M. Fernanda Dreccer

Breeding for the future: what are the potential impacts of future frost and heat events on sowing and flowering time requirements for Australian bread wheat (Triticum aestivium) varieties?

Extreme climate, especially temperature, can severely reduce wheat yield. As global warming has already begun to increase mean temperature and the occurrence of extreme temperatures, it has become urgent to accelerate the 5-20xa0year process of breeding for new wheat varieties, to adapt to future climate. We analyzed the patterns of frost and heat events across the Australian wheatbelt based on 50xa0years of historical records (1960-2009) for 2864 weather stations. Flowering dates of three contrasting-maturity wheat varieties were simulated for a wide range of sowing dates in 22 locations for current climate (1960-2009) and eight future scenarios (high and low CO2 emission, dry and wet precipitation scenarios, in 2030 and 2050). The results highlighted the substantial spatial variability of frost and heat events across the Australian wheatbelt in current and future climates. As both last frost and first heat events would occur earlier in the season, the target sowing and flowering windows (defined as risk less than 10% for frost (<0xa0°C) and less than 30% for heat (>35xa0°C) around flowering) would be shifted earlier by up to 2 and 1xa0month(s), respectively, in 2050. A short-season variety would require a shift in target sowing window 2-fold greater than long- and medium-season varieties by 2050 (8 vs. 4 days on average across locations and scenarios, respectively), but would suffer a lesser decrease in the length of the vegetative period (4 vs. 7 days). Overall, warmer winters would shorten the wheat season by up to 6 weeks, especially during preflowering. This faster crop cycle is associated with a reduced time for resource acquisition, and potential yield loss. As far as favourable rain and modern equipment would allow, early sowing and longer season varieties (i.e. in current climate) would be the best strategies to adapt to future climates.

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

There is little consensus on whether having a large root system is the best strategy in adapting wheat (Triticum aestivum L.) to water-limited environments. We explore the reasons for the lack of consensus and aim to answer the question of whether a large root system is useful in adapting wheat to dry environments. We used unpublished data from glasshouse and field experiments examining the relationship between root system size and their functional implication for water capture. Individual root traits for water uptake do not describe a root system as being large or small. However, the recent invigoration of the root system in wheat by indirect selection for increased leaf vigour has enlarged the root system through increases in root biomass and length and root length density. This large root system contributes to increasing the capture of water and nitrogen early in the season, and facilitates the capture of additional water for grain filling. The usefulness of a vigorous root system in increasing wheat yields under water-limited conditions maybe greater in environments where crops rely largely on seasonal rainfall, such as the Mediterranean-type environments. In environments where crops are reliant on stored soil water, a vigorous root system increases the risk of depleting soil water before completion of grain filling.

Plant adaptation to climate change—opportunities and priorities in breeding

Abstract. n Climate change in Australia is expected to influence crop growing conditions through direct increases in elevated carbon dioxide (CO2) and average temperature, and through increases in the variability of climate, with potential to increase the occurrence of abiotic stresses such as heat, drought, waterlogging, and salinity. Associated effects of climate change and higher CO2 concentrations include impacts on the water-use efficiency of dryland and irrigated crop production, and potential effects on biosecurity, production, and quality of product via impacts on endemic and introduced pests and diseases, and tolerance to these challenges. Direct adaptation to these changes can occur through changes in crop, farm, and value-chain management and via economically driven, geographic shifts where different production systems operate. Within specific crops, a longer term adaptation is the breeding of new varieties that have an improved performance in ‘future’ growing conditions compared with existing varieties. In crops, breeding is an appropriate adaptation response where it complements management changes, or when the required management changes are too expensive or impractical. Breeding requires the assessment of genetic diversity for adaptation, and the selection and recombining of genetic resources into new varieties for production systems for projected future climate and atmospheric conditions. As in the past, an essential priority entering into a ‘climate-changed’ era will be breeding for resistance or tolerance to the effects of existing and new pests and diseases. Hence, research on the potential incidence and intensity of biotic stresses, and the opportunities for breeding solutions, is essential to prioritise investment, as the consequences could be catastrophic. The values of breeding activities to adapt to the five major abiotic effects of climate change (heat, drought, waterlogging, salinity, and elevated CO2) are more difficult to rank, and vary with species and production area, with impacts on both yield and quality of product. Although there is a high likelihood of future increases in atmospheric CO2 concentrations and temperatures across Australia, there is uncertainty about the direction and magnitude of rainfall change, particularly in the northern farming regions. Consequently, the clearest opportunities for ‘in-situ’ genetic gains for abiotic stresses are in developing better adaptation to higher temperatures (e.g. control of phenological stage durations, and tolerance to stress) and, for C3 species, in exploiting the (relatively small) fertilisation effects of elevated CO2. For most cultivated plant species, it remains to be demonstrated how much genetic variation exists for these traits and what value can be delivered via commercial varieties. Biotechnology-based breeding technologies (marker-assisted breeding and genetic modification) will be essential to accelerate genetic gain, but their application requires additional investment in the understanding, genetic characterisation, and phenotyping of complex adaptive traits for climate-change conditions.

