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Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases catalyze the production of superoxide, a type of reactive oxygen species (ROS). In plants, the NADPH oxidase homologs have been identified as respiratory burst oxidase homologs (Rboh). They are involved in ROS production in response to drought stress. Three entries of tall fescue (Festuca arundinacea Schreb.) were used for analyses in the present study: tolerant ('Isfahan') and sensitive ('Quchan') accessions to drought during the germination stage, selected from 14 wild populations in Iran, as well as 'Barvado' as a control. Partial sequence of the Festuca respiratory burst oxidase-D (FrbohD) gene was isolated from Barvado. We compared expression levels of the FrbohD gene as well as hydrogen peroxide (H2O2), catalase activity and some biochemical responses among the three entries. Gene expression was evaluated for leaf and shoot samples subjected to 3, 6, and 9 d without water. The transcript level of FrbohD, H2O2 content, and catalase activity increased in Quchan under drought stress. It appears that lower levels of FrbohD gene transcription and H2O2 concentration in F. arundinacea leaves contributed to drought stress tolerance in Isfahan. Total protein and total soluble carbohydrate content also increased significantly in Isfahan when it was subjected to drought stress. Isfahan exhibited drought resistance through various strategies, which could serve as selection criteria for improving drought resistance in turfgrass breeding programs. [ABSTRACT FROM AUTHOR]

Water deficit stress is a major factor limiting soybean [Glycine max (L.) Merr.] yield. High water use efficiency (WUE) offers a means to potentially ameliorate drought impact, but increased WUE is often associated with a reduction in transpiration (T) and an accompanied reduction in photosynthesis. This interdependence of T and photosynthesis is a major constraint in selection for high WUE by breeding programs. Measurement of genetic variability in WUE and T through carbon isotope ratio (δ13C) and oxygen isotope ratio (δ18O), respectively, could be important in identifying genotypes with high WUE that also have relatively high T and thus higher rates of biomass production. This study's objective was to identify genomic regions associated with δ13C and δ18O. A diverse collection of 373 soybean genotypes was grown in four field environments and whole-plant samples collected at early reproductive growth were characterized for δ13C and δ18O. After quality assessment, 31,260 polymorphic single-nucleotide polymorphism (SNP) markers with a minor allele frequency ⩾5% were used for association analysis. Genome-wide association analysis identified 54 environment-specific SNPs associated with δ13C and 47 SNPs associated with δ18O. These SNP markers tagged 46 putative loci for δ13C and 21 putative loci for δ18O and may represent an important resource for pyramiding favorable alleles for drought tolerance and identifying genotypes with high WUE. [ABSTRACT FROM AUTHOR]

Although it is known that drought tolerance can be associated with membrane fatty acid (FA) unsaturation, a relevant study is lacking in zoysiagrass (Zoysia spp.) and St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze.]. Our objectives were (i) to substantiate that variation exists among species and genotypes for leaf tissue FA composition under well-watered conditions; (ii) to evaluate the relationship between well-watered leaf FA composition and turf performance under drought stress; and (iii) to determine if modifications in FA content occur during drought stress and if the changes associate with improved drought tolerance. Nine genotypes of three species were subjected to both controlled dry down and well-watered conditions for 12 d in a greenhouse. Plants were evaluated for cumulative water use, transpiration response, turfgrass quality, and leaf FA composition (palmitic acid, stearic acid, palmitoleic acid, hexadecadienoic acid, oleic acid, linoleic acid, and linolenic acid). St. Augustinegrass had a constitutively higher unsaturation FA fraction than two zoysiagrass species, owing to its higher linolenic acid and low palmitic acid fractions. During dry down, relative FA contents remained stable and no early unsaturation alteration was found. Two genotypes, 'UF182' Japanese lawngrass (Z. japonica Steud.) and 'Zeon' manilagrass [Z. matrella (L.) Merr.], displayed an increase in unsaturated FAs when severe drought stress occurred (rapid decline in turfgrass quality), which was associated with good turfgrass quality and apparent drought tolerance. The result in zoysiagrass supports previous reports suggesting increased levels of linolenic acid under drought stress to be a defensive mechanism. [ABSTRACT FROM AUTHOR]

