Take home messages

• Continued genetic gain relies on a clear and repeatable environmental signal to ensure important adaptation genetics are selected from one testing season to the next
• Climate change and particularly year-to-year climate variability is forecast to adversely affect reliability of rainfed crop production in the future
• Breeding varieties that are more opportunistic in dealing with seasonal unpredictability should provide synergies with grower-directed management decisions to better ‘play the seasons’
• Long coleoptiles/hypocotyls for deep sowing, rapid biomass and leaf area development for later sowing and weed competitiveness, and greater responsiveness to in-crop actives (e.g. plant growth regulators) are under investigation to improve reliability of crop performance with varying seasonal conditions.

Background

To a grower, climate change encompasses in-paddock changes in air and soil temperature and rainfall, and the associated aerial aridity as increased vapour pressure deficit. These changes have arisen as a direct result of linear increases in CO₂ and so are systematic and somewhat predictive particularly for air and soil temperature (IPCC, 2019). Where predictive, agricultural scientists have the knowledge and capacity to develop agronomic and genetic tools that can adapt to the change. Unfortunately, variability in extremes in weather are less predictable and likely to increase the frequency of extremes in climatic events into the future (Steffen et al., 2011). In Australia, changes in climate have reduced broadacre farming profitability by 22% since 2000 (Hughes et al., 2019). As recently as 2024, much of the southern and western Australian wheatbelt experienced the driest February-May period on record (BOM, 2024) delaying sowing and emergence of winter cereals, oilseeds and pulses. Together with changes in the distribution and severity of pests and diseases (e.g. Juroszek and von Tiedemann, 2013), climate change is likely to continue to significantly affect crop yields and their reliability, affecting global food security.

The separate effects of changes in temperature, water and CO₂ are well understood for most crops with well-defined optima reported above which growth is impaired (e.g. Porter and Gawith, 1999). Rising air temperatures alone have been reported using a global meta-analysis of field warming experiments predicting 89% loss in wheat yield of c. 2.9% °C^-1 (Wang et al., 2020). Increasing night temperatures complicate this through contribution to asymmetric increases in ambient temperatures (Easterling et al.,1997). While well understood and somewhat predictive into the future these defined crop yield limits ignore climate interactions and how the integrative nature of abiotic stresses conspire to increase damage to developing crops. For example, increasing air temperature is being linked to greater risk of more extreme and both earlier and later frost events particularly at vulnerable crop developmental stages (Crimp et al., 2016). Efforts to avoid increasingly warmer and drier conditions with climate change and increasing cropping program sizes is promoting earlier sowing in some regions, further increasing the risk of frost damage with more rapid development and earlier flowering. For example, in southern Australia, there has been a 26-day extension in the length of the frost window compared to the average frost period between 1960-1990, and in some cases, frosting is occurring an average four weeks later than in 1960 (Crimp et al., 2016). Phenology types that enable a flexible sowing window (sowing earlier) while still ensuring an acceptable flowering time have gained increased attention in recent years. The use of quick- to quick-mid winter wheat allows for broader sowing windows to capitalise on more sporadic rainfall events. Recent modelling indicates an average benefit of 0.5 t/ha across southern Australia (Hunt et al., 2019).

Breeding methods and targets

Commercial breeding focuses on development and release of improved commercial crop varieties. In contrast, pre-breeding emphasises research focussed toward breeding methodology and traits aimed at enhancing adaptation and genetic gain. There have been no reported commercial efforts directly targeting improved performance with climate change. Selection of breeding lines across a wide range of environmental challenges may deliver varieties with greater resilience to climate extremes (e.g. mid-west US corn; Messina and Cooper, 2022) but risk limited sampling of environments over repeated breeding cycles (Rosielle and Hamblin, 1981). Similarly, improved breeding methodologies to enrich populations early (e.g. genomic selection) and hasten the interval between successive crosses (e.g. speed-breeding) have been argued in aiding the rapid-cycling and selection of adaptation genes in changing environments (Atlin et al., 2017). Together, Snowdon et al., (2021) expressed confidence that continued per se breeding should deliver improved performance through fixation of existing genetics, improved modern breeding methods, and exploiting of climate adaptation through improved understanding of G × E × M (genetics x environment x management). However, such promise relies on having the necessary genetics already present in elite breeding populations and pipelines.

By contrast, pre-breeding efforts are focussed on improving genotypic performance to specific environmental challenges. Understanding underlying biological mechanisms should tailor responses and associated alleles that can then reduce the impact of the stress. Scientific understanding provides learnings that then contribute to frameworks relevant to climate adaptation. Pre-breeding efforts targeting adaptation to climate change largely mirror previous activities aimed at addressing long-standing abiotic constraints to crop performance. For example, the climate change literature commonly highlights previous abiotic stress targets (e.g. heat and drought) of which very few if any have proven successful in delivery of improved commercial crop varieties (see Table 1). These include a focus on ‘survival’ traits and use of diverse ‘stress’ alleles from wild populations (Dempewolf et al., 2014) through to the incorporation of simple morphological traits to improve resilience (Hunt et al., 2018). A unique but as yet untested approach is deployment of evolutionary populations and genetic mixtures, allowing for changes in gene frequency through selection from within heterogeneous populations (Ceccarelli and Grando, 2020).

Despite significant efforts underpinned by a strong science-driven focus, few abiotic stress traits have translated successfully and delivered into commercial breeding. There are many reasons for this that largely reflect the many and complex components required of selection and delivery in a finished and industry-competitive crop variety. Table 1 summarises many of the published morphological and physiological traits reported to have potential for improving performance with climate change. For many traits they represent traits previously reported to improve adaptation to drought and heat. Unfortunately, few of the traits shown in Table 1 have been successfully adopted in a commercial cereal breeding variety owing to uncertainties with trait value, complex genetic control or challenges in selection, and in some cases, limited repeatable genetic variation for the trait.

Opportunities through G × E × M synergies

Success with selection for adaptation relies heavily on a repeatable screening environment i.e. a strong climate or soil signal that reliably elicits a response from which elite breeding lines can be identified (Rosielle and Hamblin, 1981). Climate variability will reduce the signal to inflate genotype × environment interaction in turn reducing genetic gain and maintenance of climate adaptation alleles across breeding cycles. Growers have the greatest understanding of their systems and the paddocks on their farms. Their knowledge is built on years of observation across seasons and crops, and response with different agronomic interventions. Climate resilience at a farm-scale should therefore consider local knowledge and opportunities with management and then linking with genetics under a dynamic yet farm-relevant G × E × M framework (Wang et al., 2019).

Table 1. Summary of proposed traits for target climate constraints and their reported value and utility in commercial breeding.

New ‘resilience’ genetics underpinning G × E × M

Genetic variation that provides opportunistic performance with changing climate allows growers to ‘play the season’. Currently, flexibility to respond to climate is limited to decisions between crops with some opportunity in wheat with varieties adapted to early sowing (e.g. Hunt et al., 2019).

We report on different traits with potential to provide growers with options in improving resilience in variable climates. Importantly, these traits are unlikely to be associated with any penalty in yield or quality, and link closely with opportunities in improved agronomic management in exploiting G × E × M:

1. Improving crop establishment with deep sowing
2. Late sowing with rapidly growing, high biomass crops
3. Awnless cereals for frost-prone regions
4. Rapid grain-filling rate
5. Changes in crop phenology
6. Greater varietal responsiveness to in-crop actives (e.g. plant growth regulators)

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Contact details

Greg Rebetzke
CSIRO
Greg.Rebetzke@csiro.au

Date published
February 2025