Development of unique and novel lines for early-maturing hybrids: moving GEM germplasm northward and westward

Future maize (Zea mays L.) genetic gains are dependent on the incorporation of unique and useful genetic diversity to breeding programs actively improving germplasm and developing cultivars. Our ultimate goal is to increase the genetic diversity currently available in early maturing maize hybrids by developing novel lines that can be utilized competitively in the northern US Corn Belt. A long-term breeding project (EarlyGEM) was initiated to move US Germplasm Enhancement Maize (GEM) germplasm northward and westward. Nine out of 152 breeding crosses were adapted and data from one breeding cross is presented. Five hundred BC₁:S₁ lines derived from (AR16026:S17-66-1-B × ND2000) × ND2000 were advanced, selected, and crossed to several commercial testers for early and late generation hybrid testing. Experiments were arranged in various partially balanced lattice designs and grown across 23 North Dakota (ND) environments. Data showed experimental GEM-derived hybrids had better grain yield (10.4 vs. 9.2 t ha^?1), test weight (72.5 vs. 70.1 kg h L^?1), extractable starch (67.8 vs. 64.2%) and fermentable starch, grain oil (4.3 vs. 3.5%), and grain protein (10.5 vs. 9.4%) when compared to popular hybrids at similar grain moisture at harvest. This is the first research incorporating GEM-derived tropical and late-temperate genetic materials for inbred line development representing a relative maturity (RM) below 90 days. As a consequence of these breeding efforts GEM materials were adapted to the northern US Corn Belt and are not only sources of useful and unique novel genetic diversity but also competitive products for industry use as requests for experimental EarlyGEM lines have been extensive. This research has practical implications with regards to new ways of conducting maize breeding for high latitudes.     

Adaptation of tropical maize germplasm to temperate environments

Maize (Zea mays L.) is one of few crops that can offer significant genetic gains with the utilization of genetic diversity. Genetically broad-based germplasm has the potential to contribute useful and unique alleles to U.S. Corn Belt breeding programs not present in current U.S. genome sequences (e.g. B73, NAM, etc.). Our objectives were to determine if unique tropical genetic materials have been effectively adapted to temperate environments and how their agronomic performance was relative to adapted populations. An important long-term objective of the Iowa and North Dakota maize breeding programs has been, in addition to the typical elite by elite line pedigree selection cultivar development process, to adapt exotic and unique germplasm, maximize their genetic improvement, and develop unique products for breeding and commercial uses. Stratified mass selection methodology for earliness has been utilized for the adaptation of tropical and temperate populations to Iowa and North Dakota environments. This method has allowed screening of up to 25,000 genotypes per population cycle at a rate of one cycle per year. In addition, the estimated cost per year our programs had for the adaptation of each population was less than $2,000 which could successfully be applied in any breeding program across the globe. This cost has been less than 1 % of the total cost for finding minor genes on the same trait. Our results showed the successful adaptation of exotic populations was independent from genetic background. We can speculate there are a few major genes responsible for most of flowering date expression. We encourage the use of technology to target traits according to their genetic complexity. Stratified mass selection at the phenotypic level has been successful. Each of the populations with either 25 of 100 % tropical germplasm are available for anyone who may desire to expand the germplasm base of their breeding programs with tropical germplasm adapted to temperate mid- and short-season U.S. Corn Belt environments.     

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.     

The characterization and assessment of genetic diversity among maize (Zea mays L.) hybrids that are widely grown in France: Chromatographic data and isozymic data

