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Given the worldwide effort to improve crop drought resistance, it is crucial to understand the mechanisms of root system adaptation of ploidy wheat to water‐deficient environments. A meta‐analysis was performed to examine the changes in root system mechanisms under drought conditions. Data used in the analysis were drawn from 192 papers, taking into account wheat ploidy levels as well as pot and field studies. The results illustrated that water stress reduced grain yield and aboveground biomass to a greater extent in diploid and tetraploid compared with hexaploid genotypes. In contrast, drought reduced root biomass, root surface area and root volume more in hexaploid than in diploid and tetraploid wheat. Under water‐limited conditions, diploid and tetraploid genotypes exhibited greater root biomass and root length densities in the topsoil. Hexaploid genotypes greatly reduced root biomass and root length density in the topsoil and maintained higher root biomass and root length density in subsoil. These genotypes also showed smaller root diameter and xylem centre vessel diameter under drought conditions. The analysis revealed that grain yield was negatively correlated with topsoil root biomass and root length density, root volume, root diameter and xylem centre vessel, but positively correlated with subsoil root mass, root length density and root vigour. The study demonstrated that domestication and selection pressures of ploidy wheat have altered wheat root system traits while improving grain yield. Greater root mass and root length densities in the subsoil facilitate access to soil moisture from deep layers, contributing to high yields in drought environments. [ABSTRACT FROM AUTHOR]

Background and Aims: Barley breeding has increased yield over the last century, but the associated changes in the phenotype are largely unknown. Our aim was to quantify the rate of genetic gain in a collection of Australian barley cultivars representing seven decades of breeding, and the associated changes in the phenotype. Methods: Thirteen barley cultivars were grown in the field at Roseworthy and Mintaro, South Australia, to evaluate shifts in phenology, yield, and its components. A subset of five cultivars was grown under controlled conditions to probe for changes in root traits and nutrient uptake. Results: Grain yield increased at 16.0 ± 5.3 kg ha−1 yr−1 or 0.43 ± 0.15% yr−1 at Roseworthy, where average yield was 3.1 t ha−1. There was no relation between yield and year of registration at Mintaro, where severe, extended frost disrupted reproduction. Changes in phenology with year of registration were not apparent. The main drivers of yield gain were grain number per m2 and harvest index, with a minor contribution of shoot biomass. Root length density, specific root length, root extension rate, and nutrient uptake per cm of root length increased with year of registration. Conclusions: The rate of genetic gain of Australian barley aligned with rates reported for other breeding programs worldwide and compared to 21.0 ± 2.3 kg ha−1 yr−1 for actual yield in Australian farms between 1961 and 2019. Changes in the growth and functionality of the root system highlight the indirect effects of selective pressure for yield and agronomic adaptation. [ABSTRACT FROM AUTHOR]

Crop avoidance and tolerance strategies are critical adaptive mechanisms of drought stress and play different roles in grain yield. However, little is known about the contribution of these two mechanisms to grain yield in old and modern wheat genotypes. Here, pot and field experiments were carried out to characterize and compare the mechanisms of drought avoidance and drought tolerance, and determine their differential contributions to the yield in six wheat genotypes. The pot experiment results demonstrated that the old genotypes acquired a better avoidance ability to adapt to drought stress. These avoidance abilities include larger root systems, lower leaf areas, low stomatal conductance, pale green leaf colour, higher degrees of leaf rolling and leaf waxiness. The modern genotypes displayed stronger drought tolerance advantages, such as high osmotic adjustment and antioxidant enzyme activity, and a smaller root system. Our field experiment further showed that under severe water-deficit conditions, the old genotypes with stronger drought avoidance traits had higher yields and water use efficiency (WUEg), whereas the modern genotypes with strong drought tolerance characteristics produced higher yields and had higher WUEg under mild and intermediate water deficits. The results indicate that the relative contribution of drought tolerance and drought avoidance to grain yield depends to a large extent on the degree of drought stress and genotypes. Understanding the differential plant response depending on genotype and drought stress may help plant breeders develop drought-resistant varieties suitable for drought-prone environments under anticipated climate change scenarios. [ABSTRACT FROM AUTHOR]

