Quantitative trait loci for carbon isotope discrimination are repeatable across environments and wheat mapping populations

Wheat productivity is commonly limited by a lack of water essential for growth. Carbon isotope discrimination (Delta), through its negative relationship with transpiration efficiency, has been used in selection of higher wheat yields in breeding for rainfed environments. The potential also exists for selection of increased Delta for improved adaptation to irrigated and high rainfall environments. Selection efficiency of Delta would be enhanced with a better understanding of its genetic control. Three wheat mapping populations (Cranbrook/Halberd, Sunco/Tasman and CD87/Katepwa) containing between 161 and 190 F(1)-derived, doubled-haploid progeny were phenotyped for Delta and agronomic traits in 3-5 well-watered environments. The range for Delta was large among progeny (c. 1.2-2.3 per thousand), contributing to moderate-to-high single environment (h (2) = 0.37-0.91) and line-mean (0.63-0.86) heritabilities. Transgressive segregation was large and genetic control complex with between 9 and 13 Delta quantitative trait loci (QTL) identified in each cross. The Delta QTL effects were commonly small, accounting for a modest 1-10% of the total additive genetic variance, while a number of chromosomal regions appeared in two or more populations (e.g. 1BL, 2BS, 3BS, 4AS, 4BS, 5AS, 7AS and 7BS). Some of the Delta genomic regions were associated with variation in heading date (e.g. 2DS, 4AS and 7AL) and/or plant height (e.g. 1BL, 4BS and 4DS) to confound genotypic associations between Delta and grain yield. As a group, high Delta progeny were significantly (P < 0.10-0.01) taller and flowered earlier but produced more biomass and grain yield in favorable environments. After removing the effect of height and heading date, strong genotypic correlations were observed for Delta and both yield and biomass across populations (r (g) = 0.29-0.57, P < 0.05) as might be expected for the favorable experimental conditions. Thus selection for Delta appears beneficial in increasing grain yield and biomass in favorable environments. However, care must be taken to avoid confounding genotypic differences in Delta with stature and development time when selecting for improved biomass and yield especially in environments experiencing terminal droughts. Polygenic control and small size of individual QTL for Delta may reduce the potential for QTL in marker-assisted selection for improved yield of wheat.     

人工选择下旱地小麦生长塑性与产量形成特征

旱地小麦在进化过程中经受了自然和人工的双重选择,其中人工选择在品种驯化和改良过程中扮演了关键的角色.本文综述了人工选择下旱地小麦进化特征、生理可塑性、形态可塑性和种群属性演变等几个相对独立、但又相互联系的问题,探讨了旱地小麦适应逆境胁迫的生理生态机理,并勾画了其进化路线.在旱地小麦从二倍体到六倍体的漫长进化历程中,自然选择对小麦适应外界环境起到关键作用;随着人工选择的介入,以产量为主要目标的性状选择不断得到强化,从群体上呈现适应逆境的形态特征.人工选择下旱地小麦的水分及养分利用效率不断提升,生物量分配呈现出地下部减少、地上部增加的分配特征,对密度胁迫和高温胁迫的耐受性不断增强,但单位面积光合速率呈逐渐降低趋势.旱地小麦生产是复杂的群体过程,而非简单的个体反应.人工选择提高了旱地小麦的种群适合度和个体繁殖分配,强化了与环境的协同性,却弱化了其自然种群属性.本文还对旱地小麦的进化图进行了描绘,对气候变化下旱地小麦育种和栽培管理提出几点建议.     

