The tiller inhibition (tin) and Reduced height (Rht) genes strongly influence the carbon partitioning and architecture of wheat shoots, but their effects on the energy economy of roots have not been examined in detail. We examined multiple root traits in three sets of near-isogenic wheat lines (NILs) that differ in the tin gene or various dwarfing gene alleles (Rht-B1b, Rht-D1b, Rht-B1c and Rht-B1b + Rht-D1b) to determine their effects on root structure, anatomy and carbon allocation. The tin gene resulted in fewer tillers but more costly roots in an extreme tin phenotype with a Banks genetic background due to increases in root-to-shoot ratio, total root length, and whole root respiration. However, this effect depended on the genetic background as tin caused both smaller shoots and roots in a different genetic background. The semi-dwarf gene Rht-B1b caused few changes to the root structure, whereas Rht-D1b, Rht-B1c and the double dwarf (Rht-B1b + Rht-D1b) decreased the root biomass. Rht-B1c reduced the energy cost of roots by increasing specific root length, increasing the volume of cortical aerenchyma and by reducing root length, number, and biomass without affecting the root-to-shoot ratio. This work informs researchers using tin and Rht genes how to modify root system architecture to suit specific environments.

Root architecture is key in determining how effective plants are at intercepting and absorbing nutrients and water. Previously, the wheat (Triticum aestivum) cultivars Spica and Maringa were shown to have contrasting root morphologies. These cultivars were crossed to generate an F6:1 population of recombinant inbred lines (RILs) which was genotyped using a 90 K single nucleotide polymorphisms (SNP) chip. A total of 227 recombinant inbred lines (RILs) were grown in soil for 21 days in replicated trials under controlled conditions. At harvest, the plants were scored for seven root traits and two shoot traits. An average of 7.5 quantitative trait loci (QTL) were associated with each trait and, for each of these, physical locations of the flanking markers were identified using the Chinese Spring reference genome. We also compiled a list of genes from wheat and other monocotyledons that have previously been associated with root growth and morphology to determine their physical locations on the Chinese Spring reference genome. This allowed us to determine whether the QTL discovered in our study encompassed genes previously associated with root morphology in wheat or other monocotyledons. Furthermore, it allowed us to establish if the QTL were co-located with the QTL identified from previously published studies. The parental lines together with the genetic markers generated here will enable specific root traits to be introgressed into elite wheat lines. Moreover, the comprehensive list of genes associated with root development, and their physical locations, will be a useful resource for researchers investigating the genetics of root morphology in cereals.

Empirical soybean breeding has improved its yield in arid and semi-arid areas of China. The objective of this study was to identify the important traits found in successful commercial soybean cultivars following the domestication of landraces through breeding in the semi-arid region of North-west China. A further objective was to identify any key traits that can be targeted using trait-based selection to improve yield under drought. Seed yield, phenology, water-use, water-use efficiency and their related traits in soybean landraces and successful cultivars were compared over a four year period in the field and this was supplemented with an outdoor pot experiment. The results in both field and pot experiments showed that successful soybean cultivars have a reduced thermal time to flowering but the thermal time for seed filling has increased. This change in partitioning of phenological time in the commercial cultivars resulted in a lower number of pods, fewer seeds per unit area but an increase in 100-seed weight, harvest index and seed yield. New soybean cultivars with high seed yield also had a lower vegetative biomass and less water use in both field and pot experiments than landraces but the lower water use did not compromise seed yield. The commercial cultivars also had a lower pod wall ratio (ratio of pod wall weight to total pod weight at maturity) which also contributed to yield by improving harvest index. We conclude that the key traits that have been altered as a result of soybean breeding in arid and semi-arid areas of China have been (1) a shortening of the duration between sowing and flowering but an extension of the seed filling period, (2) fewer pods but an increase in seed number per pod and 100-seed weight and also a decreased pod wall ratio, (3) an increased harvest index and (4) a reduced water use, particularly in the deeper soil layers.

