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Lint percentage is a major yield component in cotton breeding programmes. To identify quantitative trait loci (QTLs) and candidate genes related to lint percentage, we used an intraspecific recombinant inbred line population of 137 lines derived from Gossypium hirsutum cv. CCRI36 and G. hirsutum acc. G2005 for QTL mapping of lint percentage. Based on a high-density genetic map and phenotype data collected in four growing environments, we identified a total of 28 QTLs for lint percentage. Three stable QTLs (qLP-At5-2, qLP-Dt7-1 and qLP-Dt7-2) were detected in at least two environments. Two genes (Gh_A05G1584 and Gh_A05G1689) containing nonsynonymous single nucleotide polymorphisms (SNPs) were identified by association analysis using published data. The quantitative real-time PCR results showed that the expression levels of Gh_A05G1584 were higher in cv. CCRI36 than in acc. G2005 during all fibre development stages; Gh_A05G1689 was mainly expressed in 15 and 25 days post-anthesis fibres and its expression level was higher in cv. CCRI36. These results suggest candidate genes for lint percentage and provide molecular information for use in cotton breeding programmes aimed at improving yield.

Fiber length is an important parameter to spin cotton fibers. Cotton breeders work to improve length, and research samples may be machine-harvested, resulting in variability for trash content between samples within the same experiment. There is evidence that trash may directly or indirectly affect the measurement of some fiber quality parameters like micronaire and strength. We hypothesize that the presence of trash particles in the samples may compromise the quality of the length measurement and screening decisions in breeding programs. In order to test this hypothesis, we developed an experiment to evaluate the heritability of length parameters for entries with the same genetic background and affected by the same environment with different trash content. The heritability estimates for samples with high trash content are different from the estimates for samples with native low trash content. Cleaning trashy samples with a laboratory-scale lint cleaner brings the heritability estimates closer to the calculated values for samples with native low trash content. Although the values are similar, the types of variation are not the same. These results indicate that breeders must avoid making decisions based on samples with high trash content. Breeders should base their decisions on samples with low original trash content because this type of sample provides research results closer to the native length distribution.

This research evaluated the potential for using sexual crosses for genetic improvement of fiber yield, lint percent, AFIS fiber quality, and fiber initiation of two naked-tufted mutants of cotton (Gossypium hirsutum L.). The naked tufted lines were crossed with ten fuzzy breeding lines to generate 10 F2 populations. The F2 distributions were tested with Chi Square for Goodness of Fit to two monogenic and two digenetic segregation ratios. Five of the six F2 populations made with Atlas-NS-129 segregated as either a single dominant gene (3 Naked-tufted: 1 fuzzy) or as two dominant genes (9 Naked-tufted: 7 fuzzy). Three of the four F2 populations made with SC 9023-ns-57 segregated as either a single recessive gene (3 Fuzzy: 1 naked-tufted) or as duplicate recessive genes (9 Fuzzy: 7 naked-tufted). However, the F2 populations when crossed with the Fuzzy line of Tejas 48 showed a reversal of dominance. The F2 population of Atlas-NS-129 X Tejas 48 fit a 9 Fuzzy: 7 naked tufted ratio expected of two recessive genes. The F2 population of the cross of SC 9023-ns X Tejas 48 fit a 3 Naked-tufted: 1 fuzzy ratio expected of a single dominant gene. Additional studies will be necessary to fully determine the number of gene(s) and the expected phenotypic ratios of individual naked-tufted mutants in crosses with fuzzy seeded breeding lines. Eight of the F2 and F3 populations were also evaluated for lint yield, lint percent and AFIS fiber quality traits. The F2 and F3 populations of the cross of Atlas-NS-129 X Holland 338 produced the highest average lint yields (1089 kg ha−1) as well as excellent fiber quality. These data indicate that it may be possible to develop relatively high yielding naked tufted cultivars by crossing these mutant lines with elite higher yielding breeding lines.

The Texas High Plains often has extended periods between rainfall events, which can lead to a reduction in the yield and fiber quality of cotton (Gossypium hirsutum L.). It is known that cultivated cotton suffers from low levels of genetic diversity due to the over-use in breeding of similar gene pools, which may hinder breeding for drought tolerance. In this study, for the first time the novel variability or genetic diversity of morphological and agronomic traits possibly created by the chemical mutagen ethyl methanesulfonate (EMS) was evaluated to improve drought tolerance in cotton by traits’ response to different irrigation regimes. EMS is a chemical mutagen that has been shown to cause point mutations in the DNA of many model plants and crop species. Three EMS treated lines were advanced from the M1 to M4 generation as bulk-harvested populations. A diverse selection scheme was applied to capture most of the genetic trait-variability or diversity and superior lines in these populations. In 2014–2016 the diversity of these populations was evaluated based on four agronomic and thirteen morphological traits to determine differences in response to multiple irrigation rates. Analyses of these traits showed statistically significant (p ≤ 0.05) differences between and within populations when compared to the original non-treated EMS source, with most of the variability being observed in the high irrigation rate. However, none of the EMS treated populations had significantly (p ≤ 0.05) better lint yield than the commercial cultivar (control) in 2016. EMS yield performance was possibly constrained by the applied diverse selection scheme of this study. Traits such as total number of bolls, bolls retained at node 7 and below, and those retained between nodes 8 and 12, and bolls retained at node of first fruiting branch may be predictors to improve cotton production (yield) in water limiting environments.

The complex genetic and environmental control of lint fiber yield and quality of cotton has long motivated interest in whether information from genetically-simpler trichome variations might contribute knowledge salient to cotton improvement. To investigate this question, from 3164 M5 lines resulting from EMS mutagenesis of two Gossypium hirsutum breeding lines, TAM 94L25 and Acala 1517-99, 106 lines with leaf and stem trichome variations and 55 control lines were further studied to investigate associations between trichome variation and lint fiber development. Although only weak correlation was found between stem/leaf trichome and fiber traits, we still found that among nine fiber traits measured in replicated trials, lines with mutations affecting stem trichome development had significant alterations for seven traits in the TAM 94L25 mutants, and six in the Acala 1517-99 mutants. While the small number of leaf trichome mutants found offered only minimal statistical power to resolve differences, mutant lines had significant alterations for three of the nine traits in the TAM 94L25 mutants, and two in the Acala 1517-99 mutants. In summary, mutants in leaf and/or stem trichome development often have altered lint fiber characteristics, supporting the hypothesis that there is considerable overlap in the sets of genetic factors acting in the development of these analogous organs. Moreover, visual selection of trichome mutants may be an effective screen to identify potential new alleles affecting lint fiber development.

