Browsing by Subject "loblolly pine"
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Item A physiological and morphological analysis of the effects of nitrogen supply on the relative growth rates of nine loblolly pine (Pinus taeda L.) clones(Texas A&M University, 2006-08-16) Stover, Corey MichaelThe influence of nitrogen supply on relationships of relative growth rate (RGR) to leaf physiology, structural and non-structural carbon partitioning, and nitrogen- and water-use efficiencies were examined in loblolly pine (Pinus taeda L.) clonal lines differing in growth potential. Nine 18-month-old loblolly pine clones were grown in a climate-controlled greenhouse for 20 weeks under two contrasting nitrogen (N) regimes (50 and 250 ppm) and a growth analysis was carried out. Higher nitrogen increased plant RGR and largely resulted in proportional shifts in biomass from roots and stems to needles. The RGR of plants receiving higher nitrogen was increased primarily through increased leaf area ratio (LAR), which was increased through higher leaf mass fraction (LMF) and not through changes in needle morphology. Although concentrations of needle glucose in plants receiving 250 ppm N were 22 percent higher than plants receiving lower N, total non-structural carbohydrate concentrations in needles of plants receiving 50 ppm N were nearly double that of clones receiving 250 pm N, primarily due to starch accumulation of the nitrogen-deficient plants. Plants receiving 250 ppm N also had 39 and 18 percent lower starch in the coarse and fine roots, respectively. Plants receiving higher nitrogen were also more water-use efficient, but had lower photosynthetic nitrogen-use efficiency. LAR, net assimilation rate (NAR), specific leaf area (SLA), and LMF were all positively correlated with RGR, but the main influence on RGR differences among clones was LAR. In addition, leaf-level rates of photosynthesis and respiration were positively correlated with RGR; however, faster-growing clones did not exhibit greater carbon economy at the leaf level. Both instantaneous water-use efficiency (A/E) and δ13C were positively correlated with RGR and photosynthetic nitrogen-use efficiency was negatively correlated with RGR. The identification of physiological and morphological traits underpinning differences in RGR among clones and how these traits are affected by nitrogen supply provides new information on trait correlations within species and parallels broader patterns observed among species.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 Identification of drought responsive genes in aleppo pine (Pinus halepensis) and loblolly pine (Pinus taeda.L)(Texas A&M University, 2005-02-17) Sathyan, PratheeshDrought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.Item Population Structure, Association Mapping of Economic Traits and Landscape Genomics of East Texas Loblolly Pine ( Pinus taeda L.)(2013-05-07) Chhatre, Vikram E.Loblolly pine (Pinus taeda L.) is an ecologically and economically important southern pine, distributed across the southeastern United States. Its genetic improvement for breeding and deployment is a major goal of the Western Gulf Forest Tree Improvement Program (WGFTIP) hosted by the Texas A&M Forest Service. Rapid advances in genomics and molecular marker technology have created potential for application of Marker Assisted Selection (MAS) and Genomic Selection (GS) for accelerated breeding in forest trees. First-generation selection (FGS) and second- generation selection (SGS) breeding populations of loblolly pine from east Texas were studied to estimate the genetic diversity, population structure, linkage disequilibrium (LD), signatures of selection and association of breeding traits with genetic markers using a genome-wide panel of 4264 single nucleotide polymorphisms (SNPs). Under- standing the genetic basis of local adaptation is crucial to disentangle the dynamics of gene flow, drift and selection and to address climate change. Bayesian mixed linear models and logistic regression were used to associate SNP variation with geography, climate, aridity and growth season length and markers with strong correlations were investigated for biological functions. Relatively high levels of observed (Ho = 0.178?0.198) and expected (He = 0.180-0.198) heterozygosities were found in all populations. The amount of inbreeding was very low, and many populations exhibited a slight excess of heterozygotes. The population substructure was weak, but FST indicated more pronounced differentiation in the SGS populations. As expected for outcrossing natural populations, the genome-wide LD was low, but marker density was insufficient to deduce the decay rate. Numerous associations were found between various phenotypes and SNPs, but few remained significant after false positive correction. Signatures of diversifying and balancing selection were found in markers representing important biological functions. Strong correlations supported by Bayes factors were found between various environmental variables and several SNPs. Logistic regression found hundreds of significant marker-environment associations, but none remained significant after false-positive correction, which was likely too stringent and will require further investigation. Annotations of significant markers implicated them in crucial biological functions. These results present the first step in the application of MAS to the WGFTIP for loblolly pine genetic improvement and will contribute to the knowledgebase necessary for genomic selection technology. Results from environmental association study provide important information for designing breeding strategies to address climate change and for genetic conservation purposes.Item The Drought Response of Physiological and Structural Traits in Loblolly Pine (P. taeda L.) Clones with a Focus on Mesophyll Conductance to CO_(2)(2014-07-10) Wilson, Elizabeth SusanClimate change will likely affect the productivity of forests through changes in precipitation and moisture availability. An important measure of a plant?s ability to assimilate carbon in photosynthesis with limited water loss, water use efficiency (WUE), is assessed by carbon stable isotopes using the Farquhar model. However, recent work has shown that mesophyll conductance to CO_(2) (g_(m)) is affected by environmental conditions, and the simplified model does not take into account this variability. Variation in this parameter could decrease the effectiveness of the stable isotope tool. A coupled gas exchange and carbon isotope system was developed and tested on well-watered loblolly pine seedlings. A cavity ring-down spectroscopy (CRDS) laser connected to a LI-6400XT gas exchange system allowed simultaneous measurements of photosynthesis and instantaneous carbon isotope discrimination. The standard deviation of two minute averaged delta over ten minute intervals ranged from 0.31? to 0.51?. Mesophyll conductance measured by this system on well-watered loblolly pine seedlings ranged from -0.74 to 0.99 mol m^(-2) s^(-1) and averaged 0.07 ? 0.04 mol m^(-2) s^(-1). A greenhouse study was conducted of the drought effects on g_(m) and other physical and biochemical traits in three clones of loblolly pine (P. taeda L.). Stomatal and hydraulic sensitivity to drought was assessed in the clones. Mesophyll conductance was estimated using several methods: gas exchange curve fitting, the variable J method of chlorophyll fluorescence, carbon isotope discrimination from leaf soluble carbohydrates, and instantaneous carbon isotope discrimination using a cavity ring-down spectroscopy laser. The three clones exhibited plasticity in stomatal conductivity and hydraulic conductivity in response to drought. The fastest growing clone also had the highest hydraulic conductivity and lowest WUE in well-watered conditions. There were no significant clonal or drought effects on g_(m), suggesting that the simplified Farquhar model is adequate for the use of stable isotopes as a proxy for WUE.