QTL mapping for economic traits based on a dense genetic map of cotton with PCR-based markers using the interspecific cross of Gossypium hirsutum × Gossypium barbadense

A high-density molecular marker linkage map of cotton based entirely on polymerase chain reaction-based markers is useful for a marker-assisted breeding program. Four kinds of markers—simple sequence repeats (SSRs), sequence-related amplified polymorphism (SRAP), random amplified polymorphic DNA (RAPD), and retrotransposon-microsatellite amplified polymorphism (REMAP)—were used to assay an F₂ population from a cross between “Handan208” (Gossypium hirsutum) and “Pima90” (Gossypium barbadense). Sixty-nine F₂ plants were used for map construction using 834 SSRs, 437 SRAPs, 107 RAPDs, and 16 REMAPs. Linkage analysis revealed that 1,029 loci could be mapped to 26 linkage groups that extended for 5,472.3 cM, with an average distance between 2 loci of 5.32 cM. The corresponding 69 F_2:3 families were grown, arranged in two replicates, and scored for eight phenotypes. Quantitative trait loci (QTL) analysis was performed by means of composite interval mapping using WinQtlCart ver 2.0. A total of 52 distinct QTLs were detected: 4 QTLs for lint index, 8 for seed index, 11 for lint yield, 4 for seed cotton yield, 9 for number of seed per boll, 3 for fiber strength, 5 for fiber length, and 8 for micronaire value. The present map and QTL analysis may provide a useful tool for breeders to transfer desirable traits from G. barbadense to the mainly cultivated species, G. hirsutum.     

Identification of quantitative trait loci across interspecific F2, F2:3 and testcross populations for agronomic and fiber traits in tetraploid cotton

The most widely grown tetraploid Gossypium hirsutum and G. barbadense differ greatly in yield potential and fiber quality and numerous quantitative trait loci (QTLs) have been reported. However, correspondence of QTLs between experiments and populations is poor due to limited number of markers, small population size and inaccurate phenotyping. The purpose of the present study was to map QTLs for yield, yield components and fiber quality traits using testcross progenies between a large interspecific F₂ population and a commercial cotton cultivar as the tester. The results were compared to these from its F₂ and F_2:3 progenies. Of the 177 QTLs identified from the three populations, 65 fiber QTLs and 51 yield QTLs were unique with an average of 8–12 QTLs per traits. All the 26 chromosomes carried QTLs, but differed in the number of QTLs and the number of QTLs between fiber and yield QTLs. The congruence of QTLs identified across populations was higher (20–60 %) for traits with higher heritabilities including fiber quality, seed index and lint percentage, but lower (10–25 %) for lower heritability traits-seedcotton and lint yields. Major QTLs, QTL clusters for the same traits and QTL ‘hotspots’ for different traits were also identified. This research represents the first report using a testcross population in QTL mapping in interspecific cotton crosses and provides useful information for further comparative analysis and marker-assisted selection.     

Relationship between molecular marker heterozygosity and hybrid performance in intra- and interspecific hybrids of cotton

The present study was conducted to investigate the relationship between parental molecular marker diversity and hybrid performance in both intra‐ and interspecific hybrids of cotton to evaluate the feasibility of predicting hybrid performance using molecular markers. Three cytoplasmic male sterile (CMS) lines were crossed with 10 restorer lines to produce 22 F₁ hybrids during 2003. Of 22 F₁s, 14 hybrids were intraspecific (Gossypium hirsutum × G. hirsutum) and eight interspecific (G. hirsutum × G. barbadense). These 22 F₁ hybrids and their parents were evaluated for yield and fibre quality traits at Zhejiang University, Hangzhou, China during 2004 and 2005. Genetic distances (GD) among the parents were calculated from 56 random‐amplified polymorphic DNAs (RAPD) and 66 simple sequence repeat (SSR) marker data, and their correlation with hybrid performance and heterosis were analysed. The parents could be discriminated into G. hirsutum and G. barbadense clusters by cluster analysis based on both RAPD and SSR markers data. The correlation (r = 0.503, P ≤ 0.05) was calculated between GD_rapd (GD based on RAPD markers) and GD_ssr (GD based on SSR markers). Correlation of GD with hybrid performance and heterosis differed considerably between intra‐ and interspecific hybrids. The correlation between GD and hybrid performance was non‐significant for most of traits within the hybrids of G. hirsutum species. However, it was significantly and positively correlated for fibre length, fibre strength and elongation in interspecific hybrids. The relationship between GD and heterosis was observed to be positively significant for boll weight within hybrids of G. hirsutum with significant and negative correlations for fibre length and elongation. In conclusion, the power of predicting hybrid performance using molecular markers in cotton is low. But, the relationship between SSR marker heterozygosity and hybrid performance can be used to predict fibre length during interspecific hybrid cotton breeding.     