Field variation is one of the important factors that can have a significant impact on genetic data analysis. Ineffective control of field variation may result in an inflated residual variance and/or biased estimation of genetic variations and/or effects. In this study, we addressed this problem by merging genetic models with the information from a rectangular cotton field layout (referred to row and column directions). Data from a genetic mapping study in Upland cotton (Gossypium hirsutum L.) was used to validate the proposed methodology. This study included model evaluation based on simulations and actual data analysis on four agronomic traits (seed yield, lint yield, lint percentage, and boll weight) in cotton. Results based on simulations suggested that when there were no row and column effects, the conventional and the extended genetic models yielded similar results. However, when either field row and/or column effects were significant, the conventional genetic model yielded biased estimates for residual variance component with larger mean square error whereas the extended genetic models yielded more unbiased estimates. Actual data analysis revealed that lint yield and seed yield were significantly influenced by the systematic variation present in the field. With the extended model, the residual variance associated with these traits was reduced approximately 65 % compared to the conventional block model. Accordingly, the averaged heritability estimate increased by about 18 % for these traits. Thus, the results suggested that genetic data analysis can be improved when field variation is considered.

Six short-season cotton cultivars (Gossypium hirsutum L.) were crossed in a diallel crossing system to evaluate inheritance and interrelationship of phenotype and genotype of yield and yield-related traits (cottonseed yield, lint yield, cottonseed yield before frost, lint yield before frost, lint percentage, boll weight and boll number) and their correlation with earliness traits. The study was carried out from year 2005 to year 2008. The experiment design was a randomized complete block design with three replications. Additive, dominance and epistasis effects were analyzed with ADAA model. The results showed that yield and yield-related traits were mainly controlled by dominant genetic effects and also had a definitely proportion additive by environment interaction effects. Cottonseed yield, lint yield, cottonseed yield before frost, boll weight, lint percentage, boll number and lint yield before frost had the highest broad sense by environment interaction heritability (HBE) estimates, 0.653, 0.602, 0.600, 0.528, 0.416, 0.387 and 0.324, respectively. Lint percentage, cottonseed yield, lint yield and cottonseed yield before frost had higher narrow sense by environment interaction heritability (HNE), 0.416, 0.301, 0.263 and 0.185, respectively. Only boll weight and boll number had the highest narrow sense heritability (HN), 0.345 and 0.139, respectively. Some F1 hybrids had positive significant heterozygous dominance effects. Some F1 hybrids had significant positive epistatic effects and affected by environment. Among yield and yield-related traits, they all had significant positive genetic and phenotypic correlation, excepting lint percentage and boll weight, boll weight and boll number had significant negative genetic and phenotypic correlation. Yield and yield-related traits had a negative correlation with earliness traits except lint percentage and boll number. Lint percentage with harvested rate before frost, date of first square and number of node first sympodial branch, boll number with yield and relative traits showed significant negative genetic correlation. The results showed that the higher the lint percentage, boll weight and boll number and the higher harvested yield and the later the maturing. Based on these results, it is suggested to selection of yield and yield-related traits should be undertaken at late generation (F4, F5), and early-maturing parents A1, B1, B2 and B3 could be used to improve yield and yield-related traits in short-season cotton breeding programs.

In a hypothetic population of cotton, Gossypium hirsutum L., segregating for 26 independent alleles, individuals with all desired alleles are more abundant in early generations (F2 or F3), but a high proportion of allelic loci are homozygous in late generations (F4 or F5). This dichotomy needs to be considered to establish a successful breeding strategy. In this study, we examined the effectiveness of two pedigree procedures in cotton with their key difference in the self-generations used for single plant selection. The conventional procedure started single plant selection at F3 by hand-harvest of a 30-boll sample from individual plants, then in the follow-up generation, only those derived lines retained after culling for lint percent and High Volume Instrument (HVI) fibre quality entered the progeny row test. The alternative procedure used single-locule descent for pass-through of early generations; at F5, only two mature bolls were harvested from selected individual plants, and their derived lines were grown and culled in single-row plot nursery by visual assessment, and by lint percent and HVI fibre properties measured from a 30-boll sample. When each procedure was used to develop elite inbred lines in two populations derived from outstanding cotton lines, both procedures were effective at identifying elite lines from the populations. The alternative procedure captured more elites than the conventional one, based on the retention rate against the initial population size, particularly in one population, and required less resources in the process. Thus, the alternative procedure with delayed single plant selection is effective and efficient for cotton improvement.

American Pima cotton (Gossypium barbadense L.) is grown in the southwest United States, and no Pima cotton hybrid is commercially grown. In this study, six commercial Pima cultivars (Pima S-7, Pima S-6, Phy 76, BR 007, DP 340, and DP 744) and three elite germplasm lines (SI 1331, 93252, and 8810) were crossed in a diallel mating scheme without reciprocals, and their 36 F2 and F3 progeny were planted in replicated tests at two locations (L) in 2004–2005. Yield and fiber traits were analyzed using Griffing’s Model 1, Method 2 diallel analysis. Genetic distance (GD) of parent lines was determined using 661 AFLP molecular markers. Across locations, significant genotype (G) and general combining ability (GCA) effects were detected for yield, boll size, lint percent, micronaire, 2.5% fiber length, fiber strength, and elongation. Significant specific combining ability (SCA) effects were detected for yield, micronaire, and strength. Lint yield and the yield components- boll size and lint percent exhibited significant G × L interactions. Significant GCA × L interactions occurred for yield and lint percent. Yield, boll size, and micronaire also had significant SCA × L interactions. No significant GCA or SCA by L interactions were detected for fiber length, strength, and elongation. The mean mid-parent heterosis (MPH) of the 36 hybrids in lint yield was low in F2, but non-existent in F3. Among the nine parents, Pima S-7 and DP 340 had the highest and significant positive GCA effects for lint yield, lint percent, and boll weight across tests. Only several F2 hybrids with Pima S-7 and DP 340 as one parent displayed some levels of useful heterosis in lint yield in the two locations, as compared to Pima S-7 as the check. MPH for other agronomic and fiber quality traits was low to non-existent in both generations. The average GD of the parents were not significantly correlated with their GCA effects, and GD between parents was also not correlated with SCA and MPH of their hybrids, with the exception of lint yield at the Las Cruces location where a significant negative correlation was obtained. However, GD of the parents was correlated with the performance of hybrids in lint yield, fiber length, fiber strength and elongation in one or two tests. This study represented one of the first studies to estimate heterosis, combining ability, and their relationship with genetic distance of parents in a representative subset of Pima cotton genotypes.

The cultivated tetraploid Gossypium barbadense L. cotton produces superior natural fibers for the textile industry in the world. However, the possibility in utilization of heterosis to further increase its lint yield has not been extensively explored. In this study, two commercial US Pima cotton cultivars and three exotic G. barbadense lines, together with all of their possible hybrids in F1 and F2 progeny without reciprocals, were tested for lint yield, yield components, and fiber quality traits in four environments in 2005–2007. With a few exceptions, genotype (G), environment (E), and G × E were all significant or highly significant for all the traits studied. General combining ability (GCA) variances for all the traits in both F1 and F2 were also significant, while specific combining ability (SCA) variances were detected only for lint yield, fiber length, and micronaire in both generations and boll weight in F1. GCA × E was also detected for lint percent, seed index, and fiber length in both F1 and F2, and boll weight in F1, but none of the traits had significant SCA × E. As a group, F1 and F2 out-yielded the parent group by 20–40% and 6–10%, respectively. Mid-parent heterosis (MPH) for lint yield in F1 was generally positive, ranging from −4.7 to 116.4% with an average of 21.2–48.7%, while lint yield MPH in F2 ranged from −23.3 to 69.4% with an average of 6.4–12.4%. However, useful heterosis in lint yield was only detected in the hybrid between the two US commercial cultivars Pima S-7 and DP 340. MPH for other traits was low or not detected. MPH in F2 was lower than that in F1 but they were generally positively correlated. The genetic distances (GD) of the parents (based on 467 polymorphic RAPD and AFLP markers) between the five parents was not consistently correlated with MPH and SCA of their hybrids and dominant effects for lint yield and other traits. However, significant and positive correlations between GD of parents and the performance of their hybrids were detected for lint yield, lint percentage, and lint index in both F1 and F2 in most of the tests. GD of parents was also correlated with their GCA and additive effects in lint yield, lint percent, lint index, micronaire, plant height, and elongation. The results suggest that the close correlation between GD and hybrid performance per se was mainly due to the existence of GCA and additive effects from parents.

