Genetic Improvement Of Cotton Research Articles

GhFP positively regulates chlorophyll content and seedling biomass in upland cotton

Cotton is one of the most important cash crops worldwide. Chlorophyll is a critical photosynthetic pigment in plants, which could significantly affect the growth and development of cotton. In this study, one insertion mutant, ZD131, was found to have darker leaves and higher chlorophyll content than wild-type (WT) at the seedling and flowering stages. The chlorophyll contents were also higher in F1 and F2 heterozygous plants crossed by ZD131 and WT than that in WT. Through genome resequencing of mutant ZD131, a coding gene Ghir_D07G020490, we named it GhFP, was found at 2347 bp downstream of the insertion site in ZD131, which has not been studied yet. GhFP was localized in the cytoplasm and expressed higher in ZD131 than that in WT. Furthermore, virus-induced gene silencing (VIGS) of GhFP in cotton and overexpression of GhFP in Arabidopsis verified that GhFP could positively regulate the chlorophyll content and biomass. Therefore, this study revealed that a novel gene GhFP could regulate chlorophyll biosynthesis and biomass accumulation, which laid a theoretical foundation for understanding the regulatory mechanism of chlorophyll accumulation and provided essential gene resources for cotton genetic improvement.

Population Genomics Unravels the Characteristic Relationship between Introgression and Geographical Distribution in Upland Cotton

Introgression is an important driver of new genetic variation that increases species and genetic diversity. However, the relationship between introgression and geographic distribution of upland cotton is still unclear. Herein, we explored geographically comprehensive genomic data based on 890 upland cotton accessions to decipher the degree of introgression between different geographic distributions and its effect on selection and fiber quality. We found introgression intervals to exist across different geographic distributions. Introgression is affected by the similarity of the environment in which they live, and those with similar ecological environments tend to share the same introgression area. Introgression is affected by artificial selection. A genome-wide association study (GWAS) meta-analysis was performed with 6 fiber traits and identified 261 quantitative trait loci (QTLs). We found that 67 QTLs had introgression signals, and the genome interval size was 118.81 Mb, while 123 QTLs had selection signals, and the genomic interval was 28.38 Mb. These results provide insights into the population-scaled introgression landscape, suggesting that introgression contributed to the cotton genetic improvement, which provides a useful reference for studying intraspecific introgressions from different geographical distributions in other species.

Identification of quantitative trait loci for fiber quality, yield, and plant height traits in Upland cotton

AbstractIn cotton, most agronomic traits are controlled by polygenes. In this study, 110 F6 recombinant inbred lines (RILs), derived from Upland cotton cross NC05AZ06 x NC11‐2100, were used to develop a linkage map and to identify quantitative trait loci (QTL) for six fiber quality traits, three yield traits, and plant height. These RILs were genotyped using the CottonSNP63K array and phenotyped for fiber quality, yield traits, and plant height in 2‐year field trials. Analysis of variance revealed significant (p < 0.05) differences among RILs for all traits studied, and the heritability estimates were moderate (30%–60%) to high (> 60%). Both positive and negative correlations were observed for fiber quality and yield traits. A total of 3,774 polymorphic SNP markers were used to develop a genetic map with an average marker density of 1.54 SNP/cM. Thirty QTL for fiber quality traits, yield traits, and plant height were detected on 15 different chromosomes, explaining 6.80%–20.02% of the phenotypic variance (PVE). Of these, 14 were major QTL (PVE > 10%), and three major QTL were detected in both years. Candidate gene analysis in the major QTL detected in both years and plant height QTL with PVE of 20.02% revealed five putative genes for fiber quality traits and one putative gene for plant height. The linkage map and identified QTL along with the candidate genes in the study could serve as additional breeding resources for Upland cotton genetic improvement.