Water and labor shortages are currently driving the shift from continuously flooded, puddled transplanted rice (Oryza sativa L.) (PTR-cf) to alternative crop establishment practices, such as dry-seeded rice (DSR). To improve water productivity by using DSR, fields are often kept under aerobic conditions. This shift could induce sensitivity to critical developmental processes during the early reproductive stages such as floral meristem (panicle) initiation and growth, when this coincides with water-limited conditions. To study the physiological impact of different establishment methods with different water available conditions, rice cultivar NSICRc 222 was evaluated, under PTR-cf, dry-seeded rice (DSR) with daily irrigation (DSR-d) and DSR with cyclic irrigation whenever soil water tension reached 10 kPa (DSR-10) and 40 kPa (DSR- 40). Young developing inflorescences showed a morphological shift towards a slender shape under DSR-10 and a further increase in slenderness under DSR-40. We document a significant negative impact on developing inflorescence differentiation, a reduction in panicle neck diameter, and lower panicle nonstructural carbohydrate (NSC) content and grain length with a shift from PTR-cf to DSR-d. Key physiological traits such as retaining a globular-shaped floral meristem as a marker for optimal spikelet number and increased panicle sink size and panicle neck diameter, and NSC content for minimizing yield penalty are recommended when developing rice varieties for DSR, particularly under water-limited DSR conditions. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate Maize (Zea mays L.) elite lines currently available in CIMMYT's lowland tropical breeding program in Latin America under multiple abiotic stresses and identify lines with tolerance to drought, N deficiency, and combined heat and drought stress (HTDS). An incomplete line-by-tester design was used to evaluate 436 testcrosses under nonstressed conditions, 507 under N deficiency, 417 under drought stress (DS), and 368 under HTDS in 30 season-by-location combinations between 2012 and 2015. Elite lines CLRCY016, CML269, CML550, and CML551 performed well across all conditions, while CLQRCWQ118, CLWN306, and CML576 showed good performance under DS and N deficiency. CML574 was tolerant to DS and HTDS. Moreover, CML550 and CML574 are known for their partial tolerance to maize lethal necrosis. Grain yield measured under DS was to some extent predictive of attainable grain yield under N-deficient conditions (r = 0.65; P < 0.01) and HTDS (r = 0.54; P < 0.01) as indicated by the correlation across treatments. The fact that only a few lines were tolerant across treatments re-emphasizes the need to separately screen germplasm under each abiotic stress. Based on high best linear unbiased predicted general combining ability (BLUP GCA), it will be possible to develop hybrids tolerant to multiple abiotic stresses without incurring any yield penalty under nonstressed conditions using these inbred lines. [ABSTRACT FROM AUTHOR]

Whole-plant-based measurements do not always accurately reflect the effect of drought on cotton because of its indeterminate growth habits. We conducted pot experiments with cotton and imposed three soil water levels (75 ± 5, 60 ± 5, and 45 ± 5% of field capacity [FC]) during boll development to determine influences of drought on yield distribution and fiber quality on different fruiting branches (FB). Drought not only reduced lint yield (decreased by 31 to 35 and 57 to 60% under 60 ± 5% FC and 45 ± 5% FC, respectively) but also altered yield distribution on different FB. Drought plants produced fewer and smaller bolls on higher FB than did the well-watered plants. Boll biomass distribution and seed number per boll on upper FB were also altered by drought. Fiber length and strength declined progressively with decreasing water availability, being more pronounced on higher FB. Micronaire value was greater on higher FB under the same water regime, while no consistent influences of drought on micronaire were obtained. Boll weight, seed index, and fiber length and strength declined linearly with decreasing mean midday leaf water potential (LWP) during fruit maturation period (FMP) in the range of about 0.7 g, 1.0 g, 2.4 mm, and 3.4 cN tex-1 per MPa, respectively. Our findings showed that the bolls at various FB differed in drought response. The LWP was a suitable index for fiber properties under production environment. These data will be valuable for designing better irrigation strategies and improving cotton simulation models. [ABSTRACT FROM AUTHOR]

In parts of Central Europe, such as Germany, climate change will lead to increasing area utilization for winter types of faba bean (Vicia faba L.) with improved tolerance to drought and freezing. Here, we present the first genome-wide association analysis focusing on drought and freezing stress in a set of 189 German winter faba bean lines. We assessed proline, glycine betaine, soluble sugars, water content, membrane stability, and chlorophyll content in leaves of juvenile plants, with and without drought stress. To describe freezing tolerance under growth chamber conditions, we monitored the freezing symptoms of juvenile plants, such as loss of color and turgidity, freezing survival, and regrowth after freezing-- achieving medium to high repeatabilities (0.43 < h2 < 0.93). With 175 single-nucleotide polymorphism (SNP) assays and 1147 amplified fragment length polymorphism (AFLP) assays, a total of 1322 (mostly mapped) DNA markers were utilized. We detected a total of 21 putative quantitative trait loci (QTL) for six of the traits, each explaining 6 to 15% of the phenotypic variance. Several phenotypically promising inbred lines were identified. The present results will greatly improve the prospects for including winter faba bean into German crop rotations in the near future. [ABSTRACT FROM AUTHOR]

Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) has emerged as an important technique for gene-expression analysis. However, for accurate and reliable results, the data normalization using appropriated reference genes is critical, and a systematic validation of reference genes in cowpea (Vigna unguiculata L. Walp), a high stress-tolerant leguminous, has not been performed. To provide suitable reference genes in this strategic leguminous species under drought stress, we evaluated the expression stability of eight candidate genes using geNorm and NormFinder algorithms. The analyses were performed in nodules and leaves separately (organ-specific analysis) or grouping the two organs (global analysis). Our results showed VuPp2A and VuUbq28 as the best reference genes--by both algorithms--for global analysis. For organ-specific analyses, geNorm identified VuPp2A/VuYls8 as the most stable genes for nodules and NormFinder identified VuPolyP/VuPp2A as the most stable ones for leaves. Moreover, VuUbq28 was always identified among the top three genes. The proposed reference genes were validated by two stressresponsive genes (VusHsp17.7 and VuNced1). In conclusion, VuPp2A was the best reference gene in all analyses, followed by VuUbq28, VuYls8, and VuPolyP as the most stable genes for RT-qPCR data normalization in cowpea under drought stress. These genes could be a good starting point for reference-gene validation in other leguminous species under stress and BNF conditions. [ABSTRACT FROM AUTHOR]

