QTLs conferring FOV 7 resistance detected by linkage and association mapping in Upland cotton

Fusarium wilt is a worldwide disease that affects cotton production. Molecular markers tightly linked to resistance genes can be used for marker-assisted and/or genomic selection. We performed both family-based linkage mapping and population-based association mapping (AM) to detect quantitative trait loci (QTLs) conferring resistance against Fusarium oxysporum f. sp. vasinfectum race 7 (FOV 7) in Upland cotton. To identify QTLs underlying FOV 7 resistance by linkage mapping, three Upland cotton cultivars/lines, Xuzhou 142, Yumian 21 and Shang 9901, were used to obtain the composite cross population, designated as Xuzhou 142/Yumian 21//Xuzhou 142/Shang 9901. A linkage map containing 185 simple sequence repeat loci and 40 linkage groups was constructed with an average distance of 7.5 cM between adjacent markers. Seven QTLs were detected by linkage mapping, explaining 2.9–6.6 % of the total phenotypic variance. We also performed marker–trait AM with the MLM model (Q + K) in a panel composed of 356 Upland cotton cultivars. In total, 27 loci were significantly associated with FOV 7 resistance at the α = 0.01 level (?log₁₀ P ≥ 2), which were distributed on 16 chromosomes and explained 1.48–12.99 % of phenotypic variation. Three of the 7 QTLs identified by linkage mapping could be detected in AM. We identified the favorable allele for each of the 27 associated loci and investigated the number of favorable alleles in each accession. The results should increase our understanding of the genetic basis of FOV resistance and facilitate future resistance breeding in Upland cotton.     

陆地棉产量相关性状的QTL定位

中棉所28和湘杂棉2号分别是以中棉所12×4133和中棉所12×8891配制而成的两个陆地棉强优势杂交种。以其F₂为作图群体,筛选6000多对SSR引物,利用两群体间27个共有多态位点,通过JoinMap 3.0软件整合了一张包含245个多态位点、全长1847.81 cM的遗传图谱。利用Win QTLCart 2.5复合区间作图法分别对两群体8个产量相关性状在F₂和F_2:3中进行QTL定位,在中棉所28群体多环境平均值的联合分析中检测到16个QTL,三环境分离分析中检测到43个QTL;在湘杂棉2号群体分别检测到20个和66个QTL。在A3、D8、D9等染色体上有QTL成簇分布现象,同时在两个群体中发现一些不受环境影响且稳定遗传的QTL。对考察的8个性状在两个群体中发现12对共有QTL,控制果枝数、衣分和籽指的QTL增效基因位点均来源于共同亲本中棉所12。综合分析推测中棉所12的育种价值主要是通过提高后代的结铃性来实现的。研究结果为棉花产量性状的分子设计育种提供了有用的信息。     

陆地棉遗传图谱构建及产量和纤维品质性状QTL定位

利用3 458对SSR引物筛选陆地棉中棉所35和渝棉1号间的多态性引物, 获得173对。以多态性引物检测(渝棉1号×中棉所35)F₂群体180个单株的标记基因型, 共获得178个标记位点。构建的遗传连锁图谱包括148个标记, 36个连锁群, 总长1 309.2 cM, 标记间平均距离8.8 cM, 覆盖棉花基因组的29.5%。36个连锁群中的28个分别被定位于20条染色体, 8个连锁群未定位于染色体。以渝棉1号×中棉所35的F₂、F_2:3群体的产量、纤维品质性状鉴定结果, 利用区间作图方法, 检测到4个产量性状QTL, 即2个衣分(LP)、1个铃重(BW)、1个籽指(SD); 5个纤维品质性状QTL, 即1个纤维长度(FL)、2个纤维比强度(FS)和2个纤维细度(FF)。LP1、BW、SD、FL和FS1被定位于第7染色体, LP2、FS2、FF1和FF2被分别位于第15、21、9和20染色体。5个纤维品质QTL的有利等位基因均来源于渝棉1号。     

