Protein quality and endosperm modification of quality protein maize (Zea mays L.) under two contrasting soil nitrogen environments

Quality protein maize (QPM) breeding involves the combined use of the opaque-2 (o2) gene and the genetic modifiers of the o2 locus to develop cultivars with modified kernel endosperm, and increased concentrations of lysine and tryptophan. This study was designed to assess grain yield performance, endosperm modification, and protein quality and quantity under two contrasting soil nitrogen environments. A 15-parent diallel cross was evaluated under one low nitrogen stress and one optimal nitrogen environment each at Harare (Zimbabwe) and Bako (Ethiopia). Most QPM hybrids showed higher protein quality levels than the best non-QPM check under both conditions. Protein concentration tended to vary across nitrogen levels, but not endosperm type. Significant differences were found for the test of main effect (nitrogen-level) for endosperm modification and tryptophan concentration. This indicated that QPM maintains quality even under low soil nitrogen, a widespread condition in Africa. General combining ability (GCA) mean squares were highly significant for most protein quality traits for each environment and across environments whereas specific combining ability (SCA) mean squares were not significant in most cases. This indicated that additive gene effects were primarily responsible for variation of most traits evaluated and hence progeny performance can adequately be predicted on the basis of parental performance. Inbred lines P2, P4 and P12 had desirable GCA effects for endosperm modification while P1 and P3 had the best GCA for tryptophan concentration in grain. The current study suggests that hybrids with desirable endosperm modification, protein quality and stable performance under low nitrogen stress and optimal conditions can be produced with careful selection.     

优质蛋白玉米育种研究进展

普通玉米蛋白质品质差,以改良玉米蛋白质品质为目标的优质蛋白玉米(QPM)育种一直是玉米研究的重要课题。本文简要回顾了利用o2基因改善玉米蛋白质品质的育种历程,重点介绍了QPM的营养价值、遗传基础、种质选育和应用以及分子标记应用于QPM辅助育种,分析了目前QPM种质遗传基础狭窄、杂种优势研究滞后和QPM品种抗逆性差、适应性窄等问题,提出了针对这些问题的解决策略,并展望了QPM的重大应用前景。     

不同品种、密度、肥料对甜糯玉米产量的影响研究

根据正交设计原理,对甜糯玉米的产量在品种、密度、肥料配比等三个因素影响下的变化进行了研究,结果表明三因素对甜糯玉米鲜穗产量的影响效果依次为:品种、密度、肥料;在一定范围内,甜糯玉米鲜穗产量随密度的升高而增加;适量施用K肥可以提高产量;并找到了适宜本地的甜糯玉米高产栽培措施的优化组合.     

Evaluation of the Lime-Cooking and Tortilla Making Properties of Quality Protein Maize Hybrids Grown in Mexico

Eleven experimental and three commercial white quality protein maize (QPM) hybrids and two regular endosperm controls were planted at Celaya, Guanajuato, Mexico with the aim of comparing grain physical characteristics, protein quality, lime-cooking and tortilla making properties. All genotypes were planted under irrigation using a density of 80,000 plants/ha and fertilized with 250 kg N-60 P-60 K per hectare. When compared with the controls these QPM genotypes had lower test (77.4 vs. 76.5 kg/hL) and 1,000 kernel weights (327 vs. 307 g), softer endosperm texture (2.5 vs. 1.8 where 1 = soft, 2 intermediate and 3 hard endosperm), lower protein (10.0 vs. 8.0%), higher nixtamal water uptake after 30 min lime-cooking (50.0 vs. 53.1% moisture) and lower pericarp removal scores. The lower thousand-kernel weight and softer endosperm texture observed in the QPM genotypes lowered the optimum lime-cooking time as estimated with regression equations. Most QPM genotypes had higher amounts of lysine, tryptophan and albumins/globulins when compared with the controls. QPMs HEC 424973, HEC 774986 and HEC 734286 had the best grain traits for nixtamalization and therefore the best potential for industrial utilization. The commercial use of these QPM hybrids should benefit Mexicans who depend on tortillas as the main staple.     

