Abstract
Identifying markers for physiological traits of proven value in breeding, especially ones that are consistent across environments with different patterns of stress, strengthens the toolkit to increase confidence in the value and delivery from physiological breeding. To identify markers relevant to drought adaptation, this review will highlight the importance of development and implementation of robust and repeatable phenotyping that is relevant to the different target drought types, and practical examples of managed environment facilities in Australia and Mexico are given. These facilities can be used as models to: (i) improve reliability and consistency of environments and genetic responses to the environment at a global scale; (ii) improve the capacity to deliver quantitative trait loci (QTLs) as user-friendly markers for enriching populations; and (iii) illustrate the use of populations with a narrow range of variation for phenology allowing the identification of QTLs for drought-adaptive traits. However, the importance of further optimizing phenology and plant height at a global scale is highlighted. Finally, the impact of physiological trait-based crossing is demonstrated and supports the need for urgent development of robust genetic markers.
Highlights
The yield of wheat has doubled over the last 30 years due to a combination of advanced agronomic practices and improved germplasm through selective breeding
The Semi-Arid Wheat Yield Trial (SAWYT), one of the nurseries from CIMMYT targeted at maintaining yields under stressed conditions, showed the strongest genetic gains at the warmest temperatures, whereas nurseries targeted to high-yielding conditions did not have an impact on hot environments (Gourdji et al, 2013)
Traits that are currently applied in CIMMYT’s breeding and pre-breeding for drought are listed under three main drivers to yield: (i) traits to increase water use or evapotranspiration (WU), including deeper roots to tap subsoil water, and early ground cover to reduce losses of water at the soil surface back to the atmosphere; phenotying protocols such as infrared thermometry and spectral radiometry, respectively, are discussed later; (ii) traits to increase water use efficiency (WUE), including transpiration efficiency, epicuticular wax expressed on stressed plants, and biomass; and (iii) the main trait selected to increase partitioning of carbon to grain—accumulation and remobilization of water-soluble carbohydrates to grains
Summary
The yield of wheat has doubled over the last 30 years due to a combination of advanced agronomic practices and improved germplasm through selective breeding. It has not been possible to further extend these findings to functional markers associated with drought or other abiotic stress adaptation This has been hampered by the complexity of plant responses to stress and to the difficulties associated with determining all possible genetic responses and interactions or epistasis to specific environmental parameters that happen to occur in random combinations in real environments. This particular bottleneck will restrict the use of markers in selection (from marker-assisted selection to genomic selection) to adaptation to specific environmental conditions (Edae et al, 2014), which may not be desirable for global breeding progress, where wide adaptation has been the pillar of success. It attempts to describe up-to-date phenotypic and genetic tools available and how these two must integrate effectively to return more efficient identification of parental lines for crossing, together with defining the genetic variation available for relevant traits for targeted introgression and physiological breeding (Reynolds et al, 2009)
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