We wanted to develop rapid and cost-effective drought tolerance screening methods for mass amounts of germplasm. In 2009 and 2010, we evaluated sixty-two maize inbred lines and their hybrid testcross progeny using seedling stress response and epicuticular wax accumulation as predictors of drought tolerance. The seedling screening method measured germination, survival and recovery percentages after a series of drought cycles in a greenhouse environment. Eight inbred lines had significantly (P < 0.05) lower germination than the mean estimate, but hybrid testcrosses were not significantly different. The second-to-last day of survival cycle and the second day of recovery cycle best explained genotypic differences for inbred lines and hybrid testcrosses respectively. One inbred line performed well as both an inbred line and hybrid testcross, but poor correlation over the sample set (R2 = 0.0097) was observed. Flag leaves taken at flowering from plants under full and limited irrigation regimes were sampled for epicuticular wax. Extracted wax weight for genotypes was compared as a percentage of leaf weight (percent wxlfwt) and leaf area (percent wxwta). Eleven genotypes had above average percent wxlfwt as both inbred lines and hybrid testcrosses. Thirteen genotypes had above average percent wxwta as either inbred lines or hybrid testcrosses. Irrigation treatment was not significant (P > 0.05). Heritability of percent wxlfwt was 0.17 (inbred lines) and 0.58 (hybrid testcrosses). Heritability of percent wxwta was 0.41 (inbred lines) and 0.59 (hybrid testcrosses). Correlations (R2) for percent wxlfwt and percent wxwta were 0.19 and 0.03, respectively. Heritability of grams of grain per ear and total grain yield was highest in hybrid testcrosses, with no correlation between inbreds and hybrids. The developed seedling screening method easily allowed visible drought tolerance observations in inbred lines and hybrid testcrosses but does not seem heritable in our germplasm. Epicuticular wax weight is not an ideal primary trait to evaluate for drought tolerance, but may be a good candidate to observe as a secondary trait in relation to grain yield production in hybrids. Results from this research best supports breeder selection of hybrid germplasm using seedling drought tolerance in conjunction with epicuticular wax.

Water potential, leaf conductance, growth, nitrogen content, and seedling survival of Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis) following defoliation of the herbaceous understory were assessed during two growing seasons. Precipitation was 107% and 63% of the long-term mean (283 mm) in 1989 and 1990, respectively, which presented an opportunity to study impacts during a drought and a non-drought year. Response of Artemisia was measured on a site seeded to Agropyron desertorum in the late 1960s, and a native site with Stipa thurberiana, Festuca idahoensis and Poa sandbergii in the understory. The two sites were analyzed as separate experiments. The dry year had a significant effect on plant water relations and growth of Artemisia on both sites. Pre-dawn water potentials averaged 1.23 MPa more negative on the seeded site and 1.22 MPa more negative on the native site in 1990 compared to the previous year. Mid-day water potential averaged 1.22 MPa more negative on the seeded site and 1.13 MPa more negative on the native site in 1990 compared to 1989. Morning leaf conductance in 1990 was 61% lower on the seeded site and 51% lower on the native site than in 1989. Mean afternoon leaf conductance in the drought year was 62% less on the seeded site and 63% less on the native site. Nitrogen content in current year's growth was reduced 29% on the seeded site and 18% on the native site from 1989 to 1990. Vegetative and reproductive shoot (stem plus leaves) weights were reduced by over 80% in 1990 compared to 1989. Other production variables showed similar reductions in the drought year. Nitrogen content was 11% greater in current year's growth from shrubs on control as opposed to defoliated plots on the native site in 1989. Shrubs on control plots had 8% heavier reproductive stems per unit of canopy, and 7% longer vegetative stems than shrubs on defoliated plots in 1989 on the seeded site. Shrubs on control plots had 18% fewer annual leaves per unit of vegetative shoot, but 12% more primary ephemeral leaves per vegetative shoot than shrubs on defoliated plots in 1990 on the seeded site. In 1990, shrubs on control plots on the seeded site had 11% more ephemeral leaves per vegetative shoot while shrubs on the control plots on the native site had 8% fewer ephemeral leaves per vegetative shoot. Large shrubs generally had more and heavier leaves, and longer and heavier stems than medium shrubs. Exceptions included large shrub lateral stems were 30% shorter than those of medium shrubs, and large shrubs had 37% fewer annual leaves per vegetative shoot than medium shrubs in 1989 on the seeded site. Drought had substantial negative impact on water relations and growth of Wyoming big sagebrush, while defoliation of understory vegetation had little effect. / Graduation date: 1993