Quantitative trait locus (QTL) mapping lays the foundation for marker-assisted selection (MAS) for lint yield and fiber quality in cotton (Gossypium hirsutum). Boll-related traits affect yield and fiber quality, but few studies have focused on boll-related traits. Here, we detected QTLs related to cotton boll, yield and fiber quality traits using intraspecific F2 and F2:3 populations from the cross AQ × 08-10604. A total of 91 QTLs for 17 traits related to boll, yield and fiber quality in the F2 and F2:3 populations were mapped, including 37 significant QTLs. Six pairs of common QTLs were detected, including two pairs for boll coat weight (BCW) in the same or similar positions on Chr. A10 and D1, two pairs for boll length (BL) in similar positions on Chr. A10 and A13, with a higher percentage of phenotype variation and two pairs for boll diameter (BD) in similar positions on Chr. A10 and D1. These results suggest that the traits BCW, BL and BD have high levels of stability. Five QTL clusters for the same or different traits were also identified on Chr. A10 (2), A13, D1 and D5. We also detected 64 epistatic QTLs for boll- and yield-related traits that play important roles in genetic variation. Correlation analysis revealed significant positive correlations between seed yield and boll number per plant and between boll weight and BCW, BL and BD. The results of this study enhance our understanding of the genetic basis of boll-related traits and will enable further MAS of upland cotton.

Six short season cotton cultivars (Gossypium hirsutum L.) were crossed in a dillalel crossing system to evaluate inheritance and interrelationship of phenotype and genotype of fiber quality traits (fiber length, uniformity index, fiber strength, micronaire and fiber elongation) and their correlation with earliness and yield traits. The study was carried out from year 2005 to 2008. The experiment design was a randomized complete block design with three replications. Additive, dominance and epistasis effects were analyzed with ADAA model. The results showed that fiber quality traits were mainly controlled by dominant genetic effects and also had a definitely proportion additive genetic effects. Micronaire, fiber length, fiber strength and fiber elongation had the highest broad sense heritability (HB) and by environment interaction (HBE) estimates, 0.618 (HB) and 0.267 (HBE) for micronaire, 0.510 (HB) and 0.287 (HBE) for fiber length, 0.452 (HB) and 0.316 (HBE) for fiber strength, 0.294 (HB) and 0.494(HBE) for fiber elongation, respectively. Narrow sense heritability (HN) was 0.258 for fiber elongation, 0.136 for fiber length, 0.127 for fiber strength and 0.110 for micronaire. Some F1 hybrids (A1×B2), (A2×A3) and (B1×A3) for fiber length, F1 (A2×B3) and (B1×B2) for fiber strength, F1 (B1×A2), (A2×B2), (A2×B3), (B1×A3), (B2×A3) and (B1×B2) for micronaire and F1 (A1×A2), (A1×A3), (A1×B1), (A1×B3) and (B2×A3) for fiber elongation had significant positive heterozygous dominance effects and affected by environment. Some F1 hybrids (A1×A2), (A1×B1), (A1×B3), (B1×A2) and (B2×A3) for fiber length, (A1×A3), (A1×B1) and (A1×B3) for fiber strength, (A1×A3), (A1×B1), (A1×B2) and (B2×B3) for micronaire and (A2×A3), (A2×B2), (A2×B3) and (B1×B2) for fiber elongation had significant positive epistatic effects. Among fiber quality traits, fiber length with fiber strength, uniformity index with fiber strength and micronaire, fiber strength with micronaire showed a positive and significant correlation. Only elongation had a significant negative correlation with fiber quality traits. Fiber quality traits had a negative correlation with earliness traits except micronaire. Fiber length and strength showed a significant negative correlation with lint yield, lint yield before frost, lint percentage and boll number. Uniformity index, micronaire and fiber elongation had a significant positive correlation with yield traits except boll weight and lint percentage. The results showed that the higher the yield and the earlier the maturing and the worse the fiber quality. Therefore, selections of fiber properties and integration of high yield, good fiber quality and early maturing traits should be performed in higher generations in short season cotton variety breeding program.

Relationships between lint yield and within-boll yield components are important for genetic improvement of lint yield in cotton (Gossypium hirsutum L.) cultivars. F2 plants derived from crosses between germplasm lines and high yielding cultivars were analyzed to determine the contributions of within-boll yield components to lint yield and to select parents with desirable combining ability for multiple within-boll yield components. Forty-five F2 hybrids were planted at two field sites in 2010 and 2011 with 4 and 3 replicates, respectively. There were a total of six yield components analyzed including lint percentage (LP), seed number per boll, lint weight per seed (LW_S), seed surface area per seed, lint weight per unit seed surface area (LW_SA), and lint number per unit seed surface area (LN_SA). The contributions of these yield components to lint yield were analyzed by commonality analysis that separated the contributions to lint yield into the unique contributions of single yield components and the common contributions of the single yield components with one or more other yield components. The unique contributions of the six yield components to lint yield ranged from 1.6 to 21 % of total variation for lint yield in the 2-year experiments. The greatest common contributions to lint yield among all combinations of the six yield components were identified for a combination of four components, LP, LW_S, LW_SA, and LN_SA with 67 and 44 % of the total variation of lint yield in 2010 and 2011, respectively. Results suggest that all four of these yield components should be considered simultaneously in breeding for genetic improvement of lint yield. The germplasm line SP225 was detected as a good combiner with positive general combining ability (GCA) for LP (1.4 %), LW_SA (0.03 mg mm−2), and LN_SA (14.3 no mm−2), and favorable GCA for fineness (−3.1 mg km−1).