四川盆地稻田多熟高效保护性耕作模式的生态系统服务价值评估

运用生态系统服务功能价值评估方法,对四川盆地稻田保护性耕作条件下多熟高效保护性种植模式进行生态经济评价。结果表明,油-稻-芋模式比油-稻传统耕作种植模式的农产品服务价值高32．42％,固定CO2和释放O2的价值高17．03％;麦-稻保护性耕作模式比麦-稻传统种植模式农产品服务价值高55．21％。固定CO2和释放O2的价值高9．40％。油-稻秸秆还田双免耕模式比油-稻传统耕作种植模式土壤积累有机质的价值高0．23％,农田生态系统维持营养物质循环的价值高12．35％;麦-稻保护性耕作种植模式比麦-稻传统耕作种植模式土壤积累有机质的价值高0．39％,农田生态系统维持营养物质循环的价值高12.81％;稻草覆盖还田后油菜田的农田涵养水分价值增加11．66％,小麦田农田涵养水分价值增加32．63％。     

利用APSIM模型分析不同播期和耕作方式对旱地小麦籽粒干物质积累的影响

黄土丘陵区旱地小麦籽粒干物质积累的准确模拟可为调控小麦生产提供重要的技术支持。本研究利用甘肃省定西市安定区1971—2017年的气象资料和甘肃省定西市安定区凤翔镇安家沟村2016—2017年的大田试验数据,基于APSIM模型对旱地小麦籽粒干物质积累与分配进行模拟,并在模型验证的基础上,定量分析了播期和耕作方式对小麦籽粒干物质积累的影响。结果表明: 3个播期(早播、正常播、晚播)和4种耕作方式(传统耕作、传统耕作+覆盖、免耕、免耕+覆盖)下,籽粒干物质模拟值与实测值间的均方根误差(RMSE)为57.5～143.1 kg·hm^-2,归一化均方根误差(NRMSE)为1.4%～9.9%,模型模拟精度较高。不同播期下,耕作方式对籽粒干物质积累的促进效果排序均表现为: 免耕+覆盖>传统耕作+覆盖>免耕>传统耕作,免耕+覆盖最有利于小麦籽粒干物质积累,而免耕与传统耕作差异不显著。不同耕作方式下,小麦干物质积累过程均表现为早播好于正常播和晚播,晚播对干物质积累的影响较大,积累过程最不理想。     

Marker-assisted pyramiding of eight QTLs/genes for seven different traits in common wheat (Triticum aestivum L.)

Common wheat (Triticum aestivum L.) contributes substantially to global food and nutritional security. Thus, an important goal of wheat breeding is to develop high-yielding varieties with better nutritional quality and resistance to all major diseases. During the present study, in the background of a popular elite wheat cultivar PBW343, we pyramided eight quantitative trait loci (QTLs)/genes for four grain quality traits (high grain weight, high grain protein content, pre-harvest sprouting tolerance, and desirable high-molecular-weight glutenin subunits) and resistance against the three rusts. For pyramiding eight QTLs/genes, four improved PBW343 lines, each carrying different combinations of the desired QTLs/genes (developed by us earlier), were crossed in pairs to produce two single-cross F₁ hybrids. The single-cross F₁ hybrids were intercrossed to produce a double-cross hybrid (DCH). Using marker-assisted selection in five consecutive generations (DCHF₁–DCHF₅), four pyramided lines (PYLs) were selected, each with all the eight desired QTLs/genes in homozygous state. The phenotypic characterization of the progenies of these PYLs suggested that the genetic background of PBW343 was retained in all these four PYLs. Therefore, these PYLs should prove useful in future wheat breeding programs for improving not only the grain quality, but also the durability of resistance against all three rusts. Multi-year/multi-location trials are planned for these pyramided lines to evaluate their potential for release as a next-generation improved version of wheat cv. PBW343 for commercial cultivation.     

