Browsing by Subject "plant breeding"
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Item Determining Salt Tolerance Among Sunflower Genotypes(2012-02-14) Masor, Laura LeeCrop lands around the world are becoming more salt-affected due to natural processes and agricultural practices. Due to this increase of salinization, acquisition of saline tolerant germplasm for breeding purposes is becoming a priority. Although cultivated sunflower is classified as a moderately salt tolerant crop, highly tolerant germplasm may be of value. The goal of this study was to screen Helianthus spp. in order to determine the salt tolerance of different genotypes. To accomplish this goal, a novel method of rapid screening was developed. Screening for tolerance at initial growth stages was accomplished by germinating seeds in varying concentrations of NaCl solution in petri dishes. Radicle lengths were measured as an indicator of tolerance. This method identified genotypes that are more tolerant than others during germination. Greenhouse trials were also conducted to ascertain morphological measurements during vegetative stages. Two field locations were chosen to screen germplasm for tolerance through physiological maturity; College Station, TX with low salt concentrations and Pecos, TX with high concentrations of salt in the soil and water. Vegetative growth measurements showed a significant genotype by environment interaction. Due to insect infestation in both locations, yields could not be accurately measured and thus compared between sites in 2010. Yields between locations in 2011 showed significant differences and identified germplasm more suited for cropping in salt affected soil. Seed oil content was determined with Fourier Transform Near-Infrared Spectroscopy. Seed oil content was not significantly different between locations, but was highly significant between genotypes. These screenings identified genotypes that are more salt tolerant than others.Item Diallel analysis of within-boll seed yield components and fiber properties in upland cotton (Gossypium hirsutum L.) and breeding potential for heat tolerance(Texas A&M University, 2004-09-30) Ragsdale, Paul IrwinA diallel analysis of eight upland cotton (Gossypium hirsutum L.) genotypes was conducted in the field over two years to determine the potential for improvement in within-boll seed yield components and fiber quality parameters. Four exotic germplasm lines from the converted race stock (CRS) collection and four commercial types representing Texas, mid-South, and Eastern production regions were crossed and evaluated in a diallel with parents but without reciprocals according to Griffing's Model I, Method 2. Significant variation for genotypic, general combining ability (GCA) effects, and specific combining ability (SCA) effects (P 0.05) were identified for all traits studied indicating potential for improvements through selection. Significant interactions of these parameters with years were also observed, suggesting that selection should be based on multiple years and or locations. In addition to effects on yield, individual seed number traits were found to respond to heat stress under controlled growth chamber conditions, suggesting their potential for use in screening genotypes for heat tolerance. These traits were not found to interact with temperature, which indicates that selection for improvements in these traits could be conducted in any environment. Improvements in seed yield components and, putatively, in heat tolerance could be achieved using CRS M-9044-0162. As expected, CRS accessions reduced fiber quality parameters in addition to other agronomic traits, suggesting that improvements for within-boll seed yield components and heat tolerance should be made utilizing a backcross approach. Also observed in this population was a superior hybrid for fiber length and fiber strength from the cross of TAM 94L-25 with PD 6186. This combination could lead to improved fiber length and strength potential in upland cotton.Item Fine Mapping and Characterization of the iap Gene in Sorghum [Sorghum bicolor (L.) Moench](2014-05-27) Gill, JohnThe production of interspecific or intergeneric progeny using sorghum [Sorghum bicolor (L.) Moench] is greatly enhanced by the presence of the iap (Inhibition of Alien Pollen) allele. Hybridization between S. bicolor homozygous for iap and divergent species of sorghum and sugarcane (Saccharum spp.) has been demonstrated with introgression occurring in hybrids between S. bicolor and S. macrospermum. The intergeneric F1 hybrids between sorghum and sugarcane were male and female sterile, so the plants were doubled with colchicine in an attempt to restore fertility. The objectives of this research were to determine the viability of the sorghum ? sugarcane amphidiploids as a bioenergy crop, determine the optimum humidity for maize (Zea mays L.) pollen tube growth on the pistils of sorghum homozygous for iap, and fine map the Iap locus and identify candidate genes. Sorghum ? sugarcane amphidiploids were evaluated in a yield trial in Weslaco, TX. Although the amphidiploid genotypes were inferior to the intergeneric F1?s for most agronomic traits, genotypic variation among families indicates that continued selection and breeding could produce more desirable genotypes. Somatic chromosome counts on selected genotypes revealed that chromosome transmission between generations appears to be occurring normally. Knowing the ideal environmental conditions could lead to greater success rates in future wide crosses. The greatest maize pollen adhesion and germination on the pistils of Tx3361 (iap iap) was observed at 45% humidity. Multiple maize pollen tubes were observed in the sorghum style and ovary at 45% humidity but not at higher humidity levels. Future interspecific and intergeneric crosses with iap sorghum should be performed at low humidity levels. Knowledge of the identity and function of the iap allele could lead to discovery of additional genes that regulate barriers to intergeneric hybridization. Fine mapping resolved the location of the Iap gene to a 48 kb region on the short arm of chromosome 2. There are three putative