Mapping of QTL associated with heading time in winter wheat

The duration of periods to heading has been investigated for 107 winter wheat cultivars of different origins. To reveal the DNA markers to QTL associated with the heading rate, the cultivars and individual plants of the F₂ progeny from a cross between the Omskaya Ozimaya and Numbu Komugi cultivars, which contrasted most in respect of the analyzed trait, have been analyzed by SSR-PCR. Two revealed loci—Xgwm512 and Xgwm429—explain 19.3% (8.9% and 10.4%, respectively) of all differences in the duration of periods to heading, which were observed in individual F₂ plants under field conditions.     

Inheritance of heading date in crosses of wheat cultivar responsiveness to light intensity

The inheritance of heading date has been studied in crosses of spring bread wheat cultivars differing in their reaction to various light intensities. The parental cultivars were similar in their Vrn and Ppd gene systems and differed in heading dates. Domination of higher reaction to light intensity has been shown in F1 on duration of "ear emergence-heading" period. Analysis of F2 populations has shown the identity of earliness per se genetic systems in Novosibirskaya 22 and Ordynskaya cultivars. Digenic differences have been revealed for both these cultivars from Tyumenskaya rannyaya cultivar on duration of "ear emergence--heading" period.     

Identification of quantitative trait loci (QTL) for resistance to Fusarium crown rot (Fusarium pseudograminearum) in multiple assay environments in the Pacific Northwestern US

Fusarium crown rot (FCR), caused by Fusarium pseudograminearum and F. culmorum, reduces wheat (Triticum aestivum L.) yields in the Pacific Northwest (PNW) of the US by as much as 35%. Resistance to FCR has not yet been discovered in currently grown PNW wheat cultivars. Several significant quantitative trait loci (QTL) for FCR resistance have been documented on chromosomes 1A, 1D, 2B, 3B, and 4B in resistant Australian cultivars. Our objective was to identify QTL and tightly linked SSR markers for FCR resistance in the partially resistant Australian spring wheat cultivar Sunco using PNW isolates of F. pseudograminerarum in greenhouse and field based screening nurseries. A second objective was to compare heritabilities of FCR resistance in multiple types of disease assaying environments (seedling, terrace, and field) using multiple disease rating methods. Two recombinant inbred line (RIL) mapping populations were derived from crosses between Sunco and PNW spring wheat cultivars Macon and Otis. The Sunco/Macon population comprised 219 F(6):F(7) lines and the Sunco/Otis population comprised 151 F(5):F(6) lines. Plants were inoculated with a single PNW F. pseudograminearum isolate (006-13) in growth room (seedling), outdoor terrace (adult) and field (adult) assays conducted from 2008 through 2010. Crown and lower stem tissues of seedling and adult plants were rated for disease severity on several different scales, but mainly on a numeric scale from 0 to 10 where 0?=?no discoloration and 10?=?severe disease. Significant QTL were identified on chromosomes 2B, 3B, 4B, 4D, and 7A with LOD scores ranging from 3 to 22. The most significant and consistent QTL across screening environments was located on chromosome 3BL, inherited from the PNW cultivars Macon and Otis, with maximum LOD scores of 22 and 9 explaining 36 and 23% of the variation, respectively for the Sunco/Macon and Sunco/Otis populations. The SSR markers Xgwm247 and Xgwm299 flank these QTL and are being validated for use in marker-assisted selection for FCR resistance. This is the first report of QTL associated with FCR resistance in the US.     

小麦抗赤霉病突变体的诱导与筛选研究

用~(60)Co-γ射线辐照和Ar~+离子束注入分别处理2个小麦品种皖麦19和丰华8903的干种子,在M_2代的抽穗期接种赤霉菌进行抗赤霉病突变体筛选,获得了两个抗病性明显提高的突变株.通过SSR分子鉴定表明,皖麦19的突变株其突变发生在Xgwm261、Xgwm493、Xwmc41和Xgwm212等4个基因座位,突变位点分别位于2D、3B、5A和5D染色体上;丰华8903的突变株其突变发生在Xgwm493、Xbarc164、Xgwm161、Xgwm312、Xgwm156和Xgwm427等6个基因座位上,突变位点分别位于3B、2A和5A染色体上.     

黄淮麦区小麦品种(系)中Yr26基因的SSR检测

选用与Yr26紧密连锁的SSR标记Xgwm11和Xgwm18结合田间抗性鉴定,对239份黄淮麦区小麦品种(系)进行检测,以明确Yr26基因在黄淮麦区小麦品种资源中的分布.结果表明:共有35份品种(系)含有与Yr26紧密连锁的SSR标记Xgwm18或Xgwm11的特征带,占检测样本的14.6%.在这35份材料中,31份田间抗性鉴定表现免疫至中抗,4份表现中感.分子标记检测与田间抗病性检测吻合度较好,该标记可以用于Yr26基因的分子标记辅助选择.综合分子标记和田间鉴定,31份小麦(系)含有Yr26基因,占102份抗病材料的30.39%.     

