Browsing by Subject "Breeding"
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Item A study of the breeding efficiency of bulls in the Texas Tech bull stud(Texas Tech University, 1950-12) Baumhardt, Roland E.Not availableItem Genetic diversity and combining ability among sorghum conversion lines(Texas A&M University, 2007-04-25) Mateo Moncada, Rafael ArturoSorghum (Sorghum bicolor [L] Moench) was first introduced to the United States in the 1800s. These introductions consisted of tropical varieties with a short day photoperiod response that limited their use in temperate hybrid breeding programs. Commercial exploitation of F1 hybrids in grain sorghum started by the mid 1950s with the use of cytoplasmic male sterility system CMS (A1). Even though other CMS are available, most sorghum hybrid seed production still relies on the A1 system. Genetic gain in most agronomic crop species is limited by several factors. In the specific case of sorghum, the uniform use of the CMS (A1) system and the recent introduction of sorghum to the United States have resulted in a reduction of its genetic base. In order to create enough genetic variability, plant breeders might utilize exotic non adapted material, exotic adapted material or existing elite material as a source of new alleles that will protect and improve genetic gain through selection. This study provides an estimate of the genetic diversity existing in a set of sorghum conversion lines. The objectives of this study were: (1) to estimate the genetic diversity present among a set of 16 sorghum conversion lines???? (2) to classify this set of lines based on genetic similarities estimated using AFLP markers and (3) to estimate heterosis, general and specific combining ability for grain yield among the set of conversion lines. Genetic diversity was present in the set of conversion lines evaluated. For the lines included only in this study, Caudatum was the most homogenous race (average GS = 0.69), and this race was closely related to the Durra race (Average GS = 0.66). Two other homogenous races were Bicolor and Kafir with average GS of 0.67. Highest GCA effects were obtained from the Kafir and Caudatum races. Good heterotic responses were obtained from DurraKafir races and CaudatumKafir races. Estimation of SCA, MPH and BPH identified specific crosses that were numerically superior than those of the checks. The use of AFLP markers allowed the identification of five strong clusters through estimates of genetic similarities. This classification did not group the lines by either their genetic background or their fertility reaction. This study provides information to identify specific combinations that would help to understand heterotic relationships in sorghum, and support the suggestions made by Menz and Gabriel that races in sorghum are not well defined.Item Introgression of reniform nematode resistance and other germplasm from G. longicalyx and G. armourianum into G. hirsutum(2009-05-15) Dighe, Nilesh DeoramThe Gossypium genus includes 45 diploid and 5 tetraploid cotton species of which only 2 diploids and 2 tetraploids are cultivated in different parts of the tropics and sub-tropics, leaving the remaining diploid and tetraploid species as potential genetic sources for novel trait introgression. The reniform nematode (Rotylenchulus reniformis Linford and Oliveira) poses significant problems to US cultivated Upland cottons (Gossypium hirsutum L., 2n=52), all of which lack high resistance. This work was in collaboration with the USDA-ARS team that focussed on introgressing reniform nematode-resistance from a diploid cotton species, Gossypium longicalyx Hutch. & Lee into G. hirsutum by creating a tri-species hybrid, HLA and backcross breeding (Bell et al., 2007; Robinson et al., 2007). The main objectives of this work were [1] to cytogenetically evaluate and help select superior types at each introgressed generation; [2] to identify molecular markers tightly linked to the reniform nematode-resistance gene and to map the resistance loci; [3] (A) to introgress germplasm on a genome-wide basis, (B) to evaluate introgressed germplasm for traits of economic importance other than reniform nematode resistance, and (C) to evaluate breeding methodologies in terms of this specialized breeding material. Reniform nematode resistant plants were of diverse cytogenetic constitution but individuals that modally formed 26II chromosomal configuration were identified at BC2F1, BC3F1, BC4F1, and BC5F1 generations. Three SSR markers, BNL3279_114, BNL1066_156, and BNL836_215 and one phenotypic marker, green-colored fuzz (Fzglon), were identified to be tightly-linked to the resistance locus. Extension of the association analysis and linkage estimation to 16 susceptible self progeny (BC1S1, BC3S1 and BC6S1) and 374 susceptible backcross hybrids (BC2F1-BC8F1) mapped the resistance locus to chromosome 11 of cotton with BNL3279_114 on one side and Fzglon on the other at 0.8 cM and 2.8 cM, respectively. Besides reniform nematode-resistance introgression, genome-wide introgression efforts were also conducted. Low micronaire and high fiber strength were the two most promising traits identified in the HLA-derived introgressed generations. Most of the introgressed generations had high variability for the fiber-quality traits than the commercial checks, thus providing more opportunities for selection and improvement.Item Ranges, movements, and spatial distribution of radio-tagged Rio Grande wild turkeys in the Edwards Plateau of Texas(Texas A&M University, 2006-08-16) Schaap, Jody NealTo determine possible causes of declining Rio Grande wild turkey (RGWT; Meleagris gallopavo intermedia) abundance in the southern Edwards Plateau, research was conducted on 4 sites, 2 with stable (S [SA and SB]; Kerr and Real counties) and 2 with declining (D [DA and DB]; Bandera County) RGWT populations. RGWTs were trapped, radio-tagged, and tracked. Ranges were constructed with 95% kernels. Data on brood survival and invertebrate and predator abundances were combined with range characteristics to assess habitat at a landscape scale. Annual range sizes did not differ in year 1, but were larger in S than in D in year 2. Range sizes in S increased from year 1 to year 2 while there was no change in range sizes in D. Range overlap was higher in D than S in both years. Movement distances remained consistent in S for both years, but were larger in D during year 1. During year 1 and year 2, RGWT females exhibited larger reproductive ranges and less range overlap in S. Invertebrate abundance for 4 insect orders was 2.5??15.9 times greater in S than in D while coyote abundance was 2??3 times greater in D than in S. Results were similar in year 3, with the exception of SB, where