There is a renewed interest in research and use of glandless (free of gossypol) Upland cotton (Gossypium hirsutum L.) that can produce edible seeds for human food and animal feed. However, there was a lack of information on yield potential of existing glandless germplasm since intermittent breeding activities for glandless cotton were stopped in the U.S. before 2000. The objectives of the present study were to test obsolete and exotic glandless germplasm for possible production and evaluate progress in direct pedigree selection within the existing glandless germplasm in eight field tests. In multiple tests, the glandless cotton Acala GLS yielded only 65–80 % lint of the glanded control Acala 1517-08 and 46–75 % lint of commercial transgenic cultivars. Most of obsolete glandless germplasm and their selections yielded

Upland cotton (Gossypium hirsutum L.) hybrids display commercially useful levels of heterosis for lint yield. Cotton lint yield is primarily a multiplicative product of boll number and lint per boll, both of which can be further dissected into sub-components. Relationships among the yield components are complex where they further interact with the environment. To identify different yield components of hybrid cotton lint yield and their relationship with environment, three cotton varieties, DP51, STV474 and LA887 and, their respective hybrids were evaluated for lint yield components across five environments. Heterosis was observed for lint yield as well as yield components. The relationship between heterosis and mean environmental yield was negative for two hybrid combinations, whereas one hybrid showed increased heterosis from low to high yielding environments. Boll number was the major yield component contributing to lint yield. However, yield components contributing to the change in heterosis from low to high yielding environments were different for the three hybrids. The change in lint yield heterosis across environments was correlated with lint per boll and lint per seed for DP51 × STV474 and LA887 × DP51. Whereas, bolls number and boll retention were the main yield components contributing to higher lint yield heterosis of STV474 × LA887 in low yielding environments. Results also reveal effects of parental entries on lint yield as well as relationship of heterosis and environment.

The analysis of genetic correlations between fiber length (Len), strength (Str), micronaire, and 12 other traits was conducted using the additive (A)-dominance (D) genetic model, which considers genotype × environment interaction effects, in intraspecific upland cotton (Gossypium hirsutum L.) hybrids to effectively improve the quality of cotton cultivars in high planting density cases. Decision-making coefficients were computed based on the genetic correlation and path analysis of three fiber quality traits. The decision-making coefficient analysis of three fiber traits in cross breeding was beneficial for the improvement of Len by increasing the additive effects of Str and length of boll (LB) and decreasing lint percentage (LP), boll number of the top three fruit-bearing branches. The analysis was also beneficial for the improvement of Str and fiber fineness by increasing or decreasing the additive effects of other traits. Utilizing heterosis in hybrids was beneficial to the heterosis of Len by selecting the high dominance effects of number of nodes of the 1st fruit-bearing branch and LB and decreasing the dominance effects of diameter of boll (DB) and LP and for improving Str by increasing the dominance effects of DB and decreasing the dominance effects of number of fruit-bearing branches and number of nodes of the main stem (NNMS). Utilizing heterosis was also beneficial for improving fineness by increasing the dominance effects of LB, Str, and lint yield and decreasing the dominance effects of NNMS and Len.

Within-boll yield components are the most basic contributors to lint and seed yield of cotton (Gossypium hirsutum L.), which is a major source of natural fiber and edible oil throughout the world. Little information is available on genetic effects and heterosis of these traits in cotton. Three cotton cultivars and six breeding lines differing in within-boll yield components were used for this study. Parents and their F1 progeny with reciprocals from a 3×6 factorial mating design were grown at Jiangxi Agricultural University experimental farm in 2008 and 2009. Seven within-boll yield components and two boll bur characters were analyzed under an additive-dominance genetic model with genotype and environment interaction. Additive effects were significant for all traits and dominance effects were significant for all traits except seed mass per seed. Genetic variances for lint mass per seed, SM/S and boll bur weight were primarily additive variances ranging from 39.6 to 58.9 %. Lint mass per boll and seed number per boll variances were primarily due to dominance genetic effects ranging from 36.4 to 48.8 %. Dominance and additive effects were equally important for boll weight, seed mass per boll and boll bur percentage. Additive and additive × environment effects were more important than other effects for lint percentage. A802-1 had the best mean performance and additive effects increasing BW, SM/B, S/B and SM/S, but reduced LP and LM/S. A9-1 and Lu40534 had additive effects associated with increasing LP. The two crosses A9-1×Lu40534 and Tezsh×33B were detected with favorable heterozygous dominant effects and heterosis over best parent for BW, LP, LM/B, SM/B and S/B. Favorable genotypic and phenotypic correlations were identified between within-boll lint yield components (LM/B, LM/S) and within-boll seed yield components (SM/B, S/B, SM/S). These results indicate that simultaneous genetic improvement of multiple within-boll yield components can be expected in breeding populations derived from these cotton cultivars and breeding lines.

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 F2:3 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.

With climate change manifested in cotton growing regions primarily as a combination of rising temperatures and prolonged periods of low rainfall, it has become critical to improve the resiliency of upland cotton (Gossypium hirsutum L.) to concurrent heat and drought stress. However, few investigations have considered the effect of this combined stress exposure on the phenotypic and genotypic correlations between important cotton traits, or on their respective heritabilities. To that end, we evaluated two upland cotton recombinant inbred line (RIL) populations under managed well-watered (WW) and water-limited (WL) irrigation regimes in the presence of high temperature across multiple environments. In both RIL populations, the broad-sense heritability for lint yield was higher under WW relative to WL conditions. The highest broad-sense heritabilities in both irrigation regimes were observed for lint percentage and fiber quality (micronaire, length, strength, uniformity, and elongation) traits. The genotypic correlations between lint yield and percentage were among the strongest values estimated, followed by a range of non-significant to moderately strong genotypic correlations between lint percentage and the five fiber quality traits in the two RIL populations. Within a RIL population, the strength and direction of between-trait phenotypic and genotypic correlations were similar for WW relative to WL conditions, although there were notable differences for them between RIL populations. Taken together, these results have the potential to benefit climate-oriented breeding programs when developing selection and testing schemes for the genetic improvement of cotton traits with a variable range of environmental stability under heat and drought stress.

Utilization of cotton (Gossypium hirsutum L.) germplasm for genetic improvement of fiber properties requires determination of genetic effects in the germplasm lines. A study was designed to analyze genetic populations derived from multiple crosses between nine germplasm lines as male parents and five cultivars and elite breeding lines as female parents to determine genetic values of fiber properties. Parents and F2 populations were planted at 2 field sites in 2010 and 2011 with 4 and 3 replicates, respectively, and parents and F3 populations were planted at 2 field sites in 2011 with 3 replicates. Lint yield and seven fiber properties were analyzed by an additive and dominant model with genotype by environment interaction effects. Significant additive and dominant effects were identified for both lint yield and fiber properties. Germplasm lines JC60, JC65, JC186, and SP205 were good general combiners for micronaire, elongation, strength, 50 % span length, short fiber content, and fineness. Six to fifteen crosses were detected with favorable heterozygous dominant effects for lint yield and diverse fiber traits, which suggest useful heterosis of these hybrids. Favorable additive correlations were identified between fiber properties such as micronaire versus 50 % span length (−0.57), micronaire versus fineness (0.82), strength versus 50 % span length (0.54), strength versus short fiber content (−0.69), and 50 % span length versus short fiber content (−0.78) while unfavorable additive correlations were not identified among fiber properties. These results indicated potential of simultaneous genetic improvement for these multiple properties in breeding populations derived from these germplasm lines.