Developmental and growth controls of tillering and water-soluble carbohydrate accumulation in contrasting wheat (Triticum aestivum L.) genotypes: can we dissect them?

In wheat, tillering and water-soluble carbohydrates (WSCs) in the stem are potential traits for adaptation to different environments and are of interest as targets for selective breeding. This study investigated the observation that a high stem WSC concentration (WSCc) is often related to low tillering. The proposition tested was that stem WSC accumulation is plant density dependent and could be an emergent property of tillering, whether driven by genotype or by environment. A small subset of recombinant inbred lines (RILs) contrasting for tillering was grown at different plant densities or on different sowing dates in multiple field experiments. Both tillering and WSCc were highly influenced by the environment, with a smaller, distinct genotypic component; the genotype×environment range covered 350–750 stems m–2 and 25–210mg g–1 WSCc. Stem WSCc was inversely related to stem number m–2, but genotypic rankings for stem WSCc persisted when RILs were compared at similar stem density. Low tillering–high WSCc RILs had similar leaf area index, larger individual leaves, and stems with larger internode cross-section and wall area when compared with high tillering–low WSCc RILs. The maximum number of stems per plant was positively associated with growth and relative growth rate per plant, tillering rate and duration, and also, in some treatments, with leaf appearance rate and final leaf number. A common threshold of the red:far red ratio (0.39–0.44; standard error of the difference=0.055) coincided with the maximum stem number per plant across genotypes and plant densities, and could be effectively used in crop simulation modelling as a ‘cut-off’ rule for tillering. The relationship between tillering, WSCc, and their component traits, as well as the possible implications for crop simulation and breeding, is discussed.

Adaptation of wheat, barley, canola, field pea and chickpea to the thermal environments of Australia

Abstract. n Warming trends involve two agronomically relevant aspects: a gradual increase in long-term mean temperature with the primary effect of shifting phenological patterns, and an increasing incidence of heat waves. Depending on timing, intensity and duration, heat can reduce crop growth and disrupt reproduction. Agronomic and breeding adaptations to elevated temperature have been listed but there is an overall lack of frameworks for systematic analysis. This paper provides agronomic and physiological background for the quantitative assessment of spatial patterns of the thermal regimes for wheat, barley, canola, field pea and chickpea. First, we revise the notion that Australian agriculture is ‘European’ and ill-adapted to the local environments. By showing that Australian agriculture in the southern and western regions is rather Levantine, we advance a more accurate and relevant framework to the thermal regimes of winter crops. Second, we outline the direct and indirect effects of temperature on crop traits and highlight the limitations of different approaches to investigate crop responses to temperature. This is important to make explicit the assumptions of studies dealing with crop responses to temperature; for example, indirect effects of temperature on crops mediated by effects on weeds, pathogens or herbivores could be important. Third, we compare the cardinal temperatures (including base, optimal, and critical thresholds) of our target crops. Cardinal temperatures respond to both natural and agronomic selection and are relevant for crop adaptation. Fourth, we develop a conceptual framework to assess thermal effects on crop yield and adaptive practices and traits, based on the notions of yield being a primary function of seed number, the species-specific critical window for the determination of seed number, and two complementary perspectives involving the photothermal quotient and crop growth rate in the critical window. The framework accounts for both aspects of warming: non-stressful elevated temperature and heat stress. Testable propositions are advanced that inform future research on crop adaptation to elevated temperature.

More fertile florets and grains per spike can be achieved at higher temperature in wheat lines with high spike biomass and sugar content at booting

An understanding of processes regulating wheat floret and grain number at higher temperatures is required to better exploit genetic variation. In this study we tested the hypothesis that at higher temperatures, a reduction in floret fertility is associated with a decrease in soluble sugars and this response is exacerbated in genotypes low in water soluble carbohydrates (WSC). Four recombinant inbred lines contrasting for stem WSC were grown at 20/10°C and 11h photoperiod until terminal spikelet, and then continued in a factorial combination of 20/10°C or 28/14°C with 11h or 16h photoperiod until anthesis. Across environments, High WSC lines had more grains per spike associated with more florets per spike. The number of fertile florets was associated with spike biomass at booting and, by extension, with glucose amount, both higher in High WSC lines. At booting, High WSC lines had higher fixed 13C and higher levels of expression of genes involved in photosynthesis and sucrose transport and lower in sucrose degradation compared with Low WSC lines. At higher temperature, the intrinsic rate of floret development rate before booting was slower in High WSC lines. Grain set declined with the intrinsic rate of floret development before booting, with an advantage for High WSC lines at 28/14°C and 16h. Genotypic and environmental action on floret fertility and grain set was summarised in a model.