玉米品质相关的opaque基因研究进展

玉米中的opaque突变体改变了胚乳的蛋白特性,导致胚乳表现柔软且不透明的粉质状。粉质胚乳的高赖氨酸营养特性引起人们的极大关注,研究人员先后发现了13个opaque胚乳突变体,只有o2的分子机理研究较为清楚,对提高赖氨酸含量的作用最大。为了研究胚乳中储藏物质合成、装配、转运的调控机理,从而将这些有益突变基因应用于农业生产,研究人员继而发现了多个胚乳修饰的主效位点及基因(Opm)。本文综述玉米opaque突变体及相关基因的研究进展,对当前育种中利用该类基因培育优质蛋白玉米(QPM)的研究状况进行分析,为高赖氨酸玉米的分子标记辅助选择(MAS)和基因聚合育种提供参考。     

在构建QPM近等基因系过程中对回交群体的SSR标记选择

优质蛋白玉米(QPM)遗传基础狭窄,以普通玉米自交系为遗传背景培育opaque-2近等基因系是QPM种质改良的重要途径。本文利用SSR标记技术,以opaque-2基因序列为背景开发的特异SSR引物phi057和umc1066作为标记,对构建中的95个QPM近等基因系回交群体BC1F1和BC2F1进行目标基因选择。结果表明,SSR标记phi057对大多数回交群体中的opaque-2基因的选择是有效的;在少数回交群体,如(多黄29×CA335)×多黄29,SSR标记phi057和umc1066不能区分单株间的基因型变异,针对这些材料,需要进行更深入的研究或开发新的SSR。     

玉米种质改良与相关理论研究进展

自上世纪70年代以来,优质、抗逆、高配合力和适应性广的新种质匮乏,已成为影响玉米商业育种进一步发展“的瓶颈”。生产用种质的遗传脆弱性受到普遍关注,种质扩增、改良与创新成为作物育种研究最重要的发展方向。综述了CIMMYT和美国玉米遗传资源的搜集、评价、改良和利用情况,玉米遗传多样性的演变趋势与动力,杂种优势群和杂种优势模式研究进展,群体改良理论和技术的新发展及对杂种优势遗传机理的探索。Hallauer于2003年提出的两个杂种优势列(heteroticalignment)的概念,把对玉米杂种优势模式的认识从温带种质扩展到所有生态类型,为玉米种质扩增、改良和创新奠定了理论和方法学基础。两个群体间的相互轮回选择改良技术,是把种质资源大规模推向杂交育种应用的关键步骤。     

辅助选择优质蛋白玉米种质的ELISA方法

基于玉米胚乳中赖氨酸含量与EF-1α含量呈显著正相关,利用ELISA技术定量检测胚乳中EF-1α含量,进而估测胚乳中赖氨酸含量,建立了辅助选择优质蛋白玉米种质的ELISA技术体系.通过对653份QPM家系的检测,表明该方法具有简便、快速、准确的特点,可有效辅助选择优质蛋白玉米种质。     

Use of SSR data to determine relationships and potential heterotic groupings within medium to late maturing Iranian maize inbred lines

Information on germplasm diversity and relationships among elite materials is fundamentally important in crop improvement. The main objectives of our study were to: (1) determine the level of genetic diversity within and relationships among the most commonly used medium to late maturing Iranian maize inbred lines using simple sequence repeat (SSR) markers, and to (2) suggest heterotic groups among the lines using genetic distance as measured by the SSR markers. Fifty-six inbred lines, which are the most commonly used in maize breeding programs in Iran, and two lines from CIMMYT, Mexico (used as checks) were fingerprinted with 46 SSR markers. A total of 225 alleles were detected. The UPGMA clustering grouped the Iranian inbreds into four clusters (in addition to one group which included only the CIMMYT control lines), which were consistent with the pedigrees or known information about source materials. The highest distance was found between the cluster of Reid Yellow Dent related lines and the cluster of Lancaster Sure Crop related lines, and this pattern has produced some of the highest yielding hybrids in Iran. Other heterotic patterns based on the SSR markers are suggested, but must be field tested to confirm what appears to be promising alternative heterotic patterns.     

青饲(贮)玉米育种与优质蛋白玉米种质的商业化创新利用

结合近30年来我国优质蛋白玉米(QPM)的发展演变,通过对国外青饲(贮)玉米部分标准的分析与国内优质蛋白玉米(QPM)、青饲(贮)玉米发展现状的研究,提出促进我国优质蛋白玉米种质的经济实用化(商业化)创新利用,加快青饲(贮)玉米、粮饲型玉米育种发展步伐的优先序:青饲(贮)玉米--粮饲型玉米--优质玉米--优质蛋白玉米。     

Nutritive quality and energy yield of high oil,opaque-2 and waxy maize hybrids compared to normal maize hybrids