陆地棉衣分差异群体产量及产量构成因素

 以衣分差异较大的陆地棉品种为材料,构建了包含188个F₂单株的作图群体,应用6111对SSR引物对亲本进行了分子标记筛选,结果仅获得了123个多态性位点,其中88个位点构建了总长为666.7 cM、平均距离为7.57 cM的遗传图谱,覆盖棉花基因组的14.9%。通过复合区间作图法对F₂单株和F_2∶3家系进行QTL检测,共鉴定出了18个控制产量及产量构成因素变异的QTLs,包括2个衣分QTLs、4个子棉产量QTLs、4个皮棉产量QTLs、2个衣指QTLs、3个单株铃数QTLs、2个铃重QTLs和1个子指QTL。 解释的表型变异分别为\{6.9%\}～16.9%、5.6%～16.2%、4.8%～15.6%、7.7%～13.3%、8.2%～11.6%、6.1%～7%和6.6%。不同QTLs在相同染色体区段上的成簇分布表明与产量性状相关的基因可能紧密连锁或一因多效。产量及产量构成因素QTLs的遗传方式主要以显性和超显性效应为主。检测到的主效QTLs可以用于棉花产量及产量构成因素的分子标记辅助选择。     

Genetic mapping of quantitative trait loci for fiber quality and yield trait by RIL approach in Upland cotton

The improvement of cotton fiber quality has become more important because of changes in spinning technology. Stable quantitative trait loci (QTLs) for fiber quality will enable molecular marker-assisted selection to improve fiber quality of future cotton cultivars. A simple sequence repeat (SSR) genetic linkage map consisting of 156 loci covering 1,024.4 cM was constructed using a series of recombinant inbred lines (RIL) developed from an F₂ population of an Upland cotton (Gossypium hirsutum L.) cross 7235 × TM-1. Phenotypic data were collected at Nanjing and Guanyun County in 2002 and 2003 for 5 fiber quality and 6 yield traits. We found 25 major QTLs (LOD ≥ 3.0) and 28 putative QTLs (2.0 < LOD < 3.0) for fiber quality and yield components in two or four environments independently. Among the 25 QTLs with LOD ≥ 3, we found 4 QTLs with large effects on fiber quality and 7 QTLs with large effects on yield components. The most important chromosome D8 in the present study was densely populated with markers and QTLs, in which 36 SSR loci within a chromosomal region of 72.7 cM and 9 QTLs for 8 traits were detected.     

利用海岛棉染色体片段导入系定位衣分和籽指QTL

以染色体片段导入系IL-15-5和IL-15-5-1构建的F2和F2:3分离群体,利用SSR标记对数量性状衣分和籽指QTL进行了定位。应用复合区间作图法分析两个组合的774个F2单株和F2:3家系衣分和籽指,检测到2个衣分的QTL,1个籽指的QTL。衣分QTLqLP-15-1在两世代中都被检测到,位于相同的分子标记置信区间JESPR152～NAU3040,置信的遗传距离分别为5.40cM和3.20cM;qLP-15-2只在F2:3中被检测到,位于分子标记NAU5302～NAU2901之间,置信的遗传距离为0.08cM。籽指QTLqSI-15-1在F2和F2:3中都被检测到,分别位于分子标记NAU2814～NAU3040和JESPR152～NAU3040,置信的遗传距离分别为6.70cM和5.70cM。利用染色体片段导入系能准确地定位产量组分的QTL,为棉花产量的分子设计育种奠定基础。     

Construction of a genetic linkage map and QTL analysis of fiber-related traits in upland cotton (Gossypium hirsutum L.)

A genetic linkage map with 70 loci (55 SSR, 12 AFLP and 3 morphological loci) was constructed using 117 F₂ plants obtained from a cross between two upland cotton cultivars Yumian 1 and T586, which have relatively high levels of DNA marker polymorphism and differ remarkably in fiber-related traits. The linkage map comprised of 20 linkage groups, covering 525 cM with an average distance of 7.5 cM between two markers, or approximately 11.8% of the recombination length of the cotton genome. The present genetic linkage map was used to identify and map the quantitative trait loci (QTLs) affecting lint percentage and fiber quality traits in 117 F_2:3 family lines. Sixteen QTLs for lint percentage and fiber quality traits were identified in six linkage groups by multiple interval mapping: four QTLs for lint percentage, two QTLs for fiber 2.5% span length, three QTLs for fiber length uniformity, three QTLs for fiber strength, two QTLs for fiber elongation and two QTLs for micronaire reading. The QTL controlling fiber-related traits were mainly additive, and meanwhile including dominant and overdominant. Several QTLs affecting different fiber-related traits were detected within the same chromosome region, suggesting that genes controlling fiber traits may be linked or the result of pleiotropy.     

