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Premise of the study Introgression is widely acknowledged as a potential source of valuable genetic variation, and growing effort is being invested in analysis of interspecific crosses conferring transgressive variation. Experimental backcross populations provide an opportunity to study transmission genetics following interspecific hybridization, identifying opportunities and constraints to introgressive crop improvement. The evolutionary consequences of introgression have been addressed at the theoretical level, however, issues related to levels and patterns of introgression among (plant) species remain inadequately explored, including such factors as polyploidization, subgenome interaction inhabiting a common nucleus, and the genomic distribution and linkage relationships of introgressant alleles. Methods We analyze introgression into the polyploid Gossypium hirsutum (upland cotton) from its sister G. tomentosum and compare the level and pattern with that of G. barbadense representing a different clade tracing to the same polyploidization. Key results Across the genome, recurrent backcrossing to Gossypium hirsutum yielded only one-third of the expected average frequency of the G. tomentosum allele, although one unusual region showed preferential introgression. Although a similar rate of introgression is found in the two subgenomes of polyploid (AtDt) G. hirsutum, a preponderance of multilocus interactions were largely within the Dt subgenome. Conclusions Skewed G. tomentosum chromatin transmission is polymorphic among two elite G. hirsutum genotypes, which suggests that genetic background may profoundly affect introgression of particular chromosomal regions. Only limited correspondence is found between G. hirsutum chromosomal regions that are intolerant to introgression from the two species, G. barbadense and G. tomentosum, concentrated near possible inversion polymorphisms. Complex transmission of introgressed chromatin highlights the challenges to utilization of exotic germplasm in crop improvement.

Seventeen backcross-self families from crosses between two Gossypium hirsutum recurrent parent lines (CA3084, CA3093) and G. tomentosum were used to identify quantitative trait loci (QTLs) controlling fiber quality traits. A total of 28 QTLs for fiber quality traits were identified (P0.001), including four for fiber elongation, eight for fiber fineness, four for fiber length, four for fiber strength, six for fiber uniformity, one for boll weight, and one for boll number. Three statistically significant marker-trait associations for lint yield were found in a single environment, but need further validation. Two-way analysis of variance revealed one locus with significant genotype × family interaction (P0.001) for fiber strength and a second locus with significant genotype × environment interaction (P0.001) in the CA3084 background, and two loci with significant genotype × background interaction (P0.001) for the 28 common markers segregating in both of the two recurrent backgrounds. Co-location of many QTLs for fiber quality traits partially explained correlations among these traits. Some G. tomentosum alleles were associated with multiple favorable effects, offering the possibility of rapid genetic gain by introgression. Many G. tomentosum alleles were recalcitrant to homozygosity, suggesting that they might be most effectively deployed in hybrid cottons. DNA markers linked to G. tomentosum QTLs identified in the present study promise to assist breeders in transferring and maintaining valuable traits from this exotic source during Upland cotton cultivar development. This study also adds further evidence to prior studies indicating that the majority of genetic variation associated with fiber quality in tetraploid cotton traces to the D-subgenome from a diploid ancestor that does not produce spinnable fiber.

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.

In this study, the bundle elongation and tenacity of cotton fibers were measured using a modified tensile testing instrument to which Pressley clamps (1/8” gage length) were adapted. 32 cotton genotypes with a range of bundle tenacity and elongation were carefully selected based on their distinct physical properties. The work of rupture was calculated from the load vs. elongation curves for each type of cotton. Results demonstrated the importance of fiber bundle elongation in the work of rupture of fiber bundles, which is critically important to processing performance. This study lays a foundation for future efforts to calibrate the high volume instrument elongation measurements and to breed new cultivars with improved work of rupture. This should result in lower fiber breakage when the cotton fibers are submitted to different mechanical stresses (ginning, carding, spinning, and weaving).

