玉米产量-密度关系年代演化趋势的Meta分析

为明确中国玉米产量-密度试验结果的年代演化趋势,进一步探索提高玉米产量的突破方向和理论依据,汇集从1950s到2000s中国玉米产量-密度的文献结果,拟合产量-密度抛物线模型,剔除异常后进行直方图、相关、通径等Meta分析。结果表明,1950s和1960s玉米产量明显低于1970s和1980s,1990s以来产量持续增加,2000s最大,为10.5 t hm^-2,1960s以来年均增益150 kg hm^-2。最佳密度年代均值在4.5~6.8株 m^-2之间,呈现1950s 和1960s<1970s 和1980s<1990s,但是, 2000s却小于1990s。单株产量年代均值在0.08~0.17 kg之间,呈现1950s>1960s和1970s<1980s,且1990s以来持续上升,2000s上升幅度更为明显。1990s以来密度偏离最佳值引起的减产幅度呈现上升趋势。在持续增加密度的同时,通过育种和栽培途径提高单株产量,是玉米更高产的努力方向。     

Changes in the morphological traits of maize genotypes in China between the 1950s and 2000s

Maize (Zea mays L.) morphological traits influence light attenuation within the canopy, and, ultimately, yield. The objectives of this 3-year field study were to: (i) examine the morphological characteristics of specific genotypes using varieties of maize that were widely used in Chinese agriculture from the 1950s to the 2000s; (ii) assess the canopies and yields of maize populations in relation to changes in their morphological characteristics. There were significant decrease on the ear ratio, center of gravity height and leaf angle with improved genotypes regardless of plant density. However, the ear leaves and adjacent leaves appeared to be longer in improved maize varieties. The mean leaf orientation value (LOV) and individual LOVs increased considerably during the time series of the genotypes, but more obvious changes in LOV occurred in the uppermost leaves. The average leaf area (LA) per plant and LA on the ears increased significantly from the 1950s to the 2000s. At the optimum density, current hybrid's canopy architecture was more compact, having short plant height and more upright leaf. The SDLA above or under ear significantly increased with improving genotypes, mainly due to new hybrids allowing the use of more individuals per area and thus increasing leaf area index (LAI). At the highest plant density, new hybrids had the rates of light transmittance (0.04–0.05), low attenuation coefficient (K = 0.47) and gained the highest yield. Leaf angle and LOV were highly correlated with TPAR/IPAR on ear, K, grain yield. Consequently, yield improvement in maize was probably a result of increased plant density tolerance through dependence on changes in leaf orientation characteristics.     

Association of Vertical Root-Pulling Resistance with Root Lodging and Grain Yield in Selected S1 Maize Lines Derived from a Tropical Low-Nitrogen Population

Root lodging and poor soil fertility are major constraints to maize production in the Guinea savannah of West Africa. Vertical root‐pulling resistance is an indicator of the rooting characteristics of maize cultivars and could be used to select cultivars which have higher resistance to root lodging, take up nitrogen efficiently and have high yield. Twenty maize breeding lines were evaluated in the southern Guinea savannah of Nigeria for vertical root‐pulling resistance, yield and root lodging in the 2000 and 2001 cropping seasons. There were significant differences amongst the breeding lines for all the characteristics measured. Vertical root‐pulling resistance correlated positively with grain yield (r = 0.71, P < 0.01). There was a moderate negative correlation between vertical root‐pulling resistance and root lodging (r = ?0.46, P < 0.05). This suggested that selecting for high root‐pulling resistance will improve grain yield and reduce root lodging. There was no significant association between root lodging and grain yield (r = ?0.14, P < 0.22). This was attributed to two factors; weak root systems and high cob weight, both of which caused significant lodging.     