Advances of CRISPR/Cas9 activation system

Gene editing technology has been a hotspot in the field of biotechnology. CRISPR/Cas systems are efficient gene editing tools because of its specificity, simplicity and flexibility, these features enabled the rapid application of CRISPR/Cas systems in a variety of organisms. Moreover, the combination of transcriptional activator with dead Cas protein can achieve specific regulation of gene expression at the transcription level, which has made important contributions to the development of biotechnology in medical and agriculture. Overexpression of foreign genes is a common method to verify gene function and regulation. However, due to the limitation of vector capacity, it is difficult to achieve overexpression of multiple genes. CRISPR/Cas9 activation system can regulate the expression of multiple genes under the guidance of different guide RNAs to verify gene functions at the regulatory level. This review summarizes the composition of the CRISPR/Cas9 activation system and different activation strategies, and summarizes solutions for excessive activation. It may facilitate the application of CRISPR/Cas9 activation system in genetic improvement of cotton and herbicide resistance research.

Construction of a high-density genetic map and identification of QTLs related to agronomic and physiological traits in an interspecific (Gossypium hirsutum\u2009\xd7\u2009Gossypium barbadense) F2 population

BackgroundAdvances in genome sequencing technology, particularly restriction-site associated DNA sequence (RAD-seq) and whole-genome resequencing, have greatly aided the construction of cotton interspecific genetic maps based on single nucleotide polymorphism (SNPs), Indels, and other types of markers. High-density genetic maps can improve accuracy of quantitative trait locus (QTL) mapping, narrow down location intervals, and facilitate identification of the candidate genes.ResultIn this study, 249 individuals from an interspecific F2 population (TM-1 and Hai7124) were re-sequenced, yielding 6303 high-confidence bin markers spanning 5057.13 cM across 26 cotton chromosomes. A total of 3380 recombination hot regions RHRs were identified which unevenly distributed on the 26 chromosomes. Based on this map, 112 QTLs relating to agronomic and physiological traits from seedling to boll opening stage were identified, including 15 loci associated with 14 traits that contained genes harboring nonsynonymous SNPs. We analyzed the sequence and expression of these ten candidate genes and discovered that GhRHD3 (GH_D10G0500) may affect fiber yield while GhGPAT6 (GH_D04G1426) may affect photosynthesis efficiency.ConclusionOur research illustrates the efficiency of constructing a genetic map using binmap and QTL mapping on the basis of a certain size of the early-generation population. High-density genetic map features high recombination exchanges in number and distribution. The QTLs and the candidate genes identified based on this high-density genetic map may provide important gene resources for the genetic improvement of cotton.

Genetics, Breeding and Genetic Engineering to Improve Cottonseed Oil and Protein: A Review.

Upland cotton (Gossypium hirsutum) is the world’s leading fiber crop and one of the most important oilseed crops. Genetic improvement of cotton has primarily focused on fiber yield and quality. However, there is an increased interest and demand for enhanced cottonseed traits, including protein, oil, fatty acids, and amino acids for broad food, feed and biofuel applications. As a byproduct of cotton production, cottonseed is an important source of edible oil in many countries and could also be a vital source of protein for human consumption. The focus of cotton breeding on high yield and better fiber quality has substantially reduced the natural genetic variation available for effective cottonseed quality improvement within Upland cotton. However, genetic variation in cottonseed oil and protein content exists within the genus of Gossypium and cultivated cotton. A plethora of genes and quantitative trait loci (QTLs) (associated with cottonseed oil, fatty acids, protein and amino acids) have been identified, providing important information for genetic improvement of cottonseed quality. Genetic engineering in cotton through RNA interference and insertions of additional genes of other genetic sources, in addition to the more recent development of genome editing technology has achieved considerable progress in altering the relative levels of protein, oil, fatty acid profile, and amino acids composition in cottonseed for enhanced nutritional value and expanded industrial applications. The objective of this review is to summarize and discuss the cottonseed oil biosynthetic pathway and major genes involved, genetic basis of cottonseed oil and protein content, genetic engineering, genome editing through CRISPR/Cas9, and QTLs associated with quantity and quality enhancement of cottonseed oil and protein.

