Prospects for utilising plant-adaptive mechanisms to improve wheat and other crops in drought- and salinity-prone environments

Abstract

Breeding for adaptation to abiotic stress is extremely challenging due to the complexity of the target environments as well as that of the stress-adaptive mechanisms adopted by plants. While many traits have been reported in the literature, these must be considered with respect to the type of environment for which a cultivar is targeted. In theory, stress-adaptive traits can be divided into groups whose genes and/or physiological effects are likely to be relatively independent such that when parents with contrasting traits are crossed, adaptive genes will be pyramided. Currently the following groups of candidate traits are being considered for drought adaptation in wheat: traits relating to: (i) pre-anthesis growth, (ii) water extraction, (iii) water use effi ciency, (iv) photo-protection. A number of mechanisms relating to root function have potential to ameliorate drought stress. Hydraulic redistribution (HR) of water by roots of dryland shrubs enables even relatively small amounts of rainwater to be moved down into the soil profi le actively by the root system before it evaporates from the soil surface. Another example is the symbiotic relationship of plants with mycorrhizal fungi that produce a glycoprotein that has a positive effect on soil structure and moisture characteristics. From an agronomic point of view, crop water use effi ciency can be increased by exploiting the stress-adaptive mechanism whereby leaves reduce transpiration rate in response to a chemical root signal in response to drying soil. While there is limited genetic diversity for adaptation to salinity in wheat, tolerance has been found in the ancestral genomes of polyploid wheat and their relatives associated with sodium exclusion into the xylem. Wide crossing techniques such as production of synthetic hexaploids are being exploited to tap into this source of genetic diversity. Looking further into the future, progress is being made into understanding the regulatory mechanisms that are expressed under abiotic stress to maintain cellular homeostasis, as well as in the ability to genetically transform crop plants with genes from alien species.

Whole-Genome Mapping of Agronomic and Metabolic Traits to Identify Novel Quantitative Trait Loci in Bread Wheat Grown in a Water-Limited Environment

“…Drought stress, which has been identified as the most devastating abiotic constraint on crop productivity (Francia et al, 2005;Reynolds et al, 2005), causes substantial perturbations in plant metabolism (Bowne et al, 2011(Bowne et al, , 2012. Previous QTL studies of agronomic traits in wheat have lacked information on the biochemical pathways underlying those traits and their responses to drought.…”

Large root systems: are they useful in adapting wheat to dry environments?

“…Surrogate approaches such as screening for differences in canopy temperature may prove important (Slafer et al 2005). Marker assisted selection offers promise under both controlled and field conditions, although limitations exist for its use with complex traits (Reynolds et al 2005;Slafer et al 2005).…”

Using Ridge Regression Models to Estimate Grain Yield from Field Spectral Data in Bread Wheat (Triticum Aestivum L.) Grown under Three Water Regimes

“…Therefore, evaluation of genotypes yields in different environments and growing seasons is required [1,4]. Breeding based on GY has been restricted to Mediterranean dryland environments because the most limiting factor of yield is drought stress [5][6][7]. Thus, creating methods that are able to indirectly estimate the GY of different genotypes in intermediate stages of development could reduce costs and the time needed to measure them [8,9].…”