A novel bioassay for the evaluation of plant water status was developed by Burke (2007). The research reported herein was designed to evaluate this new protocol as a tool for use in cotton breeding programs for the identification of drought tolerant genotypes. Twenty genotypes were selected to represent diverse germplasm pools for a two-year field evaluation. Replicated tests were performed in Lubbock, TX and College Station, TX in 2005, 2006, and 2007. Dryland and irrigated treatments were administered in a split plot arrangement of a randomized complete block design. Fluorescence measurements were taken at mid-bloom and late bloom growth stages of growth. Source leaf tissue was harvested at predawn and subjected to high temperature incubation with fluorescence measurements subsequently taken hourly for five hours. Drought stressed plants had not mobilized their carbohydrate reserves from their source leaves overnight and thus maintained cell viability and therefore higher chlorophyll fluorescence values throughout the incubation with the opposite being true for nonstressed plants. Fiber lint yield and fiber properties were measured at the conclusion of the 2005 season in College Station and the 2006 season in College Station and Lubbock for comparison with the fluorescence data. Five genotypes, ‘Acala 1517-99’, ‘Deltapine 491’ (PVP no. 200100159), ‘Tamcot CAMD-E’, ‘Tamcot 22’ and TAM 89E-51, an unreleased breeding line, were selected based on field evaluation results in a preliminary study in 2005 to be included in a diallel analysis to determine the heritability of fluorescence measurements. Genotype x treatment effects complicated the classification of genotypic responses to drought. Few and inconsistent correlations were found among fluorescence values and lint yield or fiber properties. The diallel analysis did not identify general combining ability or specific combining ability effects for chlorophyll fluorescence measurements. Thus this procedure provides little potential in selecting plants for drought tolerance when plants are grown under field culture. Selection among Tamcot 22 and TAM 89E-51 plants for high and low genotypes according to fluorescence values did not yield progeny different from unselected Tamcot 22 and TAM 89E-51.

Since Texas normally receives most of its precipitation in the warm season, precipitation deficits in summertime may bring serious agricultural and hydrological disasters. While the underlying physical processes of summer precipitation deficit and drought are unclear, they can be understood in terms of convective instability. This research is designed to investigate how convective instability influences monthly mean precipitation in Texas in the summertime and to examine the modulation of convective instability and precipitation by upper-level circulations, soil moisture, vertical motion, and low-tropospheric warm air transport using NCEP/NCAR reanalysis data. Statistical approaches including correlation analysis, multiple linear regression analysis and back trajectory analysis were used to reveal the underlying dynamics of their linkage and causality. The results show that warming at 700 mb and surface dryness result in excessive convective inhibition (CIN), leading to precipitation deficits on a monthly time-scale. Temperature at 700 mb (Tlt) and surface dewpoint have little correlation suggesting different processes contribute to warming at 700 mb and surface dryness, respectively. Correlation analysis among the surface variables emphasizes the role of soil moisture on the dewpoint and thermodynamics at the surface. Back trajectory analysis indicates that a significant contributor to warming at 700 mb is the inversion caused by warm air transport from the Rocky Mountains and the Mexican Plateau where the surface potential temperature is greater than 307.5K rather than by subsidence. It was found that downward motion and warm air transport are enhanced in Texas when upper-level anticyclonic circulation develops in the southern US. Upper-level anticyclonic circulations in the southern US strongly affect Texas summertime precipitation by modulating the principal processes as follows. They increase CIN not only by enhancing warm air transport from the high terrain but also by suppressing occurrence of disturbances. The resulting reduced precipitation and dry soil significantly modulate surface conditions, which elevates CIN and decreases precipitation. The aforementioned chain-reaction of upper-level anticyclone influences can be understood in the context of CIN.

The key to an efficient screening method is the ability to screen large amounts of plant material in the shortest time possible. Unfortunately, due to the complexity of drought tolerance, a quick and effective screen for this trait has yet to be established. The research reported herein was designed to evaluate a screening method for drought tolerance in cotton (Gossypium hirsutum L.) seedlings. Twenty-one converted race stocks (CRS) and two cultivars were evaluated for seedling drought tolerance on an individual plant basis. CRS are day-sensitive primitive lines derived from various wild race stocks that were converted to day neutrality for use in temperate region plant improvement programs (McCarty et al., 1993). Genotypes were evaluated October - November 2004 and February - March 2005 under greenhouse conditions at the Norman E. Borlaug Center for Southern Crop Improvement, College Station, TX. Seedlings were subjected to three sequential cycles of drought at 15 days after planting (DAP). Drought cycles consisted of withholding water until the moisture content of "indicator" cone-tainers, containing Deltapine 491 (DP 491), had an average volumetric water content of 0.07. Plants were then watered to field capacity and percent survival was recorded after 48 hours. Genotypes differed in their percent survival following three consecutive drought cycles. Drought cycles 2 and 3 did not contribute to the separation of genotypes. DP 491 was the most tolerant genotype evaluated. None of the CRS were more or less tolerant than Acala 1517-99. CRS M-9044-0165 was the most stable genotype across the two experiments.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 8, 2010). Includes bibliographical references (p. 32-33).