QTL mapping experiments yield heterogeneous results due to the use of different genotypes, environments, and sampling variation. Compilation of QTL mapping results yields a more complete picture of the genetic control of a trait and reveals patterns in organization of trait variation. A total of 432 QTL mapped in one diploid and 10 tetraploid interspecific cotton populations were aligned using a reference map and depicted in a CMap resource. Early demonstrations that genes from the non-fiber-producing diploid ancestor contribute to tetraploid lint fiber genetics gain further support from multiple populations and environments and advanced-generation studies detecting QTL of small phenotypic effect. Both tetraploid subgenomes contribute QTL at largely non-homeologous locations, suggesting divergent selection acting on many corresponding genes before and/or after polyploid formation. QTL correspondence across studies was only modest, suggesting that additional QTL for the target traits remain to be discovered. Crosses between closely-related genotypes differing by single-gene mutants yield profoundly different QTL landscapes, suggesting that fiber variation involves a complex network of interacting genes. Members of the lint fiber development network appear clustered, with cluster members showing heterogeneous phenotypic effects. Meta-analysis linked to synteny-based and expression-based information provides clues about specific genes and families involved in QTL networks.

Universal attenuated total reflectance Fourier transform infrared (UATR-FTIR) spectroscopy and thermogravimetric analysis (TGA) were used to investigate the structural changes of cotton (Gossypium hirsutum L.) fibers as a function of developmental programming. The presence of noncellulosic compounds (wax, protein, hemicelluloses, pectic substances, amino acids, etc.) was evident from FTIR spectra of fibers at 10, 14, 17, and 20 dpa (day postanthesis). The vibration corresponding to the noncellulosic compounds disappeared at 36 dpa. Furthermore, independent TGA analysis supported the results obtained with FTIR, showing that the transition from primary cell wall synthesis to secondary cell wall synthesis occurs at or around 20 dpa. This study is the first to report on the use of the UATR-FTIR and TGA to elucidate structural changes during cotton fiber development. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Field experiments from 1997 to 1999 examined cotton cv. ‘Coker 312’ that was genetically transformed to tolerate glufosinate. None of the glufosinate treatments caused visible injury to the glufosinate-tolerant cotton, but treatments were lethal to nontransformed or nonexpressing cotton. No glufosinate treatment adversely affected plant height at maturity, total number of nodes, bolls per plant, or boll positions. Glufosinate applications of 0.6 kg ha−1 made at eight stages of growth, ranging from cotyledon stage to 50% open boll, did not adversely affect yield or fiber quality as measured by micronaire or fiber length and strength. Sequential glufosinate applications up to four stages of growth from the zero- to one-leaf stage to the 14- to 15-leaf stage or individual glufosinate applications at 3.3 kg ha−1 made at the two- to three-leaf stage of growth also did not adversely affect yield or fiber quality. Overall yields in these studies were low relative to normal Texas Southern High Plains cot...

Seedling diseases of cotton (Gossypium hirsutum L.) limit production in the High Plains of Texas. Field studies were conducted from 1992 through 1995 to determine the influence of tillage (conventional or terminated wheat [Triticum aestivum L.] conservation tillage system), seed quality, and fungicide seed treatments (specific for Rhizoctonia solani, Pythium spp., and Thielaviopsis basicola) on cotton emergence and lint yield. Seed quality positively affected plant emergence and yield in all years. Increases in plant emergence and yield were generally found with conventional rather than conservation tillage. Emergence 21 d or later was generally lower for untreated seed or Captan (C) (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) treated seed than seed treatments that included triadimenol (Baytan 30 [B]) (Beta-(4-Chlorophenoxy)-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) in 3 of 4 yr; carboxin-PCNB (Vitavax-PCNB [V]) (5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide-Pentachloronitrobenzene) in 2 of 3 yr and metalaxyl (Apron 2.66F [A]) (N-(2,6-dimethyl-phenyl)-N-(methoxyacetyl)alanine methyl ester) + C in one year. Yields were affected by seed treatments in 3 yr, with B being associated with higher yields every year, and lower yields associated with chloroneb (Nuflow ND [N]) (1,4-dichloro-2,5-dimethoxybenzene) + TCMTB (2-(thiocyanomethylthio) benzothizaole (1992), untreated seed (1994) and C (1995). Plants were infected most frequently with R. solani and T. basicola. The most consistent factor affecting seedling disease was seed quality. Conventional tillage and seed treatments specific for Rhizoctonia and Thielaviopsis improved seedling emergence and yield most years. Interactions between chemical seed treatments, seed quality, and tillage systems were inconsistent between years and even among different evaluation times in the same year.

