Quantitative trait loci for aluminum resistance in wheat

Quantitative trait loci (QTL) for wheat resistance to aluminum (Al) toxicity were analyzed using simple sequence repeats (SSRs) in a population of 192 F₆ recombinant inbred lines (RILs) derived from a cross between an Al-resistant cultivar, Atlas 66 and an Al-sensitive cultivar, Chisholm. Wheat reaction to Al was measured by relative root growth and root response to hematoxylin stain in nutrient-solution culture. After screening 1,028 SSR markers for polymorphisms between the parents and bulks, we identified two QTLs for Al resistance in Atlas 66. One major QTL was mapped on chromosome 4D that co-segregated with the Al-activated malate transporter gene (ALMT1). Another minor QTL was located on chromosome 3BL. Together, these two QTLs accounted for about 57% of the phenotypic variation in hematoxylin staining score and 50% of the variation in net root growth (NRG). Expression of the minor QTL on 3BL was suppressed by the major QTL on 4DL. The two QTLs for Al resistance in Atlas 66 were also verified in an additional RIL population derived from Atlas 66/Century. Several SSR markers closely linked to the QTLs were identified and have potential to be used for marker-assisted selection (MAS) to improve Al-resistance of wheat cultivars in breeding programs.     

家畜抗性等级性状的QTL定位方法

在广义线性模型的框架内模拟研究了家畜抗性等级性状的QTL定位方法,QTL参数的估计采用最大似然方法,比较了阈模型方法与一般线性方法的QTL定位效率,并对影响等级性状QTL定位效率的主要因素（QTL效应、性状的遗传力）进行了模拟研究,实验设计为多个家系的女儿设计,资源群体大小为500头。研究结果表明：在QTL位置参数估计及检验功效方面,阈模型方法具有一定的优势,对抗性等级性状QTL定位的功效也高于线性方法。另外,性状遗传力和QTL效应的大小对QTL定位的准确度也有直接的影响,随着性状遗传力QTL效应的     

作物数量性状基因研究进展

分子生物技术的发展对作物数量性状基因（QTL）研究提供了条件,不同的定位群体各有其特点,相继出现的QTL定位也逐步完善。大量的研究揭示了QTL的基本特征,剖析了重要农艺4性状的遗传基础,给作物遗传改良带来了新的策略,不断深入的研究已经完成了特定的QTL的精细定位和克隆。本从QTL的定位群体,定位方法,研究现状,精细定位与克隆,以及QTL利用等方面对作物数量性状基因的研究进行了综述。     

Molecular mapping of a quantitative trait locus for aluminum tolerance in wheat cultivar Atlas 66

Genetic improvement of aluminum (Al) tolerance is one of the cost-effective solutions to improve wheat (Triticum aestivum) productivity in acidic soils. The objectives of the present study were to identify quantitative trait loci (QTL) for Al-tolerance and associated PCR-based markers for marker-assisted breeding utilizing cultivar Atlas 66. A population of recombinant inbred lines (RILs) from the cross Atlas 66/Century was screened for Al-tolerance by measuring root-growth rate during Al treatment in hydroponics and root response to hematoxylin stain of Al treatment. After 797 pairs of SSR primers were screened for polymorphisms between the parents, 131 pairs were selected for bulk segregant analysis (BSA). A QTL analysis based on SSR markers revealed one QTL on the distal region of chromosome arm 4DL where a malate transporter gene was mapped. This major QTL accounted for nearly 50% of the phenotypic variation for Al-tolerance. The SSR markers Xgdm125 and Xwmc331 were the flanking markers for the QTL and have the potential to be used for high-throughput, marker-assisted selection in wheat-breeding programs.     