Linkage map construction and mapping QTL for cotton fibre quality using SRAP, SSR and RAPD

Tetraploid cotton is one of the most extensively cultivated species. Two tetraploid species, Gossypium hirsutum L. and G. barbadense L., dominate the world's cotton production. To better understand the genetic basis of cotton fibre traits for the improvement of fibre quality, a genetic linkage map of tetraploid cotton was constructed using sequence‐related amplified polymorphisms (SRAPs), simple sequence repeats (SSRs) and random amplified polymorphic DNAs (RAPDs). A total of 238 SRAP primer combinations, 368 SSR primer pairs and 600 RAPD primers were used to screen polymorphisms between G. hirsutum cv. Handan208 and G. barbadense cv. Pima90 which revealed 749 polymorphic loci in total (205 SSRs, 107 RAPDs and 437 SRAPs). Sixty‐nine F₂ progeny from the interspecific cross of ‘Handan208’בPima90’ were genotyped with the 749 polymorphic markers. A total of 566 loci were assembled into 41 linkage groups with at least three loci in each group. Twenty‐eight linkage groups were assigned to corresponding chromosomes by SSR markers with known chromosome locations. The map covered 5141.8 cM with a mean interlocus space of 9.08 cM. A × test for significance of deviations from the expected ratio (1: 2: 1 or 3: 1) identified 135 loci (18.0%) with skewed segregation, most of which had an excess of maternal parental alleles. In total, 13 QTL associated with fibre traits were detected, among which two QTL were for fibre strength, four for fibre length and seven for micronaire value. These QTL were on nine linkage groups explaining 16.18‐28.92% of the trait variation. Six QTL were located in the A subgenome, six QTL in the D subgenome and one QTL in an unassigned linkage group. There were three QTL for micronaire value clustered on LG1, which would be very useful for improving this trait by molecular marker‐assisted selection.     

陆地棉重组自交系产量及产量构成因子性状的上位性QTL分析

棉花的产量及产量构成因子性状是以复杂的方式遗传,遗传力较低并易受环境条件影响。经典数量遗传学指出,上位性是复杂性状的遗传基础。本研究以湘杂棉2号F8和F9世代重组自交系为材料,调查了3个环境下的产量及产量构成因子性状,并构建了遗传连锁图。旨在定位产量及产量构成因子性状的上位性QTL并分析QTL与环境的互作效应。所有产量及产量构成因子性状均检测到上位性QTL,共检测到16对加性互作QTL（AA）,涉及的位点中仅4个有单位点效应,这反映了上位性的复杂性及其对产量和产量构成因子性状的重要贡献。共检测到17对QTL加性和环境互作（AE）,以及14对上位性QTL与环境的互作,表明环境因素对产量和产量构成因子性状起重要影响作用。研究结果还表明上位性效应作为湘杂棉2号的遗传基础起着重要作用。对各性状在不同环境的优良基因型进行了预测。综合优良家系（GSL）和特定环境下的优良家系（SL）的性状表现高于两亲本,表明湘杂棉2号重组自交系各性状都有提高的潜力。由于QTL加性和环境互作以及上位性QTL与环境互作的影响,预测的优良家系基因型会随着环境的改变而不同,表明应针对特定环境开展棉花育种。     