黑龙江省不同年代玉米杂交种产量对种植密度和施氮水平的响应

明确不同年代春玉米生产力对种植密度和氮肥水平的响应特征及其趋势,对高产高效的耐密品种选育和密植抗倒栽培具有重要的理论参考和技术指导意义。本文以黑龙江近50年来第一积温带大面积种植的8个典型春玉米品种为材料,于2009和2010年进行密度和施肥的田间试验,比较不同年代主栽品种生产力演变特征。结果显示,黑龙江省1970s—2000s玉米品种更替过程中,单株生产力与群体产量均明显提高,平均增幅分别为16.96 g 10年^-1和790 kg hm^-2 10年^-1;植株空秆率和倒伏率显著下降,株高、穗位、单株叶面积、穗粒数、千粒重显著提高。随着密度的提高,各年代玉米的单株产量呈显著下降趋势,群体产量呈抛物线形上升,群体最高产量的理论密度增幅为3 507株 hm^-2 10 年^-1;空秆率显著提高,但倒伏率仅1970s和1980s的品种呈递增趋势;株高、单株叶面积、棒三叶面积、穗粒数与千粒重均呈现下降趋势,穗位随密度增加呈显著上升趋势。各年代品种株高、穗位、单株叶面积和千粒重随氮肥水平提高呈增加趋势。在150~450 kg hm^-2的施氮水平范围,随着氮肥水平的提高,各年代品种增产效果不明显。各主要指标在年代、密度和氮肥水平之间存在显著的互作效应。对照东北玉米现有的品种特性、种植密度和施肥现状表明,选育耐密品种和实施密植抗倒栽培的增产潜力大,在现在的施肥水平上进一步提高种植密度是东北春玉米高产增效耕作栽培的技术创新方向。     

Effects of Population Density on the Yield and Yield Components of Leafy Reduced-stature Maize in Short-season Areas

Maize hybrids which yield well, mature earlier and tolerate higher population densities better than the currently available hybrids would be more suitable for production in short-season areas. Leafy reduced-stature maize hybrids, which have only recently become available, have traits which address these criteria. The objective of this study was to evaluate the effects of different population densities (50000, 100000, 150000, and 200000 plants ha⁻¹) on the yield and yield components of one leafy reduced-stature (LRS), one non-leafy reduced-stature (NLRS), and two conventional control hybrids (Pioneer 3979, <2500 CHU; and Pioneer 3902, 2600–2700 CHU) at two locations. All hybrids had the highest kernel number per row and single plant grain yields at the lowest population densities, however, as plant density increased these variables decreased more in the conventional hybrids than the LRS and NLRS hybrids, which demonstrates the greater tolerance of the latter to the stresses associated with higher plant densities. Grain yield was highest for all hybrids, except for NLRS, at 100 000 plants ha⁻¹ with the LRS hybrid and Pioneer 3902 having the highest yields (11.4 vs. 9.8; 12.0 vs. 10.4) at locations 1 and 2 respectively. The LRS hybrid matured before either of the conventional hybrids and out yielded Pioneer 3979 at both sites. Harvest index was not affected by population density and this value was not different among the NLRS and conventional hybrids. However, the harvest index of the LRS hybrid was greater than the others. LRS and NLRS hybrids had lower moisture contents and earlier maturities than conventional hybrids. Rapid growth of the first ear, a higher yield per unit leaf area, and a higher harvest index are indications that LRS hybrids should be more tolerant of higher population densities than the conventional hybrids.     