In the Mediterranean-type environment of Australia and other parts of the world, end-of- season or terminal drought is the most significant abiotic stress affecting wheat grain yields. This study examined the response of two wheat cultivars with contrasting root system size to terminal drought and the effect of terminal drought on grain yield and yield components. The cultivars were grown in 1.0 m deep PVC columns filled with soil in a glasshouse under well-watered conditions until the onset of ear emergence (Z51) when well-watered and terminal drought treatments were imposed. Terminal drought reduced stomatal conductance, leaf photosynthesis, and transpiration rates faster in Bahatans-87 (larger root system size) than Tincurrin (smaller root system size). Terminal drought reduced grain yield in both cultivars, more so in Bahatans-87 (80%) with the large root system than Tincurrin (67%) with the small root system, which was mainly due to a reduction in grain number and grain size in Bahatans-87 and grain size in Tincurrin. In the terminal drought treatment, Bahatans-87 had 59% lower water use efficiency than Tincurrin, as Bahatans-87 used 39% more water and reduced grain yield more than Tincurrin. The lesser reduction in grain yield in Tincurrin was associated with slower water extraction by the small root system and slower decline in stomatal conductance, leaf photosynthesis, and transpiration rates, but more importantly to faster phenological development, which enabled grain filling to be completed before the severe effects of water stress. [ABSTRACT FROM AUTHOR]

Competition among plants for limited soil resources is influenced, in part, by seeding rate. This study aimed to investigate how cultivars that differ in root traits affect water acquisition and the optimal seeding rate. Three cultivars of winter wheat (Triticum aestivum L.) with contrasting root systems (CW134, more roots in topsoil and less roots in subsoil; CH58, small root biomass; CH1, less roots in topsoil and more roots in subsoil) were sown at 180, 225, and 280 seeds m-2 in 2014-2015 and 2015-2016 in a semiarid farmland on the Loess Plateau of China. As the seeding rate increased, grain yield declined in CW134, with topsoil roots increasing and subsoil roots decreasing in both seasons. In contrast, both grain yield and subsoil roots increased in CH1, and the highest grain yield was produced by CH1 at 280 seeds m-2 in both seasons. Subsoil root traits had a positive effect on soil water consumption after anthesis, which was strongly affected by yield components in the dryer season (2015-016). However, the reverse was true for topsoil root traits. In 2014-2015, the topsoil roots had a positive effect on soil water consumption before anthesis, and aboveground traits at anthesis had a greater positive effect on yield components. To maintain higher yields in semiarid environments, genotypes with more topsoil roots should have lower seeding rates to alleviate the negative effect of excessive topsoil roots on postanthesis water absorption, while the reverse may be true for genotypes with more roots in subsoil layers. [ABSTRACT FROM AUTHOR]

Wheat ( Triticum aestivum L.) and rice ( Oryza sativa L.), which belong to the Poaceae family, are starch-grain crops, but wheat is adapted to cooler temperature conditions than rice. In this study, the difference between the two contrasting crops in grain-filling adaptability in response to temperature was investigated. Two spring wheat cultivars were grown in the Mediterranean-type environments of Western Australia and Southeast Turkey, and four temperate-zone rice cultivars were grown in several locations in Japan under irrigated conditions. Portions of the crops were enclosed under a plastic canopy to elevate the temperature after anthesis. Average temperatures during grain filling ranged from 14 to 24 °C for wheat and from 23 to 29 °C for rice. Grain yield varied from 280 to 599 g m −2 in wheat and 354 to 736 g m −2 in rice. When plant density was halved at flowering to estimate the potential grain-filling rate under an increased supply of assimilates, the grain-filling percentages [%F, observed grain weight (G)/potential grain weight (PG)] of both crops were represented by similar logistic curves of cumulative temperatures during the grain filling period. These results suggest that grain-filling responses to temperature scarcely differ between spring wheat and temperate-zone rice. G was estimated for the spring wheat and temperate-zone rice cultivars under different temperatures after anthesis using an assimilate-limited grain-potentiality model consisting of the following parameters: rate of whole-plant weight increase (ΔW/Δ t ), rate of potential grain dry weight increase (ΔPG/Δ t ) based on rate of%F (%F/Δ t ) and PG, and the amount of stem reserves (SP). The observed data showed that the decrease in ΔW/Δ t with an increase in temperature in wheat was greater than in rice. According to the model, G started to decrease at lower temperatures in wheat than in rice, and this decrease was accelerated by lower amounts of SP. Therefore, the difference in the optimal temperatures for G during grain filling between the two crops was suggested to mainly result from the sensitivity of assimilation to high temperatures. [ABSTRACT FROM AUTHOR]