Fine mapping the QTL qFS‐chr.23, using a CSIL

In an earlier advanced‐backcross quantitative trait locus (QTL) analysis of an interspecific cross of Gossypium hirsutum cv. ‘Xinluzhong 36’(‘XLZH36’) and G. barbadense cv. ‘Xinhai 21’(‘XH21’), a QTL for fibre strength in the chromosome segment introgression line IL23‐09 was analysed. Single marker analysis revealed that the markers on chro.23 were associated with fibre strength. Using composite interval mapping with the F₂ population (1296 plants), a QTL for fibre strength was detected on chro. 23. The QTL explained 8.9% and 15.9% of phenotypic variances in the F₂ and F_2 : 3 generations, respectively. Substitution mapping suggested that the QTL was located at a physical distance of 23.4 kb between the markers BNL1414 and the single nucleotide polymorphism (SNP) locus D09_43776813 C‐G. We designated this QTL as qFS‐chr.23 (quantitative trait locus for fibre strength on chro.23). This work provides a valuable genetic resource for the breeding of high fibre quality in cotton and will facilitate future efforts for map‐based cloning.     

Heterosis performance of yield and fibre quality in F1 and F2 hybrids in upland cotton

Because of the difficulty of producing F₁ hybrid seeds by hand emasculation and pollination, wide use of heterosis in cotton production has been limited in China. The objective of this study was to evaluate the potential of F₂ hybrids for yield and fibre quality. A half diallel involving eight parents and their F₁ and F₂ hybrids was grown in replicated studies at Linqing and Nanjing in 1999 and Nanjing in 2000. Yield and fibre quality was determined for all 64 entries. Fibre quality was also determined for parents and F₁s, but only for Zhongmiansuo 28 (ZMS28), Xiangzamian 2 (XZM2) and Wanmian 13 (WM13) F₂s. These three F₂ hybrids are extensively planted in China and provide experimental controls with which to compare the performance of new hybrids. Average yield heterosis for F₁s and F₂s was 15.9 and 9.2%, respectively. Inbreeding depression for yield varied but some F₂s greatly out‐yielded the best variety. Average F₁ heterosis was 6.7, 6.2 and 2.9%, respectively for number of bolls per unit area, boll weight, and lint percentage. The average F₂ heterosis for the same traits was 4.4, 3.3 and 1.6%, respectively. F₁ heterosis for fibre traits was low. In general, parental average was a good indicator of the yield and fibre quality of F₁ hybrids. These encouraging results suggest there is sufficient heterosis for yield to use F₂s in China.     

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。     

Potential for effective marker-assisted selection of three quantitative trait loci conferring adult plant resistance to powdery mildew in elite wheat breeding populations

Three quantitative trait loci (QTL) associated with adult plant resistance (APR) to powdery mildew (Blumeria graminis) in wheat (Triticum aestivum) cultivar ‘Massey’ were mapped in a previous study. The three QTL were located on chromosomes 2A, 2B and 1B, and explained 50% of the total phenotypic variation. A 293 recombinant inbred line (RIL) breeding population (UJ) derived from the cross of ‘USG 3209’, a derivative of ‘Massey’, and ‘Jaypee’ was used to evaluate the potential effectiveness of marker‐assisted selection (MAS) for APR. Powdery mildew severities of the 293 UJ RILs were evaluated in 2002 (F_{5 : 6}) and 2003 (F_{6 : 7}) under natural disease pressure in the field. The 293 RILs were also evaluated for disease severity in a 2004 (F_{7 : 8}) greenhouse experiment using a composite of five different isolates of B. graminis. Selection of RILs possessing the QTL on chromosome 2A, and to a lesser extent, the one on chromosome 1B was effective in identifying powdery mildew resistance in both greenhouse and field experiments. Overall, selecting RILs with QTL on chromosomes 2A and 2B was most successful in identifying highly resistant RILs, which had mean mildew severities of 4.4% and 3.2% in 2002 and 2003 field experiments, respectively. Breeders implementing MAS programs for APR to powdery mildew via selection of RILs containing the two QTL on chromosomes 2A and 2B likely will obtain RILs having high levels of resistance in the field, however combining all three QTL may ensure greater durability.     