Grain yield, chemical composition, protein quality and digestible energy were measured for 18 maize varieties (opaque-2, high oil, waxy hybrids, normal hybrids) cultivated in Yugoslavia. Protein quality assessment was based on amino acid composition, and true protein digestibility, biological value, net protein utilization and utilizable protein as determined in nitrogen balance experiments with rats. The protein concentration in dry matter varied from 8.63–18.81% while the fat concentration varied from 4.45–16.13%. There were only minor differences in ash and crude fibre, while starch and sugar varied inversely to fat and protein concentration. Lysine levels were approximately 30% higher for the opaque-2 varieties compared with normal maize, while leucine levels were about 30% lower. Yields were extremely high for all varieties with the highest value being 10.3 tonnes/ha. Due to the high yields, protein production/ha was high in range of 822–977 kg. This resulted in high yields of amino acids/ha. Protein utilization was very high in the opaque-2 varieties, which had the highest lysine contents. The biological values were close to 80 in these varieties, whereas they were only 60–65 in the normal maize varieties.     

Protein quality evaluation of sprouted maize

Protein, lysine, tryptophan, crude fibre (CF) and neutral detergent fibre (NDF) of sprouted, normal and hard endosperm opaque-2 (QPM) kernels increased, whereas in vitro protein digestibility (IVPD) decreased substantially up to five days of germination. Following the removal of radicles alone or both radicles and plumules from sprouted kernels, IVPD improved at all the stages of germination. However, the contents of lysine and tryptophan were not affected significantly. For some stages of germination, these amino acids decreased slightly. In sprouted normal kernels, IVPD was higher whereas protein, lysine and tryptophan content was lower than that of sprouted QPM kernels respectively at all the stages of germination. In four days old sprouted normal kernels, after the removal of both radicles and plumules biological value (BV), net protein utilization (NPU) and utilizable protein (UP) increased over non-sprouted kernels whereas true digestibility (TD) reach at par with non-sprouted kernels.     

郑单958带给我们的创新思路和发展机遇

玉米商业育种要求协调高产与稳产的关系,缩小遗传产量与实际产量之间的差距,就要对育种材料和技术路线做出新的选择。循环育种策略的实践基础是统一和简化的杂种优势模式。商业育种满足生产栽培技术进步对品种的需求,追求高效率不断地培育创新型新杂交种,就要采用高密度育种策略。     

Assessing the relationship between endosperm type and grain yield potential in sorghum (Sorghum bicolor L. Moench).

Sorghum hybrids with waxy endosperm (either homozygous or heterozygous waxy) have lower grain yield potential compared to non-waxy endosperm hybrids. The cause of this yield reduction is not known. From a genetic perspective, the yield reduction could be due to pleiotrophy or genetic linkage between the wx locus and other loci that influence grain yield. The specific cause of the relationship is important because an effective breeding program can alleviate the problem if it is due to linkage. The objective of this study was to determine whether linkage or pleiotrophy is causing the negative relationship between grain yield and waxy endosperm. From each of two F₂ breeding populations segregating for waxy endosperm, between 40 and 50 inbred lines were derived, with equal numbers of waxy and non-waxy endosperm lines. No selection for yield was practiced during the development of these lines. The lines from these two populations and a set of testcross hybrids (derived from one population) were evaluated in four environments in Texas from 1998 to 2000. Across all tests and environments, the combined yield of the waxy genotypes was 17% lower than non-waxy genotypes. While yields were lower in waxy genotypes, analysis of the individual inbred lines and hybrids revealed that several waxy inbred lines were not statistically different from the best non-waxy inbreds. These results imply that selection of high yielding waxy genotypes is possible, but a significant breeding emphasis on their development is required to effectively identify those genotypes.     

优质蛋白玉米的分子标记辅助选择

综述了应用于优质蛋白玉米种质辅助选择的分子标记,提出了优质蛋白玉米的分子标记辅助选择策略;通过对回交家系赖氨酸分析和SSR分子标记检测结果,对该技术的可靠性进行了验证;考虑到成本核算和可操作性,认为该分子标记辅助选择技术,应用于育种实践是非常经济有效的。     

Downy mildew resistance in maize (Zea mays L.) across Peronosclerospora species in lowland tropical Asia