Los organismos vivos intercambian gases con la atmósfera. Estos gases llamados Compuestos Orgánicos Volátiles Biogénicos (COVBs) son muy importantes para la química de la troposfera y el ciclo global del carbono. Las plantas producen una gran variedad de hidrocarburos de los cuales el grupo más representativo y abundante son los isoprenoides. El isopreno, los monoterpenos y sesquiterpenos representan una pequeña proporción de esta gran diversidad de productos vegetales dentro del grupo de los isoprenoides. Además de isoprenoides, las plantas emiten otros compuestos orgánicos volátiles, por ejemplo, el metanol, metil jasmonato, etileno y muchos compuestos orgánicos oxigenados de carbono. Existen muchos procesos de retroalimentación entre la biosfera y la atmósfera. Por un lado las plantas juegan un papel importante en la química de la zona baja de la atmósfera. La foto-oxidación atmosférica de las emisiones de COVs produce dos productos importantes en la baja atmósfera, el ozono y los aerosoles orgánicos. Ambos tienen importantes consecuencias para la calidad del aire y el clima. Por otro lado, el clima, es decir, los cambios en la variabilidad o estado medio de la atmósfera a través del tiempo, está afectando a su vez las actividades de la biosfera. Por lo tanto, es de gran importancia estimar los flujos biogénicos COVs a la atmósfera y sus variaciones en el contexto del cambio climático, especialmente ante las predicciones, por parte de modelos climáticos y ecofisiológicos, de un aumento de la sequía durante las próximas décadas.La mayor parte de la investigación acerca de los flujos de COVs (sin incluir el metano) se ha centrado en los flujos de las partes aéreas de las plantas a diferentes niveles, desde la cubierta foliar hasta flores y tallos. Sin embargo, hasta los últimos años, la información sobre los flujos COV procedentes las partes subterráneas de las plantas, por ejemplo las raíces, era muy escasa. En esta tesis nos hemos interesado por el intercambio de gases traza diferentes al metano biogénico: CO2 y COVs. El principal método utilizado para medir los flujos de gases del suelo en este trabajo es una variante del método de cámara cerrada. El modo de funcionamiento en este caso es dinámico. Un flujo continuo de aire se bombea a través de la cámara, y el gas emitido desde el suelo se mide directamente en la corriente de aire o es adsorbido en un material adecuado para la captura y posterior análisis de la emisión del suelo.Los objetivos generales de esta tesis doctoral fueron: 1) caracterizar el contenido y el intercambio de COVs en suelos Mediterráneos, en particular monoterpenos por su importante papel en la ecología, la fisiología vegetal y la química atmosférica, y también de otros compuestos orgánicos volátiles, y 2) evaluar los posibles cambios en el intercambio de COVs y CO2 del suelo ante la perspectiva de un cambio ambiental global hacia unas condiciones más áridas y secas en la región Mediterránea. Las principales conclusiones son las siguientes: Las tasas de intercambio de COVs totales y de monoterpenos entre la superficie del suelo y la atmósfera son muy bajas. La contribución de las emisiones del suelo por unidad de superficie al total de emisiones monoterpenos de origen biogénico a la atmósfera, es relativamente baja. Las tasas absorción de COVs y monoterpenos del suelo son también bajas, sin embargo, son comparables con algunas tasas de absorción foliar de monoterpenos. Se requieren más estudios para corroborar estos resultados y la posible importancia del suelo como un sumidero de COVs en el los modelos químico-climáticos. Los resultados sugieren que la reducción en la disponibilidad de agua y el incremento de las temperaturas previstos para las próximas décadas podría afectar de manera importante las tasas de intercambio de COVs del suelo con la atmósfera, sin embargo se necesitan estudios a largo término para determinar con exactitud esta respuesta frente al cambio climático.En este trabajo hemos encontrado que la sequía y las altas temperaturas tienden a incrementar las tasas de emisión de COVs del suelo. Los resultados sugieren que las causas podrían ser más bien debidas al efecto físico de la sequía y