Summary Zein chromatographic and isozyme electrophoretic data were used to characterize 61 hybrids of maize (Zea mays L.) that are of current widespread usage in France. A similar study was also carried out for 88 hybrids that are widely available in the central corn belt of the U.S. Objectives were to 1) investigate the degree to which isozyme and chromatographic data could provide unique hybrid identification; 2) to evaluate the wealth of genetic diversity available among hybrids that are currently cultivated in France and in the U.S.; and 3) to compare the patterns and extent of genetic diversity found in both countries with respect to their registration, breeding, and seed production practices.Isozyme data showed that all French hybrids were unique germplasm. However, numerous hybrids had chromatographic profiles that were identical for 11 major peaks and these hybrids could thus have some common germplasm at least among their female parental lines. Although there was a broad base of isozymic diversity among French hybrids, the amount in cultivation was less since the few most widely used hybrids, which were planted on approximately half the cultivated area, were similar for their isozymic and zein chromatographic profiles. Approximately only 50% of the U.S. hybrids were shown to be unique with the remainder classified into groups; at least some of the hybrids within each group could be genetically identical products. Leading U.S. hybrids were unique germplasm but numerous hybrids that collectively covered a large acreage appeared to encompass a relatively narrow genetic base.For the continued success of agriculture, it will be important to improve breeding, registration, and marketing practices in order to ensure the continued supply of genetically different and improved elite hybrids.     

Combining ability amongst CIMMYT’s early maturing maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) germplasm under stress and non-stress conditions and identification of testers

CIMMYT (International Maize and Wheat Research Institute) Zimbabwe’s early maturing maize program, which aims to supply seed to approximately 4 million hectares of maize area in eastern and southern Africa, lacks adequate information on heterotic relationships among early maturing germplasm and has no early maturing testers for hybrid development. Open-pollinated varieties (OPVs) and hybrids are the products targeted for this region. Among the hybrids, three-way and double-cross hybrids are desired. Thus the use of single crosses as testers would be an appropriate choice for such a breeding program as one could potentially identify three-way combinations during the early generation test. A twelve-parent diallel was formed and crosses evaluated to identify heterotic groups and single-cross testers. Crosses were evaluated under four different environments in Zimbabwe, two optimal, one low nitrogen stress and one drought stress. P5 (an early maturing line from heterotic group A) and CML 395 (a late maturing inbred line from heterotic group B) were used as reference parents to establish heterotic groupings of germplasm used in the diallel. The single cross (P7/P8) was identified as a potential group A tester because of: (a) co-classification of inbred lines into heterotic group A, (b) good yields-9.8 t/ha (optimal), 3.4 t/ha (low nitrogen) and 2.1 t/ha (drought); and (c) good GCA effects for grain yield (0.49 t/ha) of line P7 while line P8 contributed to reduced height and anthesis-silking interval.     

玉米新品种‘裕丰303’的商业育种问题讨论

在大田生产中,‘先玉335’等美系新品种在耐密植、抗倒伏、抗南方锈病、抗大斑病、抗高温热害等方面的能力都较弱。为了通过育种手段解决以上问题,本研究以玉米新品种‘裕丰303’为试验材料,通过对其在国家（黄淮海夏播、东华北中晚熟、西北春播）以及各省区域试验和生产试验中的产量、抗旱性、耐高温热害、耐密性、籽粒品质等品种特性进行分析。结果表明‘裕丰303’不仅具备美系新品种的优良特征特性,还具有耐旱、耐高温热害、抗倒伏、抗南方锈病等性状优势,实现并大幅度超越笔者原定的育种目标。以此为基础,讨论了今后种质扩增、改良、创新的技术路线和避免遗传脆弱性风险出现等相关商业育种问题。强调在育种实践中应高度重视耐高温热害性状和耐旱性状的选育,特别要注重通过不断提升基因型与环境互作的正向超正常表达选育具有广泛适应性的新品种。     