Determination of genetic effects for lint yield and yield components in cotton (Gossypium hirsutum L.) germplasm is critical for its utilization in breeding programs. This study was designed to apply the conditional approach and an additive and dominant model to analyze genetic effects for lint yield and yield components. Forty-eight F2 populations derived from crosses between four existent Upland cotton cultivars as female parents and 12 germplasm lines as male parents were evaluated at two locations in 2008 and 2009. Conditional and unconditional variance components were estimated by the mixed linear model based conditional approach. Lint yield and yield components were mainly controlled by genotypic effects, i.e., additive variance and dominance variance (≥66 % of total phenotypic variation). Lint percentage and lint index had the highest proportions of additive variance component to the total phenotypic variances. SP156 and SP205 had positive additive effects for lint yield and yield components, and were also parents of the most hybrids with positive predicted dominant effects. Therefore, these two lines are good combiners for development of both pure lines and hybrids. Positive additive contribution effects to lint yield from lint percentage, boll number, boll weight, and seed index were detected in different parents. Adding seed index to boll number and lint percentage increased additive contribution effects to lint yield from these two components relative to the contribution effects from either boll number or lint percentage alone. Results in this study suggest that boll number, lint percentage, and seed index should be balanced in pure line development.

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.

Verticillium wilt (VW, Verticillium dahliae) is a worldwide destructive soil-borne fungal disease and employment of VW resistant cultivars is the most economic and efficient method in sustainable cotton production. However, information concerning VW resistance in current commercial cotton cultivars and transfer of VW resistance from Pima (Gossypium barbadense) to Upland (Gossypium hirsutum) cotton is lacking. The objective of the current study was to report findings in evaluating commercial cotton cultivars and germplasm lines for VW resistance in field and greenhouse (GH) experiments conducted in 2003, 2006, and 2007. In the study, 267 cultivars and germplasm lines were screened in the GH, while 357 genotypes were screened in the field. The results indicated that (1) VW significantly reduced cotton yield, lint percentage, 50% span length and micronaire, but not 2.5% span length and fiber strength, when healthy and diseased plants in 23 cultivars were compared; (2) some commercial cotton cultivars developed by major cotton seed companies in the US displayed good VW resistance; (3) many Acala cotton cultivars released in the past also had good VW resistance, but not all Acala cotton germplasm are resistant; (4) Pima cotton possessed higher levels of VW resistance than Upland cotton, but the performance was reversed when the root system was wounded after inoculation; (5) VW resistance in some conventional cultivars was transferred into their transgenic version through backcrossing; and (6) some advanced backcross inbred lines developed from a cross between Upland and Pima cotton showed good VW resistance. The successful development of VW resistant transgenic cultivars and transfer of VW resistance from Pima to Upland cotton implies that VW resistance is associated with a few genes if not a major one.

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.

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/F2:3 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.

Forty-eight colored cotton lines and hybrids were studied on the wax, cellulose content and fiber quality. The result were as follow: The wax content of green cotton was five to eight times greater than that of white cotton. As for the brown cotton lines, the darker the brown fiber color, the greater the content of the fiber wax. The wax content of dark brown cotton was two times greater than that of white cotton. However, the content of the cellulose of white cotton was the greatest, next was that of the brown cotton, and the content of the cellulose of green fiber was the lowest. There were differences in fiber length, fiber strength, and fiber uniformity, not only among different varieties with the same color fiber, but also among different coloring types. The content of cellulose had a significantly negative correlation with the content of wax and fiber elongation, but significantly positive correlations between the content of cellulose and fiber length, fiber strength, fiber fineness, lint index, boll weight, and fiber uniformity were observed in the color cotton lines used in this experiment. The study on wax and cellulose contents will give constructive advice for the breeding and molecular research of the colored cotton, and help increasing the color stability of the fiber and its textiles.

This research detected QTL or molecular markers associated with yield, fiber, and seed traits within multiple fuzz and fiber loci genetic backgrounds. Two F2 populations from crosses of MD17, a fuzzless-lintless line containing three fuzzless loci, N1, n2 and a postulated n3, with line 181, fuzzless-linted and with FM966, a fuzzy-linted cultivar, were used. QTL explaining 68.3 (population with FM966) to 87.1% (population with 181) of the phenotypic variation for lint percentage and 62.8% (population with 181) for lint index were detected in the vicinity of BNL3482-138 on chromosome 26. Single marker regression analyses indicated STV79-108, on the long arm of chromosome 12 had significant association with lint percentage (R2 26.7%), lint index (R2 30.6%), embryo protein percentage (R2 15.4%) and micronaire (R2 20.0%). Two-locus epistatic interactions were also observed. Results from this research will facilitate further understanding the complex mechanisms of yield, fiber, and seed traits of cotton.

Cotton breeders must be concerned with yield and fibre quality of naturally coloured cottons as these are inferior than to white linted cottons. Limited use of heterosis and correlation studies have been made in coloured cotton in India to maintain a strong, competitive edge in today’s world market. Totally 18 F1 (Gossypiumhirsutum) coloured cotton hybrids were produced in 1995 and 1996 by crossing six white linted female lines F-505, LRK-516, F-846, HS-6, P-31 and LH-1134 with three colour linted male testers 84 (green linted), 2,077 (medium brown linted) and H.Taskant (dark brown linted). Hybrids and parents were assessed in 1996 and 1997 for heterobeltosis, correlations and to know the direct and indirect effects of eight agronomic and four fibre quality traits. Analysis of variance indicated the existence of significant variation among F1 hybrids and parents for agronomic and fibre quality traits. F1 coloured cotton hybrids had higher seed cotton yield, number of bolls/plant, fibre length, fibre strength and heavier bolls in comparison to parents. Positive heterotic potential in three different F1 coloured cotton hybrids P-31 × 84 (green), F-846 × H.Taskant (dark brown), F-505 × 2077 (medium brown) and LH-1134 × H.Taskant (dark brown) indicated that there is no lint colour specificity for production of higher yielding hybrids. Similar results have been obtained for important fibre quality trait like fibre strength. It was also observed that even low yielding white and coloured linted parents can be crossed to select for high heterosis. Both at genotypic and phenotypic levels, seed cotton yield exhibited positive and significant association with number of bolls, seed cotton weight per boll, plant height, number of monopodia/plant, fibre strength and mature fibre % suggesting that any selection among correlated traits might lead to improvement in seed cotton yield. Number of sympodial branches, seed index and 2.5% span length and micronaire value had non-significant negative association with seed cotton yield. Path analysis identified boll number per plant and seed cotton weight per boll as the principal yield contributing attributes.

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.