玉米茎秆弯曲性能与抗倒能力的研究

为探讨不同玉米品种茎秆抗倒伏相关的力学特点, 选用不同抗倒性品种登海3719、京科519和农大108, 设置3.00、5.25、7.50、9.25和12.00万 hm-2 5个密度, 分别于玉米抽雄前和蜡熟期取样, 用WDW3020型电子万能试验机对茎秆第3、5、7节间进行悬臂梁弯曲试验, 同时测定节间形态特征。结果表明, 随密度的增加, 茎秆基部节间直径变细、节间长度增长。品种间有一定的差异, 在3个品种中登海3719的平均直径和长度均低于其他2个品种; 品种间茎秆惯性矩也有较大差异。基部节间弹性模量、最大抗弯应力均随生育进程而增加, 但随群体密度的增加和节位的上升而逐渐降低, 登海3719在两个生育期均为最大, 且随密度增加的下降幅度较小。以京科519最低, 其对密度反应较敏感, 下降幅度大, 易发生倒伏。在玉米抽雄期, 基部节间平均弹性模量为40.0 MPa, 最大抗弯应力为2.8 MPa, 可能是茎秆抗折力学指标的下限。茎秆弹性模量与最大抗弯应力极显著相关, 茎秆直径与弹性模量和最大抗弯应力在抽雄前显著正相关, 而到蜡熟期相关不显著。它们与田间倒伏率呈极显著负相关。茎秆弯曲弹性模量反映茎秆的耐密能力, 茎秆最大抗弯应力反映品种茎秆的抗折能力, 而茎秆直径不能作为评价茎秆抗弯强弱的主要指标。玉米抽雄前期与蜡熟期茎秆抗弯性状的变化规律基本一致, 因此利用抽雄前茎秆基部弯曲力学性能鉴定与评价玉米茎秆抗倒、耐密性是可行的。     

Effects of Population Density and Planting Pattern on the Yield and Yield Components of Leafy Reduced-Stature Maize in a Short-Season Area

Maize hybrids that yield well, mature earlier with low grain moisture contents, tolerate higher population densities and take advantage of narrow row spacings better than the currently available hybrids would be more suitable for production in short-season areas. Leafy reduced-stature maize hybrids, which have only recently been developed, have traits which address these criteria. The objective of this study was to evaluate the effects of different population densities (65 000 and 130000 plants ha^?1) and planting patterns (single rows 76 cm apart and paired rows with 20 cm between rows within a pair of 56 cm between rows of adjacent pairs) on the yield and yield components of two leafy reduced-stature (LRS1 and LRS2), one non-leafy reduced-stature (NLRS), and two conventional corn hybrids (Pioneer 3979, < 2500 CHU; and Pioneer 3902, 2600-2700 CHU) at two locations. All hybrids had higher kernel numbers per row and single plant grain yields at the lower population densities when in paired rows. However, as plant density increased, these variables decreased more in the conventional hybrids than the LRS and NLRS hybrids, which demonstrates the greater tolerance of the latter to the stresses associated with higher plant densities. Grain yield was higher for the two LRS hybrids and the NLRS hybrid at 130000 plants ha^?1 than 65 000 plants ha^?1 Grain yield of conventional hybrids was reduced at the higher population density. The LRS hybrids matured before both conventional hybrids and out yielded Pioneer 3979 at the higher plant population density in both row spacings at both sites. Harvest index was not affected by population density and this value was not different among the NLRS and conventional hybrids. However, the harvest index of the LRS hybrids was greater than the others. LRS and NLRS hybrids had lower moisture contents and earlier maturities than conventional hybrids. Rapid growth of the first ear and higher harvest index values might are indications that LRS hybrids are more tolerant of higher population densities than the conventional hybrids.     

黑龙江省不同年代玉米杂交种氮肥利用效率对种植密度和施氮水平的响应

以黑龙江省近50年来第I积温带大面积种植的8个典型春玉米品种为材料,于2009-2010年进行密度和施肥的田间试验,比较不同年代主栽品种氮肥偏生产力(PFP)、氮肥农学效率(NAE)、氮肥吸收利用率(NRE)及主要器官氮含量对密度和氮素的响应差异。结果显示,1970s-2000s品种更替过程中,PFP和NRE呈递增趋势,增幅分别为3.41 kg kg^-1 10年^-1和2.26个百分点10年^-1。NAE在1970s-1990s呈显著递增趋势,之后呈下降趋势。氮收获指数随年代递增呈显著下降趋势,平均每10年下降1.51个百分点;茎、叶和籽粒氮积累量随年代推进呈显著递增趋势,平均每10年分别递增0.09、0.07和0.12 g株^-1;上述各主要指标在年代、密度和氮肥水平之间存在显著的互作效应。各年代品种的氮肥利用效率均随氮肥水平的提高而显著下降,随密度的增加呈抛物线形变化趋势,最高效率值出现在50 000-70 000株 hm^-2范围内,现代品种的最高氮效率的种植密度高于老品种。各年代品种籽粒、叶片、茎氮素积累量和氮收获指数随密度增加呈显著递减趋势。各年代品种籽粒、茎和叶片氮素积累量随施氮量增加呈增加趋势,施氮量对氮收获指数影响各年代品种表现不同。上述结果表明,品种改良的氮肥增效潜力较大。在现有的品种状况下,增密不仅可以增产,而且可以显著提高肥料效率。     