End-of-season drought or "terminal drought," which occurs after flowering, is considered the most significant abiotic stress affecting crop yields. Wheat crop production in Mediterranean-type environments is often exposed to terminal drought due to decreasing rainfall and rapid increases in temperature and evapotranspiration during spring when wheat crops enter the reproductive stage. Under such conditions, every millimeter of extra soil water extracted by the roots benefits grain filling and yield and improves water use efficiency (WUE). When terminal drought develops, soil dries from the top, exposing the top part of the root system to dry soil while the bottom part is in contact with available soil water. Plant roots sense the drying soil and produce signals, which on transmission to shoots trigger stomatal closure to regulate crop water use through transpiration. However, transpiration is linked to crop growth and productivity and limiting transpiration may reduce potential yield. While an early and high degree of stomatal closure affects photosynthesis and hence biomass production, a late and low degree of stomatal closure exhausts available soil water rapidly which results in yield losses through a reduction in post-anthesis water use. The plant hormone abscisic acid (ABA) is considered the major chemical signal involved in stomatal regulation. Wheat genotypes differ in their ability to produce ABA under drought and also in their stomatal sensitivity to ABA. In this viewpoint article we discuss the possibilities of exploiting genotypic differences in ABA response to soil drying in regulating the use of water under terminal drought. Root density distribution in the upper drying layers of the soil profile is identified as a candidate trait that can affect ABA accumulation and subsequent stomatal closure. We also examine whether leaf ABA can be designated as a surrogate characteristic for improved WUE in wheat to sustain grain yield under terminal drought. Ease of collecting leaf samples to quantify ABA compared to extracting xylem sap will facilitate rapid screening of a large number of germplasm for drought tolerance. [ABSTRACT FROM AUTHOR]

Background and aims: Given the worldwide effort to improve the nitrogen (N) economy of crops, it is critical to understand the mechanisms of improved N uptake which have resulted from selection pressure for grain yield in Australian wheat ( Triticum aestivum L.). Changes in root system traits and N uptake were examined in nine Australian wheat varieties released between 1958 and 2007. Methods: Wheat varieties were grown in rhizo-boxes in a glasshouse. We measured nitrogen uptake and mapped root growth and proliferation to quantify root length density (RLD), root length per plant, root biomass, specific root length, and plant nitrogen uptake per unit root length. Results: Selection for yield reduced total RLD and total root length, and increased N uptake per unit root length that overrode the reduction in root system size, effectively explaining the increase in N uptake. Importantly, N uptake in our experiment under controlled conditions matched field measurements, reinforcing the agronomic significance of the present study. Conclusions: Wheat varieties released in Australia between 1958 and 2007 increased their N uptake, not because of increasing their root length and RLD, but for progressively increasing the efficiency of their root system in capturing N. Our collection of varieties is therefore an interesting model to probe for variation in the affinity of the root system for nitrate. [ABSTRACT FROM AUTHOR]