Genetic analysis and QTL mapping of oil content and seed index using two recombinant inbred lines and two backcross populations in Upland cotton

Cottonseed is one of the main by‐products of cotton. To explore the genetic composition of oil content (OC) and seed index (SI) is helpful for utilizing the cottonseed. Under multiple environmental conditions, the genetic structures of OC and SI were explored using two recombinant inbred lines (RILs) and corresponding backcross (BC) populations in Upland cotton. Twenty‐four and 31 quantitative trait loci (QTLs) for OC and SI, respectively, were detected using composite interval mapping, in which 9 QTLs for OC and 18 QTLs controlling SI were simultaneously identified in more than two environments or two populations. Forty‐seven and 37 QTLs with main effects (M‐QTLs) for OC and SI and 114 and 74 QTLs involved in digenic interactions (E‐QTLs), respectively, identified by inclusive composite interval mapping. On average, the E‐QTLs explained a larger portion of the phenotypic variation than the M‐QTLs did. It was concluded that additive effects of single‐locus and epistasis derived from complementary loci with few detectable single‐locus effects played an important role in oil content and seed index in Upland cotton.     

Identification of quantitative trait loci with main and epistatic effects for plant architecture traits in Upland cotton (Gossypium hirsutum L.)

Plant architecture is important for cotton cultivation and breeding. In this study, two mapping generations/populations F₂ and F_2:3 in Upland cotton (Gossypium hirsutum L.), derived from ‘Baimian1’ and TM‐1, were used to identify quantitative trait loci (QTLs) for 10 plant architecture traits. A total of 55 main‐effect QTLs (M‐QTLs) were detected. Four common M‐QTLs, qTFB‐10(F₂/F_2:3) for total fruit branches, qFBL‐26b(F₂)/qFBL‐26(F_2:3) for fruit branch length, qFBA‐5(F₂/F_2:3) for fruit branch angle and qFBN‐26b(F₂)/qFBN‐26(F_2:3) for fruit branch nodes, were found. The synergistic alleles and the negative alleles can be utilized in cotton plant architecture breeding programmes according to specific breeding objectives. Altogether 54 pairs of epistatic QTLs (E‐QTLs) exhibiting the interactions of additive‐by‐additive (AA), additive‐by‐dominant (AD), dominant‐by‐additive (DA) and dominant‐by‐dominant (DD) were detected. The epistasis appeared to be an important contributor to genetic variation in cotton plant architecture traits. Therefore, the identified markers associated with E‐QTLs as well as M‐QTLs will be of importance in future breeding programmes to develop cotton cultivars exhibiting desirable plant architecture.     

Fine‐mapping a fibre strength QTL QFS‐D11‐1 on cotton chromosome 21 using introgressed lines

An initial F₂ mapping population of 223 plants of the cross between TM‐1 (Gossypium hirsutum L.) × H102 (Gossypium barbadense L.) was used to map QTLs controlling fibre strength in cotton. A genetic linkage map with 408 SSR markers was constructed with a total length of 3872.6 cM. Multiple‐QTL model of the software MapQTL version 5.0 was used to map QTLs related to fibre strength of the F_2 : 3 population. QTL QFS‐D11‐1 conferring fibre strength was mapped between NAU2950 and NAU4855 on chromosome 21 (Chr. 21) which explained 23.4% of phenotypic variation. Introgressed lines (ILs), that is, IL‐D11‐1, IL‐D11‐2 and IL‐D11‐3 were obtained through marker‐assisted backcrossing in TM‐1 background. An F₂ population of 758 plants derived from cross IL‐D11‐2 × TM‐1 was used for fine‐mapping QTL QFS‐D11‐1. QFS‐D11‐1 was mapped between markers NAU2110 and NAU2950, adjacent to its initial interval NAU2950–NAU4855 with phenotypic variation explaining 35.8%. QFS‐D11‐1 was further mapped to 0.6 cM from the flanking marker NAU2950. The results will give a basis for marker‐assisted selection of QFS‐D11‐1 in cotton breeding and to lay the foundation for cloning QFS‐D11‐1.     