The wheat Green Revolution Rht-B1b and Rht-D1b dwarfing alleles are associated with increased grain yields but also with reduced early growth and seedling emergence, especially if sowing conditions are unfavourable. The gibberellic acid-responsive, mutagen-derived Rht18 dwarfing gene was backcrossed from durum wheat (Triticum turgidum subsp. durum L.) cv. Icaro into tall bread wheat (Triticum aestivum L.) cv. Halberd using phenotypic selection for reduced plant height. The Rht18 allele was confirmed among homozygous BC1F2-derived, F5:7 recombinant inbred lines by using a chromosome 6AS-linked, microsatellite molecular marker (Xwms4608), and then assessed for agronomic performance across multiple field sites ranging in yield from 3.6 to 6.4 t/ha. The Rht18-containing lines were significantly (P < 0.05) shorter in height (−24%) and reduced in plant lodging (−51%) compared with tall sister lines. Reductions in plant height were associated with significant increases in grain yield (+16%), reflecting increases in grain number (+21%), number of spikes (+7%) and number of grains per spike (+12%). Coleoptile length, early shoot biomass and ground cover percentage were unaffected by the presence of the Rht18 dwarfing gene. Comparisons of effects of gibberellic acid-insensitive Rht-B1b and Rht18 on early growth and agronomic performance were assessed separately for a set of 30 BC5F6-derived Halberd near-isogenic lines in the field in 2015. Ground cover and coleoptile length were significantly greater for Rht18 lines, whereas plant height, lodging, harvest index, grain number and yield were similar for Rht-B1b and Rht18 sister lines. Reduced lodging and increased grain number and yield, together with greater coleoptile length, indicate a potentially useful role for Rht18 in improving wheat performance.

Soybean breeding is typically conducted in soils with favourable soil phosphorus yet soil P levels are typically low in sub-tropical regions. This study was conducted to determine yield progress of soybean cultivars released between 1995 and 2016 in sub-tropical parts of south-west China and grown at both low and high P availability. The principal factors that changed indirectly with breeding and that contribute to soybean yield were also determined. Field experiments were conducted in three consecutive years with two different sites each year. A more detailed investigation of traits contributing to soybean yield was investigated in one year at two sites. The rate of genetic gain in seed yield was around 2% per year and this was found at both low P and high P. Thus, breeding under favourable conditions has also resulted in substantial gains in soils with low P. Yield gains were attributed to a longer duration of pod filling but there was no change in the duration from sowing to flowering. The extended pod filling duration increased both above-ground biomass and harvest index (HI) at both P levels and both were important in contributing to yield gains. The increase in HI was also a result of the changed allocation of assimilates away from stems and instead to the pods and growing seeds. The allometric analysis (ratios between log transformations of the leaf, stem and pod dry weight) showed that the stem weight decreased as pod dry weight became heavier whereas leaf weight remained constant as stems became lighter as a result of breeding. Breeding also progressively increased pod number and the total seed number but there was no change in average seed weight.

Climate change and future warming will significantly affect crop yield. The capacity of crops to dynamically adjust physiological processes (i.e., acclimate) to warming might improve overall performance. Understanding and quantifying the degree of acclimation in field crops could ensure better parameterization of crop and Earth System models and predictions of crop performance. We hypothesized that for field-grown wheat, when measured at a common temperature (25°C), crops grown under warmer conditions would exhibit acclimation, leading to enhanced crop performance and yield. Acclimation was defined as (a) decreased rates of net photosynthesis at 25°C (A25 ) coupled with lower maximum carboxylation capacity (Vcmax25 ), (b) reduced leaf dark respiration at 25°C (both in terms of O2 consumption Rdark _O225 and CO2 efflux Rdark _CO225 ) and (c) lower Rdark _CO225 to Vcmax25 ratio. Field experiments were conducted over two seasons with 20 wheat genotypes, sown at three different planting dates, to test these hypotheses. Leaf-level CO2 -based traits (A25 , Rdark _CO225 and Vcmax25 ) did not show the classic acclimation responses that we hypothesized; by contrast, the hypothesized changes in Rdark_ O2 were observed. These findings have implications for predictive crop models that assume similar temperature response among these physiological processes and for predictions of crop performance in a future warmer world.