genes present in this region, however none of them are easily identified as Iap. This research provides valuable insight to proper and efficient utilization of the iap allele and a foundation for continued mapping and characterization of Iap.Item High-biomass sorghums for biomass biofuel production(2011-05-09) Packer, DanielHigh-biomass sorghums are being developed as a dedicated energy crop for biofuels. Their high biomass yields provide large quantities of structural carbohydrates (cellulose, lignin, etc.) for energy production. Sorghum improvement for applications such as grain or fodder production is well established, but development of high-biomass sorghums for biofuels is not. Thus the objectives of this research were to develop information on sorghum improvement methods and criteria for high-biomass sorghums including marker-assisted selection, use of exotic germplasm, heterosis, and GxE variability of biomass composition. Marker-assisted selection was compared to testcross selection for identifying photoperiod-insensitive (PI) experimental lines that yield photoperiod-sensitive (PS) hybrids within the Ma1/Ma5/Ma6 hybrid production system. High-biomass sorghums are PS and the Ma1/Ma5/Ma6 hybrid production system produces PS hybrids with PI parents by manipulating alleles at the Ma1, Ma5 and Ma6 sorghum maturity loci. Four hundred eighty three sorghum lines were genotyped at the Ma1 and Ma5 loci to predict their hybrid photoperiod reactions and testcrossed to establish their actual hybrid photoperiod reactions. Ma1/Ma5 marker selections for lines producing PI hybrids were reliable and could be used to discard such lines. Ma1/Ma5 marker selections for lines producing PS hybrids were not reliable and identification of such lines will require testcrossing or potentially, genotyping at Ma6 or other additional loci. An attempt was made to determine whether meaningful relationships exist between the passport data (geographic origin) of exotic sorghum accessions and high-biomass desirability. Such a relationship could be used to prioritize exotic sorghum accessions for breeding evaluations. Seventeen hundred ninety two exotic sorghum accessions from 7 different geographic origins were evaluated for high-biomass desirability in 3 environments. Significant relationships between passport data and high-biomass desirability were identified within environments but were not applicable across environments because of large GxE interactions. A larger sampling of environments will be needed to understand and establish reliable passport data and high-biomass desirability GxE patterns. High-parent heterosis can improve yields in high-biomass sorghums and hybrid entries derived from high-biomass sorghum pollinators and grain sorghum females were evaluated for biomass heterosis. Grain sorghum females enable commercial seed production of high-biomass sorghums. Moderate levels of biomass high-parent heterosis were widely available in the hybrids. Heterosis and biomass yields were maximized in specific hybrid combinations and were subject to GxE interactions. Biomass composition (percent cellulose, hemicellulose, etc.) affects the conversion efficiency of biomass to liquid fuels and may be altered via breeding selections. Breeding methods and genotype recommendations for biomass composition will require consideration of GxE variability. The biomass composition of 12 sorghums grown across 5 environments was estimated using Near-Infrared Spectroscopy to identify GxE patterns. Significant GxE interactions for biomass composition were identified, but most compositional variability was attributable to environmental differences. Differences between genotypes for compositional traits were small (1-3 percent), but may prove important with large-scale biomass processing.Item Inheritance of Cotton Fiber Length and Strength(2014-04-23) Joy, Kolbyn SethThe U.S. cotton industry has become predominantly an export market which requires a higher standard of fiber quality than does the domestic market. To remain competitive, U.S. cotton must meet the quality standards demanded by the consumers of raw cotton whether domestic or abroad. Diallel and generation means analyses (GMA) were conducted on fiber quality data of nine and five parental genotypes, respectively, to gain a better understanding of the genetic control of cotton fiber length and strength as well as to ascertain the value of the reported genotypes toward the improvement of fiber quality. Parental genotypes included extra-long staple uplands (Gossypium hirsutum, L.), EMS mutated uplands, high strength uplands, and interspecific hybrids. General combining ability (GCA) and specific combining ability (SCA) were estimated according to Griffing?s diallel Model I, Method 4 for lint percent, high volume instrument (HVI) upper half mean length (UHML), fiber bundle strength (Str), uniformity index, elongation, micronaire, advanced fiber information system (AFIS) upper quartile length on a weight basis, mean length on a number basis, short fiber content on a number basis, immature fiber content, maturity ratio, and standard fineness. Estimates of GCA were significant across environments for all traits. SCA effects were significant for most traits but accounted for a smaller proportion of the variability in comparison to GCA effects. TAM B182-33 ELS would be the parent of choice to simultaneously improve fiber length and Str. The GMA was conducted on the parental, F_(1), F_(2), and backcross generations. Low levels of transgressive segregation for both UHML and Str were observed for some populations. Broad sense heritability ranged from 0.00 to 0.67 for UHML and from 0.22 to 0.82 for Str. Additive gene action was significant for all but three parental combinations for UHML and for all parental combinations for Str. Generally, the significance and magnitude of additive genetic effects were more consistent among parental combinations and years than were non-additive genetic effects for both UHML and Str. Dominance and epistatic genetic effects often were of a greater magnitude than additive genetic effects but in an inconsistent manner, and in both positive and negative directions.