Effects of Different Selenium Application Methods on Wheat (<i>Triticum aestivum</i> L.) Biofortification and Nutritional Quality

Mineral nutrient malnutrition, especially deficiency in selenium (Se), affects the health of approximately 1 billion people worldwide. Wheat, a staple food crop, plays an important role in producing Se-enriched foodstuffs to increase the Se intake of humans. This study aimed to evaluate the effects of different Se application methods on grain yield and nutritional quality, grain Se absorption and accumulation, as well as 14 other trace elements concentrations in wheat grains. A sand culture experiment was conducted via a completely randomized 3 × 2 × 1 factorial scheme (three Se levels × two methods of Se application, foliar or soil × one Se sources, selenite), with two wheat cultivars (Guizi No.1, Chinese Spring). The results showed that both foliar Se and soil Se application methods had effects on wheat pollination. Foliar Se application resulted in early flowering of wheat, while soil Se application caused early flowering of wheat at low Se levels (5 mg kg⁻¹ ) and delayed wheat flowering at high selenium levels (10 mg kg⁻¹ ), respectively. For trace elements, human essential trace elements (Fe, Zn, Mn, Cu, Cr, Mo, Co and Ni) concentrations in wheat grains were dependent of Se application methods and wheat cultivars. However, toxic trace elements (Cd, Pb, Hg, As, Li and Al) concentrations can be decreased by both methods, indicating a possible antagonistic effect. Moreover, both methods increased Se concentrations, and improved grain yield and nutritional quality, while the foliar application was better than soil. Accordingly, this study provided useful information concerning nutritional biofortification of wheat, indicating that it is feasible to apply Se to conduct Se biofortification, inhibit the heavy metal elements concentrations and improve yield and quality in crops, which caused human health benefits.     

耕作播种方式对稻茬小麦生长和养分吸收利用的影响

2016—2018年,在四川省广汉市分析了深旋耕播种(DRT)、浅旋耕播种(SRT)和免耕带旋播种(NT)3种耕播方式对稻茬小麦生长和养分吸收利用的影响。结果表明:与DRT相比,SRT和NT处理提高了小麦分蘖、成穗能力。2016—2017年,处理间产量无显著差异;2017—2018年,NT处理产量显著高于DRT,增幅10.9%。处理间干物质积累的差异主要在苗期。NT处理下植株对氮的吸收量高于DRT,平均增幅9.9%,而氮收获指数DRT高于NT;各处理植株磷吸收量差异不显著;NT处理对钾的吸收量显著高于DRT。与传统的深旋耕播种方式相比,免耕带旋播种技术是提高稻茬小麦产量和养分吸收的有效途径。     

Relationship between Carbon Isotope Discrimination and Grain Yield in Spring Wheat Cultivated under Different Water Regimes

In C3 plants, carbon isotope discrimination (△) has been proposed as an indirect selection criterion for grain yield. Reported correlations between △ and grain yield however, differ highly according to the analyzed organ or tissue, the stage of sampling, and the environment and water regime. In a first experiment carried out in spring wheat during two consecutive seasons in the dry conditions of northwest Mexico (Ciudad Obregon, Sonora), different water treatments were applied,corresponding to the main water regimes available to spring wheat worldwide, and the relationships between △ values of different organs and grain yield were examined. Under terminal (post-anthesis) water stress, grain yield was positively associated with △ in grain at maturity and in leaf at anthesis, confirming results previously obtained under Mediterranean environments. Under early (pre-anthesis) water stress and residual moisture stress, the association between grain △ and yield was weaker and highly depended on the quantity of water stored in the soil at sowing. No correlation was found between △ and grain yield under optimal irrigation. The relationship between △ and grain yield was also studied during two consecutive seasons in 20 bread wheat cultivars in the Ningxia region (Northern China), characterized by winter drought(pre-anthesis water stress). Wheat was grown under rainfed conditions in two locations (Guyuan and Pengyang) and under irrigated conditions in another two (Yinchuan and Huinong). In Huinong, the crop was also exposed to salt stress.Highly significant positive associations were found between leaf and grain △ and grain yields across the environments.The relationship between △ and yield within environments highly depended on the quantity of water stored in the soil at sowing, the quantity and distribution of rainfall during the growth cycle, the presence of salt in the soil, and the occurrence of irrigation before anthesis. These two experiments confirmed the value of △ as an indirect selection criterion for yield and a phenotyping tool under post-anthesis water stress (including limited irrigation).     