Identification of microsatellite markers linked to Russian wheat aphid resistance genes Dn4 and Dn6

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a serious economic pest of wheat worldwide. Host plant resistance is the preferred method to control RWA infestations. The identification and mapping of RWA-resistant genes and the development of resistant wheat cultivars can be facilitated through the use of molecular markers. In the present study, microsatellite (SSR) markers linked to the RWA-resistant genes Dn4 and Dn6 were identified using several F(2) mapping populations derived from crosses of susceptible wheat cultivars and resistant sources. Two flanking microsatellite markers Xgwm106 and Xgwm337 are linked in coupling phase with Dn4 on the short arm of wheat chromosome 1D at 7.4 cM and 12.9 cM, respectively. Two other microsatellite markers Xgwm44 and Xgwm111 are linked to Dn6 in coupling phase near the centromere on the short arm of chromosome 7D at 14.6 cM and 3.0 cM, respectively. This is the first report on the chromosomal location of Dn6, which proved to be either allelic or tightly linked to Dn1, Dn2 and Dn5. This result of Dn6 location contradicts previous reports that Dn6 was independent of Dn1, Dn2 and Dn5. The linked markers can be conveniently used for marker-assisted selection in wheat breeding programs for the identification and/or pyramiding of Dn4 and Dn6 genes.     

Transfer and mapping of a gene conferring later-growth-stage powdery mildew resistance in a tetraploid wheat accession

Wheat powdery mildew is a severe foliar disease and causes significant yield losses in epidemic years. Breeding and using resistant cultivars is the most widely employed strategy to curb this disease. To identify and transfer powdery mildew resistance genes in wild emmer wheat accession TA1410 into common wheat, a resistant F3 line derived from the cross of TA1410 × durum wheat line Zhongyin1320 was crossed with common wheat cultivar Yangmai158. The homozygous resistant BC5F2 lines derived from the backcross with Yangmai158 exhibited susceptibility at seedling stage and conferred increasing resistance when the plants were closer to heading stage. In two segregating BC5F3 families investigated at heading stage, the segregation of the resistance fit a 3:1 ratio, suggesting that a single dominant gene controls the resistance. This resistance gene, designated HSM1, was mapped to the 0.6-cM Xmag5825.1–Xgwm344 interval on chromosome 7AL and co-segregated with Xrga-C3 and Xrga-C6. A mapping position comparison with other powdery mildew resistance genes on this chromosome suggested that HSM1 belongs to the Pm1 resistance gene cluster. HSM1 is a useful candidate gene for resistance breeding, particularly in winter-wheat growing areas.     

Assessing wheat (Triticum aestivum) genotypes for "Yr" resistance genes using conserved regions and simple-sequence motifs

Analysis of DNA sequence variation among genotypes is useful for differentiation of wheat accessions, selection strategies and genetic development of crop plants. We screened molecular markers for yellow rust resistance genes (Yr7, Yr9, Yr15, Yr18, Yr26, and YrH52), which are in the gene-rich regions of wheat chromosomes 1B, 2B, and 7D, to investigate DNA sequence differences and repeat motifs and numbers between wheat cultivars resistant (Izgi2001, Sonmez2001, PI178383) and susceptible (Aytin98, ES14, Harmankaya99) to yellow rust. The F(2) individuals derived from the crosses were evaluated for yellow rust resistance at both the seedling and adult stages to identify DNA markers genetically linked to yellow rust resistance. The most repeated motif was found to be GA and the least repeated motif TAGA among the cultivars. When we examined DNA sequence differences (insertion, deletion and single nucleotide changes), the molecular markers Xgwm526 (Yr7) and Xgwm273 (YrH52) were found to have the most conserved regions and Yr15 (Xgwm413) the least conserved regions among the cultivars. This DNA sequence information can be used for selection of suitable parents, creating mapping populations and developing molecular markers associated with yellow rust resistance in plant breeding programs.     