玉米Iodent种质在Suwan材料改良利用中的有效性分析

种质资源狭窄和杂种优势单一,是制约我国玉米产业发展的重要因素之一。拓宽玉米种质基础,培育突破性育种新材料是选育优良玉米杂交种的基础与前提。热带、亚热带种质已经被证明具有较温带种质丰富的遗传多样性,其引入、改良和应用对丰富我国玉米种质多样性具有十分重要的意义。本研究以28份温热玉米自交系、4份Suwan群体来源自交系(QR 273、ZHL 908、T 32和QB 48)作母本,来自Iodent、Reid、PB、Lancaster和塘四平头类群的8个温带玉米自交系作父本的杂交后代为材料,2015年分别在河南郑州和河南华县对28份自交系和32个杂交组合进行农艺性状评价。结果显示,Suwan×Iodent杂交组合的株型、生育期、感光性等与温带地区杂交种相近;而Suwan自交系与其他类群自交系的杂交组合则表现出植株繁茂、抗倒性差、感光性强和生育期太晚等问题。利用Iodent种质早熟、马齿的特性能够有效改良Suwan种质生育期晚、光周期敏感的不足,获得较高的配合力。     

优质蛋白玉米发展回顾与前景展望

优质蛋白玉米（QPM）是过去植物育种领域中取得最意想不到的成就之一，它的赖氨酸和色氨酸含量比普通玉米高，从而改善玉米蛋白质品质，因此其营养价值优于普通玉米。文章回顾了优质蛋白玉米的发展历史以及中国优质蛋白玉米研究的发展历程，提出政府支持，重视科技投入，加强研究力度，实施多学科合作尤其是现代生物技术的引进利用，加强种质资源创新与利用研究，把普通玉米自交系和杂种优势群转育为优质蛋白玉米资源，挖掘新的种质源，探索新的检测方法和应用领域，形成科研——种植——加工业——养殖业产业链联合开发是中国优质蛋白玉米研究的发展方向。     

Assessing the breeding potential of day-neutral converted racestock germplasm in the Pee Dee cotton germplasm enhancement program

The primitive, upland cotton landrace collection represents one of the untapped genetic resources in cotton breeding programs. Efforts to utilize these resources have been slow, but the development of day-neutral converted germplasm lines offers tremendous potential for broadening the genetic base in upland cotton. Using topcross hybrids involving elite germplasm from the unique Pee Dee germplasm enhancement program, we evaluated the breeding potential of a select number of day-neutral converted racestocks. The mean performance of parental lines and F₂ topcross hybrids along with genetic effect estimates indicate that day-neutral converted germplasm lines decreased agronomic performance while increasing fiber quality performance. Results suggest that crosses between day-neutral converted racestocks and elite Pee Dee germplasm lines result in new allelic combinations associated with improved fiber quality performance that interact in a non-additive way. However, it appears that converted racestocks transmit negatively correlated alleles for agronomic performance and fiber quality. These negatively correlated allelic combinations present a major challenge for cotton breeding programs. Future efforts that incorporate DNA based selection methods to identify and fix introgressed segments from converted racestocks and their offspring should enhance the use of the genetic variation present in the primitive racestock germplasm accessions.     

Breeding for provitamin A biofortification of maize (Zea mays L.)

Vitamin A deficiency is widely prevailing in children and women of developing countries. Deficiency of vitamin A causes night blindness, growth retardation, xerophthalmia and increases the susceptibility against epidemic diseases. Among different interventions of overcoming malnutrition, biofortification is the most acceptable and preferred intervention among researchers, growers and consumers. Maize is grown and consumed in those regions where vitamin A deficiency is most prevalent; thus, targeting this crop for provitamin A biofortification is the most appropriate solution. Different breeding strategies including diversity analysis, introduction and stability analysis of exotic germplasm, hybridization, heterosis breeding, mutagenesis and marker‐assisted selection are practised for exploring maize germplasm and development of provitamin A‐enriched cultivars. Genome‐wide association selection and development of transgenic maize genotypes are also being practised, whereas RNA interference and genome editing tools could also be used as potential strategies for provitamin A biofortification of maize genotypes. The use of these breeding strategies for provitamin A biofortification of maize is comprehensively reviewed to provide a working outline for maize breeders.     