Dynamic Expression, Differential Regulation and Functional Diversity of the CNGC Family Genes in Cotton.

Cyclic nucleotide-gated channels (CNGCs) constitute a family of non-selective cation channels that are primarily permeable to Ca2+ and activated by the direct binding of cyclic nucleotides (i.e., cAMP and cGMP) to mediate cellular signaling, both in animals and plants. Until now, our understanding of CNGCs in cotton (Gossypium spp.) remains poorly addressed. In the present study, we have identified 40, 41, 20, 20, and 20 CNGC genes in G. hirsutum, G. barbadense, G. herbaceum, G. arboreum, and G. raimondii, respectively, and demonstrated characteristics of the phylogenetic relationships, gene structures, chromosomal localization, gene duplication, and synteny. Further investigation of CNGC genes in G. hirsutum, named GhCNGC1-40, indicated that they are not only extensively expressed in various tissues and at different developmental stages, but also display diverse expression patterns in response to hormones (abscisic acid, salicylic acid, methyl jasmonate, ethylene), abiotic (salt stress) and biotic (Verticillium dahlia infection) stimuli, which conform with a variety of cis-acting regulatory elements residing in the promoter regions; moreover, a set of GhCNGCs are responsive to cAMP signaling during cotton fiber development. Protein–protein interactions supported the functional aspects of GhCNGCs in plant growth, development, and stress responses. Accordingly, the silencing of the homoeologous gene pair GhCNGC1&18 and GhCNGC12&31 impaired plant growth and development; however, GhCNGC1&18-silenced plants enhanced Verticillium wilt resistance and salt tolerance, whereas GhCNGC12&31-silenced plants had opposite effects. Together, these results unveiled the dynamic expression, differential regulation, and functional diversity of the CNGC family genes in cotton. The present work has laid the foundation for further studies and the utilization of CNGCs in cotton genetic improvement.

Multi-omics assisted identification of the key and species-specific regulatory components of drought-tolerant mechanisms in Gossypium stocksii.

Cotton (Gossypium spp.) is one of the most important fiber crops globally, with the main cultivated species Gossypium hirsutum L. and G. barbadence L. contributing more than 90% of the total fiber production (Wang et al., 2019). However, low genetic diversity in germplasm has largely impeded the continuous improvement of cultivated cotton. Wild cotton species have desirable characters such as resistance to various biotic and abiotic stresses and high-quality fiber products, which are therefore natural reservoirs for cotton genetic improvement (Wendel and Cronn, 2003).

Weighted Gene Co-Expression Network Analysis Reveals Hub Genes Contributing to Fuzz Development in Gossypium arboreum.

Fuzzless mutants are ideal materials to decipher the regulatory network and mechanism underlying fuzz initiation and formation. In this study, we utilized two Gossypium arboreum accessions differing in fuzz characteristics to explore expression pattern differences and discriminate genes involved in fuzz development using RNA sequencing. Gene ontology (GO) analysis was conducted and found that DEGs were mainly enriched in the regulation of transcription, metabolic processes and oxidation–reduction-related processes. Weighted gene co-expression network analysis discerned the MEmagenta module highly associated with a fuzz/fuzzless trait, which included a total of 50 hub genes differentially expressed between two materials. GaFZ, which negatively regulates trichome and fuzz formation, was found involved in MEmagenta cluster1. In addition, twenty-eight hub genes in MEmagenta cluster1 were significantly up-regulated and expressed in fuzzless mutant DPL972. It is noteworthy that Ga04G1219 and Ga04G1240, which, respectively, encode Fasciclin-like arabinogalactan protein 18(FLA18) and transport protein, showed remarkable differences of expression level and implied that they may be involved in protein glycosylation to regulate fuzz formation and development. This module and hub genes identified in this study will provide new insights on fiber and fuzz formation and be useful for the molecular design breeding of cotton genetic improvement.

