Improving Drought Tolerance of Rice by Designed QTL Pyramiding

Drought is the most important factor limiting rice yields in the rainfed areas of Asia. To overcome the problem, we developed a new strategy ＇designed QTL pyramiding＇ to more efficiently develop drought tolerant （DT） rice cultivars. In the first phase of this strategy, we developed large numbers of introgression lines （ILs） in elite backgrounds using backcross （BC） breeding, each of which carries multiple genomic segments for improved DT from a known donor. Then, we genotyped all ILs with SSR markers to track the genomewide pattern of introgression in the DT ILs of 16 BC populations derived from crosses between 2 recipients （IR64 and Teqing） and four different donors. X^2 tests and linkage disequilibrium analyses of introgression in the DT ILs revealed significant frequency shifts at many loci across the genome and non-random associations at the multilocus level as a result of selection for DT in the ILs, which led us to the discovery of putative genetic networks underlying DT in the ILs. The networks each containing all DT loci detected in ILs from a BC population showed some interesting features.     

Construction of Genetic Linkage Map of Bread Wheat （Triticum aestivum L.） Using an Intervarietal Cross and QTL Map for Spike Related Traits

Most often a genetic linkage map is prepared using populations obtained from two highly diverse genotypes. However, the markers from such a map may not be useful in a breeding program as these markers may not be polymorphic among the varieties used in breeding. For the past nine years, intraspecific maps have been gaining importance and such maps based on Swiss （PaiUard et al., 2003）, Japanese （Suenaga et al., 2005）, Australian （Chaimcrs et al., 2001） wheat varieties arc available. A map based on Indian wheat varieties however has not been reported. We constructed a genetic linkage map based on a cross between two Indian bread wheat （Triticum aestivum L.） varieties, Sonalika and Kalyansona. One hundred and fifty F2 individuals were analyzed for arbitrarilyprimed polymerase Chain reaction （AP-PCR）, random amplified polymorphic DNA （RAPD）, inter simple sequence repeats （ISSR）, Sequence Tagged Microsatelhte Sites （STMS）, Amplified Fragment Length Polymorphism （AFLP） markers, seed storage proteins and known genes. A linkage map was constructed consisting of 236 markers and spanning a distance of 3 639 cM with 1 211.2 cM for A genome, 1 669.2 cM for B genome, 192.4 cM for D genome and 566.2 cM for unassigned groups,     

QTL遗传效应正反交差异研究

应用改良AD模型对转基因棉花QTL突变体系进行遗传效应的正反交比较分析,结果表明,农艺性状的主要遗传方差组分分解正反交表现一致,除铃重存在显著的遗传背景加性效应(A2)外,子棉产量、皮棉产量、衣分和铃数均存在显著或极显著的 dQTL加性效应(A1)和显性效应(D1),农艺性状均有显著或极显著的遗传背景显性效应(D2);棉花纤维性状的主要遗传效应正反交之间无显著差异.铃重的dQTL的加性和显性效应与环境的互作存在显著差异.对转基因系、受体及三个品系的dQTL加性效应分解结果也表明,正反交对不同材料各性状的加性效应估计也是一致的.本文还对不同组合正反交时的纯合及杂合显性效应进行预测比较.     

QTLs and candidate genes for chlorate resistance in rice (Oryzasativa L.)