Inheritance of the light intensity response in spring cultivars of common wheat

The effects of low/high light intensities and day length on ear emergence time in climatic chambers were studied in 12 common wheat (Triticum aestivum L.) cultivars of different ecogeographical origin. Low light intensity (LI) affected the time to ear emergence in all the wheat cultivars of both the photoperiod sensitive and insensitive genotypes, increasing the number of days to ear emergence (DEE). Based on the increase in DEE, we chose samples with different light intensity responses among the cultivars and analyzed their F2 hybrids to see if they were segregating. Taken together, the data for the F2 plants and test cross showed that the strong response to light intensity is a recessive trait and that the parental cultivars differ by the two genes controlling the LI response in common wheat. Besides heading time, low LI increased the number of days to tillering in all the cultivars except Pitic 62, but short day affected the period to tillering less than low LI. The symbol Rli (the response to light intensity) is suggested to designate the genetic control of the response to LI in wheat. Thus, the response to LI may influence the adaptability to changing environmental conditions and yield of wheat cultivars.     

Novel QTLs for photoperiodic flowering revealed by using reciprocal backcross inbred lines from crosses between japonica rice cultivars

The rice japonica cultivars Nipponbare and Koshihikari differ in heading date and response of heading to photoperiod (photoperiod sensitivity). Using simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers, we conducted quantitative trait locus (QTL) analyses for heading date in a set of reciprocal backcross inbred lines (BILs) from crosses between Nipponbare and Koshihikari. Under natural-day conditions, transgressive segregation in days to heading (DTH) toward both early and late heading was observed in both BIL populations. QTL analyses revealed that two QTLs-on chromosomes 3 and 6-were involved in the difference in heading date between the parental cultivars. The Nipponbare allele at the QTLs on chromosomes 3 and 6 showed, respectively, increasing and decreasing effects on DTH in both BIL populations. The transgressive segregation observed in the BILs could be accounted for mainly by the complementary action of a set of alleles with opposing effects. Both QTLs were finely mapped as single Mendelian factors in secondary mapping populations (BC(2)F(2) plants/BC(2)F(3) lines). The QTL on chromosome 3 was mapped in the 1,140-kb interval between 94O03-4 (SSR) and OJ21G19-4 (SNP) and was designated Hd16. The QTL on chromosome 6 was mapped in the 328-kb interval between P548D347 (SSR) and 0007O20 (SSR) and was designated Hd17. Both Hd16 and Hd17 were involved in photoperiod sensitivity, as revealed by observation of the DTH of nearly isogenic lines of Nipponbare under short- and long-day conditions, suggesting that allelic differences in both Hd16 and Hd17 account for most of the difference in photoperiod sensitivity between the parental cultivars.     

水稻感光性和光敏不育性的发育遗传关系

在人工气候室控制的光长与温度下,用光敏不育系7001S与早中熟粳稻(Oryza sativa ssp,japoni-ca)感光性弱的“秋光”、“有芒早粳”和“CPSLO-l7”3个品种分别杂交,分析了杂种F_1、F_2植株育性与感光性的表现,以及两者的关系。结果表明:这3个组合的恢复亲本均属于具两对光敏不育的恢复基因的品种。F_1植株均倾向晚熟亲本,说明控制感光性强的基因属于显性。F_2植株在长日照下表现为不育株的感光性均倾向感光性强的亲本;且有不少不育株为晚熟超亲;在少数弱感光性的植株中没有不育株。说明光敏不育基因与感光性基因关系密切,可能两者有连锁关系,光敏不育基因要在感光性基因表达的基础上才能表达。     

用微卫星标记定位小麦T型CMS的恢复基因

以T型细胞质雄性不育系 75 336 9A×恢复系 72 6 9 10的F2 群体作为育性调查和基因定位群体。通过育性分析 ,确定该恢复系含有 2个主效恢复基因 ;结合群分法 ,对恢复基因进行了SSR分子标记定位 ,在 2 30对微卫星引物中 ,微卫星标记Xgwm136和Xgwm5 5 0分别与 2个主效恢复基因连锁。这两个标记与Rf基因之间的遗传距离分别为 6 7cM和 5 1cM ,从而将该恢复基因定位在 1AS、1BS染色体上。     

Quantitative trait loci responsible for Fusarium head blight resistance in Chinese landrace Baishanyuehuang