Investigation of cotton nutritional components is important because its seeds provide a useful nutritional profile and can possibly serve as a biofuel resource. In this study, five cultivars, 13 cotton chromosome substitution (CS-B) lines, their donor parent, '3-79', and their recurrent parent, 'TM-1', were evaluated for seed traits over four environments. A mixed linear model approach with the jackknife method was employed to estimate variance components and to predict genotypic effects for each seed trait. Genotypic effects were more important than genotype by environment interaction for all seed traits. Chromosome associations with these seed traits were detected using the comparative method by comparing the differences between each CS-B line and TM-1. For example, chromosome 4 of 3-79 in TM-1 background was associated with reduced seed index (SI), embryo percentage, protein percentage while associated with increased seed oil percentage and seed fiber percentage. Other chromosome associations with these seed traits were also observed in this study. SI was highly correlated with three seed index traits: seed protein index, seed oil index (OI), and seed fiber index. Lint percentage, boll number, and lint yield were positively correlated with protein percentage while negatively correlated with SI and OI. SI and seed fiber content exhibited negative correlations with micronaire but positive correlations with fiber length and strength. Results suggested that agronomic traits and seed nutrition components can be improved simultaneously.

Use of chemical mutagenesis has been highly successful in most major crops. The objective of this research was to develop ‘naked-tufted’ seed mutants and to incorporate this genetic trait into cotton to enhance crop quality and reduce processing costs. In 1997, six commercial cultivars were treated with 2.45% v/v ethyl methane sulfonate. In 1999, three M3 plants were identified that had partially naked seed coats. The trait was stabilized through individual plant selections from 2000 to 2004. During 2005 and 2006, the homozygous naked-tufted M8 mutant lines were evaluated for lint yield, lint percent, fibers/seed, fibers/mm2, fiber quality, seed oil content, ginning efficiency and yarn spinning performance. Overall, the naked-tufted seed mutants had lower lint yield, lower fibers/seed, lower lint/seed, and lower fibers/mm2 when compared with their original fuzzy parents. The lint turnout from the mutants was similar to the fuzzy parents and the commercial cultivars. The naked-tufted seed mutants had higher seed oil percent, 6–17% lower short fiber contents, significantly reduced seed coat neps (37–42%), higher elongation and yarn tenacity than their fuzzy counterparts. Preliminary data also showed that the naked-tufted mutants required less energy to gin.

Dissection of the genetic relationship between lint yield and its yield components at the chromosome level may provide an additional avenue for yield enhancement in cotton (Gossypium hirsutum L.). Based on the conditional additive-dominance (AD) genetic model, we investigated the genetic structures of lint yield with its three component traits, lint percentage, boll weight, and boll number, using a two-location data set containing cotton chromosome substitution lines (chromosome or chromosome arm substituted from G. barbadense L. into G. hirsutum L., TM-1) which are defined as CS-B lines and their F2 hybrids with CS-B recurrent parent TM-1. We calculated the conditional variance components, contribution ratios, and contribution effects subject to the additive and dominant components. Our results showed that boll number or boll number with boll weight greatly reduced the conditional variance components and phenotypic variance for lint yield and thus indicated that boll number plays a more important role in lint yield than the other two component traits. We demonstrated that the G. barbadense chromosomes in CS-B16, CS-B18, and CS-B4sh were directly associated with reduced lint yield. Substituted chromosome arms 14sh, 22sh, and 22Lo were associated with reduced additive effects for lint yield through the component of boll weight, thus suggesting that some substituted chromosomes or chromosome arms may be indirectly associated with lint yield through yield component traits. This study provides a better understanding of cotton yield and its component traits at the chromosome level and this information should be useful in cotton breeding.

Segregating populations were developed to evaluate the inheritance of the fiberless seed phenotype of upland cotton (Gossypium hirsutum L.) line SL1-7-1. We report the inheritance of fuzzy, fuzzless and fiberless seed from crosses of SL1-7-1 with wildtype DP5690, Mexican fuzzless seed UA 3-3 (accession 143), Ballard fuzzless seed (accession 243), and MD17. Results from the F1, F2 and F2:3 progeny derived from the SL1-7-1 X DP5690 indicated that the expression of the fiberless phenotype fit a three loci model with one locus being the dominant fuzzless seed allele N 1 . The other two loci were tested to verify whether they were allelic to either recessive fuzzless seed alleles n 2 or n 3 . Using the segregation ratios of the F2 progeny derived from the 143 X SL1-7-1 cross and F2-derived F3 families from SL1-7-1 X DP5690 with fuzzy seed (lacked N 1 ), it is proposed that SL1-7-1 lacks the recessive n 2 allele, but contains the n 3 allele in the genotype of SL1-7-1. The third locus was previously not characterized and has been designated as fl 1 (fiberless), therefore, the genotype for the fiberless phenotype of SL1-7-1 is N 1 N 1 fl 1 fl 1 n 3 n 3 . Fiberless lines MD17 X SL1-7-1 were crossed to verify similarities in genotypes between line and the genotype model predictability. Various combinations of the homozygous and heterozygous expression of N 1 , n 2 , n 3 and fl 1 allele produced plants with lower lint percentages.

Sticky cotton causes severe processing problems at textile mills and can be caused by plant sugars deposited directly from the plant to the lint in the absence of insects. A partial diallel design was used to investigate the combining ability of six upland cotton, Gossypium hirsutum L., genotypes in Lubbock, Texas. Sucrose and glucose on fibers were measured as well as more mechanical fiber properties including stickiness ratings. Variance component analysis indicated significant differences among genotypes for all fiber traits and for sugar content. The greatest differentiation occurred in samples taken from more immature fruiting forms. Moreover, significant GCA and SCA differences were determined among parental lines for fiber traits including stickiness ratings. Findings suggest that breeding efforts could be directed toward lines with a low likelihood of producing sticky cotton.

The usual practice of estimating association and direct and indirect effects among various traits in Gossypium hirsutum is with ungrouped genetic material based on staple length and strength. During 2003–2004 and 2004–2005 genotypic and phenotypic association among ten characters were estimated in G. hirsutum genotypes: (i) set-1: 10 genotypes of low fibre strength (≤196.2 mN/tex) and medium staple length (≤25.0 mm), (ii) set-2: 10 genotypes of high fibre strength (≥235.44 mN/tex) and long staple length (≥28 mm) and (iii) set-3: 20 genotypes of set-1 and 2. The differences in the estimates of associations, direct and indirect effects for different characters in fibre quality groups were examined. The complete analysis of variance for the characters under study viz; days to 50% flowering, plant height (cm), number of monopodial and sympodial branches per plant, seed cotton yield per plant (g), boll weight (g), total number of bolls per plant, lint %, 2.5% span length (mm) and fibre strength (mN/tex) indicated highly significant genotypic differences for genotypes, years and genotype × years interaction. Variation within medium staple length and low strength (set-1), high staple length and high strength genotypes (set-2) and their interaction with year were also significant. Medium staple length and low strength (set-1) versus high staple length and high strength component (set-2) was significant for all the traits indicating significant variability between the sets. A true relationship and direct selection were observed for days to 50% flowering, number of monopodial and sympodial branches per plant with seed cotton yield in the three sets suggesting that separation of genetic material based on staple length and fibre strength for improvement of seed cotton yield through these traits is not required. Magnitude and direction of direct effect and association with yield of the other traits; plant height, number of total bolls per plant, boll weight, lint %, staple length and fibre strength differed between the sets. This study concluded that more successful planning of a breeding programme can be made through path coefficient analysis if the genetic material is grouped based on staple length and fibre strength.

