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Thrips are major early season insect pests that cause significant economic damage in Upland cotton in the U.S. Development and deployment of resistant cultivars is the most effective and ecologically sustainable means of reducing thrips damage in cotton. Interspecific hybridization and backcrossing were performed to introgress thrips resistance from Pima cotton (Gossypium barbadense L.) accession Coastland 320 into Upland cotton (Gossypium hirsutum L.) cultivars Acala Maxxa (AM) and Fiber Max 966 (FM966). Backcross populations were screened for thrips resistance in thrips screening summer field nurseries in North Carolina. Thirty-two BC2F2 plants with thrips resistance were identified and backcrossed further to develop BC3F2 plants. Eleven AM derived BC2F2 resistant plants and 21 FM966 derived BC2F2 resistant plants were genotyped using CottonSNP63K array to identify the Pima chromatin in the introgression lines (ILs). In the ILs, introgressed Pima chromatin was detected on chromosomes A01, A08, A09, A10, A11, D10, D11, D12, and D13. Of these, four ILs, two each in AM and FM966 background, showed overlapped introgressed Pima chromatin on chromosomes A10 and D11. Further, four introgression lines, two each in AM and FM966 background, shared a common Pima introgression on chromosome D13. Characterization of thrips species in the screening nursery showed that predominant thrips species were tobacco thrips (Frankliniella fusca (Hinds)) followed by western flower thrips (Frankliniella occidentalis (Pergande)). The identified ILs with thrips resistance should be a useful source of genetic variability for developing Upland cotton cultivars with pest resistance. [ABSTRACT FROM AUTHOR]

Assessing genetic diversity and population structure is prerequisite to the systematic utilization and conservation of germplasm resources of crop plants. The genetic diversity and population structure in a combined panel of 557 Gossypium hirsutum L. accessions including 375 cultivars and 182 race stocks using 114 pairs of simple sequence repeat primers were evaluated in the current study. Six G. barbadense L. accessions were included as an out-group. Genotyping the diversity panel of 563 accessions with the markers identified a total of 819 alleles and 662 alleles within G. hirsutum. Population structure analysis identified one G. barbadense group and five G. hirsutum groups corresponding to southwestern cultivars, Mexican collections, western cultivars, southeastern and mid-south cultivars, and Guatemalan collections. Average genetic distance of 0.253 indicated a moderate level of genetic diversity in this panel. Analysis of molecular variance revealed a low level of differentiation among cultivated cotton groups compared to landrace accessions. Genetic diversity and population structure analyses suggest landraces of Guatemala could be a potential source of novel genetic variability for U.S. cotton. Further, multiple core sets with different levels of allele richness were identified. The diversity panel and the core sets identified could be a good resource for broadening the genetic base of U.S. cotton and for genetic analysis of agronomic traits. [ABSTRACT FROM AUTHOR]

The three principles of experimental design-- randomization, replication, and blocking--have been followed routinely in field experiments. This paper addresses issues of blocking in conducting cultivar performance trials. Most agronomists design (block) their trials by considering the slope of the field at most. However, the direction of field variation might not always follow the slope of the field. Blocking in the direction of field operations is advocated. The objective of this study was to compare precision between three years of horizontal blocking with three years of vertical blocking in North Carolina Official Cotton Variety Trials. No significant difference in precision was found between the two blocking arrangements. However, the standard analysis of variance of a randomized complete block design revealed that vertical blocking produced a larger standard error than when the tests were blocked horizontally. Although vertical blocking results in increased spatial distance, the use of a spatial analysis package should mitigate this problem. [ABSTRACT FROM AUTHOR]

In the U.S., Ted Wallace coordinates a Regional Breeders Testing Network (RBTN) for cotton that is sponsored by Cotton Incorporated. The objective of this program is to provide testing sites for public breeders and geneticists across a regional basis. This study looked at various statistical aspects of field testing with emphasis on lint yield. Ten years of data (107 environments) were examined. The objectives were to: 1) determine any relationship between error variance and mean lint yield, 2) establish a procedure for rejecting less precise data, and 3) discern the most optimum testing sites in the program. To achieve the first objective the natural log of error variances were regressed on the natural log of mean environmental lint yields and tested for significance. The "b" value of 0.85 was significant indicating that the error variance increased with increasing yield levels. Using a procedure previously published on rejecting less precise data, the second objective was met. Five of the 107 environments were deemed imprecise and should not have been included in across-location tables. A genotypic index regression method was followed to ascertain the most desirable test sites in the program. Twelve of 23 test sites did an acceptable job of discriminating the entries. Thus, by eliminating nearly half of the test sites more reliable data can be produced, less seed would be required, and more efficient use of resources would be achieved. Sites with less than desirable tests might contribute by collecting data on disease tolerance, morphological traits, or insect resistance, etc. and thus might still be valuable in the cotton RBTN. [ABSTRACT FROM AUTHOR]

Trends in fiber quality of United States (U.S.) Upland cotton (Gossypium hirsutum L.) recently have been positive for the three major traits of length, strength, and micronaire. From 1980 to 2010, micronaire trended upward, but it was not highly significant; emphasis on lint yield tends to result in higher micronaire fibers. Fiber strength continues to improve despite a respite in the late 1990s when transgenic cultivars first came on the market. Much of this improvement in fiber strength can be traced back to the New Mexico State University breeding program and its impact on the cultivar Deltapine 90 which is found in many of the improved cultivars. There was one case of possible transgressive segregation for fiber strength in 2006. Fiber length trended upwards until 1997, and then declined until 2006 when it began another period of improvement that currently continues in the U.S. cotton crop. Much of the improvement in fiber length in recent years can be attributed to the introduction of Australian breeding materials into FiberMax and Deltapine cultivars. Pedigree analyses only reveals that Deltapine 90 is in the background of this genetic material, thus much of the improvement in fiber quality over these years can be traced to material developed at New Mexico State University. [ABSTRACT FROM AUTHOR]

Molecular cytogenetic techniques, especially Fluorescence In situ Hybridization (FISH) and Genomic In situ Hybridization (GISH), are excellent tools to study the structure and function of chromosomes, polyploidy, aneuploidy, alien gene introgression and genome evolution and physical mapping of genes. For many applications, in situ hybridizations require reliable and efficient methods of chromosome preparation with well preserved and dispersed chromosomes and little or no cell wall debris. However, such protocols have not yet been published for cotton mitotic chromosome preparations. In the current study, an improved method for preparing mitotic metaphase chromosomes of tetraploid cotton was developed. Root tips were collected from lab-grown three-day-old cotton seedlings and pre-treated with high-pressure nitrous oxide (N2O). Following fixation with acetic acid, root tip meristems were removed, enzymatically digested, gently macerated, and then processed to create suspensions of protoplasts in acetic acid and methanol. Suspended protoplasts were then dropped onto a glass slide in order to distribute the protoplasts and spread the chromosomes. Using this approach, acceptable mitotic indexes and high-quality chromosomal spreads with no cell wall debris were obtained. This drop method of preparing chromosome spreads was tested for its compatibility for in situ hybridization using rDNA as probe in FISH. Additionally, varying pre-treatment times with N2O were investigated. Our results show that the combination of a 95-minute N2O pre-treatment, a 55-minute enzymatic degradation, and the "drop method" efficiently produce cotton mitotic metaphase preparations. This new method will expectedly improve the efficiency and efficacy of GISH, FISH, and single-copy multicolor FISH, which will have a multitude of ramifications in cotton genetics and breeding. [ABSTRACT FROM AUTHOR]