Mapping Quantitative Trait Loci for Post-Anthesis Dry Matter Accumulation in Wheat

Post-anthesis photoassimilation is very important for wheat （Triticum aestivum L.） grain filling. The aim of the present study was to map quantitative trait loci （QTL） for post-anthesis dry matter accumulation （DMA）. A set of 120 doubled haploid （DH） lines, derived from winter wheat varieties Hanxuan 10 and Lumai 14, was grown under field conditions in two consecutive growing seasons during 2002-2004 in Beijing. Post-anthesis DMA per culm and related traits, including flag leaf greenness （FLG） and flag leaf weight （FLW; dry weight per flag leaf） at flowering, and grain weight per ear （GWE） were investigated. All traits segregated continuously in the DH population in both trials. The DMA was significantly and positively correlated with GWE, with the correlation coefficients being 0.79 and 0.66 in the 2002-2003 and 2003-2004 growing seasons （both P〈0.01）, suggesting the importance of DMA in grain filling. Further correlation analysis showed that FLW was more closely correlated with DMA and GWE than FLG in both growing seasons, indicating that FLW was more important than FLG in influencing DMA and GWE. In total, 30 QTLs for these four traits were mapped and distributed on 10 chromosomes. Phenotypic variations explained by an individual QTL were in the range 5.8%-21.3%, 5.9%-17.2%, 5.1%-18.1%, and 5.6%-16.2% for FLG, FLW, DMA, and GWE, respectively. Eight QTLs for DMA were detected, of which four （on chromosome arms 2AS, 4BL, 5AS, and 7AS） were linked with QTLs for GWE; two （on chromosome arms 5BL and 7BL） coincided with QTLs for FLW. These results may provide useful information for developing marker-assisted selection for the improvement of DMA.     

数量性状基因座的动态定位策略

分子标记辅助数量性状基因（QTL）定位和效应分析技术为深入研究数量性状的遗传基础提供了一个有力手段．但目前的QTL定位策略是静态的,只估计各QTL在某观察时刻的累积效应,无法了解QTL的表达动态．本文提出一种新的QTL定位策略,称为“动态定位”,能够揭示QTI表达的动态过程,并能极大地提高QTL定位的统计功效.     

水稻粒长QTL定位与主效基因的遗传分析

该研究利用短粒普通野生稻矮杆突变体和长粒栽培稻品种KJ01组配杂交组合F_1,构建分离群体F_2;并对该群体粒长进行性状遗传分析,利用平均分布于水稻的12条染色体上的132对多态分子标记对该群体进行QTL定位及主效QTLs遗传分析,为进一步克隆新的主效粒长基因奠定基础,并为水稻粒形育种提供理论依据。结果表明:(1)所构建的水稻杂交组合分离群体F_2的粒长性状为多基因控制的数量性状。(2)对543株F_2分离群体进行QTL连锁分析,构建了控制水稻粒长的连锁遗传图谱,总长为1 713.94 cM,共检测出24个QTLs,只有3个表现为加性遗传效应,其余位点均表现为遗传负效应。(3)检测到的3个主效QTLs分别位于3号染色体的分子标记PSM379～RID24455、RID24455～RM15689和RM571～RM16238之间,且三者对表型的贡献率分别为54.85%、31.02%和7.62%。(4)在标记PSM379～RID24455之间已克隆到的粒长基因为该研究新发现的主效QTL位点。     

林木数量性状基因定位中的若干问题

随着ＤＮＡ分子标记技术的迅速发展,ＱＴＬ定位已成为当前生物学研究领域的前沿。迄今已对许多种动、植物定位了许多重要性状的ＱＴＬ。这些研究促进了遗传学的发展,并将作为育种的新策略应用。与作物相比,林木ＱＴＬ定位有其特性。本文详细讨论了林木的生物学特性对ＱＴＬ定位的影响、ＱＴＬ定位的系谱设计和统计分析方法。     

A Novel Targeted Learning Method for Quantitative Trait Loci Mapping

We present a novel semiparametric method for quantitative trait loci (QTL) mapping in experimental crosses. Conventional genetic mapping methods typically assume parametric models with Gaussian errors and obtain parameter estimates through maximum-likelihood estimation. In contrast with univariate regression and interval-mapping methods, our model requires fewer assumptions and also accommodates various machine-learning algorithms. Estimation is performed with targeted maximum-likelihood learning methods. We demonstrate our semiparametric targeted learning approach in a simulation study and a well-studied barley data set.     