Hybrids (F 2 ) of cotton (Gossypium hirsutum L.) reportedly offer improved seedling vigor, disease tolerance, and yield for this major crop of the Texas High Plains but raise concern about increased fiber property variability. Our objective was to compare fiber variability in the F 2 generation with that in pure lines and in F 1 hybrid cultivars. A four-parent complete diallel mating system using lines with similar and divergent fiber types resulted in 28 treatments: 4 parents, 12 F 1 hybrids, and 12 F 2 hybrids (.)

Mapping of genes that play major roles in cotton fiber development is an important step toward their cloning and manipulation, and provides a test of their relationships (if any) to agriculturally-important QTLs. Seven previously identified fiber mutants, four dominant (Li 1, Li 2, N 1 and Fbl) and three recessive (n 2, sma-4(h a), and sma-4(fz)), were genetically mapped in six F2 populations comprising 124 or more plants each. For those mutants previously assigned to chromosomes by using aneuploids or by linkage to other morphological markers, all map locations were concordant except n 2, which mapped to the homoeolog of the chromosome previously reported. Three mutations with primary effects on fuzz fibers (N 1, Fbl, n 2) mapped near the likelihood peaks for QTLs that affected lint fiber productivity in the same populations, perhaps suggesting pleiotropic effects on both fiber types. However, only Li 1 mapped within the likelihood interval for 191 previously detected lint fiber QTLs discovered in non-mutant crosses, suggesting that these mutations may occur in genes that played early roles in cotton fiber evolution, and for which new allelic variants are quickly eliminated from improved germplasm. A close positional association between sma-4(h a ), two leaf and stem-borne trichome mutants (t 1 , t 2), and a gene previously implicated in fiber development, sucrose synthase, raises questions about the possibility that these genes may be functionally related. Increasing knowledge of the correspondence of the cotton and Arabidopsis genomes provides several avenues by which genetic dissection of cotton fiber development may be accelerated.

The US cotton production system exemplifiesthe complex challenges that must be met in orderto reduce the genetic vulnerability of a majorcrop.Genetic vulnerability results from acombination of a crop’s evolutionary history,trends in breeding and biotechnology practices,and grower Decisions based on inadequateinformation being available,all in response tothe inevitable pressures imposed by processor

Fiber strength is only one of several quality measures of cotton fiber. All of the quality factors influence spinning performance as exhibited by the effect each has on the end product. Fiber strength is more important for open-end than ring spinning. The development of agronomically acceptable cotton cultivars possessing high tensile strength will be a slow and deliberate process. Certain genetic associations exist which will slow the developmental process. Data indicate that the combination of high fiber strength with other favorable agronomic characteristics is being achieved.

Seven sources of cotton representing a wide range of fiber properties were roller ginned, saw ginned, or saw ginned plus processed through tandem saw lint cleaners or through an aggressive carding-type cleaner (Cottonmaster1). Lint cleaner induced changes in fiber length and nep count were compared to fiber property measurements from roller ginned samples. Fiber length deterioration from saw ginning was negatively correlated with fiber strength. Fiber breakage in lint cleaning was positively correlated with fiber fineness. Resistance to fiber length damage in ginning was explained best by fiber strength and fineness, or an estimate of individual fiber strength. Initial and final nep level were related to fineness, nonlint content, and upper quartile length, but an increase in neps due to lint cleaning had no significant relationship to fiber properties.