Anthesis date mainly explained correlations between post-anthesis leaf senescence, grain yield, and grain protein concentration in a winter wheat population segregating for flowering time QTLs

The genetic variability of the duration of leaf senescence during grain filling has been shown to affect both carbon and nitrogen acquisition. In particular, maintaining green leaves during grain filling possibly leads to increased grain yield, but its associated effect on grain protein concentration has not been studied. The aim of this study was to dissect the genetic factors contributing to correlations observed at the phenotypic level between leaf senescence during grain filling, grain protein concentration, and grain yield in winter wheat. With this aim in view, an analysis of quantitative trait locus (QTL) co-locations for these traits was carried out on a doubled haploid mapping population grown in a large multienvironment trial network. Pleiotropic QTLs affecting leaf senescence and grain yield and/or grain protein concentration were identified on chromosomes 2D, 2A, and 7D. These were associated with QTLs for anthesis date, showing that the phenotypic correlations with leaf senescence were mainly explained by flowering time in this wheat population. Study of the allelic effects of these pleiotropic QTLs showed that delaying leaf senescence was associated with increased grain yield or grain protein concentration depending on the environments considered. It is proposed that this differential effect of delaying leaf senescence on grain yield and grain protein concentration might be related to the nitrogen availability during the post-anthesis period. It is concluded that the benefit of using leaf senescence as a selection criterion to improve grain protein concentration in wheat cultivars may be limited and would largely depend on the targeted environments, particularly on their nitrogen availability during the post-anthesis period.     

夏闲期耕作对旱地小麦土壤水分及植株氮素吸收、运转特性的影响

采用大田试验,研究了夏闲期耕作对旱地小麦播种前和各生育期0～300 cm土壤水分、植株氮素吸收和运转特性的影响.结果表明: 夏闲期耕作可提高播种前和各生育期0～300 cm土壤蓄水量,且枯水年效果较好.夏闲期耕作可显著提高各生育期植株氮素积累量、开花期叶片和茎秆+茎鞘氮素积累量、成熟期籽粒氮素积累量,显著提高茎秆+茎鞘氮素运转量及其对籽粒的贡献率、叶片氮素运转量、花前氮素运转量、花后氮素积累量,最终提高氮素吸收效率,以前茬小麦收获后45 d深翻效果较好.夏闲期耕作条件下,土壤水分与花前氮素运转量及籽粒氮素积累量显著相关,且枯水年关系更密切;播种至开花期土壤水分与花后氮素积累量在丰水年显著相关,而枯水年无显著相关关系.夏闲期耕作,尤其是雨后深翻有利于蓄水保墒及植株氮素吸收和转运.     

Recent advances in the genetics underlying wheat grain protein content and grain protein deviation in hexaploid wheat

Wheat is one of the most important global crops and selection for better performance has been ongoing since ancient times. As a quantitative trait controlled by the interplay of several genomic loci and under the strong influence of the environment, grain protein content (GPC) is of major interest in breeding programs. Here, we review the most recent contributions to the genetics underlying wheat GPC and grain protein deviation (GPD, representing the relationship between grain protein content and yield), together with the performance of genomic prediction models characterizing these traits. A total of 364 significant loci related to GPC and GPD are positioned on the hexaploid wheat genome, highlighting genomic regions where significant independent QTL overlap, with special focus on two regions located on chromosomes 3A and 5A. Some of the corresponding homoeologous sequences co-locate with significant independent QTL reported on the B and D subgenomes. Overlapping independent QTL from different studies are indicative of genomic regions exhibiting stability across environments and genotypes, with promising candidates for improving grain quality.     