江苏省粳稻品种近60年演进过程中产量与形态生理特征的变化

以江苏省近60年来各阶段具有代表性的12个粳稻品种(含超级稻)为材料,依据种植推广年代结合株型和基因型将其分为20世纪50年代、60年代、70年代、80年代、90年代和2000年以后6个类型,研究了品种演进过程中产量和形态生理的变化特征。结果表明,随着品种演进产量逐步提高,其原因主要是总颖花量的增加,而这又主要由于每穗粒数的显著增多。自早期的50年代品种,结实率逐步提高,但90年代品种和2000年以后的超级稻品种,结实率有下降的趋势,穗数和千粒重无明显变化。随着品种演进,生物产量和收获指数同步提高,以抽穗后增加的量尤为明显,主要生育期根干重、根冠比、根系氧化力和叶片光合速率显著增加,但现代超级稻品种的根系活力和叶片光合速率在结实期下降较快。品种改良提高了抽穗期总叶面积、有效叶面积、高效叶面积和粒叶比,还增加了穗长、着粒密度、一次和二次枝梗数目。由20世纪50年代到90年代品种,植株高度降低,而2000年以后的超级稻品种显著上升,升至120cm左右。抽穗期顶三叶叶片角度则随品种更替显著降低。上述结果说明随品种演进,粳稻的农艺、生理性状和产量均有明显改良,但超级稻较低的结实率限制了其产量潜力的发挥。     

不同年代玉米品种苗期耐旱性的比较分析

我国北方地区时常发生春旱,严重影响玉米生产。因此苗期耐旱性是玉米育种中需要考虑的一个重要性状。本试验选用20世纪50年代以来玉米品种35个, 包括50年代农家种4个,60年代双交种4个,70年代以后的单交种27个,在旱棚内鉴定苗期耐旱性,调查幼苗的生物量(鲜重和干重), 计算各品种的耐旱系数,分析苗期耐旱系数随年代及年份变化的趋势,并根据耐旱指数对70年代以来的27个单交种进行聚类。结果表明,干旱处理对供试品种生物量的影响显著。我国玉米品种的苗期耐旱性50至60年代快速提高,60年代及70年代以后呈下降趋势,70年代以来的27个单交种可分为3类,耐旱性强杂交种有鲁单50、群单105、农大108、掖单13、掖单4号、郑单2号,耐旱性弱的杂交种有农大3138、农大60、沈单16,其余为中间类型。下一步育种工作的重点之一是在自交系选育中加大干旱压力,为进而培育耐旱的杂交种奠定基础。     

Maize commercial hybrids compared to improved population hybrids for grain yield and agronomic performance

Improved maize (Zea mays L.) populations and population hybrids can both be profitable alternatives to commercial single-cross hybrids as well as good elite sources of diverse inbred lines. The objective of this research was to compare grain yield and agronomic performance between early maturing maize population hybrids and current early maturing commercial single-cross hybrids. This is a consequence of our research program targeted at identifying alternative heterotic patterns for the northern Corn Belt. Improved maize populations and population hybrids (S₀ generations) were evaluated in experiments arranged in randomized complete block and partially balanced lattice designs across 29 environments. Grain yield potential of population hybrids was optimally expressed under irrigated conditions. Data across environments showed that 20% of the population hybrids evaluated were not different (P 0.05) from at least one of the commercial single-cross hybrids for grain yield performance, root lodging, and stalk lodging percentages. The average mid-parent heterosis value across population hybrids from different geographic regions was 20.4% with negative estimates observed in only two population hybrids. Breeding efforts toward elite populations and population hybrids have demonstrated that germplasm improvement is extremely valuable and deserves public funding. These efforts should be supported in order to enable the development of elite sources of diverse inbred lines and the development of improved population hybrids for specific markets (e.g., organic) to increase producer options. Public maize breeding programs utilizing recurrent selection methods for germplasm improvement could address the need. These programs, however, should incorporate extensive testing of population hybrids.     