Boll number, lint percentage, and boll weight are three component traits for lint yield of upland cotton, Gossypium hirsutum L. Selecting high yielding lines or hybrids depends on the ability to dissect the genetic relationship of lint yield with these component traits. In this study, 14 day-neutral lines with desirable fiber quality derived from primitive accessions were top crossed with five commercial cultivars. The F2 populations and parents were grown in one location in 1998 and two locations in 1999 at Mississippi State, MS. The F3 populations and parents were grown in two locations in 2000. Lint yield and three component traits were measured and analyzed by the ADAA genetic model with the mixed model based conditional approach. Results showed that boll number or boll number with lint percentage or boll weight contributed to the majority of the phenotypic variance and variance components for lint yield. Boll number was more important than the other two component traits in terms of various genetic effects. The results also showed that the combination of boll number and boll weight greatly increased the contribution to lint yield even though boll weight itself had no significant contribution to lint yield compared to boll number alone. The genetic contribution effects were also predicted due to single component traits or their combinations for parents and crosses. The results revealed that the balanced selection of boll weight and boll number should be considered to obtain high yielding hybrids or pure lines.

When alien DNA inserts into the cotton genome in a multicopy manner, several quantitative trait loci (QTLs) in the cotton genome are disrupted; these are called dQTL in this study. A transgenic mutant line is near-isogenic to its recipient, which is divergent for the dQTL from the remaining QTLs. Therefore, a set of data from a transgenic QTL line mutated by Agrobacterium-mediated transformation (30074), its recipient and their F1 hybrids, and three elite lines were analyzed under a modified additive-dominance model with genotype × environment interactions in three different environments to separate the genetic effects due to dQTL from whole-genome effects. Our result showed that dQTL had significant additive effects on lint percentage, boll weight, and boll number per square meter, while it had little genetic association with fiber traits, seed cotton yield, and lint yield. The dQTL in 30074 significantly increased lint percentage and boll number, while significantly decreasing boll weight, having little effect on fibre traits, while those from the recipient and three elite lines showed significant genetic effects on lint percentage. In addition, the remaining QTL other than dQTL had significant additive effects on seed cotton yield, fruiting branch number, uniformity index, micronaire, and short fibre index, and significant dominance effects on seed cotton yield, lint yield, and boll number per square meter. The additive and dominance effects under homozygous and heterozygous conditions for each line are also predicted in this study.

A genetic linkage map of chromosome 6 was constructed by using 270 recombinant inbred lines originated from an upland cotton cross (Yumian 1 × T586) F2 population. The genetic map included one morphological (T1) and 18 SSR loci, covering 96.2 cM with an average distance of 5.34 cM between two markers. Based on composite interval mapping (CIM), QTL(s) affecting lint percentage, fiber length, fiber length uniformity, fiber strength and spiny bollworm resistance (Earias spp.) were identified in the t1 locus region on chromosome 6. The allele(s) originating from T586 of QTLs controlling lint percentage increased the trait phenotypic value while the alleles originating from Yumian 1 of QTLs affecting fiber length, fiber length uniformity, fiber strength and spiny bollworm resistance increased the trait phenotypic value.

Molecular markers associated with fiber development traits have the potential to play a key role in understanding of cotton fiber development. Seventeen SSRs out of 304 markers tested from MGHES (EST-SSR), JESPR (genomic SSR), and TMB (BAC-derived SSR) collections showed significant linkage associations (using a Kurskal-Wallis non-parametric test) with lint percentage QTL in a set of recombinant inbred cotton lines (RILs) segregating for lint percentage. The permutation test of these potential markers associated with lint percentage QTL(s) determined that 12 SSR markers have stable estimates, exceeding empirically chosen threshold significance values at or above α = 0.01. Interval mapping demonstrated that 9 SSRs with stable critical LOD threshold values at α = 0.01 have significant QTL effect. Multiple QTL-mapping (MQM) revealed that at least, two highly significant fiber development QTLs exist around regions TMB0471 and MGHES–31 (explained about 23–59% of the phenotypic variation of lint percentage) and around markers MGHES–31 and TMB0366 (accounted for 5.4–12.5% phenotypic variation of lint percentage). These markers, in particular fiber-specific EST-SSRs, might be the possible ‘candidate’ loci contributing for fiber development in cotton. BAC-derived SSRs associated with fiber trait are the possible markers that are useful for the identification of physical genomic contigs that contain fiber development genes. Several lint percentage trait associated SSR markers have been located to chromosomes 12, 18, 23, and 26 using deletion analysis in aneuploid chromosome substitution lines. Outcomes of the work may prove useful in understanding and revealing the molecular basis of the fiber development, and the utilization of these markers for development of superior cotton cultivars through marker-assisted selection (MAS) programs.

Fifteen fuzzless seed lines in “obsolete” backgrounds of Upland cotton (Gossypium hirsutum L.) were obtained from the National Cotton Germplasm Collection and evaluated for fuzzless seed genotype, lint percent, and lint quality. Fourteen of these fifteen lines were found to be homozygous for the dominant fuzzless seed allele N 1. Only one line was homozygous for the recessive fuzzless seed allele n 2. The measured lint percent of each line was very stable through time, however, large variability existed between many of the N 1 lines ranging from 0.7 to 23.6% lint. The lint percent for the n 2 line was 24.4%. Scanning electron microscopy was used to differentiate patterns of lint initiation on 1 day post anthesis ovules. General patterns included: first, lint initiation restricted to the chalazal end of the seed crest; second, lint initiation along the seed crest and laterally around the chalazal end of the ovule; and third, lint initiation covered all but the micropylar end of the ovule. Lint quality was evaluated for each line using the Advanced Fiber Information System (AFIS) which included measurements of length, maturity, and fineness. The means of each measurement varied among the fuzzless seed lines with significant differences between fiber length, short fiber content, immature fiber content, fineness, and maturity ratio. No correlation was found between lint percent and any of the lint quality measurements. These lines will provide a valuable resource for the study of fiber initiation and lint quality.

Cotton (Gossypium spp.) yield is directly determined by mature bolls that developed from squares and flowers. The first four to six weeks of flowering accounts for the majority of lint yield in upland cotton (G. hirsutum L.) for most cultivated areas of the southern USA cotton belt. In this study, we evaluated 13 cotton chromosome substitution lines (CS-B) and their chromosome specific-F2 hybrids, TM-1, 3–79, and six cultivars for the number of flowers produced during the first four weeks of flowering. Results showed that CS-B05sh produced more flowers than TM-1 and 3–79 from 10 July to 5 August. The results suggest that when the short arm of chromosome 5 was substituted from 3–79 (G. barbadense L.) into TM-1 (G. hirsutum) a positive genetic association with flower numbers during this flowering period was exhibited. CS-B05sh had comparable flower numbers with three cultivars, Deltapine 90, Phytogen 355, and Stoneville 474 and more flowers than, Sure Grow 747, Sure Grow 125, and Deltapine 5415. Different patterns for additive and dominance effects on cumulative flowers were observed across weeks of flowering. Dominance effects were more apparent during the early part of the flowering period while additive effects were more apparent towards the end of the flowering period.