Gibberellin (GA)-insensitive dwarfing genes Rht-B1b and Rht-D1b that are responsible for the 'Green Revolution' have been remarkably successful in wheat improvement globally. However, these alleles result in shorter coleoptiles and reduced vigour, and hence poor establishment and growth in some environments. Rht18, on the other hand, is a GA-sensitive, dominant gene with potential to overcome some of the early growth limitations associated with Rht-B1b and Rht-D1b. We assessed progeny from both a biparental and a backcross population that contained tall, single dwarf, and double dwarf lines, to determine whether Rht18 differs from Rht-D1b and hence verify its value in wheat improvement. Progeny with Rht18 had an almost identical height to lines with Rht-D1b, and both were ~26% shorter than the tall lines, with the double dwarf 13% shorter again. However, coleoptile length of Rht18 was 42% longer than that of Rht-D1b. We detected no differences in time to terminal spikelet and anthesis, and few differences in stem or spike growth. Both dwarfing genes diverted more dry matter to the spike than tall lines from prior to heading. No differences were detected between Rht18 and Rht-D1b that could prevent the adoption of Rht18 in wheat breeding to overcome some of the limitations associated with the 'Green Revolution' genes.

Reducing the number of tillers per plant using a tiller inhibition (tin) gene has been considered as an important trait for wheat production in dryland environments. We used a spatial analysis approach with a daily time-step coupled radiation and transpiration efficiency model to simulate the impact of the reduced-tillering trait on wheat yield under different climate change scenarios across Australia's arable land. Our results show a small but consistent yield advantage of the reduced-tillering trait in the most water-limited environments both under current and likely future conditions. Our climate scenarios show that whilst elevated [CO2] (e[CO2]) alone might limit the area where the reduced-tillering trait is advantageous, the most likely climate scenario of e[CO2] combined with increased temperature and reduced rainfall consistently increased the area where restricted tillering has an advantage. Whilst long-term average yield advantages were small (ranged from 31 to 51 kg ha(-1) year(-1)), across large dryland areas the value is large (potential cost-benefits ranged from Australian dollar 23 to 60 MIL/year). It seems therefore worthwhile to further explore this reduced-tillering trait in relation to a range of different environments and climates, because its benefits are likely to grow in future dry environments where wheat is grown around the world.

We developed a photoperiod-corrected thermal model that can predict wheat phenology based solely on the combination of photoperiod (Ppd) and vernalisation (Vrn) alleles to identify the phenological suitability of germplasm across the cropping region in southern Australia. More than 200 wheat genotypes that vary in combinations of Ppd and Vrn alleles were grown at 17 locations spanning 11 degrees Latitude, thus providing a wide range in temperature and daylength gradients. The phenological sensitivities of a genotype to varying basic temperature, photoperiod and vernalisation requirement was adjusted via optimisation to minimise the least square difference between the measured and predicted dates of both terminal spike (TS) and flowering (AN). The model predicted dates of TS and AN to within 5 days of the field values. Information was used to identify the alleles required to achieve a wheat ideotype defined in a previous study. The optimum allelic combinations required to target the optimum flowering period for different locations when sown on different dates were also identified. The use of allelic based phenological models has the potential to reduce the costs to breeding programs and accelerate the release of better adapted germplasm to new and changing environments.