Genetic linkage map of Chinese native variety faba bean (Vicia faba L.) based on simple sequence repeat markers

Simple sequence repeat (SSR) marker is a powerful tool for construction of genetic linkage map which can be applied for quantitative trait loci (QTL) and marker‐assisted selection (MAS). In this study, a genetic map of faba bean was constructed with SSR markers using a 129 F₂ individuals population derived from the cross of Chinese native variety 91825 (large seed) and K1563 (small seed). By screening 11 551 SSR primers between two parents, 149 primer pairs were detected polymorphic and used for F₂ population analysis. This SSR‐based genetic linkage map consisted of 15 linkage groups with 128 SSR. The map encompassed 1587 cM with an average genetic distance of 12.4 cM. The genetic map generated in this study will be beneficial for genetic studies of faba bean for identification of marker‐locus‐trait associations as well as comparative mapping among faba bean, pea and grasspea.     

A microsatellite-based genome-wide analysis of genetic diversity and linkage disequilibrium in Upland cotton (Gossypium hirsutum L.) cultivars from major cotton-growing countries

To better understand the genetic diversity of the cultivated Upland cotton (Gossypium hirsutum L.) and its structure at the molecular level, 193 Upland cotton cultivars collected from 26 countries were genotyped using 448 microsatellite markers. These markers were selected based on their mapping positions in the high density G. hirsutum TM-1 × G. barbadense 3-79 map, and they covered the whole genome. In addition, the physical locations of these markers were also partially identified based on the reference sequence of the diploid G. raimondii (D₅) genome. The marker orders in the genetic map were largely in agreement with their orders in the physical map. These markers revealed 1,590 alleles belonging to 732 loci. Analysis of unique marker allele numbers indicated that the modern US Upland cotton had been losing its genetic diversity during the past century. Linkage disequilibrium (LD) between marker pairs was clearly un-even among chromosomes, and among regions within a chromosome. The average size of a LD block was 6.75 cM at r ² = 0.10. A neighbor-joining phylogenic tree of these cultivars was generated using marker allele frequencies based on Nei’s genetic distance. The cultivars were grouped into 15 groups according to the phylogenic tree. Grouping results were largely congruent with the breeding history and pedigrees of the cultivars with a few exceptions.     

Using three selected overlapping RILs to fine-map the yield component QTL on Chro.D8 in Upland cotton

Cotton yield improvement is vital to fulfill rising global demands. The identification of major quantitative trait loci (QTL) for yield components was helpful in molecular marker-assisted selection (MAS) to improve cotton yield. We previously identified a densely populated QTL region for fiber qualities and yield components on chromosome D8 (Chro.D8) of Upland cotton from a (7235 × TM-1)RIL. In the present study, to fine-map yield component QTLs, we chose three overlapped recombinant inbred lines (RILs) with different intervals included the yield component QTLs, and backcrossed each line with TM-1 to develop three large sized mapping populations. Phenotypic data for yield components were collected in Nanjing (JES/NAU) and Xinjiang (BES/XJ) in 2006 and 2007. Three simple sequence repeat (SSR) genetic linkage maps on chro.D8 were constructed using 907 individuals in (7TR-133 × TM-1)F₂ (Pop A), 670 in (7TR-132 × TM-1)F₂ (Pop B), and 940 in (7TR-214 × TM-1)F₂ (Pop C). Three stable QTLs for boll size, two for lint percentage and one for boll number per plant,were detected on chro.D8 following analysis of three RIL backcrossed F₂/F_2:3 progeny at JES/NAU and BES/XJ although their cultivation practices differ greatly between these two cotton-growing regions. One QTL for boll number per plant exhibited a phenotypic variance (PV) of 5.6–10.1%, three QTLs for boll size exhibited 15.0–35.5% PV and two lint percentage QTLs exhibited 10.9–19.3% PV. Negative correlation between lint yield and fiber strength was confirmed.     