Genetic analysis of plant height using two immortalized populations of “CRI12 × J8891” in Gossypium hirsutum L.

Plant height is an important plant architecture trait that determines the canopy structure, photosynthetic capacity and lodging resistance of upland cotton populations. To understand the genetic basis of plant height for marker-assisted breeding, quantitative trait loci (QTL) analysis was conducted based on the genetic map of recombinant inbred lines (RILs) derived from the cross “CRI12 × J8891” (Gossypium hirsutum L.). Three methods, including composite interval mapping, multiple interval mapping and multi-marker joint analysis, were used to detect QTL across multiple environments in the RILs and in the immortalized F₂ population developed through intermating between RILs. A total of 19 QTL with genetic main effects and/or genetic × environment interaction effects were identified on 15 chromosomes or linkage groups, each explaining 5.8–14.3 % of the phenotypic variation. Five digenic epistatic QTL pairs, mainly involving additive × additive and/or dominance × dominance, were detected in different environments. Seven out of eight interacting loci were main-effect QTL, suggesting that these loci act as major genes as well as modifying genes in the expression of plant height. The results demonstrate that additive effects, dominance and epistasis are all important for the genetic constitution of plant height, with additive effects playing a more important role in reducing plant height. QTL showing stability across environments that were repeatedly detected by different methods can be used in marker-assisted breeding.     

Genetic effects of nine <Emphasis Type="Italic">Gossypium barbadense</Emphasis> L. chromosome substitution lines in top crosses with five elite Upland cotton <Emphasis Type="Italic">G. hirsutum</Emphasis> L. cultivars

Crosses between Gossypium barbadense L and Gossypium hirsutum L. (Upland cotton) have produced limited success in introgressing fiber quality genes into the latter. Chromosome substitution lines (CSBL) have complete chromosomes or chromosome arms from G. barbadense, line 3-79, substituted for the corresponding chromosome or arms in G. hirsutum in a near isogenic background of TM-1. We top crossed nine CSBL and their parents (TM-1 and 3-79) with five cultivars. Parental lines and their F₂ populations were evaluated in four environments for agronomic and fiber quality traits. The CSBL and their F₂ hybrids showed wide ranges for both agronomic and fiber traits of economic importance. Genetic analysis showed that additive variances were larger than dominance variances for lint percentage, boll weight, lint yield, fiber length, strength, elongation, micronaire, and yellowness; whereas, dominance variances were larger than additive variances only for uniformity of fiber length and equal for fiber reflectance. For all traits, except boll weight and lint yield, significant additive effects of one or more chromosomes from 3-79 in TM-1 background were greater than the corresponding TM-1 chromosome. In addition, we identified specific chromosomes from G. barbadense (3-79) that carry alleles for improvements in specific fiber quality traits in Upland cotton. Favorable additive effects of individual chromosomes or chromosome segments from 3-79 relative to corresponding chromosomes or chromosomes segments from TM-1 were identified in this study as follows: Lint percentage, chromosome/arms 10, 16-15; longer fibers, chromosome/arms 01, 11sh, 26Lo; more uniform fibers, chromosomes/arms 01, 11sh, 10, 17-11; stronger fibers, chromosome/arms 01, 11sh, 12sh, 26Lo, 17-11; fiber elongation, chromosomes/arms 01, 11sh, 26Lo, 10, 17-11; reduced fiber micronaire, chromosome/arms 01, 12sh, 4-15, 16-15, 17-11; fibers with more reflectance, chromosome/arms 10, 4-15, 16-15, 17-11; fiber with less yellowness, chromosome arms 4-15, 17-11. Based on the present study, we concluded that by using CSBL, favorable fiber quality alleles can be introgressed into Upland cotton, thus greatly improving the breeder’s ability for improvement of Upland cotton for a variety of traits. These data should provide useful genetic information to the cotton breeding industry at large.     