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 F2:3 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.

The characterization of yield and yield components, chlorophyll, soluble sugars and N, P, K concentrations, and SOD, POD activities and MDA content was compared between F1 Bt hybrid cotton Cikangza 1 and its male (transgenic Bt gene bollworm resistant lines and female parents, and commercial hybrid Xiangzamian 2 under field condition. The result showed that the hybrid Cikangza 1 had distinct heterosis in lint yield as reflected by HOBP and HOMP values of 25.7% and 28.9%, and the heterosis of bolls per plant was significantly higher than that of boll weight and lint percentage. Significant HOBP, HOMH and HOCP in Chl a, Chl b and Chl (a+b) at SS and FFS were observed in Cikangza 1, suggesting that the higher Chl content at SS and FFS is important for achieving potential yield, and thereafter may aid in identification of parental lines and hybrid combination. The results also elucidated that the HOBP and HOMP of N, P and K concentrations, and SOD and POD activities were much smaller in comparison with those of Chl parameters. However, Cikangza 1 has higher soluble sugars content, and N and K concentrations at FFS and BOS, than that of commercial hybrid Xiangzamian 2, denoting that N and K nutrient might perform an important function in senescence, and more additional application of N and K fertilizer at late growth stages of hybrid may be beneficial to keep more nutrient for late growth stage and delay the senescence.

Upland cotton (Gossypium hirsutumL) is an important crop that is cultivated in warm climates through-out the world. Agronomic performance and fiber quality must continually be improved if cotton is to maintain economic viability. Primitive ancestors of cotton contain diversity for trait improvement; however, many of these accessions have a short-day flowering response (photoperiodic) and are not readily useable in breeding programs. In this study, 114 day-neutral derived primitive germplasm lines were evaluated in field trials for two years. Agronomic and fiber trait data were collected and analyzed. Variance components, genotypic values, and genotypic correlations were calculated. Genotypic effects for all traits studied made significant contributions to the phenotypic variation indicating genetic diversity among these lines. The predicted genotypic values showed a wide range of variation for agronomic and fiber traits. Weak genotypic correlations were found between yield and 2.5% span length and fiber strength, two important fiber traits. Although these day-neutral derived accessions had lower lint percentage, they had improved fiber length, strength, micronaire, and comparable yields with two commercial cultivars. Thus, these day-neutral derived accessions are sources of genetic variation that when used in breeding programs offer the potential to improve important traits and expand genetic diversity.

The characterization of photosynthetic, chlorophyll fluorescence parameters and yield and yield components was compared between two newly developed CMS cotton hybrids (H1, H2) and their parents, as well as currently planted hybrid and conventional cultivars (C1, artificially produced hybrid CCRI 29 and C2, conventional cultivar CCRI 12) under the field condition. The results showed that Pn, Fv/Fm, ΦPSII and qP of hybrids was significantly higher than that of C1 and C2. Furthermore, heterosis was found on photosynthetic parameters in hybrids over their parents at the first four growth stages, while only heterosis over mean of parents (HOMP) was detected in chlorophyll fluorescence parameters. It was clearly shown that one male-sterile line M2 was higher than the hybrids in Fv/Fm, ΦPSII and qP over all growth stages. Significantly positive correlations (P < 0.01) were found between LAI or Yield and Pn, Cs, Tr, Fv/Fm, ΦPSII, or qP, while significantly negative correlations between Ci and LAI or Yield, and no significance between qN and Chl a, Cs and qP were found. It was concluded that CMS hybrid cottons showed better potential to maintain relatively higher photosynthetic ability during the growth, which contributes to the increased lint yield.

Fiber yield and yield components – including lint index (LI), seed index (SI), lint yield (LY), seed cotton yield (SCY) and number of seeds per boll (NSPB) – were investigated on the farm of Huazhong Agricultural University in a population of 69 F2 individuals and corresponding F2:3 families derived from a cross between high-fiber-yield Gossypium hirsutum CV Handan 208 and a low-fiber-yield Gossypium barbadense CV Pima 90. On the basis of the genetic map constructed previously from the same population by Lin et al. (Plant Breed., 2005), quantitative trait locus (QTL) analysis was performed with the software QTL Cartographer V2.0 using composite interval mapping method (LOD ≥ 3.0). A total of 21 QTLs were identified, which were located in 15 linkage groups. The number of QTLs per trait ranged from one to seven. Of these QTLs detected, one affecting LI explained 24.3% of phenotypic variation (PV), five influencing SI explained 16.15–39.21% of PV, seven controlling LY explained 13.01–28.35% of PV, and two controlling SCY explained 22.76 and 39.97% of PV, respectively. Simultaneously, the detected six QTLs for NSPB were located on five linkage groups, which individually explained 28.01–38.32% of the total phenotypic variation. The results would give breeders further insight into the genetic basis of fiber yield.

Plant breeding programs involving a wide range of crop plants routinely practice selection (directly or indirectly) for genotypes that display stability for a given trait or set of traits across testing environments through the genotype evaluation process. Genotype stability for trait performance is a direct measure of the presence and effect of genotype × environment interactions, which result from the differential performance of a genotype or cultivar across environments. The genotype evaluation process also requires selection of the proper field trial locations that best represent the target environments the breeding program is directed toward. In this study, we assessed the extent to which genotype × environment interactions affected agronomic performance (lint yield, gin turnout) and fiber quality (fiber length, fiber strength, uniformity index, micronaire, fiber elongation) in a series of cotton (Gossypium hirsutum) performance trials in 12 location–year environments in South Carolina. Genotype × environment interactions affecting lint yield were larger in higher yielding environments, while interactions for fiber strength were greater for genotypes with lower mean fiber strength values. Two regions within the South Carolina cotton production areas were identified as proper testing locations for lint yield performance, while testing for fiber strength can be accomplished in any location within the statewide cotton production areas.

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 F2:3 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.

The narrow germplasm base of the upland cotton (Gossypium hirsutum L.), grown on the Texas high plains historically, has limited improvement of fiber quality. Chemical mutagenesis and subsequent selection have helped the development of lines with improved fiber quality in cultivars adapted to this region. This study was conducted to determine the inheritance of improvements in fiber quality. M3 lines with divergent fiber properties of micronaire, length, and strength were selected from a population of Paymaster HS 200 treated with 3% v/v ethyl methanesulfonate (EMS) for two hours. The 115 selected lines of M4 and M5 generation were evaluated for fiber quality and lint yield. Regression of the M4 and M5 on the M3 generation, as well as the M5 on the M4 was used to generate narrow sense heritability coefficients. Significant variations were observed between the mutant lines in all generations except for lint yield in the M5 (1997). The highest heritability estimates were found in fiber length (h2= 0.29** to 0.46**). Micronaire and strength showed intermediate heritability estimates of h2= 0.14 to 0.19, while lint yield had a very low heritability estimate of h2= 0.03. Fiber length and strength were correlated (r= 0.58** to 0.46**) in all the three generations. The mutants identified in these studies have the potential to improve fiber quality of upland cotton without introducing alien genes that may reduce adaptation to short growing season production regions.