Browsing by Subject "drought stress"
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Item Analysis of the Compositional Variation in the Epicuticular Wax Layer of Wheat (Triticum aestivum)(2013-05-08) Beecher, Francis WardEpicuticular waxes form a layer on the outer surface of all land plants and play a fundamental role in their interaction with the environment. Development of a rapid and accurate method for the characterization of these waxes could allow the use of wax composition as a novel phenotype during plant breeding and selection. In this study, the suitability of Direct Analysis in Real Time Mass Spectrometry (DART-MS) for the characterization of epicuticular waxes was investigated. This method provides a ?fingerprint? of the relative abundance of all constituents in the analyte based on mass, is suitable for very high throughput, requires minimal sample preparation, and is able to provide for the characterization of even complex biological mixtures. Herein, the suitability of DART-MS for analysis of epicuticular wax was investigated through analysis of samples of extracted wax collected from the flag leaves of a 279 line association mapping population grown across four environments with two replicates in both irrigated and drought treatments. Additionally, for a subset of samples, wax was collected from glumes in order to test for differences in wax composition between tissue types. In all, a total of 3,454 wax extracts were analyzed with three technical replicates. The above analysis generated a total of 13,164 mass spectra (?fingerprints?), made at an average rate of 30 seconds each. Multivariate analyses including random forest, principal component analysis, and linear discriminant analysis, were used to identify the presence of differences between the spectra of wax from different tissues (leaves/glumes) and treatment types (irrigated/drought). The peaks best serving as predictors of sample class for each comparison were examined, and tentative identifications were made through comparison of the associated mass with literature and publicly available databases. As a separate test of concept, the ability to distinguish between the epicuticular wax compositions of individual varieties was determined through analysis of a group of closely related lines developed at CIMMYT which differed in agronomic performance.Item Cotton Production under Traditional and Regulated Deficit Irrigation Schemes in Southwest Texas(2012-10-19) Wen, YujinThe urban water demand in Southwest Texas has grown rapidly in recent years due to the population increases in urban areas, which caused conflict between municipal and agricultural water use. Deficit irrigation is one important measure for solving this problem. A field experiment with seven different irrigation treatments and four cotton varieties was conducted at the Texas AgriLife Research and Extension Center at Uvalde in the summers of 2008 and 2009 to examine the water saving potential and related phenological/physiological responses in Southwest Texas. The results showed that: 1) The threshold deficit ratio for a traditional deficit irrigation scheme falls between 0.7 and 0.8 for cotton production in Southwest Texas under a low energy precision application (LEPA) sprinkler irrigation system. The 70 percent evapotranspiration (ET)-initialled regulated deficit irrigation scheme (70R) performed well in maintaining lint yield in most cotton varieties tested. The significant changes detected in lint quality failed to introduce premiums or discounts in cotton price. 2) The phenological parameters (plant height, node number and flower/fruit number) showed clear trends that illustrate the relationship between increased stress level and decreased plant growth and development. The observed inconsistency of the physiological responses in the two growing seasons may imply that physiological parameters are not good direct predictors of lint yield if measurements are conducted only on a point basis. The partitioning coefficients of boll dry weight in both years failed to show a significant difference between deficit irrigation treatments and the control, indicating that reallocation of carbohydrates may not be the major factor of maintaining lint yield for the deficit irrigation treatments. 3) Economic analysis showed that due to the low water price, it is not currently profitable to adopt deficit irrigation. In case that water price is increased, it may become more profitable to adopt deficit irrigation. This work provides reference information to water authorities and policy makers to set quotas for municipal and agricultural water use and to value water properly through setting different water prices.Item Stressed Plants and Herbivores: Exploring the Mechanisms of Drought's Impact on Cotton Physiology and Plant-Herbivore Interactions(2014-07-17) Sconiers, Warren BoyceDrought is expected to become more prevalent in our future and influence plant-insect interactions in natural and agricultural systems. There is an established interest in predicting the effects of drought on plant-insect interactions, with over 500 published studies. Despite this intensive effort, researchers cannot accurately predict the effects of water deficit stress on insect performance. To address this, I tested hypotheses aimed to predict insect performance and abundance and developed a hypothesis that may better predict herbivore performance on stressed plants. I tested the Pulsed Stress Hypothesis which predicts that insect herbivores feeding on drought stressed plants will increase in abundance on plants that are pulsed stressed rather than continuously stressed. I conducted two, 10-week field studies to test the effects of drought on arthropods using 0.6 hectares of cotton. Stress was implemented by withholding water from continuously stressed plants and using pulsed watering for pulsed stressed plants. Piercing-sucking herbivores (i.e., thrips, stinkbugs, fleahoppers) were more abundant on pulsed stressed plants than continuously stressed plants. In contrast, chewing herbivores (e.g., grasshoppers, caterpillars) were similar in abundance on stressed plants. This suggests that the variation we see in herbivore response to stressed plants is dependent upon the severity and frequency of drought in addition to herbivore feeding guild. For my third field study, I tested the interactions of the timing of cotton aphid infestation, cotton development, and only pulsed stress. I had herbivore exclusion cages with only aphids inside and either on seedling or fruiting cotton. I largely found that cotton may compensate for early season damage from aphids and pulsed stress, but the combination of the two greatly impact cotton development. I conducted a meta-analysis on herbivore performance, macronutrients, and allelochemicals to determine the relationship between stress-induced changes in plants and herbivore performance. I used Metawin 2.0 to analyze the data from 42 published studies and found that macronutrients were the most important factor in determining herbivore performance on stressed plants. With this evidence, I devised the Nutrient Availability Hypothesis which predicted that the concentration of stress-induced changes in macronutrients in stressed plants will determine herbivore performance.