Suboptimal distribution of photosynthetic capacity in relation to light among leaves reduces potential whole-canopy photosynthesis. We quantified the degree of suboptimality in 160 genotypes of wheat by directly measuring photosynthetic capacity and daily irradiance in flag and penultimate leaves. Capacity per unit daily irradiance was systematically lower in flag than penultimate leaves in most genotypes, but the ratio (γ) of capacity per unit irradiance between flag and penultimate leaves varied widely across genotypes, from less than 0.5 to over 1.2. Variation in γ was most strongly associated with differences in photosynthetic capacity in penultimate leaves, rather than with flag leaf photosynthesis or canopy light penetration. Preliminary genome-wide association analysis identified nine strong marker-trait associations with this trait, which should be validated in future work in other environments and/or materials. Our modelling suggests canopy photosynthesis could be increased by up to 5 % under sunny conditions by harnessing this variation through selective breeding for increased γ.

Modelling and limited data suggest that crops with deeper and longer roots capture more soil resources and yield more when water is available deeper in soil profiles. Interest has grown in the development of new cultivars with deeper roots. This study provides data from three field experiments to help researchers and breeders continue to assess the value of selecting for deeper roots for yield and water use efficiency gains. We asked: do genotype groups with shoot phenotypes easily selectable in pre-breeding programs express predictable root depth and length at time of grain harvest in the field? Do flowering time and shoot biomass predict deep roots measured directly in the field with coring, such that deeper roots are associated with more shoot growth and yield? Does genotype, including triticale versus wheat types, vary in roofing traits? Thirty-four wheats (Triticum aestivum L.) and two triticales ( x Triticosecale) were drawn from ten 'genotype groups'; selections from breeding programs and commercial cultivars that were distinguished on the basis of height, tillering, winter habit, and early vigour. These were grown at two independent sites and soil conditions in year 1 (experiment 1 and 2), with a subset of six wheats and two triticales repeated in year 2 at year 1 site (experiment 3). Above-ground biomass, flowering date, grain yield and root length and depth were measured with a high level of replication (four replicate plots and four soil cores per plot). Root length density was predicted from root counts obtained using the core-break method on 42 mm diameter, two m deep cores. A Bayesian multivariate mixed-effects model was used with fixed effects of the environment and random effects of genotype groups, genotypes and their interactions with the environment. Variation in roofing depth and length caused by environments was much larger than that caused by genotypes. Positive relationships between biomass, yield and root depth and length were observed across experiments and genotype groups (r = 0.62 for biomass and root depth, r = 0.61 for yield and root depth; r = 0.66 for biomass and root length, r = 0.53 for yield and root length), but the largest effects were driven by differences in soil and rainfall conditions between experiments. However, the smaller genetic effects on roofing depth and yield were positively correlated (r = 0.69). We did not find that easily selectable shoot traits like early vigour, tillering, and height reliably predicted in-field deeper roofing. Notably, the two triticales were 74 % more likely to have a deeper roofing and 82 % more likely to have less total root length, than spring wheats. We conclude that deeper and longer roots at maturity are (1) challenging to pre-select using shoot phenotype prior to field evaluation; (2) depend almost entirely on environment for expression in the field with small effects of genotype; and (3) can grow at no apparent 'cost' to shoot growth or yield and as such can remain a target for breeding.

Using a field to lab approach, mature deep-rooting traits in wheat were correlated to root phenotypes measured on young plants from controlled conditions. Mature deep-rooting root traits of 20 wheat genotypes at maturity were established via coring in three field trials across 2 years. Field traits were correlated to phenotypes expressed by the 20 genotypes after growth in four commonly used lab screens: (i) soil tubes for root emergence, elongation, length, and branching at four ages to 34 days after sowing (DAS); (ii) paper pouches 7 DAS and (iii) agar chambers for primary root (PR) number and angles at 8 DAS; and (iv) soil baskets for PR and nodal root (NR) number and angle at 42 DAS. Correlations between lab and field root traits (r2=0.45-0.73) were highly inconsistent, with many traits uncorrelated and no one lab phenotype correlating similarly across three field experiments. Phenotypes most positively associated with deep field roots were: longest PR and NR axiles from the soil tube screen at 20 DAS; and narrow PR angle and wide NR angle from soil baskets at 42 DAS. Paper and agar PR angles were positively and significantly correlated to each other, but only wide outer PRs in the paper screen correlated positively to shallower field root traits. NR phenotypes in soil baskets were not predicted by PR phenotypes in any screen, suggesting independent developmental controls and value in measuring both root types in lab screens. Strong temporal and edaphic effects on mature root traits, and a lack of understanding of root trait changes during plant development, are major challenges in creating controlled-environment root screens for mature root traits in the field.