Evaluation of genetic variances, heritabilities, and correlations for yield and fiber traits among cotton F2 hybrid populations

Summary F₂ hybrid cultivars continue to occupy a small portion of the cotton (Gossypium hirsutum L.) production are in the United States, but occupy a larger proportion of the production area in some other countries. Sixty-four F₂ hybrids resulting from crosses of four commercial cultivars and 16 pest-resistant germplasm lines were evaluated for five fiber and four yield traits in four environments at Mississippi State, MS. An additive-dominance genetic model was employed for these traits. The minimum norm quadratic unbiased estimation (MINQUE) method was used with a mixed model approach for estimating genetic variance and covariance components and for predicting genetic correlations. This study investigated genetic variances, heritabilities, and genetic and phenotypic correlations between agronomic and fiber traits among these 64 F₂ hybrid populations and discussed the usefulness of these populations for use as hybrids or for selections for pure lines.Dominance variance accounted for the major proportion of the phenotypic variances for lint yield, lint percentage, and boll size indicating that hybrids should have an advantage for these traits compared to pure lines. A low proportion of additive variance for fiber traits and the significant additive x environment variance components indicated a lack of substantial useful additive genetic variability for fiber traits. This suggests that selections for pure lines within these F₂ populations would have limited success in improving fiber traits. Genetic and phenotypic correlation coefficients were of comparable magnitude for most pairs of characters. Fiber strength showed a positive additive genetic correlation with boll weight. Dominance genetic correlations of fiber strength with elongation and 2.5% span length were also significant and positive; however, the additive genetic correlation of length and strength was zero.Contribution of the USDA-ARS in cooperation with the Mississippi Agric. and Forestry Exp. Stn.     

Genetic variance components and genetic effects among eleven diverse upland cotton lines and their F2 hybrids

Selecting high yielding upland cotton, Gossypium hirsutum L. lines with improved fiber quality is a primary breeding goal. A diverse set of ten cultivars and one breeding line were crossed in a half diallel. Parents and F₂ hybrids were grown in three environments at Mississippi State, MS. Ten agronomic and fiber traits were analyzed by a mixed linear model approach based on the additive-dominance genetic model. Variance component, genetic effects and genetic correlations were calculated. ‘Acala Ultima’ was a desirable general combiner for fiber length, uniformity, strength, micronaire, lint percentage, and boll weight. ‘FiberMax 966’ was a desirable general combiner for fiber length, uniformity, strength, and all agronomic traits. ‘Tamcot Pyramid’ and M240 were poor general combiners for both fiber and agronomic traits. ‘Coker 315’ was a good general combiner for fiber length, uniformity, micronaire, boll weight, boll number, and yield. Heterozygous dominance effects were associated with several crosses, which suggest their use as hybrids.     

Heterosis in growth and photosynthetic rate in hybrids of cotton

Summary The intraspecific (Gossipium hirsutum) and interspecific (G. hirsutum x G. barbadense) F₁ hybrids of cotton were found to exhibit a high degree of heterosis in the production of fruiting branches, number of bolls (fruits), yield of seed cotton and photosynthetic rates over the parent plants. The developing bolls of the hybrids had significantly higher weights than their parents until the 20th day after anthesis. The patterns of leaf area development among interspecific hybrids differed when compared with the parent plants. The photosynthetic rates of the hybrids were comparable with those of maize and sorghum and much higher than the average rate reported so far for the cotton plant.     