The response of wheat crops to elevated CO2 ( eCO2) was measured and modelled with the Australian Grains Free-Air CO2 Enrichment experiment, located at Horsham, Australia. Treatments included CO2 by water, N and temperature. The location represents a semi-arid environment with a seasonal VPD of around 0.5 kPa. Over 3 years, the observed mean biomass at anthesis and grain yield ranged from 4200 to 10 200 kg ha−1 and 1600 to 3900 kg ha−1, respectively, over various sowing times and irrigation regimes. The mean observed response to daytime eCO2 (from 365 to 550 μmol mol−1 CO2) was relatively consistent for biomass at stem elongation and at anthesis and LAI at anthesis and grain yield with 21%, 23%, 21% and 26%, respectively. Seasonal water use was decreased from 320 to 301 mm ( P = 0.10) by eCO2, increasing water use efficiency for biomass and yield, 36% and 31%, respectively. The performance of six models (APSIM-Wheat, APSIM-Nwheat, CAT-Wheat, CROPSYST, OLEARY- CONNOR and SALUS) in simulating crop responses to eCO2 was similar and within or close to the experimental error for accumulated biomass, yield and water use response, despite some variations in early growth and LAI. The primary mechanism of biomass accumulation via radiation use efficiency ( RUE) or transpiration efficiency ( TE) was not critical to define the overall response to eCO2. However, under irrigation, the effect of late sowing on response to eCO2 to biomass accumulation at DC65 was substantial in the observed data (~40%), but the simulated response was smaller, ranging from 17% to 28%. Simulated response from all six models under no water or nitrogen stress showed similar response to eCO2 under irrigation, but the differences compared to the dryland treatment were small. Further experimental work on the interactive effects of eCO2, water and temperature is required to resolve these model discrepancies. [ABSTRACT FROM AUTHOR]

Understanding the changes in phenotype resulting from the selection pressure and agronomic adaptation of grain yield provide an indication of the pathways for future increases in grain yield. Six dry land representative winter wheat cultivars (Triticum aestivum L.) released from 1942 to 2004 in the Loess Plateau of China were investigated to determine how the yield components of winter wheat were associated with grain yield at the Changwu Agricultural Research Station during the 2011–2012 and 2012–2013 seasons, using a completely randomized block design with three replicates. Plant height, aboveground biomass, grain yield, and yield components were measured, together with the traits of superior and inferior grains and the pre-anthesis stored dry matter remobilized to the grain was determined. In the relatively wet 2011–2012 season, there was a significant increase in grain yield and aboveground biomass with the year of release, but not in the dry 2012–2013 season. The harvest index (HI) and average grain weight (AGW) increased significantly with the year of release in both cropping seasons. HI and AGW are likely potential traits for improving grain yield of winter wheat in the Loess Plateau. The increase in HI mainly resulted from the decrease in plant height, and the increase in the use of pre-anthesis stored assimilates for grain filling. The increase in AGW mainly resulted from the increase in the proportion of superior grain (SG) and the decrease in the proportion of inferior grain (IG) in the whole spike in both cropping seasons. Depending on the climatic conditions, the different winter wheat cultivars showed different ability to use pre-anthesis stored assimilates. Modern wheat cultivars had higher yield under different rainfall conditions, and high ability to use pre-anthesis stored assimilates to fill the grain than earlier released cultivars. Both, the increase in sink capacity and source availability, should be considered as a strategy for increasing future grain yield in Loess Plateau of China. [ABSTRACT FROM AUTHOR]