Use of computational intelligence in the genetic divergence of colored cotton plants

The objective of this work was to analyze the genetic diversity using conventional methods and artificial neural networks among 12 colored fiber cotton genotypes, using technological characteristics of the fiber and productivity in terms of cottonseed and cotton fiber yield. The experiment was conducted in an experimental area located at Fazenda Capim Branco, belonging to the Federal University of Uberlândia, in the city of Uberlândia, Minas Gerais. Twelve genotypes of colored fiber cotton were evaluated, 10 from the Cotton Genetic Improvement Program (PROMALG): UFUJP - 01, UFUJP - 02, UFUJP - 05, UFUJP - 08, UFUJP - 09, UFUJP - 10, UFUJP - 11, UFUJP - 13, UFUJP - 16, UFUJP - 17 and two commercial cultivars: BRS Rubi (RC) and BRS Topázio (TC). The experimental design used was complete randomized block (CRB) with three replications. The following evaluations were carried out at full maturation: yield of cottonseed (kg ha-1) and the technological characteristics, which include, fiber length, micronaire, maturation, length uniformity, short fiber index, elongation and strength, using the HVI (High volume instrument) device. Genetic dissimilarity was measured using the generalized Mahalanobis distance and after obtaining the dissimilarity matrix, the genotypes were grouped using a hierarchical clustering method (UPGMA). A discriminant analysis and the Kohonen Self-Organizing Map (SOM) by Artificial Neural Networks (ANN’s) were performed through computational intelligence. SOM was able to detect differences and organize the similarities between accesses in a more coherent way, forming a larger number of groups, when compared to the method that uses the Mahalanobis matrix. It was also more accurate than the discriminant analysis, since it made it possible to differentiate groups more coherently when comparing their phenotypic behavior. The methods that use computational intelligence proved to be more efficient in detecting similarity, with Kohonen's Self-Organizing Map being the most adequate to classify and group cotton genotypes.

Ethyl methanesulfonate mutant library construction in Gossypiumhirsutum L. for allotetraploid functional genomics and germplasm innovation.

As the gene pool is exposed to both strain on land resources and a lack of diversity in elite allotetraploid cotton, the acquisition and identification of novel alleles has taken on epic importance in facilitating cotton genetic improvement and functional genomics research. Ethyl methanesulfonate (EMS) is an excellent mutagen that induces genome-wide efficient mutations to activate the mutagenic potential of plants with many advantages. The present study established, determined and verified the experimental procedure suitable for EMS-based mutant library construction as the general reference guide in allotetraploid upland cotton. This optimized method and procedure are efficient, and abundant EMS mutant libraries (approximately 12000) in allotetraploid cotton were successfully obtained. More than 20 mutant phenotypes were observed and screened, including phenotypes of the leaf, flower, fruit, fiber and plant architecture. Through the plants mutant library, high-throughput and high-resolution melting technology-basedvariation evaluation detected the EMS-induced site mutation. Additionally, based on overall genome-wide mutation analyses by re-sequencing and mutant library assessment, the examination results demonstrated the ideal quality of the cotton EMS-treated mutant library constructed in this study with appropriate high mutation density and saturated genome. What is more, the collection is composed of a broad repertoire of mutants, which is the valuable resource for basic genetic research and functional genomics underlying complex allotetraploid traits, as well as cotton breeding.

Genome sequence of Gossypium herbaceum and genome updates of Gossypium arboreum and Gossypium hirsutum provide insights into cotton A-genome evolution

Upon assembling the first Gossypium herbaceum (A1) genome and substantially improving the existing Gossypium arboreum (A2) and Gossypium hirsutum ((AD)1) genomes, we showed that all existing A-genomes may have originated from a common ancestor, referred to here as A0, which was more phylogenetically related to A1 than A2. Further, allotetraploid formation was shown to have preceded the speciation of A1 and A2. Both A-genomes evolved independently, with no ancestor–progeny relationship. Gaussian probability density function analysis indicates that several long-terminal-repeat bursts that occurred from 5.7 million years ago to less than 0.61 million years ago contributed compellingly to A-genome size expansion, speciation and evolution. Abundant species-specific structural variations in genic regions changed the expression of many important genes, which may have led to fiber cell improvement in (AD)1. Our findings resolve existing controversial concepts surrounding A-genome origins and provide valuable genomic resources for cotton genetic improvement.