We tested the hypothesis that lengthening the duration between the terminal spikelet stage of development and anthesis (referred to here as the construction-phase duration, CPD) will increase yield per unit area in wheat (Triticum aestivum L.). Field experiments were undertaken at 17 sites across the high-rainfall zone of south-eastern and Western Australia in 2014 and 2015. In total, 205 wheat genotypes were grown. Genetic material included a set of near-isogenic lines (NILs) varying in photoperiod and vernalisation alleles; commercial wheat cultivars and breeding lines; and lines selected from the Multiparent Advanced Generation Inter Cross population. As such, this is the only comprehensive dataset in which the effect of variation in CPD on grain yield in field plots has been evaluated in diverse field environments. Within an optimum anthesis window of 10 days, longer CPD significantly increased grain yield by >11% at two sites and tended to increase grain yield at another 11 sites (not statistically significant). The average yield increase across these sites was 5.5%. There was no consistent trend whereby a specific yield component was responsible for the increase across sites. We suggest that CPD can be extended by genetic selection and by sacrificing some of the vegetative period without any detriment to grain yield. We also found that CPD is increased by extending the duration from sowing to flowering through earlier sowing, which may be associated with increased yields in some environments. We conclude that, for the same anthesis date, a longer CPD may be beneficial in moderately favourable rainfed environments with a relatively even distribution of rainfall. We explore the basis of these relationships and implications for growers and plant breeders.

Rooting depth, a hard trait to measure in the field, was negatively correlated with canopy temperature, an easy trait to measure by airborne thermography, in large wheat populations under terminal drought

In wheat (Triticum aestivum L.) canopy architecture influences light penetration into the canopy and radiation use efficiency particularly during the period between stem elongation and anthesis which is the critical time for the determination of yield. Despite large differences in canopy architecture among spring wheat genotypes, ranging from erectophile to planophile upper leaves, there is little prior evidence to suggest that selection for canopy architecture influences yield. In this study we evaluated the variation for canopy architecture in a 4-way MAGIC population (n= similar to 1000 lines) developed from 4 Australian commercial spring wheats and an 8-way MAGIC population (n = similar to 300 lines) developed from 3 Australian and 5 northern hemisphere commercial wheats. The 4-way population was grown at both an irrigated and a dryland site in southern New South Wales whereas the 8-way population was grown at the irrigated site. We also measured grain yield, plant height and crop development stage at the irrigated site. Using a smaller subset of lines which we grouped into either erectophile or planophile we studied how canopy architecture influences grain yield and associated yield traits (above-ground biomass (AGBM), harvest index, yield components, flowering time and height). The grain yield in the latter experiments varied from 5 to 6 t ha(-1). Averaged over two years and two sowing dates in each year lines that were erectophile yielded 13% more than the planophile lines and most of this yield advantage was associated with a higher AGBM (11%). Erectophile lines had 24% more grains per unit area but a 9% lower grain weight. Erectophile lines flowered 2 days later than planophile lines and they were 7 cm shorter. Lodging, although rare in these studies, was more evident in the planophile lines. In both MAGIC populations the most erectophile lines yielded 24% more grain than the most planophile lines. Mapping was conducted on the 1000 lines from the 4-way MAGIC population grown at the irrigated and the dryland site. It showed that genetic control of canopy architecture was complex but QTL were generally repeatable at both sites. Significant QTL were identified on most chromosomes. G x E was low for canopy architecture as the scores were repeatable across years (r(2) = 0.85). This trait opens the way to improve wheat yields via increasing crop biomass which in the past has been largely intractable in breeding programs.