The Role of Peroxidase and Polyphenol Oxidase Isozymes in Wheat Resistance to Alternaria triticina

Polyphenol oxidase activity was higher in resistant wheat cultivar ACC-8226 than in susceptible cultivar MP-845 in control sets and after inoculation of Alternaria triticina. However, similar polyphenol oxidase isozyme pattern was found in control and inoculated sets of both the cultivars, but the band intensity was higher after inoculation. Three and four peroxidase isozymes were found in ACC-8226 and MP-845, respectively. An extra peroxidase isozyme band was observed in both the cultivars after inoculation. The results suggest an active role of peroxidase and polyphenol oxidase in defence mechanism of wheat plants.     

Identification of quantitative trait loci and associated candidate genes for low-temperature tolerance in cold-hardy winter wheat

Low-temperature (LT) tolerance is an important economic trait in winter wheat (Triticum aestivum L.) that determines the plants’ ability to cope with below freezing temperatures. Essential elements of the LT tolerance mechanism are associated with the winter growth habit controlled by the vernalization loci (Vrn-1) on the group 5 chromosomes. To identify genomic regions, which in addition to vrn-1 determine the level of LT tolerance in hexaploid wheat, two doubled haploid (DH) mapping populations were produced using parents with winter growth habit (vrn-A1, vrn-B1, and vrn-D1) but showing different LT tolerance levels. A total of 107 DH lines were analyzed by genetic mapping to produce a consensus map of 2,873 cM. The LT tolerance levels for the Norstar (LT₅₀=−20.7°C) × Winter Manitou (LT₅₀=−14.3°C) mapping population ranged from −12.0 to −22.0°C. Single marker analysis and interval mapping of phenotyped lines revealed a major quantitative trait locus (QTL) on chromosome 5A and a weaker QTL on chromosome 1D. The 5A QTL located 46 cM proximal to the vrn-A1 locus explained 40% of the LT tolerance variance. Two C-repeat Binding Factor (CBF) genes expressed during cold acclimation in Norstar were located at the peak of the 5A QTL.     

Mapping QTLs for Phosphorus-Deficiency Tolerance at Wheat Seedling Stage

Soil phosphorus (P) deficiency is one of the major limiting factors to crop production throughout the world. It is an important strategy to breed varieties with improved P-deficiency tolerance for sustainable agriculture. The objective of this study was to map QTLs for P-deficiency tolerance in wheat, and develop molecular marker assisted selection in breeding wheat with improved P-deficiency tolerance. A doubled haploid (DH) population, consisting of 92 DH lines (DHLs) derived from P-deficiency tolerant wheat variety Lovrin 10 and P-deficiency sensitive variety Chinese Spring, was developed for mapping QTLs for P-deficiency tolerance. A genetic linkage map consisting of 34 linkage groups was constructed using 253 SSR markers. Shoot dry weight (SDW), tiller number (TN), shoot P uptake (SPU), and shoot P utilization efficiency (PUE) were investigated at seedling stage under P deficiency (−P) and sufficiency (+P) condition in two pot trials in 2002 and 2003, respectively. All traits segregated continuously in the population under either −P or +P condition. Significant positive correlations were found in between TN, SDW and SPU, whereas significant negative correlations were observed between PUE and SPU and between PUE and TN. Twenty and 19 QTLs were detected under −P and +P condition, respectively. The 39 QTLs were distributed on 21 chromosomal regions. There were three clusters of QTLs, which were associated with Xgwm25l (on chromosomes 4B), Xgwm271.2 (on chromosome 5A), and Xgwm121 (on chromosome 5D), respectively. Compared to the DHLs with all Chinese Spring alleles at the three loci, those with all Lovrin 10 alleles had, on average, much higher SPU, SDW and TN under −P condition in both trials, suggesting the importance of the three loci in controlling P-deficiency tolerance. It was interesting to find that two of the above three loci were closely linked with vernalization requirement genes VRN-A1 (on chromosome 5A) and VRN-D1 (on chromosome 5D). Potential implication of the linkage between P-deficiency tolerance and VRN genes was discussed.     