Downy mildew (DM) is one of the most destructive diseases of maize in the humid sub-tropical and tropical regions of Asia. The most effective and efficient way of managing losses due to DM is to develop durable host-plant resistance in Asian maize across different DM pathogens. We assessed resistance in released DM (P. zeae) resistant CIMMYT maize lines (CMLs) against Peronosclerospora sorghi and Perenosclerospora heteropogoni to develop DM resistant (DMR) maize germplasm with a broad-spectrum of resistance, and identify and further improve new sources of DMR maize germplasm for use in regional breeding programs targeting DM-prone environments. Data indicated that out of 19 DM resistant CMLs, four (CML-433, 465, 466 and 472) were resistant and 15 susceptible to P. sorghi. Screening of new inbred lines from CIMMYT-Asia (CA) resulted in identification of a set of yellow maize lines with good level of DM resistance (disease score – 0.0–25%). However, the high quality protein maize (QPM) lines derived from CIMMYT Population 61 and bi-parental pedigree crosses between elite QPM lines showed very poor resistance to DM. Progenies of the bi-parental population developed by crossing DMR (P. sorghi) CA lines showed further enhanced levels of resistance to both P. sorghi and P. heteropogoni. The study resulted in identification of 10 new inbred lines, in addition to the 4 released CMLs, offering consistent high resistance to both the DM pathogens. Promising bi-parental populations (13) with combined DM resistance and other desirable agronomic traits were identified for the extraction of a new generation of DMR lines with broad-spectrum DM resistance and other commercial traits. Comparison of genotypic response under different screening methods/DM species clearly indicated that the glasshouse-based sandwich method of screening against P. sorghi was the best method for identifying promising genotypes with a high level of DM resistance that were also resistant to DM under field conditions for both the species. However, the highly controlled conditions used for sandwich screening, which is most favourable for disease development, resulted in high disease pressure potentially masking the identification of genotypes with a moderate level of DM resistance.     

两个热带玉米群体的基因效应分析

试验以2个CIMMYT热带群体Pob 25和Pool 26为基础材料,以丹340、掖478及其杂交种F1(掖单13)为测验种,采用三重测交(TTC)设计,对两群体各性状进行了基因效应分析,在两群体中均发现了部分性状存在显著的上位性效应,并提出了各类上位性分量的可能利用途径,为两群体的遗传改良打下了基础。     

国家玉米主产区预试品种的SSR分析Ⅱ. 预试品种的遗传多样性

应用SSR分子标记方法对2005年国家玉米主产区预试参试品种进行了聚类分析,并根据聚类分析结果分析了参试品种的遗传多样性。结果表明,参试品种被分成6类,88.6%的品种分布在相邻的第三和第四类中,这两类囊括了全部优良参照品种和12/13的优良新组合,反映出最新育成的和生产上正在广泛种植的玉米品种存在严重的种质趋同现象;黄改系种质成为当前国内应用最多、在新品种遗传组成中占比重最大的种质。研究还表明,采用SSR方法进行杂交种的聚类分析能够客观地分析和评价我国玉米种质遗传多样性的现状。     

籼粳交杂种不同灌浆期稻米缬氨酸含量的发育遗传

采用可以估算不同发育时期基因累加效应和特定发育时期净遗传效应的遗传模型和统计分析方法,研究了不同环境条件下籼粳交稻米灌浆过程中缬氨酸含量的发育遗传规律。结果表明,控制籼粳交稻米缬氨酸含量表现的基因在稻米多数发育时期均有表达,其中以颖花开花受精后第8~14天表达量最大。遗传率分析揭示缬氨酸含量在稻米5个不同发育时期的母体和细胞质普通遗传率及其相应的环境互作遗传率均较高,育种低世代进行单株选择可以提高稻米缬氨酸含量的育种效率。亲本遗传效应分析表明,浙38A、浙农8010A、金23A和中9308等4个亲本有利于增加籼粳交稻米的缬氨酸含量,其中浙38A受环境影响最小,可应用于配制高缬氨酸含量的杂交稻新组合。     

改良HS相互轮回选择与玉米育种

群体改良是现代玉米育种的基础环节,非常重要,在国外被称作前育种(Pre-breeding),是玉米种质改良创新的核心技术.为了适应玉米杂交育种的需要,必须把群体改良技术转向相互轮回选择.CIMMYT已经全面转向相互轮回选择,而沿用了几十年的全同胞、半同胞、S1、S2及改良穗行法等已很少使用.美国、印度、津巴布韦、巴西等国也逐渐转向相互轮回选择.文章详细介绍了CIMMYT重点利用的改良HS相互轮回选择技术,并提出了对方法的优化及与育种结合的方案。