A Phi-Class Glutathione S-Transferase Gene for Verticillium Wilt Resistance in Gossypium arboreum Identified in a Genome-Wide Association Study.

Verticillium wilt disease is one of the most destructive biotic stresses faced by cotton plants. Here, we performed a genome-wide association study (GWAS) in 215 Chinese Gossypium arboreum accessions inoculated as seedlings with Verticillium dahliae to identify candidate loci involved in wilt resistance. We identified 309 loci that had a significant association with Verticillium wilt resistance and - log(P) values >5.0; the highest signal appeared on Ca3 in a 74 kb haplotype block. Five genes were also located within this haplotype block. One of these genes, CG05, was positioned close to the most significant SNP Ca3_23037225 (14 kb); expression of the gene was induced by V. dahliae or by treatment with salicylic acid (SA). Therefore, we suggest that CG05 may respond to invasion by V. dahliae via an SA-related signaling pathway, and we designated this gene as GaGSTF9. We showed that GaGSTF9 was a positive regulator of Verticillium wilt through the use of virus-induced gene silencing (VIGS) and overexpression in Arabidopsis. In addition, the glutathione S-transferase (GST) mutant gstf9 of Arabidopsis was found to be more susceptible to Verticillium wilt than wild-type plants. The levels of endogenous SA and hydrogen peroxide had a significant effect on Arabidopsis plants that overexpressed GaGSTF9, indicating that GST may regulate reactive oxygen species content via catalytic reduction of the tripeptide glutathione (GSH), and then affect SA content. Our data demonstrated that GaGSTF9 was a key regulator mediating cotton responses to V. dahliae and a potential candidate gene for cotton genetic improvement.

Tri‐Species Shuffling of Chromosomes to Study the Effects on Fiber Traits Using Chromosome Substitution Lines

Previous studies revealed difficulties in retention and recombination of alien species germplasm by conventional introgression in upland cotton (Gossypium hirsutum L.) due to incompatibility at the whole‐genome level. An alternative approach is to use alien species chromosome substitution (CS) lines, whereby retention and recombination can be differentially increased for a specific chromosome or chromosome segment. Here we report for the first time on the development of a set of CS lines from two alien species in a common genetic background of upland cotton. The overall objective of this research is to report on the chromosomal association of important fiber traits using a partial‐diallel mating design among CS lines of G. tomentosum Nutt. Ex Seem (CS‐T), a wild tetraploid species endemic to Hawaii, G. barbadense L. (CS‐B), a cultivated tetraploid species with improved fiber quality traits, and ‘TM‐1’ (G. hirsutum), the recurrent parent with improved agronomic traits and moderate fiber quality traits. The genetic effects associated with CS lines were dissected into additive, homozygous dominance, and heterozygous dominance genetic effects using an additive–dominance statistical model. Five of six CS‐B lines and two of six CS‐T lines had significant additive genetic effects on lint percentage, indicating that the respective substituted alien chromosome carried alien alleles with potential to improve lint percentage in upland cotton. Fifty‐six percent of 16 different significant additive effects associated with the CS‐B lines could be useful to improve fiber traits in TM‐1. On the contrary, 40% of 15 significant additive genetic effects of the CS‐T lines had potential to improve fiber traits. Results suggested that CS lines can unveil many beneficial alleles harbored cryptically in the other AD‐genome species and render them more accessible for research and cotton genetic improvement.

Cotton genotypes selection through artificial neural networks.