Research and field monitoring on transgenic crops by the Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT)

The International Maize and Wheat Improvement Center (CIMMYT) aims to genetically enhance both crops and generate public sector-provided products for the resource poor, e.g., drought tolerant wheat and insect resistant maize, and through international–national partnerships facilitate the acquisition of improved germplasm for non-mandate crops in the cropping systems where maize and wheat thrives; e.g., GM-papaya through a national food security undertaking in Bangladesh. The Center also engages in public awareness campaigns in projects such as Insect Resistance Maize for Africa (IRMA), which includes food, feed and environmental safety, monitoring of resistance and establishment of refugia, non-target effects and gene flow. Monitoring of genetic resources is a wide concern among the centers of the Consultative Group on International Agricultural Research (CGIAR), with an emphasis on the quality of gene banks. Decisions, policies and procedures about monitoring should be science-based, and this requires education, an area where CIMMYT and other CGIAR centers can play an important role. There will be a need to continue to evaluate the need for, and type of monitoring, as new (and unique) products are developed and released in the emergent economies of the world.     

Creation of new maize germplasm using alien introgression from <Emphasis Type="Italic">Zea mays</Emphasis> ssp. <Emphasis Type="Italic">mexicana</Emphasis>

Zea mays ssp. mexicana, an annual wild relative of maize, has many desirable characteristics for maize improvement. To transfer alien genetic germplasm into maize background, F₁ hybrids were generated by using Z. mays ssp. mexicana as the female parent and cultivated maize inbred line Ye515 as the male parent. Alien introgression lines, with a large range of genetic diversity, were produced by backcross and successive self-pollinations. A number of alien introgression lines with the predominant traits of cultivated maize were selected. Genomic in situ hybridization (GISH) proved that small chromosome segments of Z. mays ssp. mexicana had been integrated into the maize genome. Some outstanding alien introgression lines were evaluated in performance trials which showed 54.6% hybrids had grain yield greater than that of hybrid check Yedan12 which possessed 50% Ye515 parentage, and 17.1, 9.9% hybrids had grain yield competitive or greater than those of Nongda108 and Zheng958, which were elite commercial hybrids in China, respectively. The results indicated that some of the introgression lines had excellent agronomic traits and combining ability for maize cultivar, and demonstrated that Z. mays ssp. mexicana was a valuable source for maize breeding, and could be used to broaden and enrich the maize germplasm.     

中国糯玉米wx基因种质资源遗传多样性

Waxy(Wx)基因是众多作物导致糯性突变的关键基因,在玉米作物群体内深入研究Wx基因对中国糯玉米品质育种和种质创新具有重要意义。本研究利用325份(309份来自中国,11份来自泰国和5份来自韩国)糯玉米种质材料做了wx基因突变类型的调查和表观直链淀粉含量(AAC)测定。结果表明, 中国糯玉米的wx基因的遗传多样性很低,主要存在wx-D7和wx-D10两种突变类型,占96.9%;中国北方及韩国的糯玉米wx基因突变类型都是wx-D7类型,南方及泰国糯玉米wx基因突变类型都是wx-D10类型;糯玉米地方品种的wx基因型以wx-D10为主,占78.9%,而商业杂交种和自交系的wx基因型以wx-D7为主,分别占88.7%和86.6%。分析表明,中国糯玉米商业杂交种和自交系的AAC均值较低(小于2.2%)且无显著差异,但地方品种的AAC均值较高;wx-D7基因型糯玉米的AAC均值低且变化幅度较小,而wx-D10基因型糯玉米的AAC均值最高且变化幅度较大。本文还讨论了中国糯玉米主要wx基因型的地理分布、起源以及其他的wx基因突变类型。     

X系新种质利用的技术途径与策略探讨

玉米品种的换代离不开种质的创新,外来种质是我国玉米自交系选育的重要基础材料。本文分析了近年来引进国外优良新种质的优良特征特性,提出了这批新种质的利用途径和选育成功的技术措施。认为合理利用这批新种质将会进一步提升我国瑞得种质和兰卡斯特种质的竞争力。     