In the Australian grainbelt, early winter rainfall has declined during the last 30 years, and farmers sow their crops dry, increasing the risk of early season drought. This study aimed to examine whether differences in the root systems were associated with tolerance to early season drought. Three wheat cultivars with different root systems were grown in 1 m columns in a glasshouse. Immediately after sowing in dry soil, 440 mL water (equivalent to 25 mm rainfall) was supplied to each column, and no water was added to induce the early-season drought for the next 30 days. Shoot and root traits were measured at the end of the early season drought, anthesis and at maturity, respectively. The restricted water supply reduced Ψleaf, stomatal conductance, leaf photosynthetic rate, shoot and root biomass. Early season drought delayed phenology in all cultivars, but there was recovery of root and shoot biomass at anthesis in all three cultivars. Leaf area and shoot biomass at anthesis in Bahatans-87 (large root system) recovered better than Tincurrin (small root system). At maturity, early season drought reduced grain yield more in Tincurrin than Bahatans-87. The slow phenology of Bahatans-87 allowed greater recovery after the drought in leaf area and shoot biomass, which may explain the smaller reduction in grain yield after early season drought. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) plays a central role in the plant response to water deficit by inducing stomatal closure to conserve water when the soil dries. Exogenous ABA was applied at 45 days after sowing (DAS) as a soil drench, the physiological and seed yield response of soybean to exogenous ABA were examined as the soil was drying. Three experiments were conducted using the drought-tolerant soybean cultivar Jindou 19, grown in pots at the Yuzhong Experimental Station of Lanzhou University, China. In experiment 1, plants were exposed to progressive soil drying and leaf ABA concentration, leaf photosynthesis rate, leaf relative water content (RWC) and osmotic adjustment (OA) were measured. In experiment 2, plants were under progressive soil drying and lethal leaf water potential was measured. In experiment 3, flower production and abortion, and grain yield were measured in plants under well-watered (WW), moderate (MWD) and severe water deficits (SWD). Exogenous ABA application increased ABA accumulation in leaves and reduced the rate of soil drying. It also increased leaf photosynthetic rate, stomatal conductance and transpiration rate at 7–10 days after withholding water. The intrinsic and instantaneous water use efficiency (WUE) was consistently higher with exogenous ABA than without ABA as the soil dried. Exogenous ABA increased OA when the leaf relative water content (RWC) decreased at eight days after withholding water, lowering the lethal leaf water potential by 0.4 MPa. Exogenous ABA reduced water use, increased WUE for grain yield under WW and MWD, and had no effect on flower number, flower abortion or grain yield in any water treatment. We concluded that (1) exogenous ABA induced OA, improved leaf photosynthetic rate, leaf water relations and desiccant tolerance, but did not benefit grain yield in soybean under water deficits; (2) exogenous ABA improved the WUE at the leaf level as soil drying and WUE for grain yield under moderate water deficit. [ABSTRACT FROM AUTHOR]

Root morphology and anatomical traits that occurred during the cultivar selection process are important for understanding improvements in grain yield and water use efficiency. However, little is known about the changes in root morphology and root anatomy caused by cultivar replacement and their effects on grain yield and water use efficiency. Field and pot experiments were conducted to investigate the changing trends in root morphological and anatomical traits of six dryland winter wheat cultivars widely cultivated in Shaanxi Province of China, from 1949 to 2014, and determine their relationships with grain yield and water use efficiency. The results illustrated that compared with old cultivars, the grain yield and water use efficiency of modern cultivars increased by 35.7% and 48.4% respectively, and were closely related to root system changes. With cultivar succession, root biomass, root surface area, root length and root length density all decreased in the topsoil under irrigated or rainfed conditions, whereas these traits increased in the subsoil. The subsoil root biomass, root surface area, root length and root length density of cultivars released after 2000 increased by 26.1%, 11.7%, 25.4% and 23.2% respectively compared with the older cultivars before 2000. Cultivar replacement also increased the root cortex thickness by 29.2%, but reduced the root xylem center vessel diameter by 13.2%, without obvious changes in root diameter. Our study demonstrated that cultivar replacement altered root morphology and root anatomy, thereby improving grain yield and water use efficiency. The future challenge for wheat breeding is to increase grain yield and water use efficiency under water-deficit conditions, which may be achieved by further promoting subsoil root development and optimizing root anatomy. • Assessed trends in root morphology and root anatomical traits during cultivar. • replacement is important for understanding improvements in yield performance. • Increased wheat grain yield during cultivar replacement was associated with changes in root morphology and root anatomical traits. • With cultivar succession, the distribution of roots in the topsoil layer decreased significantly, but increased in the subsoil layer. • Optimized root anatomy of modern cultivars facilitated water storage and showed yield superiority. [ABSTRACT FROM AUTHOR]