Physiological responses of 12 sorghum (Sorghum bicolor L.) genotypes previously classified as drought resistant and susceptible upon grain yield basis were evaluated under dry and wet moisture treatments at Tucson, Arizona in 1983. In addition, the relationship of these physiological responses and their heritability estimates were also determined. Apparent photosynthesis, transpiration, diffusive resistance, temperature differentials, and leaf temperature were measured under field conditions at three intervals from planting date: 48, 62, and 77 days, respectively. Stomatal density and epicuticular wax content were determined toward the end of the season when full canopy development was reached. Stress significantly affected all characteristics measured for each genotype by a reduction in apparent photosynthesis rates, transpiration, and temperature differentials, and an increase in diffusive resistance, leaf temperature and stomatal density. The wax content response varied among genotypes irrespective of the dry and wet moisture treatments. Except for the wax content and stomatal density, all the other parameters demonstrated a high significant correlation with photosynthesis at .001 level; nevertheless, greater values were observed in the stress treatment. Analysis of variance failed to detect significant differences among the 12 germplasm sources, except for the stomatal density. Multiple regression analysis showed that leaf diffusive resistance was the first variable incorporated for photosynthesis prediction in both the dry and wet treatments. The offspring and mid-parent regression for each characteristic under both treatments provided heritability estimates (h('2) (+OR-) SE), indicating higher heritability values under the dry treatment.

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Lack of water is one of the most significant issues that already threaten world agriculture as many countries are unable to meet the demand for water to grow the crops. To make matters worse, the water availability is expected to fall by half by 2050, thus severely restricting agriculture production. Genetic engineering of crops to enhance their tolerance to such unfavorable environment represents one of the few approaches that can help us address this problem. Osmotin and osmotin-like proteins are stress proteins, belonging to the plant PR-5 group of proteins, which induced in response to various types of biotic and abiotic stresses in several plant species. Carrot plants were transformed with tobacco osmotin gene that encodes a protein lacking 20 amino-acid sequence at the C terminal end under the control of CaMV 35S promoter using the Agrobacterium-mediated transformation method. The gene integration and expression were confirmed by Southern and Western blot analyses and the transgenic plants were evaluated for their ability to tolerate drought stress. Under drought conditions, transformants exhibited slower rates of wilting compared to the wild-type and gained the ability to recover faster than their untransformed counterparts when the drought stress was alleviated. Under water stress, transformants showed lower levels of H2O2 accumulation, reduced lipid peroxidation and electrolyte leakage, and higher leaf water content. Taken together with some earlier reports, our results provide additional evidence for the protective ability of tobacco osmotin protein against drought stress and suggest a possible means to achieve tolerance against a serious type of abiotic stress.

The boreal forest of Canada extends across 58% of Canada’s land area providing a large range of ecosystem services including flood control, water filtration, and carbon storage. Despite conservation efforts to protect this ecosystem, the boreal region is still under stress from global stressors including climate change. Anthropogenic climate-change is expected to raise temperatures and decrease precipitation over much of the boreal region increasing the duration and magnitude of droughts. This potential change to a more arid climate could have drastic affects on water levels and stream flows across much of the boreal region. Changes in hydrology, as a consequence of anthropogenic climate change, may result in large changes to aquatic ecosystems. To assess the susceptibility of lakes to climate in northwestern Ontario over the past two millennia, sediment cores from a headwater lake were obtained from near-shore cores to reconstruct changes in drought. The cores were located at a depth where changes in pelagic and benthic diatom assemblages (P: B boundary) were apparent in modern-day sediments because the location has been shown to be susceptible to change. The lake chosen for reconstruction was Gall Lake, a small (surface area = 19 ha, max depth = 18 m, mean depth = 8.5 m), mesotrophic lake (total phosphorus (TP) level of 12.3 μg/L, July 2008), with a gentlysloping eastern basin. This headwater lake in the Winnipeg River Drainage Basin (WRDB) is part of a hydrologically-rich region that is expected to experience increased aridity. Multivariate analysis of diatom assemblages over the past two millennia suggested that the instrumental record does not encompassed the natural variability of this system. The largest decreases in diatom-inferred (DI) depth were synonymous with iii the Medieval Climate Anomaly (MCA), a phenomenon not yet observed this far northeast in North America. The MCA has been proposed as a surrogate for climate change over the next century, therefore the prolonged aridity observed in Gall Lake could aid in the calibration of general circulation models currently used to forecast changes in climate, as well as a scenario that can be used to develop adaptation strategies to future environmental change. / Thesis (Master, Biology) -- Queen's University, 2011-05-27 17:41:02.022