Breeding programs currently use statistical analysis to assist in the identification of superior genotypes at various stages of a cultivar's development. Differently from these analyses, the computational intelligence approach has been little explored in genetic improvement of cotton. Thus, this study was carried out with the objective of presenting the use of artificial neural networks as auxiliary tools in the improvement of the cotton to improve fiber quality. To demonstrate the applicability of this approach, this research was carried out using the evaluation data of 40 genotypes. In order to classify the genotypes for fiber quality, the artificial neural networks were trained with replicate data of 20 genotypes of cotton evaluated in the harvests of 2013/14 and 2014/15, regarding fiber length, uniformity of length, fiber strength, micronaire index, elongation, short fiber index, maturity index, reflectance degree, and fiber quality index. This quality index was estimated by means of a weighted average on the determined score (1 to 5) of each characteristic of the HVI evaluated, according to its industry standards. The artificial neural networks presented a high capacity of correct classification of the 20 selected genotypes based on the fiber quality index, so that when using fiber length associated with the short fiber index, fiber maturation, and micronaire index, the artificial neural networks presented better results than using only fiber length and previous associations. It was also observed that to submit data of means of new genotypes to the neural networks trained with data of repetition, provides better results of classification of the genotypes. When observing the results obtained in the present study, it was verified that the artificial neural networks present great potential to be used in the different stages of a genetic improvement program of the cotton, aiming at the improvement of the fiber quality of the future cultivars.

Genotyping of Individually Isolated gametes from Gossypium hirsutum Chromosome Substitution Lines

As an important crop for US agricultural security and sustainable agriculture, cotton genetic improvement requires development of innovative analytical tools. Genetic analyses based on individual gametes provide several advantages including minimum sample requirement, genetic identification of male parent and overcoming the complexity of polyploidy due to haploid nature of microspores. This research used tetraploid cotton (G. hirsutum x G. barbadense) chromosome substitution (CS) lines with G. barbadense chromosomes 17 and 25 in G. hirsutum background. The individually isolated pollen grains were germinated to release their DNAs and genomic DNA was increased by modified primer extension pre-amplification (PEP) using MasterAmp™ Extra-Long PCR Kit (EPICENTRE®, Madison, WI). Also from select cotton lines, microspores just released from tetrad developmental stage were individually isolated and gamete DNA was extracted as well as amplified through multiple displacement amplification (MDA) using REPLI-g Single Cell Kit (QIAGEN, Valencia, CA). The parental samples along with PEP and MDA amplified individual gamete DNAs were then analyzed using simple sequence repeat (SSR) as well as IRD800 and IRD-700 labeled (Li-Cor, Lincoln, NE) amplified fragment length polymorphism (AFLP) methods. Nineteen SSR and 28 AFLP primer pairs were used to analyze TM-1, 3-79, CS-B17 and CS-B25 cotton lines. The amplification of parental SSR and AFLP markers from both mature pollen as well as early free microspore samples provided unique tools for comparative genetic studies using agarose and polyacrylamide gel electrophoresis, respectively.

Progress in genome sequencing will accelerate molecular breeding in cotton (Gossypium spp.).

Cotton (Gossypium spp.) is the single most important spinning fiber that has economic significance worldwide. Cotton is one of the most value-added crops and an excellent model system for the analysis of polyploidization and cell development. Thus, the Cotton Genome Consortium has made rapid and significant progress in whole genome sequencing studies in the last decade. Developments in cotton genome sequencing and assembly provide powerful tools for dissecting the genetic and molecular bases of agronomically important traits and establishing regulatory networks on these processes, which leads to molecular breeding. Here, we briefly review these advances, emphasizing their implications in the genetic improvement of cotton with a particular focus on fiber quality and yield. Moreover, major progresses in chloroplast and mitochondrial genomes have also been summarized.

Genomic heterozygosity and hybrid breakdown in cotton (Gossypium): different traits, different effects.