High temperatures account for major wheat yield losses annually and, as the climate continues to warm, these losses will probably increase. Both photosynthesis and respiration are the main determinants of carbon balance and growth in wheat, and both are sensitive to high temperature. Wheat is able to acclimate photosynthesis and respiration to high temperature, and thus reduce the negative affects on growth. The capacity to adjust these processes to better suit warmer conditions stands as a potential avenue toward reducing heat-induced yield losses in the future. However, much remains to be learnt about such phenomena. Here, we review what is known of high temperature tolerance in wheat, focusing predominantly on the high temperature responses of photosynthesis and respiration. We also identify the many unknowns that surround this area, particularly with respect to the high temperature response of wheat respiration and the consequences of this for growth and yield. It is concluded that further investigation into the response of photosynthesis and respiration to high temperature could present several methods of improving wheat high temperature tolerance. Extending our knowledge in this area could also lead to more immediate benefits, such as the enhancement of current crop models.

Crop photosynthesis and yield are limited by slow photosynthetic induction in sunflecks. We quantified variation in induction kinetics across diverse genotypes of wheat for the first time. Following a preliminary study that hinted at wide variation in induction kinetics across 58 genotypes, we grew 10 genotypes with contrasting responses in a controlled environment and quantified induction kinetics of carboxylation capacity (Vcmax) from dynamic A versus ci curves after a shift from low to high light (from 50 µmol m-2 s-1 to 1500 µmol m-2 s-1), in five flag leaves per genotype. Within-genotype median time for 95% induction (t95) of Vcmax varied 1.8-fold, from 5.2 min to 9.5 min. Our simulations suggest that non-instantaneous induction reduces daily net carbon gain by up to 15%, and that breeding to speed up Vcmax induction in the slowest of our 10 genotypes to match that in the fastest genotype could increase daily net carbon gain by up to 3.4%, particularly for leaves in mid-canopy positions (cumulative leaf area index ≤1.5 m2 m-2), those that experience predominantly short-duration sunflecks, and those with high photosynthetic capacities.

Grain number (GN) is determined by spike growth rate (SGR), fruiting efficiency (FE) and the duration of spike growth period (D-s). However, these three traits are not independent of each other and therefore quantifying their relative contribution to GN is important for improving yield potential. This study aimed to model GN as a function of SGR, FE and D-s in bread wheat and investigate the relative importance of these three traits in determining GN. A large number of commercial varieties, elite wheat breeding lines, and a Multiparent Advanced Generation InterCross population were evaluated for GN, SGR, D-s, and FE in six Australian environments in 2014 and 2015. The model explained 43-98% of the variation in GN in individual environments and 88% of the variation in GN across the six environments. The percentage of GN variance explained by the model was significantly higher than those explained by correlating GN to individual traits. The relative importance of the contribution of the three traits to GN was different and ranked as SGR > FE > D-s. The negative correlation between FE and spike dry weight at anthesis (SDWa) appears to be spurious, suggesting that there was no causality between high FE and low SDWa and vice versa. Thus, FE can be used as an independent trait to increase GN in addition to SGR and D-s. We also investigated if the wheat crop had enough source to fill the increased sink size in the southern Australian high rainfall environment. The source-sink balance analysis indicates that the available source, consisting of concurrent photosynthetic assimilate and stored water-soluble carbohydrate at anthesis, was sufficient to fill the established sink but no surplus assimilates were available to fill a larger sink in southwestern Australia. However, the opportunity to increase yield potential by further increasing grain number might exist in south-eastern Australia environments.