MS1与MS1-HS两种选择方法的比较研究Ⅱ.遗传方差、配合力及杂种优势

对ZZ4完成了4轮MS1-HS和MS1选择.结果表明,经4轮选择的群体,两种方法均有效地保留了各主要性状的遗传方差.MS1-HS选择的群体遗传方差下降速率更慢,C4群体的单株籽粒产量的遗传方差仅减少3.7%.穗长、穗粗、粒行数、行粒数、出籽率、百粒重的遗传方差的变化与单株籽粒产量一致,MS1C4的遗传方差减少了8%～15%,MS1-HSC4的遗传方差仅减少了4%～15%.株高、穗位高、抽丝期、植株保绿度、抗倒性等相关选择性状的遗传方差的变化与产量性状基本一致.MS1-HS法对改良玉米群体籽粒产量与测验种间的特殊配合力十分有效,呈逐轮上升的趋势;改良群体与测验种综系140间的杂交后代产量平均每轮提高6%,杂种优势平均每轮提高6.9%.两种方法在改良群体产量性状一般配合力方面,均得到了良好的效果.同时,穗部性状及株高、穗位、抽丝期、散粉期、抗性等田间农艺性状的一般配合力也获得了同步改良.通过ZZ4改良群体与6个测验种间杂交组合产量及杂种优势的比较研究,得出ZZ4与黄早四类种质为杂种优势模式对.     

Genetic improvement trends in agronomic performances and end-use quality characteristics among hard red winter wheat cultivars in Nebraska

Evaluation of wheat cultivars from different eras allows breeders to determine changes in agronomic and end-use quality characteristics associated with grain yield and end-use quality improvement over time. The objective of this research was to examine the trends in agronomic and end-use quality characteristics of hard red winter wheat cultivars grown in Nebraska. Thirty historically important and popular hard red winter wheat cultivars introduced or released between 1874 and 2000 were evaluated at Lincoln, Mead and North Platte, Nebraska in 2002 and 2003. An alpha lattice design with 15 incomplete blocks of two plots and three replications was used at all locations. Agronomic (days to flowering, plant height, spike length, culm length, grain yield and yield components, and grain volume weight) and end-use quality (flour yield, SDS-sedimentation value, flour protein content, and mixograph time and tolerance) traits were measured in each environment. Highly significant differences were observed among environments, genotypes and their interactions for most agronomic and end-use quality characteristics. Unlike modern cultivars, older cultivars were low yielding, and less responsive to favorable environments for grain yield and yield components. Semidwarf cultivars were more stable for plant height than traditional medium to tall cultivars. All cultivars had high grain volume weight since it is part of the grading system and highly selected for in cultivar release. Modern cultivars were less stable than older cultivars for SDS-sedimentation and mixing tolerance. However, the stability of older cultivars was attributed to their having weak mixing tolerance and reduced SDS-sedimentation values. The reduced protein content of modern cultivars was offset by increased functionality, as measured by mixograph and SDS sedimentation. In conclusion, breeders have tailored agronomic and end-use quality traits essential for hard red winter wheat production and marketing in Nebraska.     

Plant growth regulator and its interactions with environment and genotype affect maize optimal plant density and yield