BackgroundHybrid breakdown has been well documented in various species. Relationships between genomic heterozygosity and traits-fitness have been extensively explored especially in the natural populations. But correlations between genomic heterozygosity and vegetative and reproductive traits in cotton interspecific populations have not been studied. In the current study, two reciprocal F2 populations were developed using Gossypium hirsutum cv. Emian 22 and G. barbadense acc. 3–79 as parents to study hybrid breakdown in cotton. A total of 125 simple sequence repeat (SSR) markers were used to genotype the two F2 interspecific populations.ResultsTo guarantee mutual independence among the genotyped markers, the 125 SSR markers were checked by the linkage disequilibrium analysis. To our knowledge, this is a novel approach to evaluate the individual genomic heterozygosity. After marker checking, 83 common loci were used to assess the extent of genomic heterozygosity. Hybrid breakdown was found extensively in the two interspecific F2 populations particularly on the reproductive traits because of the infertility and the bare seeds. And then, the relationships between the genomic heterozygosity and the vegetative reproductive traits were investigated. The only relationships between hybrid breakdown and heterozygosity were observed in the (Emian22 × 3–79) F2 population for seed index (SI) and boll number per plant (BN). The maternal cytoplasmic environment may have a significant effect on genomic heterozygosity and on correlations between heterozygosity and reproductive traits.ConclusionsA novel approach was used to evaluate genomic heterozygosity in cotton; and hybrid breakdown was observed in reproductive traits in cotton. These findings may offer new insight into hybrid breakdown in allotetraploid cotton interspecific hybrids, and may be useful for the development of interspecific hybrids for cotton genetic improvement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0366-5) contains supplementary material, which is available to authorized users.

Nature of Genetic Divergence among Some Cotton Genotypes

Inherent divergence and parenthood of germplasm could play an important role in genetic improvement of cotton. The present investigation was conducted to assess the genetic divergence among 14 local cotton genotypes and six exotic genotypes using multivariate Mahalanobis D2 statistics and metroglyph analysis. The results showed highly significant differences among these genotypes for the studied quantitative characteristics. The Mahalanobis D2 statistics showed that the dissimilarity coefficients were significant and highly significant, and ranged from 3.263 to 190.89, indicating a high amount of genetic divergence for these cotton genotypes. The metroglyph analysis grouped these genotypes into eight different clusters based on seven quantitative cotton characteristics. The intercluster D2 values ranged from 11.381 to 178.902 among these groups, whereas the intracluster D2 values ranged from 3.263 to 47.806. On the basis of this grouping, it was concluded that hybridization between genotypes of different clusters might be expected to give new genetic recombinants for the improvement of economic characteristics. This information could be utilized for hybridization between distinct genotypes to increase cotton genetic variability.

The Negative Correlation between Fiber Color and Quality Traits Revealed by QTL Analysis.

Naturally existing colored cotton was far from perfection due to having genetic factors for lower yield, poor fiber quality and monotonous color. These factors posed a challenge to colored cotton breeding and innovation. To identify novel quantitative trait loci (QTL) for fiber color along with understanding of correlation between fiber color and quality in colored cotton, a RIL and two F2 populations were generated from crosses among Zong128 (Brown fiber cotton) and two white fiber cotton lines which were then analyzed in four environments. Two stable and major QTLs (qLC-7-1, qFC-7-1) for fiber lint and fuzz color were detected accounting for 16.01%-59.85% of the phenotypic variation across multiple generations and environments. Meanwhile, some minor QTLs were also identified on chromosomes 5, 14, 21 and 24 providing low phenotypic variation (<5%) from only F2 populations, not from the RILs population. Especially, a multiple-effect locus for fiber color and quality has been detected between flanking markers NAU1043 and NAU3654 on chromosome 7 (A genome) over multiple environments. Of which, qLC-7-1, qFC-7-1 were responsible for positive effects and improved fiber color in offsprings. Meanwhile, the QTLs (qFL-7-1, qFU-7-1, qFF-7-1, qFE-7-1, and qFS-7-1) for fiber quality had negative effects and explained 2.19%-8.78% of the phenotypic variation. This multiple-effect locus for fiber color and quality may reveal the negative correlation between the two types of above traits, so paving the way towards cotton genetic improvement.