2011). "
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    ABSTRACT: An emerging paradigm is that root traits that reduce the metabolic costs of soil exploration improve the acquisition of limiting soil resources. Here we test the hypothesis that reduced lateral root branching density will improve drought tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration, permitting greater axial root elongation, greater rooting depth, and thereby greater water acquisition from drying soil. Maize recombinant inbred lines with contrasting lateral root number and length (FL: few but long; MS: many but short) were grown under water stress in greenhouse mesocosms, in field rainout shelters, and in a second field environment with natural drought. Under water stress in mesocosms, lines with the FL phenotype had substantially less lateral root respiration per unit axial root length, deeper rooting, greater leaf relative water content, greater stomatal conductance, and 50% greater shoot biomass than lines with the MS phenotype. Under water stress in the two field sites, lines with the FL phenotype had deeper rooting, much lighter stem water δ18O signature signifying deeper water capture, 51 to 67% greater shoot biomass at flowering, and 144% greater yield than lines with the MS phenotype. These results entirely support the hypothesis that reduced lateral root branching density improves drought tolerance. The FL lateral root phenotype merits consideration as a selection target to improve the drought tolerance of maize and possibly other cereal crops. Copyright © 2015, Plant Physiology.
    Plant physiology 06/2015; 168(4). DOI:10.1104/pp.15.00187 · 6.84 Impact Factor
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