High night temperatures during grain number determination reduce wheat and barley grain yield: a field study

Warm nights are a widespread predicted feature of climate change. This study investigated the impact of high night temperatures during the critical period for grain yield determination in wheat and barley crops under field conditions, assessing the effects on development, growth and partitioning crop-level processes driving grain number per unit area (GN). Experiments combined: (i) two contrasting radiation and temperature environments: late sowing in 2011 and early sowing in 2013, (ii) two well-adapted crops with similar phenology: bread wheat and two-row malting barley and (iii) two temperature regimes: ambient and high night temperatures. The night temperature increase (ca. 3.9 °C in both crops and growing seasons) was achieved using purpose-built heating chambers placed on the crop at 19:000 hours and removed at 7:00 hours every day from the third detectable stem node to 10 days post-flowering. Across growing seasons and crops, the average minimum temperature during the critical period ranged from 11.2 to 17.2 °C. Wheat and barley grain yield were similarly reduced under warm nights (ca. 7% °C(-1) ), due to GN reductions (ca. 6% °C(-1) ) linked to a lower number of spikes per m(2) . An accelerated development under high night temperatures led to a shorter critical period duration, reducing solar radiation capture with negative consequences for biomass production, GN and therefore, grain yield. The information generated could be used as a starting point to design management and/or breeding strategies to improve crop adaptation facing climate change.

Genotypic variability in the response to elevated CO2 of wheat lines differing in adaptive traits

Atmospheric CO2 levels have increased from ~280ppm in the pre-industrial era to 391ppm in 2012. High CO2 concentrations stimulate photosynthesis in C3 plants such as wheat, but large variations have been reported in the literature in the response of yield and other traits to elevated CO2 (eCO2). Few studies have investigated genotypic variation within a species to address issues related to breeding for specific adaptation to eCO2. The objective of this study was to determine the response to eCO2 of 20 wheat lines which were chosen for their contrasting expression in tillering propensity, water soluble carbohydrate (WSC) accumulation in the stem, early vigour and transpiration efficiency. Experiments were performed in control environment chambers and in a glasshouse with CO2 levels controlled at either 420ppm (local ambient) or 700ppm (elevated). The results showed no indication of a differential response to eCO2 for any of these lines and adaptive traits were expressed in a consistent manner in ambient and elevated CO2 environments. This implies that for these traits, breeders could expect consistent rankings in the future, assuming these results are validated under field conditions. Additional climate change impacts related to drought and high temperature are also expected to interact with these traits such that genotype rankings may differ from the unstressed condition.

Linked gene networks involved in nitrogen and carbon metabolism and levels of water-soluble carbohydrate accumulation in wheat stems

High levels of water-soluble carbohydrates (WSC) provide an important source of stored assimilate for grain filling in wheat. To better understand the interaction between carbohydrate metabolism and other metabolic processes associated with the WSC trait, a genome-wide expression analysis was performed using eight field-grown lines from the high and low phenotypic tails of a wheat population segregating for WSC and the Affymetrix wheat genome array. The 259 differentially expressed probe sets could be assigned to 26 functional category bins, as defined using MapMan software. There were major differences in the categories to which the differentially expressed probe sets were assigned; for example, probe sets upregulated in high relative to low WSC lines were assigned to category bins such as amino acid metabolism, protein degradation and transport and to be involved in starch synthesis-related processes (carbohydrate metabolism bin), whereas downregulated probe sets were assigned to cell wall-related bins, amino acid synthesis and stress and were involved in sucrose breakdown. Using the set of differentially expressed genes as input, chemical–protein network analyses demonstrated a linkage between starch and N metabolism via pyridoxal phosphate. Twelve C and N metabolism-related genes were selected for analysis of their expression response to varying N and water treatments in the field in the four high and four low WSC progeny lines; the two nitrogen/amino acid metabolism genes demonstrated a consistent negative association between their level of expression and level of WSC. Our results suggest that the assimilation of nitrogen into amino acids is an important factor that influences the levels of WSC in the stems of field-grown wheat.

Heat shock factor C2a serves as a proactive mechanism for heat protection in developing grains in wheat via an ABA-mediated regulatory pathway

High temperature at grain filling can severely reduce wheat yield. Heat shock factors (Hsfs) are central regulators in heat acclimation. This study investigated the role of TaHsfC2a, a member of the monocot-specific HsfC2 subclass, in the regulation of heat protection genes in Triticum aestivum. Three TaHsfC2a homoeologous genes were highly expressed in wheat grains during grain filling and showed only transient up-regulation in the leaves by heat stress but were markedly up-regulated by drought and abscisic acid (ABA) treatment. Overexpression of TaHsfC2a-B in transgenic wheat resulted in up-regulation of a suite of heat protection genes (e.g. TaHSP70d and TaGalSyn). Most TaHsfC2a-B target genes were heat, drought and ABA inducible. Transactivation analysis of two representative targets (TaHSP70d and TaGalSyn) showed that TaHsfC2a-B activated expression of reporters driven by these target promoters. Promoter mutagenesis analyses revealed that heat shock element is responsible for transactivation by TaHsfC2a-B and heat/drought induction. TaHsfC2a-B-overexpressing wheat showed improved thermotolerance but not dehydration tolerance. Most TaHsfC2a-B target genes were co-up-regulated in developing grains with TaHsfC2a genes. These data suggest that TaHsfC2a-B is a transcriptional activator of heat protection genes and serves as a proactive mechanism for heat protection in developing wheat grains via the ABA-mediated regulatory pathway.