A major QTL controlling seed dormancy and pre-harvest sprouting resistance on chromosome 4A in a Chinese wheat landrace

Wheat pre-harvest sprouting (PHS) can cause significant reduction in yield and end-use quality of wheat grains in many wheat-growing areas worldwide. To identify a quantitative trait locus (QTL) for PHS resistance in wheat, seed dormancy and sprouting of matured spikes were investigated in a population of 162 recombinant inbred lines (RILs) derived from a cross between the white PHS-resistant Chinese landrace Totoumai A and the white PHS-susceptible cultivar Siyang 936. Following screening of 1,125 SSR primers, 236 were found to be polymorphic between parents, and were used to screen the mapping population. Both seed dormancy and PHS of matured spikes were evaluated by the percentage of germinated kernels under controlled moist conditions. Twelve SSR markers associated with both PHS and seed dormancy were located on the long arm of chromosome 4A. One QTL for both seed dormancy and PHS resistance was detected on chromosome 4AL. Two SSR markers, Xbarc 170 and Xgwm 397, are 9.14 cM apart, and flanked the QTL that explained 28.3% of the phenotypic variation for seed dormancy and 30.6% for PHS resistance. This QTL most likely contributed to both long seed dormancy period and enhanced PHS resistance. Therefore, this QTL is most likely responsible for both seed dormancy and PHS resistance. The SSR markers linked to the QTL can be used for marker-assisted selection of PHS-resistant white wheat cultivars. Shi-Bin Cai and Cui-Xia Chen contributed equally to this work.     

Mapping of Quantitative Trait Loci for Butter Content and Hardness in Cocoa Beans (Theobroma cacao L.)

Cocoa butter is an important raw material for the chocolate, pharmaceutical, and cosmetic industries. The butter content and quality in cocoa beans are genetically controlled characteristics, and affect its commercial value and industrial applicability. In the present work, an F₂ population derived from the cross between the ICS-1 and Scavina-6 cocoa clones was used for molecular mapping. A linkage map was constructed based on amplified fragment length polymorphism, random amplified polymorphic DNA, and simple sequence repeat markers, resulting in a total of 273 markers, distributed in 14 linkage groups (LGs). Phenotyping of butter content was performed after ether extraction and butter hardness was determined by sweeping differential calorimetry. One quantitative trait locus (QTL) associated to butter content was mapped at linkage group 9 (LG9) and two QTLs for butter hardness were identified at linkage groups 9 and 7 (LG9 and LG7). The two QTLs mapped at the LG9 explained 51.0% and 28.8% of the phenotypic variation for butter content and hardness, respectively. These QTLs were concentrated in the same map region, suggesting a close genetic linkage or pleiotropic effect. The QTLs identified may be useful in further marker-assisted selection breeding programs aimed at cocoa butter quality improvement.     

小麦品种潍麦8号成株抗叶锈QTL定位

小麦品种潍麦8号是一个良好的抗叶锈病资源,为了解其抗叶锈基因在染色体上的位置,对潍麦8号×郑州5389杂交组合的179个F2∶3家系进行了抗叶锈病QTL分析。在染色体2AS上检测到一个主效的QTL,暂命名为QLr.hbau-2AS。QLr.hbau-2AS由抗病亲本潍麦8号提供,位于SSR标记Xcfd36和Xbarc1138之间,区间长度为2.58 c M,2010-2011年度、2011-2012年度和2012-2013年度,QLr.hbau-2AS分别解释了25.79%、71.55%和60.72%表型变异。本研究筛选出与QLr.hbau-2AS连锁的13个分子标记。     