reproductive ranges and spatial arrangement were smaller than all other sites. My results refute the conventional assumption that larger ranges are indicative of poorer habitat quality. Range overlap suggests that useable space may have been limiting in D in the less productive year 2. In D, multiple broods used the same reproductive range, presumably depleting resources faster than in S. Greater predator abundance in D increased the risk of brood predation. The smaller reproductive spatial arrangement of SB females in year 3 correlates there being >3 times the percentage of females missing in other sites. If SB females moved further in year 3 than the detection distance of the radio telemetry equipment, the results would fit the pattern of greater dispersion distance in SA. RGWT females may attempt to separate themselves from other breeding females, possibly to avoid nest or brood predation and/or potential competition for brood resources.Item REPRODUCTIVE SUCCESS AND ANNUAL HABITAT PREFERENCE BY RED-SHOULDERED HAWKS IN SOUTHERN TEXAS(2011-05) Strobel, Bradley N.; Boal, Clint W.; Andersen, David E.; Haukos, David A.; Griffis-Kyle, Kerry; Blankenship, TerryIdentifying the vegetation characteristics resulting in habitat use by nesting raptors provides information important to species conservation and management. I examined nesting habitat preference of red-shouldered hawks (Buteo lineatus) using conditional logistic regression on characteristics measured at 27 occupied nest sites and 68 randomly selected unused sites in 2005–2009 in southern Texas. I measured vegetation characteristics of individual trees (nest trees and unused trees) and corresponding surrounding 0.04 ha plots. I evaluated the importance of tree and plot characteristics to nesting-habitat selection by comparing a priori tree-specific and plot-specific models using Akaike‘s Information Criterion corrected for small sample size (AICc). Models with only plot variables carried 14% more weight than models with only center-tree variables. The model-averaged odds ratios indicated red-shouldered hawks selected to nest in taller trees and in areas with higher average diameter at breast height (dbh) than randomly available within the forest stand. Relative to randomly selected areas, each 1-m increase in nest-tree height and 1-cm increase in the plot-average dbh increased the probability of selection by 85% and 10%, respectively. My results indicate characteristics of individual trees and the structure of the 0.04 ha area surrounding the tree, were associated with red-shouldered hawk nesting habitat selection. My results show red-shouldered hawks preferred taller nest trees (average 16.4 m) surrounded by larger diameter trees (average 25.4 cm) relative to the surrounding forest in southern Texas. Preference for taller nest trees by raptors is well documented and suggests an association with increased fitness. Further study is required to understand the mechanism responsible for this preference. Widespread alteration of forest communities combined with the well-documented preference for mature forests by breeding red-shouldered hawks (Buteo lineatus) has caused concern over the conservation of the species. Although habitat preferences of breeding red-shouldered hawks have been well documented, few data describe non-breeding-period habitat selection. I studied the seasonal habitat preferences of 12 adult red-shouldered hawks in southern Texas. I used radio-telemetry to collect >1,800 locations during 3 discrete phenological periods (winter, breeding-spring, and non-breeding-spring). I constructed phenological stage-specific discrete-choice models to compare the proportion of a 0.5-ha circle around each location (used and available) comprised of mature forests, young forests, brush, grass, wetland, and open-water cover types. I used general linear models to assess whether the amount of mature forest covertypes within used areas was dependent upon the sex of the individual, its breeding status, or the time of year the data were collected. During the breeding-spring-period, red-shouldered hawks preferred areas with greater amounts of mature forest cover types (selection ratio = 1.40, 95% CI = 1.16 - 1.69) and higher cover-type richness (selection ratio = 1.10, 95% CI = 1.04 - 1.21). Characteristics associated with habitat use during the breeding-spring-period were different than those associated with winter-period or non-breeding-spring-period habitat selection. Habitat use during the winter was associated with greener vegetation measured using the Normalized Difference Vegetation Index (NDVI), and avoidance of grasslands, brushlands, and wetlands. My data indicate the amount of forested cover types preferred by individual red-shouldered hawks depends upon the sex of the individual as well as its breeding stage (i.e., breeding, non-breeding). Habitat quality is often evaluated based on relative resource preferences, usually by examining disproportionate use of available resources. Alternatively, the Ideal Despotic Distribution hypothesis predicts that given a suite of territories to select from, an individual will select the highest quality territory in regards to its perceived fitness benefit. Presumably, the long-term occupancy rates of specific territories will be positively correlated with their quality. However, the predictions of the ideal despotic distribution hypothesis hinge upon the individual‘s ability to accurately assess territory quality (perfect knowledge), a condition that is difficult to meet under temporally and spatially variant environments. Using a 5-year data set on a resident population of red-shouldered hawks in southern Texas, I examined the predictions of the ideal despotic distribution hypothesis. My results were consistent with the prediction of the ideal despotic distribution hypothesis that the proportion of years a territory supported a nesting attempt was negatively related to the relative nest initiation dates. However, in contrast to the predictions of the ideal despotic distribution hypothesis, my data show that proportion of years a territory supported a nesting attempt was unrelated to the average number of eggs laid and negatively related to the average number of young fledged annually. Whereas the proportion of years a territory supported a nesting attempt varied across territories, the annual reproductive success of breeding red-shouldered hawks varied markedly from year to year and was positively associated with the number of breeding pairs observed. Overall, my results suggest that red-shouldered hawk reproductive success is influenced heavily by stochastic characteristics that violate the ideal despotic distribution hypothesis‘ assumption of perfect knowledge by individuals.