Production of fertile hybrid germplasm with diploid Australian Gossypium species for cotton improvement

The 17 wild Australian Gossypium species are distant diploid relatives of the commercial tetraploid cottons, G. barbadense L. and G. hirsutum L. They interest cotton breeders as a source of terpenoid-aldehyde-free seeds, a trait only found in five Australian Gossypium species. They elicit further interest because some species grow near current and projected cotton growing areas in Australia and thus could serve as unintentional recipients of transgenes from genetically engineered cotton cultivars. The utility of the wild Australian Gossypium species in cotton breeding depends on the ability to generate fertile hybrids, and to the extent this is possible under glasshouse conditions, it allows predictions regarding the probability that fertile hybrids between the transgenic cottons and spatially associated populations of wild species will arise without human manipulation. The Australian Gossypium species fall into three morphologically and cytologically distinct groups designated the C, G, and K genomes, The G-genome species hybridize most readily with G. arboretum (a diploid A-genome cultivated cotton), while the C- and K-genome species are more compatible with G. hirsutum (a tetraploid AD-genome cultivated cotton). These intergenomic hybrids are sterile, and the chromosome complement of the hybrids must be doubled prior to backcrossing to G. hirsutum. The only exceptions were four G. hirsutum × K-genome triploids, which exhibited limited female fertility when backcrossed to G. hirsutum. Two of the three diploid species geographically associated with commercial cotton fields (G. australe F. Mueller & G. rotundifolium Fryxell, Craven & Stewart) failed to produce hybrid progeny when pollinated with G. hirsutum pollen; the third species (G. sturtianum J.H. Willis) produced only 5 sterile triploids from 25 pollinations. Thus, the probability that wild species could serve as recipients of transgenes is functionally zero, especially in conjunction with the profound prezygotic barriers that separate the cultivated tetraploid cottons from their wild Australian relatives. Eighteen new fertile synthetic polyploids and 23 self-fertile derivatives of two synthetic hexaploids were produced. Synthetic tetraploids require greater effort to backcross than do synthetic hexaploids. These fertile hybrids represent a new avenue of introgression of genes from wild Australian Gossypium species into commercial cotton cultivars, an avenue limited only by the level of recombination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterosis in yield,fiber quality,and photosynthesis of okra leaf oriented hybrid cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

Leaf shape is an important factor affecting canopy structure, photosynthetic characteristics, and yield. Introducing okra leaf shape is considered an important strategy in cotton heterosis breeding. The objective of the study was to evaluate the heterosis in okra leaf cotton hybrid F₁s, which were developed by crossing two sterile near isolines and three restorer near isolines. A normal leaf check hybrid F₁, Zhongza 29, and four newly developed okra leaf oriented hybrid F₁s, including the super-okra (severely cleft and narrowly lobed leaf), okra (deeply cleft and narrowly lobed leaf), semi-okra (intermediate leaf lobe), and sub-okra (large leaf lobe) hybrids were selected in this experiment. Okra leaf oriented cotton hybrids significantly reduced leaf area index (LAI) (P < 0.0001), thus more light penetrated into the lower canopy. The LAIs for the super-okra and okra hybrids, however, were too small to supply adequate photosynthate, thus resulting in early maturity, short boll filling period, and low yield. As the LAI increases, the semi-okra and sub-okra hybrids showed certain heterosis. The semi-okra hybrid showed 7–12% heterosis over the check hybrid in lint percent, 6–11% in boll weight, 2–147% in canopy light intensity, 1–10% in net photosynthetic rate (Pn), and −3 to 3% in lint yield. As well, all tested okra leaf hybrids improved fiber quality such as micronaire compared with the normal leaf check hybrid. The results suggested that adopting okra leaf parental lines in cotton breeding provided potentials in increasing fiber quality with comparable lint yield.     

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.     

Cytogenetics of the 'glandless-seed and glanded-plant' trait from Gossypium sturtianum Willis introgressed into upland cotton (Gossypium hirsutum L.)