Relationship between Carbon Isotope Discrimination and Grain Yield in Spring Wheat Cultivated under Different Water Regimes

In C₃ plants, carbon isotope discrimination (Δ) has been proposed as an indirect selection criterion for grain yield. Reported correlations between Δ and grain yield however, differ highly according to the analyzed organ or tissue, the stage of sampling, and the environment and water regime. In a first experiment carried out in spring wheat during two consecutive seasons in the dry conditions of northwest Mexico (Ciudad Obregon, Sonora), different water treatments were applied, corresponding to the main water regimes available to spring wheat worldwide, and the relationships between Δ values of different organs and grain yield were examined. Under terminal (post‐anthesis) water stress, grain yield was positively associated with Δ in grain at maturity and in leaf at anthesis, confirming results previously obtained under Mediterranean environments. Under early (pre‐anthesis) water stress and residual moisture stress, the association between grain Δ and yield was weaker and highly depended on the quantity of water stored in the soil at sowing. No correlation was found between Δ and grain yield under optimal irrigation. The relationship between Δ and grain yield was also studied during two consecutive seasons in 20 bread wheat cultivars in the Ningxia region (Northern China), characterized by winter drought (pre‐anthesis water stress). Wheat was grown under rainfed conditions in two locations (Guyuan and Pengyang) and under irrigated conditions in another two (Yinchuan and Huinong). In Huinong, the crop was also exposed to salt stress. Highly significant positive associations were found between leaf and grain Δ and grain yields across the environments. The relationship between Δ and yield within environments highly depended on the quantity of water stored in the soil at sowing, the quantity and distribution of rainfall during the growth cycle, the presence of salt in the soil, and the occurrence of irrigation before anthesis. These two experiments confirmed the value of Δ as an indirect selection criterion for yield and a phenotyping tool under post‐anthesis water stress (including limited irrigation).     

Yield and yield components of maize and soil physical properties as affected by tillage practices and organic mulching

Maize (Zea mays L.) is an important grains cereal crop. Lots of farmers using tillage and mulching practices influence the final yield, to maintain up with the growing demand for food, fuel and feed. Field experiments were conducted to investigate the effects of tillage practices (i.e. conventional tillage CT, reduced tillage RT, deep tillage DT) and wheat straw mulching (i.e. no mulch and wheat straw mulch of 4, 8 and 12 Mg ha⁻¹, SM0, SM1, SM2 and SM3 respectively) on the growth, yield and yield components of maize and some of soil physical properties. The results showed that compared with RT, DT and CT decreased soil bulk density, as well as led to increase soil water content. Application of mulch treatments increased soil water content. DT and CT have been associated with greater plant height, yield components, grain and biomass yield than RT treatment. Plant height, yield components, grain and biomass yield as well as soil water content increased following mulching treatments. Mulching treatment of SM2 had the largest positive effects on maize yield. DT and CT that have potential to break the compacted zone in soil leading to a better soil environment and crop yield. The application of wheat straw mulch could be an efficient soil management practice for corn production in arid subtropical climate region.     

Genetic dissection of grain yield in bread wheat. I. QTL analysis

Grain yield forms one of the key economic drivers behind a successful wheat (Triticum aestivum L.) cropping enterprise and is consequently a major target for wheat breeding programmes. However, due to its complex nature, little is known regarding the genetic control of grain yield. A doubled-haploid population, comprising 182 individuals, produced from a cross between two cultivars ‘Trident’ and ‘Molineux’, was used to construct a linkage map based largely on microsatellite molecular makers. ‘Trident’ represents a lineage of wheat varieties from southern Australia that has achieved consistently high relative grain yield across a range of environments. In comparison, ‘Molineux’ would be rated as a variety with low to moderate grain yield. The doubled-haploid population was grown from 2002 to 2005 in replicated field experiments at a range of environments across the southern Australian wheat belt. In total, grain yield data were recorded for the population at 18 site-year combinations. Grain yield components were also measured at three of these environments. Many loci previously found to be involved in the control of plant height, rust resistance and ear-emergence were found to influence grain yield and grain yield components in this population. An additional nine QTL, apparently unrelated to these traits, were also associated with grain yield. A QTL associated with grain yield on chromosome 1B, with no significant relationship with plant height, ear-emergence or rust resistance, was detected (LOD ≥2) at eight of the 18 environments. The mean yield, across 18 environments, of individuals carrying the ‘Molineux’ allele at the 1B locus was 4.8% higher than the mean grain yield of those lines carrying the ‘Trident’ allele at this locus. Another QTL identified on chromosome 4D was also associated with overall gain yield at six of the 18 environments. Of the nine grain yield QTL not shown to be associated with plant height, phenology or rust resistance, two were located near QTL associated with grain yield components. A third QTL, associated with grain yield components at each of the environments used for testing, was located on chromosome 7D. However, this QTL was not associated with grain yield at any of the environments. The implications of these findings on marker-assisted selection for grain yield are discussed.     

Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops

Wheat yields globally will depend increasingly on good management to conserve rainfall and new varieties that use water efficiently for grain production. Here we propose an approach for developing new varieties to make better use of deep stored water. We focus on water-limited wheat production in the summer-dominant rainfall regions of India and Australia, but the approach is generally applicable to other environments and root-based constraints. Use of stored deep water is valuable because it is more predictable than variable in-season rainfall and can be measured prior to sowing. Further, this moisture is converted into grain with twice the efficiently of in-season rainfall since it is taken up later in crop growth during the grain-filling period when the roots reach deeper layers. We propose that wheat varieties with a deeper root system, a redistribution of branch root density from the surface to depth, and with greater radial hydraulic conductivity at depth would have higher yields in rainfed systems where crops rely on deep water for grain fill. Developing selection systems for mature root system traits is challenging as there are limited high-throughput phenotyping methods for roots in the field, and there is a risk that traits selected in the lab on young plants will not translate into mature root system traits in the field. We give an example of a breeding programme that combines laboratory and field phenotyping with proof of concept evaluation of the trait at the beginning of the selection programme. This would greatly enhance confidence in a high-throughput laboratory or field screen, and avoid investment in screens without yield value. This approach requires careful selection of field sites and years that allow expression of deep roots and increased yield. It also requires careful selection and crossing of germplasm to allow comparison of root expression among genotypes that are similar for other traits, especially flowering time and disease and toxicity resistances. Such a programme with field and laboratory evaluation at the outset will speed up delivery of varieties with improved root systems for higher yield.     

机械化保护性耕作条件下土壤质量的数值化评价

通过9年的长期田间定位试验研究了陕西关中平原中部冬小麦 夏玉米轮作条件下深松耕（ST）、旋耕（RT）、秸秆还（SR）、免耕（NTS）等保护性耕作措施及传统耕作（TT）对土壤理化性状和作物产量的影响,并采用主成分分析方法进行土壤质量的综合评价.结果表明：与传统耕作相比,保护性耕作模式提高了土壤肥力质量,改善了土壤物理环境条件;显著提高了土壤脲酶和碱性磷酸酶的活性;除秸秆覆盖免耕处理的玉米和小麦产量低于传统耕作外,其他保护性耕作措施均不同程度地提高了作物产量,其中小麦增产13%～28%,玉米增产3%～12%.与传统耕作相比,保护性耕作土壤质量指数提高了19.8%～44.0%.综合考虑经济效应和生态效益,隔年深松、秸秆粉碎联合旋耕作业以及秸秆覆盖联合深松作业不仅能增加作物产量还可改善土壤质量,可在研究区进行推广应用.     