las altas temperaturas en las características del suelo y la volatilidad de los COVs, más que un efecto en las actividad de las raíces y los microorganismos del suelo. Sin embargo, los resultados también muestran que la sequía reduce el flujo de CO2 del suelo, mientras que las altas temperaturas los aumentan. Así pues, la sequía y el calentamiento están afectando diversos procesos biológicos que se desarrollan en las partes aéreas y subterráneas del ecosistema, los cuales podrían afectar el intercambio de COVs del suelo. El efecto final del cambio climático no es, por tanto, claro, ya que es probable que las factores que afectan el intercambio de COVs del suelo estén produciendo diferentes efectos de manera desacoplada. / Living organisms exchange trace gases with the atmosphere. These gases named biogenic volatile organic compounds (BVOCs) are very important for the global tropospheric chemistry and the global carbon cycle (Fehsenfeld et al, 1992; Singh and Zimmerman, 1992). Plants produce a variety of hydrocarbons of which the most representative and abundant group is isoprenoids. Isoprene, monoterpenes and sesquiterpenes represent a small proportion of the diverse group of isoprenoid plant products. In addition to isoprenoids, several other volatile organic compounds are emitted by plants, for example methanol, methyl jasmonate, ethylene and many organic oxygenated carbon compounds. Biosphere and atmosphere show multiple regulation feedbacks in their processes. On one hand plants play an important role in the low atmosphere chemistry. The atmospheric photo-oxidation of the emitted VOCs leads to two important products in the lower atmosphere, ozone and organic aerosol, which have important consequences for air quality and climate. On the other hand, the earth's global climate, i. e. the changes in the variability or average state of the atmosphere over time, is affecting biosphere activities in turn. Hence, it is important to estimate biogenic VOC fluxes to the atmosphere and their variations under the climate warming and the increased drought projected for the next decades by climatic and ecophysiological models. Most of the research about non methane VOC fluxes has focused on fluxes from the above-ground part of the plants at different levels, from canopy to foliar/flower/stem level. However, until the last years, information about VOC fluxes from the below-ground parts of the plants was very scarce.We were interested in the soil atmosphere trace gas exchange of CO2 and non methane biogenic VOCs. The principal method used to measure soil fluxes in this work is a variant of the enclosure method. The mode of operation was dynamic. A steady stream of air is pumped though the chamber, and the gas emitted from the soil is measured directly in the air stream or adsorbed in a suitable trapping material for subsequent release and analysis.The general objectives of this PhD thesis were 1) to characterize Mediterranean soil VOC contents and exchange, particularly monoterpenes because of their important role on ecology, plant physiology and atmospheric chemistry, but also other VOCs, and 2) to assess the possible changes in soil VOC and CO2 exchange rates under the global environmental change towards more arid and warm conditions in the Mediterranean region.The major conclusions are the following ones: Total VOC and monoterpene exchange rates from soil surfaces are low. There is relatively low soil emissions contribution to total biogenic monoterpene emissions to the atmosphere on a land area basis. Soil VOC and monoterpene uptake rates were also low, though comparable with some foliar uptake rates. Further studies are needed to corroborate these results and the possible importance of the soil VOCs sink in chemistry-climate models.Results suggest that the water availability reduction and the increase of temperature expected in the next decades might greatly affect soil VOC exchange rates to the atmosphere, but longer-term studies are needed to discern the response of soil VOC exchange rates to climate change. We found that drought and high temperatures tended to increase soil VOC emission rates. Results suggest the causes may be more the physical effects on soil features and VOCs volatility than the effects on soil roots and microorganisms activities. However, results also showed that drought reduced soil CO2 fluxes, while high temperature increased them. Thus, drought and warming are affecting several biological below-ground and above-ground processes which could affect soil VOCs exchange. The final effect of climate change is not clear but uncoupling effects to different processes are thus likely to occur.