Increasing planting density is important to raise maize yield, however, high density often leads to an increase risk of lodging due to dense canopy and weak stem. Maize yield and optimal plant density are increased by applying plant growth regulator compound of ethephon and DA-6, however, we do not know if this compound would interact with location and genotype. In this study, a novel plant growth regulator, as the synthesis of N, N- diethyl − 2 − hexanoyl oxygen radicals − ethyl amine (2-ethyl chloride) phosphonic acid salt (DHEAP), combining the effects of ethephon and DA-6 in one chemical, was developed and tested at three locations, five plant densities (6.75, 8.25, 9.75, 11.25 and 12.75 plants m⁻²) and three cultivars in 2014–2015. This study aimed to quantify the interactions between environment, genotype and management (Appling DHEAP and plant density) on lodging-related optimal plant density and yield. DHEAP significantly increased grain yield by 10.7% due to the increases of kernel weight by 3.2% and kernel number per ear by 4.4%. On average across genotypes and environments, applying DHEAP increased optimum plant density by 6%. The optimal plant density interacted with cultivar, DHEAP and environment. Applying DHEAP reduced lodging percentage by lowering ear height. The yield-lodging relationship was affected by genotype and location. We concluded that maize yield could be enhanced by optimizing plant density, applying DHEAP and cultivar selection, but climatic and environmental differences of locations should be considered.     

1970-2000年代玉米单交种的遗传产量增益分析方法的比较

以田间试验为基础, 对直接种植法的不同方法进行分析, 以期找到适合我国的评估方法, 为遗传产量增益的研究提供理论支持。以1970s–2000s期间大面积推广的杂交种为材料, 分别于2005–2006年(试验1)以及2007–2008年(试验2)在新疆农业科学院和北京顺义试验基地进行。每个试验设置3种密度。依据1970年代单交种在3.0万株 hm^-2密度下的产量与2000年代的单交种在6.0万株 hm^-2密度下的年均单位面积的产量差异, 计算得到1970s–2000s期间我国玉米遗传产量年增益速率为94.7 kg hm^-2。在7.5万株 hm^-2密度下, 2000年代单交种较1970年代单交种的产量增值是遗传因素作用的结果。1970年代单交种在1.5万株hm^-2密度下的产量与2000年代单交种在7.5万株 hm^-2密度下的产量差值是育种与栽培共同作用的结果。由二者的比值得到育种对总产量增益的贡献率为52.9%。Duvick的直接种植法适用于我国评估遗传产量增益速率, Tollnaar的试验设置方法适用于评估我国玉米遗传贡献率。     

高密度对甘肃黄灌区玉米品种农艺性状和产量的影响

选择4个玉米品种,设置3种密度,于2015-2016年在甘肃中部沿黄灌区种植试验得出：同一品种在不同密度下的农艺性状和产量存在差异。对宁玉524、辽单588、高玉818、先玉335的各农艺性状和产量构成因素在密度9.75万、11.25万、12.75万株/hm ²处理下两年测得的数据均值进行了分析比较,发现随着种植密度的增大,玉米的农艺性状和产量出现趋向性变化。表现为玉米的空秆率、倒伏率、株高、穗位高和产量随着密度的增加而增加;茎粗、穗粗、穗长、穗粒数和百粒重随密度增加有所减小。其中空秆率、茎粗、穗粗、穗长、穗粒数和产量差异显著,高种植密度对他们有显著的影响。     

不同年代中籼水稻品种的产量与氮肥利用效率

本研究旨在探明中籼水稻在品种改良过程中产量与氮肥利用效率的变化特点。以江苏省近70年来不同年代在生产上广泛应用的12个代表性中籼水稻品种(含杂交稻组合)为材料,依据应用年代将其分为20世纪40—50年代、60—70年代、80—90年代和2000年以后4个类型,设置0 N(全生育期不施氮)、MN(全生育期施氮210 kg hm–2)和HN(全生育期施氮300 kg hm–2)3个施氮量处理,研究其产量、氮肥利用效率及其生理特性。结果表明,随品种应用年代的演进,不同年代中籼水稻品种的产量和氮肥利用效率均获得较大提高。2000年以后的品种(超级稻)产量和氮肥利用效率较高,根系性状和叶片光合特性以及氮代谢相关酶活性强是其重要生理基础。超级稻抽穗后根系氧化力和剑叶光合速率下降的幅度较大可能是导致超级稻结实率较低的一个重要原因。提高灌浆中后期超级稻的根系氧化力和剑叶光合速率,有望提高超级稻的结实率。     