Chlorate resistance is one of the reliable characters in Indica/Japonica classification. To understand the genetic basis of chlorate resistance is very important for revealing the evolutionary mechanism of Indica/Japonica differentiation. In this study, a doubled haploid (DH) population derived from anther culture of ZYQ8/JX17, a typical Indica and Japonica hybrid, was used as the genetic material to investigate chlorate sensitivity of the parents and DH lines. The quantitative trait loci (QTLs) of chlorate resistance were analyzed based on the molecular linkage map of this population. Total of 3 QTLs (qCHR-2, qCHR-8 and qCHR-10) for chlorate resistance were detected on chromosomes 2, 8 and 10, respectively. A QTL × QTL epistatic interaction was detected between qCHR-2 and qCHR-10. Genes involved in nitrogen assimilation, such as nitrate reduction, molybdenum cofactor biosynthesis and nitrate transport were strong candidates of QTLs for chlorate resistance. A putative nitrate reductase gene (8611.t00011), and two putative nitrate reductase genes (9319.t00010 and 9319.t00012) were in the genomic region of qCHR-2, and qCHR-8, respectively, and a putative nitrate transporter gene (756.t00011) was in the region of qCHR-10. The expression of 8611.t00011, 9319.t00010 and 756.t00011 were confirmed by the corresponding cDNAs, and 2 in/del and 12 SNPs in the coding regions of these three genes were found between Indica (cv. 9311) and Japonica (cv. Nipponbare) in silico. These results indicated that these three genes were candidates of the chlorate resistance QTLs. An in/del in the coding region of 8611.t00011 was used to develop a new PCR marker. A polymorphism was detected between JX17/Nipponbare and ZYQ8/9311. This polymorphism corresponds to the chlorate sensitivity of Nipponbare and 9311. This marker was located between Y8007R and RM250 on chromosome 2 in the DH population, where qCHR-2 was also located.     

Identification of novel QTL for resistance to crown rot in the doubled haploid wheat population 'W21MMT70' × 'Mendos'

Crown rot (causal agent Fusarium pseudograminearum) is a fungal disease of major significance to wheat cultivation in Australia. A doubled haploid wheat population was produced from a cross between line ‘W21MMT70’, which displays partial seedling and adult plant (field) resistance to crown rot, and ‘Mendos’, which is moderately susceptible in seedling tests but partially resistant in field trials. Bulked segregant analysis (BSA) based on seedling trial data did not reveal markers for crown rot resistance. A framework map was produced consisting of 128 microsatellite markers, four phenotypic markers, and one sequence tagged site marker. To this map 331 previously screened AFLP markers were then added. Three quantitative trait loci (QTL) were identified with composite interval mapping across all of the three seedling trials conducted. These QTL are located on chromosomes 2B, 2D and 5D. The 2D and 5D QTL are inherited from the line ‘W21MMT70’, whereas the 2B QTL is inherited from ‘Mendos’. These loci are different from those associated with crown rot resistance in other wheat populations that have been examined, and may represent an opportunity for pyramiding QTL to provide more durable resistance to crown rot.     

Prediction of heterosis using QTLs for yield traits in rapeseed (Brassica napus L.)

Three double low (erucic acid and glucosinolates) self-incompatible lines and 22 varieties from different origins were selected to produce 66 hybrids according to a NC II mating design. Field experiments for identification of hybrid performance and heterosis were conducted in two successive rapeseed growing seasons in Wuhan, China. After heterosis identifications, SI-1300 and Eagle were chosen to construct an F₂ segregating population. One hundred and eighty four F_2:3 lines were planted at Wuhan and Jingmen to test yield traits. F₂ plants and the 25 parents were analyzed using simultaneously AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeat) markers. A total of 270 and 718 polymorphic loci were detected in the F₂ population and among the 25 parental lines, respectively. Of the 718 polymorphic loci, 178 were significantly correlated to yield traits. With the use of one-way ANOVA, 84 common QTLs were detected for 12 traits at two trial locations. Although the genetic distances based on general/specific heterozygosities and single-locus QTLs showed significant correlations with hybrid performance and heterosis for some yield traits, the determination coefficients were low. The results suggested that neither heterozygosities nor QTLs for yield traits were suitable to predict hybrid performance and heterosis in Brassica napus.     

利用相同来源F2:3和BC2S1群体定位玉米生育期QTL

以普通玉米自交系丹232和爆裂玉米自交系N04为亲本构建259个F2:3和220个BC2S1家系群体,利用SSR标记构建分子标记遗传图谱,利用复合区间作图方法对4个生育期性状进行QTL定位和效应分析。利用F2:3群体共检测到4个抽雄期QTL、6个吐丝期QTL和3个散粉期QTL。单个QTL可解释的表型变异为6.7%~18.4%,可解释的表型总变异为28.9%~50.3%,11个QTL的增效基因来自生育期较长的亲本丹232,其余2个QTL的增效基因来自生育期较短的亲本N04;BC2S1群体检测到8个与4个生育期性状相关的QTL,单个QTL可解释的表型变异为4.5%~11.6%,可解释的表型总变异为13.2%~18.5%,增效基因来自两个亲本的QTL为3个和5个。两类群体检测出QTL的数目、位置、效应和贡献率均存在较大差异,主要原因在于BC2S1群体抽样选择所引起的群体结构差异,F2:3群体显示出较高的QTL检测能力,但回交育种过程中应慎重依据F2:3群体QTL定位结果进行标记辅助选择(MAS)。     