Rice produces a lot of biomass which is an important trait in increasing grain yield and it is a potential feedstock for bioenergy production. High biomass rice is important to meet the growing demands of grains and biomass for food, fodder and bio-fuel industries. Limited studies have been conducted to determine its response to unfavorable conditions. The main objectives of this study were to determine the response of selected high biomass rice to drought, rainfed and flooded conditions and identify best genotypes that can be grown in unfavorable areas. Two experiments were conducted in summer 2009 to evaluate biomass yield and agronomic traits of selected high biomass genotypes. A greenhouse study had genotypes grown under drought condition - different field capacity (FC) i.e. 100 percent, 75 percent and 50 percent FC, while the field study had rainfed and flooded environments. Most of the genotypes performed well under fully saturated soil conditions but some were less affected by drought. Limited water delayed first tiller emergence and reduced tiller count, rate of tiller production, plant height, rate of increase in height, shoot and root weight, root:shoot (R:S) ratio, percent dry matter (percent DM) and total biomass. The plant height, tiller plant-1, and total biomass at maturity were lower under rainfed conditions and their flowering was delayed compared to flooded conditions. Majority of these traits were correlated with high biomass yield. Genotype 11 which is tall and late maturing produced the highest number of tillers plant-1 and tillers/ 750 cm2 and had the highest biomass yield under both rainfed and flooded conditions. It performed equally well under drought conditions particularly in root and R:S ratio, but genotype 12 was the best in most parameters measured in the greenhouse. Although it was the shortest genotype, it was highest in biomass yield, earliest to tiller, had the highest shoot weight and tiller count, and had the fastest tiller production. The high biomass genotypes like conventional rice were affected by drought and performed better under flooded conditions. However, these two genotypes can produce optimum results under limited availability of water and hence be used for biomass production under stressed environments.

Abiotic stresses impact cotton (Gossypium hirsutum L.) affecting physiological, molecular, morphological, and agronomic parameters. One of the main yield components in cotton production is the number of bolls per unit area. However, boll abortion is increased when cotton experiences various stresses during its reproductive development that can consequently reduce lint yield. Prior to abscission, a burst in ethylene is observed which may be assumed to be the signal necessary to initiate abscission of that particular structure. It is desirable to prevent fruit loss that may be induced by the peak in ethylene prior to abscission. One potential option to cope with the loss of cotton reproductive structures is the use of ethylene inhibitors. The overall objective of this research was to establish if 1-MCP would synergize, ameliorate, or overcome the effects of abiotic stresses on physiological, molecular, morphological, and agronomic parameters of cotton plants under abiotic stress conditions in field and greenhouse studies. Field and greenhouse experiments were conducted from 2007 to 2009 as a randomized complete block design with four replications in the field, and as a 2x2 factorial design in a split-block arrangement with five replications in the greenhouse. Field treatments consisted of three rates of 1-MCP (0, 25 and 50 g a.i. ha-1) in combination with a surfactant applied at mid-bloom. One day later, ethephon (synthetic ethylene) was applied as a source of abiotic stress. Greenhouse treatments were two 1-MCP rates (0 and 2.4 g a.i. L-1) during a14-h overnight incubation that were then subjected to two water regimes (control and stressed) as the source of stress. Greenhouse assessments with gas exchange analysis revealed that water deficit stress started to impact plants at a moderate water stress, 5 days after 1-MCP treatment (DAT) and a water potential (ψw) of -1.4 MPa. The 1-MCP increased water use efficiency in well-watered plants at 1 DAT. Many of the yield components, plant mapping, and biomass parameters investigated were detrimentally affected by drought. However, drought increased specific leaf weight, chlorophyll content, and harvest index. The 1- MCP improved reproductive node numbers mainly during drought, but did not lead to a better harvest index, since 1-MCP caused high abscission. Ethylene synthesis and molecular investigations in greenhouse conditions showed that at 1, 5, 7, 9, 11, and 13 DAT, ethylene production of stressed plants never exceeded those of control plants. As the ψw became more negative ethylene production rate was reduced among stressed plants independent of 1-MCP treatments. However, at 1 DAT 1-MCP caused a transient climacteric stage (ethylene synthesis increase) in leaves. The two primary genes associated with ethylene synthesis, ACS6 (1-aminocyclopropane-1-carboxylic acid synthase) and ACO2 (1-aminocyclopropane-1-carboxylic acid oxidase) expression generally showed an identical trend that supported the ethylene synthesis data. The 1-MCP did not ameliorate any of the detrimental effects of water stress on gas exchange at the point where it started to impact cotton plants. 1-MCP had little or no positive effect on plant mapping, dry matter partitioning and chlorophyll content. Field investigations revealed that at harvest, fruit set in the upper portion of the canopy was influenced by 1- MCP. This portion of the canopy had a greater number of full size, yet immature bolls, which potentially could have had a positive influence on the lint yield. However, ethephon caused the highest lint yield since ethephon treated plants had more open bolls and total bolls in the lower canopy at harvest.