Density enhancement of a faba bean genetic linkage map (Vicia faba) based on simple sequence repeats markers

Genetic mapping for faba bean lags far behind other major crops. Density enhancement of the faba bean genetic linkage map was carried out by screening 5,325 genomic SSR primers and 2033 expressed sequence tag (EST)‐SSR primers on the parental cultivars '91825' and 'K1563'. Two hundred and fifteen genomic SSR and 133 EST‐SSR primer pairs that detected polymorphisms in the parents were used to screen 129 F₂ individuals. This study added 337 more SSR markers and extended the previous linkage map by 2928.45 cM to a total of 4516.75 cM. The number of SSR markers in the linkage groups varied from 12 to 136 while the length of each linkage group ranged from 129.35 to 1180.21 cM. The average distance between adjacent loci in the enhanced genetic linkage map was 9.71 cM, which is 2.79 cM shorter than the first linkage map of faba bean. The density‐enhanced genetic map of faba bean will be useful for marker‐assisted selection and breeding in this important legume crop.     

Mapping of Verticillium Wilt Resistance QTL with Interspecific Advanced Backcross Population between Upland Cotton (Gossypium hirsutum L.) and Sea-Island Cotton (G. barbadense L.)

[Objective] The aim of this study was to map quantitative trait loci (QTLs) of Verticillium wilt resistance in cotton. [Method]In this study, with the cultivar Lumianyan 28(Gossypium hirsutumL.) as the recipient parent and the F₁generation obtained from the cross Hai7124 (G. barbadense) and TM-1(G. hirsutumL.) as the donor parent, an interspecific advanced backcross population was constructed. Compared with the integrated high density genetic linkage map published, simple sequence repeat(SSR) markers of polymorphism were used to construct genetic linkage map. QTLs detection was conducted by composite interval mapping method in field and disease nursery. [Result] 216 simple sequence repeated (SSR) markers of polymorphism were assigned to 26 Chromosomes with a total map distance of 3 380 cM and an average distance of about 15.77 cM between two adjacent markers. Six QTLs located on 6 chromosomes had been detected and could explain phenotypic variance with 8.56%～20.26%. Five of Six QTLs were consistent with the previous study. Moreover, one novel QTL which located on Chromosome 1 was detected in this study. These results maybe helpful for the marker-assisted development of new cultivars which were resistant to Verticillium wilt. [Conclusion] Six QTLs were detected, one of them is a new QTL on chromosome 1.     

陆地棉高品质品系纤维品质性状QTL的分子标记及定位

为进一步挖掘利用高品质品系NM03102的优异纤维品质性状的基因,利用陆地棉鲁棉研21作为母本、NM03102为父本构建了F2和F2∶3分离群体。通过7892对SSR引物对亲本进行筛选,获得222对多态性引物,进一步对195个F2群体单株分析得到242个标记位点。其中,182个标记位点连锁构建37个连锁群,共覆盖1661.6 cM,每个连锁群平均包含4.9个标记位点,标记间平均相距9.1 cM,其中35个连锁群被定位到了20条染色体上。利用F2和F2∶3纤维品质数据,通过复合区间作图法,共检测到20个纤维品质性状QTL。其中,1个纤维强度的QTL和1个纤维整齐度的QTL与已有的报道一致,1个纤维强度的QTL和1个麦克隆值的QTL在两世代中稳定存在,这为标记辅助选择奠定了基础。     

High-density genetic map construction and QTL mapping for fiber strength on Chr24 across multiple environments in a CCRI70 recombinant inbred lines population