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, is a destructive disease that can significantly reduce grain yield and quality. Deployment of quantitative trait loci (QTLs) for FHB resistance in commercial cultivars has been the most effective approach for minimizing the disease losses. 'Baishanyuehuang' is a highly FHB-resistant landrace from China. Recombinant inbred lines (RILs) developed from a cross of 'Baishanyuehuang' and 'Jagger' were evaluated for FHB resistance in three greenhouse experiments in 2010 and 2011 by single-floret inoculation. Percentage of symptomatic spikelets in an inoculated spike was recorded 18 days post-inoculation. The RIL population was screened with 251 polymorphic simple sequence repeats. Four QTLs were associated with FHB resistance and mapped on three chromosomes. Two QTLs were located on the short arm of chromosome 3B (3BS) with one in distal of 3BS and another near centromere (3BSc), designated as Qfhb.hwwg-3BSc. The QTL in the distal of 3BS is flanked by Xgwm533 and Xgwm493, thus corresponds to Fhb1. This QTL explained up to 15.7 % of phenotypic variation. Qfhb.hwwg-3BSc flanked by Xwmc307 and Xgwwm566 showed a smaller effect than Fhb1 and explained up to 8.5 % of phenotypic variation. The other two QTLs were located on 3A, designated as Qfhb.hwwg-3A, and 5A, designated as Qfhb.hwwg-5A. Qfhb.hwwg-3A was flanked by Xwmc651 and Xbarc356 and explained 4.8-7.5 % phenotypic variation, and Qfhb.hwwg-5A was flanked by markers Xgwm186 and Xbarc141, detected in only one experiment, and explained 4.5 % phenotypic variation for FHB resistance. 'Baishanyuehuang' carried all resistance alleles of the four QTL. Qfhb.hwwg-3BSc and Qfhb.hwwg-3A were new QTLs in 'Baishanyuehuang'. 'Baishanyuehuang' carries a combination of QTLs from different sources and can be a new source of parent to pyramid FHB-resistant QTLs for improving FHB resistance in wheat.     

Genotypes of Heading Date of Middle Indica Rice in the Mid-lower Region of the Yangtze River

Middle indica cultivars are planted in the middle to lower regions of the Yangtze River. Hybrid combinations with these cultivars have a high yield potential but the presence of late-transgressive-segregants limits the further exploitation of heterosis. To understand the genetic basis of the heading date in these middle maturing cultivars, we carried out a genetic analysis of 10 typical middle-season cultivars using a number of heading date isogenic lines under both long and short day conditions. The results showed that Teqing, 752, CDR22, Bo B, 9311 and 11-32B carry two photoperiod sensitive genes E1 or Se.1 and E3, and Teqing, 752 and CDR22 carry a dominant early-heading gene Ef-1 while Bo B, 9311 and 11-32B carry a recessive late-heading gene ef-1. Based on the findings of the present and previous works on Guichao 2, Minghui 63, Nanjing 11 and Pei＇ai64S, it was concluded that all of these middle indica cultivars carried the recessive allele hd2, which could inhibit the expression of El or Se.1, and they formed rational combinations of genotype for heading date during a long period of evolution. The effects of the different combinations of genotype for heading date on rice cultivation and extension were discussed, and genetic basis of broad adaptability of hybrid middle indica cultivars was analyzed.     

Identification of leaf rust resistance genes in wheat (Triticum aestivum L.) cultivars using molecular markers

A collection of 68 cultivars of common wheat has been screened for leaf rust resistance genes with the use of molecular markers. Markers of genes Lr1, Lr9, Lr10, Lr19, Lr20, Lr21, Lr24, and Lr26 have been used. It has been suggested that allele Xgwm295 be used as a marker for identifying the Lr34 gene. The genes originating from Triticum aestivum L., as well as the Lr26 gene contained in rye translocation 1RS, are the most frequent. Genes originating from wild wheats were rarer in the cultivars studied.     

抗白粉病基因PmCH1302的遗传分析及染色体定位

CH1302是以来源于中间偃麦草的八倍体小偃麦TAI7047为桥梁亲本选育的高抗白粉病的小麦新品系,对白粉菌多个流行小种均表现出良好抗性。为了解其抗白粉病基因来源及其在染色体上的位置,对绵阳11×CH1302的F_1、F_2及F_(2∶3)家系进行了遗传分析,推断其抗白粉病基因可能来源于中间偃麦草,暂将其命名为PmCH1302。利用i Select 90K SNP芯片对抗、感病池进行扫描,发现位于2AL染色体上的多态性位点最多,为313个,占全部多态性位点的9.79%,且集中于2AL染色体100~105 c M和150~155 cM两个区域附近。在上述位点选取SSR标记,筛选出3对与Pm CH1302连锁的分子标记,Xwmc522、Xgwm356和Xgwm526,其中Xgwm356和Xgwm526位于Pm CH1302两侧,连锁距离分别为3.1 c M和7.8 cM。利用遗传图谱以及中国春缺体、双端体将PmCH1302定位于小麦2AL染色体上。进一步与位于2AL上的Pm4、Pm50比较发现,PmCH1302可能是位于2AL上的一个新基因或等位基因。     