There is an increasing need to improve crop water-use efficiency (WUE) (ratio of whole-plant biomass to cumulative transpiration) due to decreased water availability and increased food and energy demands throughout the world. The objective of the study was to estimate the genetic variation and genetic basis for transpiration efficiency A:E (CO2 assimilation rate (A) divided by transpiration rate (E)) trait and its relationship to WUE related to pre-flower drought tolerance in recombinant inbred lines (RILs) of sorghum and associated QTLs. A greenhouse study was conducted at Bushland, TX, 2008, using 71 RILs derived from cross of Tx430 x Tx7078. A randomized complete block experimental design was used, with both genotype and water regime (40 and 80 percent water regime) as experimental factors, and four replications. Genotype had a significant effect on A, E and A:E under both the environments. Among the RILs, entry means for A:E ranged from 1.58 to 3.07 mmol CO2 mol^-1 H2O and 1.18 to 4.36 mmol CO2 mol^-1 H2O under 80 percent and 40 percent water regime, respectively. Heritability estimates based on individual environments for A:E , A and E were 0.77, 0.45 and 0.37 under 80 percent water regime and 0.90, 0.33 and 0.71 under 40 percent water regime, respectively. A genetic map was constructed by digital genotyping method using Illumina GAII sequencer with 261 informative indel/ single-nucleotide polymorphism (SNP's) markers distributed over 10 linkage groups. Three significant QTLs associated with transpiration efficiency were identified; two on SBI-09 and one on SBI-10 with one logarithmic of odds (LOD) interval length ranging from 5.3 to 5.7 cM and accounting for 17 percent - 21 percent of the phenotypic variation. In field and greenhouse evaluation of agronomic of traits at College Station and Halfway, TX, 91 QTL that control variation in six major agronomic traits such as plant height, flowering, biomass, leaf area, leaf greenness and stomatal density were identified. Co-localization of transpiration efficiency QTLs with agronomic traits such as leaf area, biomass, leaf width and stomatal density indicated that these agronomically important QTLs can be used for further improving the sorghum performance through marker assisted selection (MAS) under pre-flowering drought stress conditions.

A new zone was added to the existing Livestock Early Warning System (LEWS), which is a subproject of the USAID Global Livestock Collaborative Research Support Program. LEWS uses the PHYGROW model and satellite imagery of weather and vegetation to estimate the availability of forage to livestock and wildlife. Drought advisories are then distributed to governments, development organizations, and pastoralists via the Internet, satellite radios, and written reports. The Laikipia zone was established in 2001 to provide drought early warning for the arid pastoral rangelands of the Ewaso Ngiro ecosystem in the Laikipia and southern Samburu Districts, Kenya. Field verification of PHYGROW estimates of standing crop was conducted in 2002. In addition, research was conducted to determine the ability of the warning system to provide significant advance notice of emerging drought conditions. Results of this study indicate that LEWS is capable of providing accurate estimates of forage availability on East African rangelands. There is also evidence that the use of LEWS advisories could accelerate drought response by pastoralists as much as three to seven weeks.

Telomerase is the key enzyme synthesizing telomeric DNA in most eukaryotic organisms. In mammals, telomerase expression is abundant in the germline cells but is undetectable in most other differentiated organs. Intensive studies of telomerase have focused on human cancerous cells, where over 90% of all cancerous tissues examined have telomerase activity. In wild-type Arabidopsis, telomerase expression is abundant in reproductive organs and dedifferentiated tissues such as flowers, siliques and calli but barely detectable in vegetative tissues (both rosette and cauline leaves). In this study, a biochemical screen strategy was developed for isolation of telomerase activating mutants in Arabidopsis thaliana. Through screening of Arabidopsis activation-tagged lines by a PCR-based TRAP assay, two tac (for telomerase activator) mutants were isolated. RT-PCR analysis of AtTERT expression revealed that different mechanisms are involved in alternating telomerase activity in tac1 and tac2. We cloned and characterized the TAC1 gene. TAC1 encodes a single zinc finger protein and acts synergistically with auxin to induce telomerase expression without altering cell cycles. Telomere length was unperturbed in the mutant, but other phenotypes, such as altered root development and the ability of cells to grow in culture without exogenous auxin, indicated that TAC1 not only is part of the previously reported link between auxin and telomerase expression, but also potentiates other classic responses to this phytohormone. DNA microarrays were used to analyze the expression profile of the tac1 mutant and revealed that several drought-induced genes were up-regulated 3 to 10 fold in the tac1-1D mutant. RT-PCR analysis further confirmed this up-regulation for five of these genes. Investigation of root growth also indicated that tac1-1D roots were ~20% longer relative to wild-type. Further experiments demonstrated that over-expression of TAC1 does confer drought tolerance, but not salt tolerance. In addition, our preliminary result showed that treatment with a low concentration of IAA could induce drought tolerance in wild-type Arabidopsis. Although plants with constitutive expression of telomerase have no practical utility, the ability of TAC1 to confer drought tolerance could have significant agricultural applications.