Upland cotton is an important economic crop that produces high-quality fiber for the textile industry. With the development of next-generation sequencing technology and improvements in human living standards, it has become possible to improve the fiber quality and yield of cotton with high-throughput molecular markers. Upland cotton 901-001 is an excellent, high-quality, non-transgenic cultivar, while the sGK156 strain shows high resistance to verticillium wilt. The phenotype of F₁ plants, certified in 2008 as national variety CCRI70, shows positive transgressive characteristics such as high quality, high yield, and resistance to verticillium wilt. We developed a population of 250 recombination inbred lines from a cross between 901-001 and sGK156. The fiber strength trait of plants from nine environments was collected, and a genetic linkage map of Chr24 comprising 168 SNP marker loci covering a genetic distance of 107.46 cM and with an average distance of 0.64 cM was generated. QTLs were identified across the nine environments using the composite interval mapping method. A total of eight QTLs for FS were identified on Chr24, three of which were stably expressed in at least five environments. Some candidate genes located in qFS-c24-2 and qFS-c24-4 were functionally annotated as potentially playing important roles in fiber development, with homologous genes reported in Arabidopsis thaliana. These results suggest that QTLs identified in the present study could contribute to improving FS and may be applicable for marker-assisted selection.     

Genetic analysis and quantitative trait locus mapping of PEG‐induced osmotic stress tolerance in cotton

Water stress is one of the major abiotic stresses that adversely affect cotton production. Seedlings of 142 backcross inbred lines (BILs) derived from Pima cotton ‘Pima S‐7’ (Gossypium barbadense L.) × Upland cotton ‘Sure‐Grow 747’(G. hirsutum L.) were evaluated in two tests for plant height, fresh shoot weight and root weight under two treatments (5% PEG and water‐control conditions) using a hydroponic system in the greenhouse. The experiment in each test was a randomized complete block design with three replicates. The analysis of variance for the two tests detected significant genotypic variation in PEG‐induced stress tolerance within the BIL population and between the parents. Heritabilities were moderate to high and were higher under the control conditions than under the PEG treatment, and the three traits were also significantly and positively correlated. Based on a linkage map with 292 loci, six QTLs were detected including two for plant height, and two each for fresh shoot weight and root weight. This study represents the first report in using a permanent mapping population in genetic and linkage analysis of water stress tolerance in cotton.     

陆地棉早熟基因来源的遗传分析

棉花早熟性相关的性状多为复杂的数量性状,是由多个基因和环境共同作用的结果,其遗传基础研究比较困难。利用连锁作图和关联分析方法,对目标性状进行基因定位,找出与性状相关联的位点,为解析复杂性状的基因来源提供了新的手段。本文分别以早熟亲本新陆早8号和新陆早10号为母本,以陆地棉标准系TM-1为父本构建F₂作图群体,利用在亲本间筛选出的多态性SSR引物,通过JoinMap 3.0软件构建了2张遗传图谱,以Win QTLCart 2.5复合区间作图法在F₂~F_2:3中定位到控制全生育期、苗期、蕾期、花铃期和霜前铃数等早熟性相关性状的37个QTL。控制早熟性的有利等位基因多来自早熟祖先611波和金字棉。多数性状在两类材料中由不同的基因控制,且以加性遗传为主。在由43个陆地棉品种材料构成的自然群体中通过关联分析检测到54个与这些早熟性相关性状极显著关联的位点。研究表明连锁作图和关联分析的检测结果具有较高的可比性。本研究为早熟陆地棉聚合改良以及分子标记辅助育种打下了基础。     

Evaluation of newly developed SSR markers and identification of quantitative trait loci for bast fibre cellulose in white jute (Corchorus capsularis)

Cellulose is one of the main chemical component of bast fibre in jute. However, quantitative trait loci (QTL) for bast fibre cellulose content remains elusive. In this study, we identified 846 new SSR markers from 70,792 unigenes in the NCBI and validated them in a panel of 24 diverse jute accessions. Of 846 SSRs, 748 (88.41%) were successfully amplified, and 585 (69.14%) showed polymorphisms, implying that these are high‐quality SSRs. Furthermore, 585 SSRs along with 5,074 polymorphic SLAF (specific locus amplified fragment) and 173 InDel markers were used to reconstruct a high‐dense linkage map in a recombinant inbred population with 104 F₈ lines. Totally, 835 markers were successfully mapped to a whole length of 604.5 cM with a mean distance of 2.84 cM between adjacent markers. Furthermore, five QTLs for bast fibre cellulose were identified. One major QTL (qBFC1‐1) was stable in 2 years and explained average phenotypic variance with 14.34%. These results may be useful for developing enhanced bast fibre quality in white jute through marker‐assisted selection (MAS) breeding.