抗水稻纹枯病qSB-9^Tq基因效应及作用方式分析

水稻第9染色体上存在1个抗纹枯病QTL,被命名为qSB-9,水稻品种特青在该QTL上携带抗性等位基因qSB-9Tq,而Lemont携带相对感病等位基因qSB-9Le.为精确地评价qSB-9Tq的抗病效应,分析其作用方式,利用分子标记进行前景选择和背景选择,从轮回亲本Lemont与特青回交后代群体中筛选到1个目标单株.连续3年对该单株的扩繁后代(BC6F2)及随后获得的近等基因系采用嵌入法进行接种鉴定试验.田间试验采取2种不同的设计.第一种是完全随机试验,即从BC6F2分离群体中筛选出目标区间为qSB-9TqTq纯合型、qSB-9LeLe纯合型和qSB-9TqLe杂合型个体,并对3种基因型个体间的病级平均数差异进行统计分析.第二种设计为随机区组设计,即在BC6F3和BC6F4代,分别对上述3种基因型的近等基因系群体,按3次重复的随机区组设计进行移栽和接种鉴定试验.结果表明,3年的试验结果表现出一致的趋势,即qSB-9Tq存在于分子标记RM242～Y92.5之间,可减轻病级1.0级(O～9级病情分级系统)左右,且其抗性表现为几乎完全的显性特征.本研究的结果为qSB-9Tq的精细定位和育种利用奠定了基础.     

利用Mudgo/武育粳3号F2群体分析水稻抗灰飞虱QTL

灰飞虱是我国水稻生产上的重要害虫。Mudgo是一个高抗灰飞虱的籼稻品种,对灰飞虱具有强的排驱性和抗生性抗性。利用Mudgo/武育粳3号F₂群体,构建了含有177个单株的F₂群体的遗传连锁图谱。该连锁图包含104个SSR标记和3个Indel标记,覆盖整个水稻基因组1 409.9 cM,每两个标记之间的平均距离为13.2 cM。采用改进的苗期集团筛选法对177个F_2:3家系进行了抗性鉴定,通过Windows QTL Cartographer 2.5进行复合区间作图分析,在第2、3、12染色体上分别检测到抗灰飞虱QTL Qsbph2b、Qsbph3d和Qsbph12a,分别位于标记RM5791~RM29、RM3199~RM5442和I12-17~RM333 1之间,单个LOD值分别为3.25、3.11和6.82,贡献率分别为17.3%、15.6%和35.8%,各QTL增强抗性的等位基因效应均来自Mudgo。其中Qsbph12a与标记RM3331和I12-17紧密连锁。结合表型鉴定的结果,Qsbph12a应为抗灰飞虱主效QTL,与该位点紧密连锁的标记可用于抗灰飞虱快速选择辅助育种。     

水稻染色体片段代换系对氮、磷胁迫反应差异及其QTL分析

利用来源于9311(籼稻)与日本晴(粳稻)杂交后代衍生的遗传背景为9311的染色体片段代换系群体,分析其在大田正常、低氮和低磷条件下的单株有效穗和单株产量的差异。结果表明,低磷、低氮胁迫对单株有效穗和单株产量影响较大。代换系对低磷和低氮的反应存在明显差异。在低氮(磷)水平下共检测到26个单株有效穗和单株产量片段或QTL,以及12个相对单株有效穗和相对单株产量QTL。源于日本晴的等位基因均呈减效作用。低磷和低氮下共同检测到5个导入片段影响单株有效穗或单株产量。而大部分(约81%)QTL只在单胁迫处理下被检测到。表明水稻对磷胁迫和氮胁迫的反应既存在不同的遗传基础,也存在共同的遗传机制。