离散性状QTL区间定位的最大似然方法

采用最大似然区间定位法对阈模型与一般线性模型的QTL定位效率进行了比较,并对影响离散性状QTL检测效率的主要因素（QTL效应、性状的遗传力和表型发生率）进行了模拟研究,实验设计为多个家系的女儿设计．资源群体大小为500头。研究结果表明：在QTL参数估计及检验功效方面,阈模型方法具有较大的优势,对离散性状QTL定位的效率明显高于LM（Linear Model）方法,定位的准确性也较高。另外,性状遗传力、QTL效应的大小和性状表型发生率对QTL定位的准确度也有直接的影响,随着性状遗传力和表型发生率的提高,随着QTL效应的增大,QTL定位的效率也进一步提高。     

水稻条纹叶枯病抗性位点的检测和效应分析

利用111个家系组成的热研2号（Oryza sativa subsp．japonica‘Reyan2’）／Milyang23（Oryza sativa subsp．indica‘Milyang23’）重组自交系（recombinant inbred lines,RIL）群体（F7）,采用重病区田间自然接种方法,以病情指数作为条纹叶枯病的表型值,鉴定了2个亲本及111个RIL家系对条纹叶枯病的抗性。使用QTL Cartographer软件复合区间作图法,对水稻（Oryza sativa）条纹叶枯病抗性基因进行了QTL分析。结果检测到2个抗水稻条纹叶枯病的QTL,分别位于第2和第11染色体上,其中第11染色体上的QTL贡献率为19．58％,表明这是一个主效的QTL,该QTL及其附近的分子标记,可以用于水稻条纹叶枯病抗性分子标记辅助育种。     

Effect of Enhanced Calcium Supply on Aluminum Toxicity in Relation to Cell Wall Properties in the Root Apex of Two Wheat Cultivars Differing in Aluminum Resistance

The present study was conducted to investigate the effects of enhanced Ca supply on Al toxicity in relation to cell wall properties in two wheat (Triticum aestivum L.) cultivars differing in Al resistance. Seedlings of Al-tolerant Inia66 and Al-sensitive Kalyansona cultivars were grown in complete nutrient solutions for 4 days then subjected to treatment solutions containing Al (0, 50 μM) and Ca (500, 2500 μM) at pH 4.5 for 24 h. Root elongation was affected greatly by Al treatment in the Al-sensitive cultivar and a significant improvement in root growth was observed with enhanced Ca supply during Al stress. Pectin and hemicellulose contents in the root cell walls increased with Al stress, and this increase was more conspicuous in the Al-sensitive cultivar. The molecular mass of hemicellulosic polysaccharides increased with Al treatment in the Al-sensitive cultivar and decreased with enhanced Ca supply. The increase in the molecular mass of hemicellulosic polysaccharides was attributed to increased content of glucose, arabinose and xylose in neutral sugars. Enhanced Ca supply slightly decreased the content of these components with Al stress. Aluminum treatment increased the contents of ferulic and p-coumaric acid, especially in the Al-sensitive cultivar, by increasing peroxidase (POD, EC 1.11.1.7) and phenylalanine ammonia lyase (PAL, EC 4.3.1.5) activity, whereas enhanced Ca supply during Al stress decreased the content of these components by decreasing POD and PAL activity. These results suggest that the increased molecular mass of hemicellulosic polysaccharides and phenolic compounds in the Al-sensitive cultivar with Al stress might have inhibited root elongation associated with cell wall stiffening related to cross-linking among cell-wall polymers and lignin. Enhanced Ca supply might maintain the normal synthesis of these materials even with Al stress.     

构建数量性状基因图谱的几种统计方法

以线性数学模型为线索,概述了用于构建数量性状基因图谱的几种主要统计方法,包括方差分析法、标记回归法、区间作图法、复合区间作图法、Jansen的复合区间作图法、双侧标记回归法以及新近发展的多区间作图法和多亲本作图法等.讨论了各种方法的优缺点. Abstract:Statistical methods for mapping QTLs were summarized, including one marker analysis, arker regression analysis,interval mapping (IM),composite interval mapping (CIM),Jansen's composite interval mapping, flanking marker regression analysis,multiple interval mapping (MIM) and multiple families mapping.Their advantages and disadvantages were discussed.