耕作方式及施氮量对砂姜黑土区小麦氮代谢及籽粒产量和蛋白质含量的影响

为明确砂姜黑土区小麦(Triticum aestivum)产量和品质形成的耕作方式及施氮量最优组合, 在大田试验条件下, 以深松、旋耕和常规耕作3种耕作方式为主区, 0、120、225、330 kg·hm^-2 4个施氮量为副区, 研究了不同耕作方式及施氮量组合对小麦拔节后氮代谢、籽粒产量和蛋白质含量的影响。结果表明, 随着生育期的推进, 叶片谷氨酰胺合成酶活性、游离氨基酸含量和可溶性蛋白含量均呈先升后降的趋势, 深松方式配合中高氮处理的峰值在花后10天, 而常规耕作和旋耕的4个施氮处理以及深松的低氮处理峰值多在开花期。与常规耕作和旋耕相比, 深松耕作显著降低了10-40 cm的土壤容重, 提高了土壤总空隙度和根干质量, 有利于中后期根系氮素吸收。耕作方式和施氮量对籽粒产量和蛋白质含量影响显著, 均以深松方式最高。3种耕作方式下小麦产量和蛋白质含量均随施氮量增加而增加, 籽粒产量以深松方式配合330 kg·hm^-2施氮量最高, 而常规耕作和旋耕方式的产量在施氮量为225 kg·hm^-2时达到最大。3种耕作方式下籽粒蛋白质含量均以施氮225 kg·hm^-2最高。因此, 在砂姜黑土区宜采用深松耕作方式配合适宜的施氮量, 以改善土壤条件, 促进根系氮素吸收, 延长叶片功能期, 达到产量与蛋白品质提升之目的。     

Effects of tillage and nitrogen addition rate on nitrogen metabolism,grain yield and protein content in wheat in lime concretion black soil region

Aims The purpose of this study was to determine a suitable combination of tillage method and nitrogen rate to improve wheat (Triticum aestivum) yield and protein content in lime concretion black soil.
Methods Under the field experimental conditions, three tillage methods (subsoiling and rotary tillage, rotary tillage, and conventional tillage) were used as the main treatments, and four nitrogen application rates (0, 120, 225 and 330 kg·hm^–2) were used as sub-treatments. Nitrogen assimilation after jointing stage, grain yield, and protein content were determined in wheat plants to study the effects of different tillage methods and nitrogen application rate on these variables.
Important findings Results showed that the glutamine synthetase (GS) activity, free amino acid content, and soluble protein content in wheat plants initially increased and then decreased during growth. The peaks of GS activity, free amino acid content, and soluble protein content occurred 10 days after flowering in the subsoiling treatment with 225 or 330 kg·hm^–2 nitrogen application rate, and at the flowering stage for other treatment combinations. Compared with the conventional tillage and rotary tillage, the bulk density of 10 to 40 cm soil in the subsoiling treatment was significantly reduced, and the soil total porosity and root dry weight were significantly increased. Tillage method and nitrogen application rate had a significant impact on grain yield and protein content in wheat plants. Grain yield and protein content were highest in the subsoiling treatment. Regardless of the tillage method, the grain yield and protein content both increased with increasing nitrogen application rate. The grain yield in the subsoiling treatment was highest with nitrogen application rate at 330 kg·hm^–2, whereas the outputs of conventional tillage and rotary tillage were peaked at nitrogen application rate of 225 kg·hm^–2. The grain proteincontent was highest at nitrogen application rate of 225 kg·hm^–2 under the three tillage methods. Thus, subsoiling with optimum nitrogen rate should be promoted in lime concretion black soil. Subsoiling increased grain yield and protein quality by improving soil conditions and the absorption of root systems for soil nitrogen.     

Linkage drag constrains the roots of modern wheat

Roots, the hidden half of crop plants, are essential for resource acquisition. However, knowledge about the genetic control of below‐ground plant development in wheat, one of the most important small‐grain crops in the world, is very limited. The molecular interactions connecting root and shoot development and growth, and thus modulating the plant's demand for water and nutrients along with its ability to access them, are largely unexplored. Here, we demonstrate that linkage drag in European bread wheat, driven by strong selection for a haplotype variant controlling heading date, has eliminated a specific combination of two flanking, highly conserved haplotype variants whose interaction confers increased root biomass. Reversing this inadvertent consequence of selection could recover root diversity that may prove essential for future food production in fluctuating environments. Highly conserved synteny to rice across this chromosome segment suggests that adaptive selection has shaped the diversity landscape of this locus across different, globally important cereal crops. By mining wheat gene expression data, we identified root‐expressed genes within the region of interest that could help breeders to select positive variants adapted to specific target soil environments.