Root Morphology of Maize and Its Relationship to Root Lodging

Crown root traits of maize ( Zea mays L.) such as number and diameter are the most easily accessible root traits. Their impact on root lodging resistance is little documented. We evaluated 28 flint x dent hybrids at one location for 2 years for crown root traits and for lengths of internodes. Plants were grown at normal and at supraoptimal density. A maximum number of crown roots was observed at the fifth and sixth nodes, above ground internodes 8-10 had maximum lengths. After a cool wet year maximum internode length or numbers of roots per node were found at higher tiers. A supraoptimal plant density caused an increase in lengths and a decrease in root numbers at upper internode and node levels. Crown root morphology and histology were studied at normal plant density in one growing season. From the lowest to the highest node level, root diameters increased steadily, whereas the number of late (large) metaxylem vessels in crown roots showed a strong increase at upper nodes. The diameters of metaxylem vessels increased already strongly at lower node tiers. All data were correlated with the root lodging counts from 42 hybrid tests in northern and southern Germany. In the warm year, at normal plant density, length of internodes 6 and 8 were correlated significantly positively with root lodging in about 25 % of all cases. Number of metaxylem vessels in roots at node 6 were significantly negatively correlated with root lodging in more than 20 % of all cases. Specific morphological and histological traits seem to indicate root lodging. However, their expression depends to a great extent on environment which lessens their value for selection.     

Response to long-term selection in early maturing maize synthetic varieties

Long-term continuous selection is essential for germplasm improvement. However, choice of germplasm for long-term genetic improvement might limit the success of germplasm enhancement programs. The objective of this research was to report the response to long-term selection in early maturing North Dakota (ND) synthetic varieties. We wanted to determine whether the performance of three ND maize synthetic varieties was improved by long-term mass selection (M) and if the performance of one of them was improved by long-term modified ear-to-row (MER) selection. The evaluation of long-term selection response was performed at two plant densities. An experiment in a randomized complete block design with split-plot arrangement was used to evaluate NDSM(M), NDSAB(M), NDSCD(M), and NDSAB(MER) under 75,000 and 42,500 plants per hectare across seven environments. Long-term mass selection for grain yield and stalk lodging resistance in NDSM(M), NDSAB(M), and NDSCD(M) was not successful, since there were no significant changes in grain yield or stalk lodging in these populations at either low or high densities. On the other hand, long-term modified ear-to-row selection was effective for grain yield improvement in NDSAB(MER). Grain yield increased non-linearly from 3.9 Mg ha⁻¹ in cycle 0 to 5.0 Mg ha⁻¹ in cycle 12 at a rate of 2.5% per cycle. Interaction between plant density and genotype was not detected even though selection was performed at relatively low densities (20,000 plants ha⁻¹ for mass selection and 50,000 plants ha⁻¹ for ear-to-row selection). The confirmation of a lack of interaction between plant density and genotype suggests that selection at low plant densities might still be able to provide high-density stress resistance through density-independent genotypes, allowing progeny testing across multiple locations with better accuracy and fewer resources. Selection methods that emphasize both additive and dominance effects such as full-sib recurrent selection are recommended to maximize genetic improvement of advanced population cycles of early maturing synthetics.     

种植密度对苦荞麦抗倒伏特性及产量的影响

为了明确苦荞麦抗倒伏特性和适宜的种植密度,提高产量,以‘西荞1号’苦荞麦为材料,研究了不同种植密度对苦荞麦抗倒伏特性及产量的影响。结果表明：种植密度大小显著影响茎秆和根系形态,随着种植密度的增大,田间透光率降低,株高和节间长度增加,主根长、一级侧根数和根体积减少,倒伏率增加,产量呈先升高后降低的变化趋势。相关分析发现,苦荞麦茎秆和根系的特征与植株的抗倒伏特性密切相关。株高和节间长度与茎秆强度呈显著的负相关关系,与倒伏率则呈显著的正相关关系。适宜的种植密度（9×10⁵~12×10⁵株/hm²）能够减少荞麦倒伏的发生,提高抗倒能力,增加群体产量,值得推广应用。