CIMMYT和我国玉米种质群体的配合力及杂种优势分析

采用NCⅡ遗传交配设计,以丹340、Mo17、掖478和黄早四为测验种,通过2年1点田间试验,分析27个国内外玉米群体（14个CIMMYT热带、亚热带群体和13个国内群体）的主要性状配合力和产量杂种优势,并划分杂种优势群。结果表明,大多数CIMMYT群体的产量和产量性状配合力及杂种优势明显优于国内玉米群体,以Suwan l、Pob43、Pob21     

三江平原玉米品种的种质基础分析

通过对黑龙江省三江平原1999—2004年6年间种植面积在1万hm2以上的玉米杂交种的种质基础的分析,说明三江平原所应用自交系以国外的兰卡斯特及地方种等血缘为主,应用的亲本材料过度集中,造成玉米种质遗传基础日趋狭窄。因此玉米育种工作应加强基础材料的创新,从而拓宽种质资源,解决玉米育种种质资源缺乏,遗传基础狭窄的问题。     

几种分子标记技术在玉米自交系类群划分中的应用

分子标记技术的开发利用推动了玉米育种的发展,概述了5种常用分子标记SSR、RFLP、RAPD、AFLP、SNP的原理及特点。综述了分子标记技术在玉米自交系类群划分中的应用。     

玉米与玉米近缘种可杂交性研究

本文对玉米与其近缘种及它们的杂交或回交后代的可杂交性进行了研究。结果表明，玉米近缘种的多数材料都能与玉米杂交结实，它们的杂种F1均表现出强的杂种优势和光敏反应；远缘杂交亲和性的母本效应较大，且与物种间遗传距离直接相关。此外，还对玉米近缘材料在玉米遗传育种中的应用进行了探讨。     

Combining ability and testcross performance of drought‐tolerant maize inbred lines under stress and non‐stress environments in Kenya

Drought and poor soil fertility are among the major abiotic stresses affecting maize productivity in sub‐Saharan Africa. Maize breeding efforts at the International Maize and Wheat Improvement Center (CIMMYT) have focused on incorporating drought stress tolerance and nitrogen‐use efficiency (NUE) into tropical maize germplasm. The objectives of this study were to estimate the general combining ability (GCA) and specific combining ability (SCA) of selected maize inbred lines under drought stress (DS), low‐nitrogen (LN) and optimum moisture and nitrogen (optimum) conditions, and to assess the yield potential and stability of experimental hybrids under these management conditions. Forty‐nine experimental three‐way cross hybrids, generated from a 7 × 7 line by tester crosses, and six commercial checks were evaluated across 11 optimum, DS and LN sites in Kenya in 2014 using an alpha lattice design with two replicates per entry at each site. DS reduced both grain yield (GY) and plant height (PH), while anthesis–silking interval (ASI) increased under both DS and LN. Hybrids ‘L4/T2’ and ‘L4/T1’ were found to be superior and stable, while inbreds ‘L4’ and ‘L6’ were good combiners for GY and other secondary traits across sites. Additive variance played a greater role for most traits under the three management conditions, suggesting that further progress in the improvement of these traits should be possible. GY under optimum conditions was positively correlated with GY under both DS and LN conditions, but GY under DS and LN was not correlated. Our results suggest the feasibility for simultaneous improvement in grain yield performance of genotypes under optimum, DS and LN conditions.     

Analyses on the Germplasm Base and Breed Selection Course of Hybrids Maize in Hejiang Institute

笔者通过对黑龙江省农科院合江农科所育成的合玉1号~合玉18号玉米品种选育历程及种质基础的分析，说明合江农科所应用自交系以国外的兰卡斯特（MO17）、垦44、国内冬黄等血缘为主，应用的亲本材料过度集中，造成合江农科所玉米种质遗传基础日趋狭窄。因此玉米育种工作应加强基础材料的创新，从而拓宽种质资源，解决合江农科所玉米育种种质资源缺乏，遗传基础狭窄的问题。