• Evaluation of drought avoidance and drought tolerance traits during wheat domestication and breeding. • Observed wheat breeding strengthening drought tolerance while eluding drought avoidance. • Identified the need to incorporate drought avoidance into drought tolerant genotypes for future cultivar improvement. Crop tolerance and avoidance are critical adaptation mechanisms to cope with drought stress but they contribute differently to grain yield formation. Little is known about the different roles of these two mechanisms in long-term crop breeding. A meta-analysis was conducted to determine the different effects of drought tolerance and avoidance mechanisms on the drought adaptation of wheat crops. The meta-analysis summarized the results of 283 published papers in international journals, and illustrated that primitive wheat genotypes, including wild, cultivated diploids, tetraploids and old hexaploids, preferentially showed a drought avoidance strategy, as evidenced by large root biomass, small leaf area, and reduced stomatal conductance under water deficits. Modern hexaploid genotypes showed stronger drought tolerance advantages, such as high leaf water potential and osmotic adjustment, with a small root system. The meta-analysis indicated that the breeding process of dryland wheat has been continuously enhancing drought tolerance while weakening drought avoidance. Under severe water deficits, old hexaploid wheat genotypes with drought avoidance characteristics showed lower reduction of aboveground biomass and yield than modern genotypes with stronger drought tolerance features, while under mild and moderate water deficits genotypes with stronger drought tolerance features had higher yields and aboveground biomass. The meta-analysis provide information for making decisions on the direction of modern crop breeding and the implementing of managing practices to cope with drought stress, which frequency and severity is increasing with the advent of climate change. [ABSTRACT FROM AUTHOR]

Overuse of phosphorus (P) fertilizer in maize production in China is causing severe environmental pollution and cropping issues, requiring an integrative P fertilizer strategy that improves P use efficiency (PUE) and sustainable production. This meta-analysis on P fertilizer use for maize cropping in China used 786 paired observations to quantify the effects of P fertilizer management (P fertilizer variety, P application rate, application method) and different soil properties (pH, available P, organic matter) on grain yield, PUE, and the environmental cost. The mean maize grain yield of 8.86 t ha 1 with a PUE of 97.2 kg kg 1 and an environmental cost of 1.51 $ kg 1. There was a linear plus plateau relationship between yield and P application rate under different soil available P and growing regions. No significant differences in yield increase occurred between P fertilizer type or P application rate, except for triple superphosphate and P application rate > 26 kg P ha 1. Significant yield increases with P fertilizer application occurred on soil with pH< 7, 10–20 mg kg-1 soil available P, or > 30 g kg-1 organic matter content. Adopting optimized P fertilizer management in different regions not only enhanced maize yield by 23.3 % and PUE by 39.2 %, but also effectively reduced the P application rate by 12.4–34.1 % and the environmental cost by 24.3 %. Consequently, prioritizing suitable P fertilizer recommendation strategy will significantly benefit the pursuit of sustainable maize production in China and similar regions. [Display omitted] • Maize yield increased with P application rate in a linear plus plateau way. • Soil pH, Olsen-P and organic matter had impacts on yield increases by P application. • Average partial productivity of P fertilizer (PFPP) in China's maize was 97.2 kg kg 1. • For each 10 kg ha-1 increase in P fertilizer, the environmental cost increased by 0.24 $ kg 1. • Rational P strategy increased yield and PUE, and reduced environmental cost. [ABSTRACT FROM AUTHOR]

