Browsing by Subject "disease"
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Item Gene Expression and Association Analyses of Stress Responses in Loblolly Pine (Pinus taeda L.)(2012-02-14) Seeve, Candace MarieThe molecular mechanisms underlying disease-resistance and drought-resistance in forest trees are not well understood. Linking variation in gene expression with genetic polymorphisms and with variations in disease- and drought-resistance phenotypes can provide information about these complex traits. We used real-time quantitative polymerase chain reaction (PCR) to detect variations in the expression of 88 disease- and drought-responsive genes within an association population of 354 loblolly pine trees (Pinus taeda L.). Using association genetics approaches, we then linked 3,938 single nucleotide polymorphisms (SNPs) in candidate genes with gene expression phenotypes to identify novel disease- and drought-responsive genes. To further examine differences in gene expression induced by drought, Fusarium circinatum (responsible for pitch canker disease), and drought F. circinatum, the expression of 114 genes identified through comparative and association genetics approaches was analyzed on a subset of 24 loblolly pine trees possessing a range of pitch canker- and drought-resistance phenotypes. Significant differences in the uninduced expression of all 88 genes measured on the association population were observed among loblolly pine trees. Principal component analysis showed that some variation within the association population could be accounted for by population substructure of geographic origin. Hierarchical clustering of genes based on uninduced expression did not consistently group together functionally similar genes probably because expression was collected on unstressed stem tissue. This was supported in the smaller expression study as correlations between expression values of genes in the same functional networks were usually stronger when induced by a treatment compared with correlations between the uninduced expression of genes in the control group. Gene expression frequently changed by up to 4-fold in response to one or more treatments, but PtMYB12 was the only gene that exhibited a statistically significant change in response to treatments. ANOVA analyses of gene expression controlling for pitch canker resistance and for water use efficiency phenotypes identified differentially expressed genes suggesting that they may be contributing to these phenotypes. Finally, association genetics approaches detected 101 significant associations between SNPs in 94 candidate genes potentially involved in stress responses and 27 gene expression phenotypes.Item Selenium nutrition of Morone hybrids including dietary requirements, bioavailability, toxicity and effects on immune responses and disease resistance(Texas A&M University, 2006-08-16) Jaramillo, Francisco , JrAquacultural production of hybrid striped bass (HSB) Morone chrysops ?? M. saxatilis is highly vulnerable to losses from bacterial pathogens such as Streptococcus iniae. Therefore, research was conducted to evaluate various dietary factors that may enhance immunocompetence and disease resistance of HSB. In the first experiment, purified and practical diets were supplemented with β-glucan and selenium in a factorial arrangement and fed to juvenile HSB for 6 wk followed by a S. iniae challenge. Weight gain (WG) and feed efficiency (FE) were higher for fish fed either practical diets or purified diets supplemented with selenium, but not those supplemented with β-glucan. Survival after disease challenge for fish fed the selenium-supplemented practical and purified diets was 75% and 35%, respectively. Because selenium supplementation also improved WG and FE, and because selenium and vitamin E have complementary biochemical functions, a second experiment evaluated potential interactions by feeding purified diets with or without vitamin E or sodium selenite (Na2SeO3), singularly or in combination, for 12 wk. Dietary selenium significantly affected whole-body selenium concentration but there was no effect of dietary selenium, vitamin E or their interaction on WG, FE, survival or blood neutrophil oxidative radical production. Three additional 12-wk experiments were conducted to establish selenium essentiality, toxicity, tissue deposition, dietary requirements, bioavailability and nonspecific immune responses using purified diets with a basal selenium level of 0.11 mg/kg. In one experiment, diets had selenium concentrations of 1.19, 2.00, 5.17 and 21.23 mg/kg from Na2SeO3. Another experiment had selenium concentrations of 0.90, 1.26 and 2.55 mg/kg from seleno-DL-methionine. The third trial utilized selenium from Na2SeO3, seleno-DL-methionine and selenium yeast at approximately 0.15, 0.30 and 0.60 mg/kg diet. No overt selenium deficiency signs were observed in any of the three latter experiments, but based on selenium retention values, a minimum dietary requirement of approximately 0.1 mg/kg was estimated. Selenium toxicity was observed in fish fed the diet containing more than 20 mg/kg. Bioavailability of selenium sources was ranked as seleno-DL-methionine > selenium yeast > Na2SeO3.Item Spatio-temporal relationships between feral hogs and cattle with implicatons for disease transmission(Texas A&M University, 2007-09-17) Deck, Aubrey LynnIt is widely recognized that livestock industries are vulnerable to intentional or accidental introductions of Foreign Animal Diseases (FADs). Combating disease is difficult because of unknown wildlife-livestock interactions. Feral hogs (Sus scrofa) could harbor and shed disease in areas used by domestic livestock such as cattle (Bos taurus). Extent of risk logically depends on spatio-temporal interactions between species. I used Global Positioning System (GPS) collars on cattle and hogs in combination with a Geographic Information Systems (GIS) for detailed analysis on movement patterns of these 2 species on a ranch in southwestern Texas, USA. Motion-triggered video recorders were also utilized to determine interspecific activity patterns. I tested hypotheses that spatio-temporal distributions of domestic cattle and feral hogs on rangeland overlap and that interspecific contact occurs. If these posits are true, it is possible that introduced pathogens like foot-and-mouth disease (FMD) could be transmitted from feral hogs to cattle. Using a rate of 1 GPS fix/15 min (96 fixes/day), I found that spatial distribution of individual hogs and cattle overlapped on both the 95% and 50% kernel area use among 4 seasons. Both cows and feral hogs used Clay Flat, Clay Loam, and Rolling Hardland more so than other range sites. During Summer 2004, riparian zones were the most used feature, identified at 14% (2,760/19,365) of cattle and 70% (445/632) of hog fixes. Other than brush strips, cattle and feral hogs primarily interacted at riparian zones, fencelines, and roads. There were no direct interspecific contacts evident from GPS data, but 3 cases were recorded from video data. Indirect interspecific contacts that may be sufficient for disease transmission occurred much more frequently (GPS = 3.35 indirect contacts/day, video = cows follow hogs: 0.69 indirect contacts/day and hogs follow cows: 0.54 indirect contacts/day). Research results suggested that both species often travel along the same roads and fencelines to water and food sources, especially during extreme heat and low-precipitation conditions. This research provides basic information needed to improve models for management of FAD outbreaks in the U.S., based on specific knowledge of landscape usage and movement patterns of feral hogs and cattle.