利用小麦微卫星引物建立簇毛麦染色体组特异性标记

选位于普通小麦1A-7A、1B-7B、1D-7D染色体上的102对微卫星引物对多年生簇毛麦、二倍体簇毛麦、小麦-簇毛麦双二倍体与后代和普通小麦中国春、R25、R111、MY11进行了PCR扩增, 发现引物对Xgwm301可以在含簇毛麦染色体的材料中扩出一条长415 bp的特异片段(命名为Xgwm301/415), 而所有供试小麦均未扩出此片段。进而用一套中国春-二倍体簇毛麦附加系来进行扩增, 发现1V-7V染色体均可以扩出该片段, 说明该片段为簇毛麦1V-7V染色体所共有。因此, Xgwm301/415是簇毛麦染色体组上的一个特异片段, 可以用来快速跟踪检测导入到普通小麦背景中的簇毛麦染色体。     

Fine mapping a domestication-related QTL for spike-related traits in a synthetic wheat

QTL analysis using a BC5F2:3 mapping population derived from a cross between Am3, a synthetic hexaploid wheat as a donor parent, and Laizhou953, a Chinese winter wheat cultivar as a recurrent parent, showed that variation at the microsatellite locus Xgwm113 on chromosome 4B was associated with variation in grain number per spike (GN), spike length (SL), and spikelet number per spike (SPI). The Qgn.caas-4B, Qsl.caas-4B, and Qspi.caas-4B were responsible for 16.6%-35.6%, 18.0%-32.3%, and 23.7%-25.9% of the phenotypic variation present in two environments, respectively. Segregation for GN fit a Mendelian monogenic ratio. A subpopulation consisting of 497 plants was used to map the QTL to a 1.2?cM interval between Xgwm113 and Xgwm857. The three spike traits, GN, SL, and SPI, were correlated and were thus probably under the pleiotropic control of the QTL. The Am3 allele had a reduction effect on all three spike traits. Evidence for positive selective history on SSR locus Xgwm113 was supported using Ewens-Watterson's statistic test on a germplasm panel of wild and landrace entries, suggesting that this genomic region may contain genes under selection during wheat domestication.     

Molecular markers for tracking variation in lipoxygenase activity in wheat breeding

Lipoxygenase (LOX) activity is an important factor determining the color of flour and end-use products of wheat. In the present study, quantitative trait loci (QTL) for LOX activity in common wheat were mapped using 71 doubled haploid (DH) lines derived from a Zhongyou 9507 × CA9632 cross, and SSR markers. Two QTL, QLpx.caas.1AL and QLpx.caas-4B, were identified on chromosomes 1AL and 4B, closely associated with LOX activity. The SSR loci Xwmc312 and Xgwm251 proved to be diagnostic and explained 13.4–25.2% of the phenotypic variance for the 1AL locus and 14.3–27.0% for the 4B locus across four environments. The SSR markers Xgwm251 and Xwmc312 were validated across 198 Chinese wheat cultivars and advanced lines and showed highly significant (P < 0.01) association with LOX activity. We further established a multiplexed PCR with SSR marker combination Xwmc312/Xgwm251 to test these wheat cultivars and advanced lines. The results suggested that the marker combination Xwmc312/Xgwm251 is efficient and reliable for evaluating LOX activity and can be used in marker-assisted selection (MAS) for targeting flour color attributes to noodle and other wheat-based products.     

Effects of an intercultivaral chromosome substitution on winterhardiness and vernalization in wheat

During a study on the genetic control of winterhardiness in winter wheat (Triticum aestivum L. group aestivum), a gene that affected vernalization was found on chromosome 3B in the winter wheat cultivar `Wichita.' When chromosome 3B from Wichita was substituted into the winter wheat cultivar `Cheyenne,' the resultant substitution line exhibited a spring growth habit. This is unusual since a cross between the cultivars Wichita and Cheyenne results in progeny that exhibit the winter growth habit. The F(2) plants from a cross of the 3B substitution line to Cheyenne, the recipient parent, segregated 3:1 for heading/no heading response in the absence of vernalization (χ(2) = 2.44). Earliness of heading appeared to be due to an additive effect of the 3B gene as shown by the segregation ratio 1:2:1 (early heading-later heading-no heading) (χ(2) = 2.74). This vernalization gene differs from previously described vernalization genes because, while dominant in a Cheyenne background, its expression is suppressed in Wichita. The gene may have an effect on winter hardiness in Wichita. In a field test for winter survival the 3B substitution line had only 5% survival, while Wichita and Cheyenne had 50 and 80% survival, respectively. No other substitution line significantly reduced winter survival. The difference between Wichita and Cheyenne in winterhardiness may be due to the vernalization gene carried on the 3B chromosome.