High yield and grain quality are the targets in wheat production. Plastic sheet mulching has improved wheat grain yield in under dryland agriculture, but its impact on grain quality, particularly grain zinc (Zn) concentration is not well known. Seven-site field experiments were conducted during 2014–2016 on drylands of three provinces in the Loess Plateau of China to examine the effect of plastic sheet mulching on wheat grain Zn concentration under different N applications. A split-plot design was adopted with the two main plots (no mulching and plastic sheet mulching) and the subplots with different N application rate. Measurements of Zn uptake, Zn remobilization, Zn distribution to the grain and bioavailability were made, together with biomass, yield and yield components. Study found plastic sheet mulching reduced the grain Zn concentration, and increased the molar ratio of P/Zn, decreasing the Zn bioavailability. Plastic sheet mulching also increased the aboveground Zn accumulation at anthesis by 14.4 %, the straw Zn accumulation at maturity by 14.8 % and the Zn remobilization to the grain by14.2 % but did not affect the availability of soil Zn. For each 100 kg N ha−1 applied under plastic sheet mulching, the grain Zn concentration, the Zn requirement, the aboveground Zn accumulation and remobilization to the grain increased by 3.6 mg kg−1, 2.8 g Mg−1, 6.6 g ha−1 and 3.8 g ha−1, respectively. Aboveground Zn accumulation at maturity and post-anthesis Zn uptake varied with N rates in a linear-plus-plateau model. The reduction in post-anthesis Zn uptake and Zn harvest index were the factors leading to the decrease in grain Zn concentration under plastic sheet mulching. Consequently, under plastic sheet mulching, a rational N fertilizer strategy should be considered to improve the grain Zn concentration in wheat grown in dryland. • Plastic sheet mulching reduces wheat grain Zn bioavailability. • Post-anthesis Zn uptake and Zn harvest index influence wheat grain Zn content. • Rational N fertilization can improve grain Zn content and bioavailability in wheat. • Grain Zn content increased linearly with glutenin content in wheat grain. [ABSTRACT FROM AUTHOR]

• Wheat cultivars with small root mass in topsoil associate with terminal drought tolerance. • Small root in topsoil improved grain yield and grain N under terminal drought. • The increased availability of soil water during grain filling enhanced post-anthesis biomass and N accumulation. Large distribution of roots in topsoil layers allow more uptake of soil water and nutrients during the vegetative growth, but it may be disadvantageous if soil water deficit develops during the reproductive stage. The relationship between the distribution of roots in topsoil (0–0.4 m) and soil water use, dry matter and nitrogen (N) accumulations, and grain yield was examined in winter wheat (Triticum aestivum L.) with contrasting root size in the topsoil. Two old landraces (CW134 and JM47, larger root length and biomass in the topsoil) and two modern wheat cultivars (CH58 and LH7, smaller root system size in the topsoil), were grown in the field during two seasons (2016–2017 and 2017–2018) under rainfed and irrigation conditions in the semi-arid farmland on the Loess Plateau. Root biomass and root length density (RLD) in topsoil (0–0.4 m) was significantly higher in the old landraces than in the modern cultivars (P < 0.05) under rainfed and irrigation in both seasons (no such difference in subsoil, 0.4–1.0 m). The modern cultivars had significantly higher grain yield, grain N concentration, water-use efficiency (WUE), and 1000-grain weight (P < 0.05). Seasonal water use was similar among all cultivars, but post-anthesis water use was higher in the modern cultivars, particularly under rainfed conditions in both seasons. Root biomass and RLD in the topsoil was positively correlated with pre-anthesis water use, but negatively correlated with after anthesis water use. Post-anthesis water use was closely related to post-anthesis dry matter, N accumulation, yield and WUE under rainfed conditions. To conclude, large distribution of roots in the topsoil had non-advantage for wheat grown under rainfed conditions. The small distribution of roots in the topsoil (characteristics of modern wheat cultivars) enhanced post-anthesis water use, increased post-anthesis dry matter and N accumulation, and hence attained higher grain yield and grain N when grown in the semi-arid environment. [ABSTRACT FROM AUTHOR]