Forests play an important role in the earth system, regulating climate, maintaining biodiversity, and provisioning human communities with water, food and fuel. Interactions between climate and forest dynamics are not well constrained, and high uncertainty characterizes projections of global warming impacts on forests and associated ecosystem services. Recently observed tree mortality and forest die-off forewarn an acceleration of forest change with rising temperature and increased drought. However, the processes leading to tree death during drought are poorly understood, limiting our ability to anticipate future forest dynamics. The objective of this dissertation was to improve understanding of drought-associated tree mortality through literature synthesis and tree-ring studies on trees that survived and died during droughts in the southwestern USA. Specifically, this dissertation 1) documented global tree mortality patterns and identified emerging trends and research gaps; 2) quantified relationships between growth, climate, competition and mortality of piñon pine during droughts in New Mexico; 3) investigated tree defense anatomy as a potentially key element in piñon avoidance of death; and, 4) characterized the climate sensitivity of piñon resin ducts in order to gain insight into potential trends in tree defenses with climate variability and change. There has been an increase in studies reporting tree mortality linked to drought, heat, and the associated activity of insects and pathogens. Cases span the forested continents and occurred in water, light and temperature-limited forests. We hypothesized that increased tree mortality may be an emerging global phenomenon related to rising temperatures and drought (Appendix A). Recent radial growth was 53% higher on average in piñon that survived versus died during two episodes of drought-associated mortality, and statistical models of mortality risk based on average growth, growth variability, and abrupt growth changes correctly classified the status of ~70% of trees. Climate responses and competitive interactions partly explained growth differences between dying and surviving trees, with muted response to wet/cool conditions and enhanced sensitivity to competition from congeners linked to growth patterns associated with death. Discrimination and validation of models of mortality risk varied widely across sites and drought events, indicating shifting growth-mortality relationships and differences in mortality processes across space and time (Appendix B). Pre-formed defense anatomy is strongly associated with piñon survivorship over a range of sites and stand conditions. Models of mortality risk that account for both growth and resin duct attributes had≈10¹⁹ more support than models that contained only growth. The greatest improvement in classification was among trees from the 2000s drought, suggesting an enhanced role for tree defense allocation and/or bark beetle activity during recent warm versus historic cool drought. Accounting for defense characteristics and growth-defense allocation is likely to be important for improving representation of drought-associated mortality (Appendix C). Piñon resin duct chronologies contain climate responses that are coherent and distinct from those of radial growth. Growth responds positively and strongly to previous fall and current winter precipitation, and negatively to late spring and early summer temperature. A relatively equal positive resin duct response to winter precipitation and positive response to mid-to-late summer drought suggests that changes in climate will affect tree defense anatomy in complex ways, with the outcome determined by seasonal changes in precipitation and temperature (Appendix D).

We compared water deficit responses of 'Tifsport', 'Tifway 419', 'Tifgreen 328', and 'MidIron' bermudagrass (Cynodon dactylon x Cynodon transvaalensis), and 'SeaSpray', 'SeaDwarf', and 'Sea Isle 1' seashore paspalum (Paspalum vaginatum Swartz) under a linear gradient irrigation system in the desert Southwest. Target irrigation levels were 100, 80, 60, and 40% (2009) and 100, 80, 70, 60, and 40% (2010) of standard reference evapotranspiration (ETo). Actual water applied (including rainfall) was 100%, 83%, 66%, and 49% of ETo (2009) and 100%, 83%, 75%, 66%, and 49% (2010). Canopy temperatures increased, and quality and dry matter production declined with reduced irrigation. For optimum turfgrass quality, 75 to 83% ETo replacement was required; for acceptable quality turfgrass, 66 to 75% ETo replacement was needed for bermudagrass, and 75 to 80% ETo for seashore paspalum. Spring green-up was delayed by drought. Bermudagrasses, particularly 'MidIron', performed better than seashore paspalums under water stress conditions.