In order to introgress the ‘glandless-seed and glanded-plant’ trait from Gossypium sturtianum Willis (2n= 2x= 26, C₁ genome) into the cultivated upland cotton Gossypium hirsutum L. (2n= Ax= 52 (AD), genome), two trispecific hybrids have been created using either Gossypium thurberi Torado (2n= 2x= 26, D₁ genome) or Gossypium raimondii Ulbrich (2n= 2x= 26, D₅ genome) as bridge species. The cross of both trispecific hybrids by G. hirsutum produced the first backcross progenies (BCl). Cytogenetic analysis showed that the trispecific hybrids had 52 chromosomes, their chromosome configurations at metaphase I (Ml) being 15.071 + 15.3411 + 0.93III + 0.69IV + 0.26VI in G. thurberi×G. sturtianum×G. hirsutum (TSH) and 14.421 + 17.0311 + 0.82III + 0.15IV + 0.07VI in G. hirsutum × G. raimondii ×. G. sturtianum (HRS), respectively. Among six BCl plants analysed, the only plant expressing the ‘glandless-seed and glanded-plant’ trait had 52 chromosomes and a meiotic configuration of 5.261 + 20.61II + 0.69III + 0.77IV at MI. Pollen fertility was 2.90% in TSH, 8.97% in HRS, and ranged from 0% to 40.28% in the BCl progenies. The introgressed BCl plant is perennial in growth habit. It can be used in breeding programmes aiming at the introgression of the ‘glandless-seed and glanded-plant’ trait into a cultivar of upland cotton.     

Molecular mapping and characterization of traits controlling fiber quality in cotton

Cotton (Gossypium spp) is the world's leading natural fiber crop. Genetic manipulation continues to play a key role in the improvement of fiber quality properties. By use of DNA-based molecular markers and a polymorphic mapping population derived from an inter specific cross between TM-1 (G. hirsutum) and 3-79 (G. barbadense), thirteen quantitative trait loci (QTLs) controlling fiber quality properties were identified in 3-79, an extra long staple (ELS) cotton. Four QTLs influenced bundle fiber strength, three influenced fiber length, and six influenced fiber fineness. These QTLs were located on different chromosomes or linkage groups and collectively explained 30% to 60%of the total phenotypic variance for each fiber quality property in the F₂ population. The effects and modes of action for the individual QTLs were characterized with 3-79 alleles in TM-1 genetic background. The results indicated more recessive than dominant, with much less additive effect in the gene mode. Transgressive segregation was observed for fiber fineness that could be beneficial to improvement of this trait. Molecular markers linked to fiber quality QTLs would be most effective in marker-assisted selection (MAS) of these recessive alleles in cotton breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic effects of introgression genomic components from Sea Island cotton (<Emphasis Type="Italic">Gossypium barbadense</Emphasis> L.) on fiber related traits in upland cotton (<Emphasis Type="Italic">G</Emphasis>. <Emphasis Type="Italic">hirsutum</Emphasis> L.)

The germplasm with exotic genomic components especially from Sea Island cotton (Gossypium barbadense L. Gb) is the dominant genetic resources to enhance fiber quality of upland cotton (G. hirsutum L., Gh). Due to low efficiency of phenotypic evaluation and selection on fiber quality, genetic dissection of favorable alleles using molecular markers is essential. Genetic dissection on putative Gb introgressions related to fiber traits were conducted by SSR markers with mapping populations derived from a cross between Luyuan343 (LY343), a superior fiber quality introgression line (IL) with genomic components from Gb, and an elite Upland cotton cv. Lumianyan#22 (LMY22). Among 82 polymorphic loci screened out from 4050 SSRs, 42 were identified as putative introgression alleles. A total of 29 fiber-related QTLs (23 for fiber quality and six for lint percentage) were detected and most of which clustered on the putative Gb introgression chromosomal segments of Chr.2, Chr.16, Chr.23 and Chr.25. As expected, a majority of favorable alleles of fiber quality QTLs (12/17, not considering the QTLs for fiber fineness) came from the IL parent and most of which (11/12) were conferred by the introgression genomic components while three of the six (3/6) favorable alleles for lint percentage came from the Gh parent. Validation of these QTLs using an F₈ breeding population from the same cross made previously indicated that 13 out of 29 QTLs showed considerable stability. The results suggest that fiber quality improvement using the introgression components could be facilitated by marker-assisted selection in cotton breeding program.