Climate change will have an influence on crop production and lead to a focus on stable and high-yielding varieties in breeding programs. Winter rye (Secale cereale L.) is an important crop in Central and Eastern Europe, especially in marginal environments where varying weather conditions have a strong impact on grain yield. Because these environments are the first to suffer from abiotic stress, yield stability is an important breeding goal for rye. The objectives were to evaluate phenotypic diversity for genotype by irrigation interaction (GII) and the potential of hybrid rye to combine high yield potential with superior yield stability. Two intrapool and one interpool population with each of 218 to 220 testcross progenies were grown in a total of 16 to 18 environments (location by year combinations). In six of these environments, managed drought stress trials (rainfed vs. irrigated) were conducted. We observed a wide range of grain yield, from 4.9 to 11.5 Mg ha-1. In the managed drought stress experiments yield reduction in the rainfed regime ranged from 2 to 41% with an average of 18%. Only in a few environments did significant GII occur, although in most environments yield reduction was significant. Genotypic correlations of grain yield between irrigated and rainfed regimes were generally high (0.8-1.0). The coefficient of linear regression (bi) was not significantly different from 1 among progenies. Mean square deviation from linear regression (S² di), however, varied significantly (P < 0.01). To ensure broad adaptability of germplasm, managed drought stress environments should be included in test environments, but they need no special selection procedures. In conclusion, modern rye breeding material already combines high yield potential and stability. [ABSTRACT FROM AUTHOR]

Seedling establishment is obviously the first step in having successful crop production. In seasons and locations that experience early drought, potential differences among species in plant survival of drought could result in greater probability of crop establishment. In this study, plant survival capacity during crop establishment was tested for five grain legume species: soybean [Glycine max (L.) Merr.], common bean (Phaseolus vulgaris L.), groundnut (Arachis hypogaea L.), cowpea (Vigna unguiculata L. Walp.), and pigeon pea (Cajanus cajan L. Huth). Experiments were done for four sowing conditions (two soil textures × two initial soil-water contents). Cowpea and pigeon pea had the greatest capacity for survival, while soybean, bean, and groundnut were more sensitive. Differences among species could not be explained by differences in the temporal dynamics of water use. Conversely, plant wilting and senescence in response to soil dehydration varied among species; initial wilting of cowpea and pigeon pea occurred at lower soil-water contents. These two species also had the longest survival after fraction transpirable soil water (FTSW) reached zero. In a comparison of 10 genotypes of each species, genotypic variation in the wilting profile during the survival phase was observed in cowpea, bean, and, to a lesser extent, groundnut and pigeon pea, but no differences were found in soybean. [ABSTRACT FROM AUTHOR]

Timothy (Phleum pratense L.) is one of the most winter-hardy, cool-season perennial grasses used for forage production. However, its lack of tolerance to water stress requires supplemental irrigation for successful production in more arid areas of the world. A set of 112 timothy accessions and 6 check cultivars were evaluated for dry matter yield, in vitro true digestibility, neutral detergent fiber, crude protein, and water soluble carbohydrates across two production years at Lewiston, UT, and Tetonia, ID. Supplemental irrigation was not supplied at Tetonia. For each of the traits except water-soluble carbohydrates, the variance due to the main effect of accessions differed from zero. There was also accession ' environment interaction for each of the traits. Within-environment broad-sense heritability estimates differed from zero and ranged from 0.45 ±0.16 to 0.80 ±0.40. Thus, genetic determinants exerted substantial influence on the expression of the traits in each environment. Most of the commercial cultivars exhibited no benefit over the accessions for these traits, and there was a relationship between the accessions' geographic origin and their potential for timothy improvement. Asian and Northwest and Northeast European accessions possessed the greatest potential for increasing timothy nutritive value under western North American conditions. Yet there was little evidence that any accessions would provide a yield improvement. [ABSTRACT FROM AUTHOR]

Water-use efficiency is often genetically correlated with specific leaf area (SLA) and leaf C isotopic composition (δ13C) in peanut (Arachis hypogaea L.). The objectives of this study were to examine the effects of environment, genotype, and genotype × environment interaction on SLA, δ13C, harvest index (HI), and yield and to estimate heritability and the genetic relationships. Fifteen genotypes were tested at two locations with different drought intensities for 2 yr. The additive main effects and multiplicative interaction analysis based on yield data divided eight environments (locations × treatments × years) into four clusters, which reflected a gradient in drought stress, indicating yield trait is a good indication of drought stress. The genotype Exp8-12 was identified as a best drought tolerant germplasm across environments. Heritability estimates for HI (0.68 to 0.89) and δ13C (0.75 to 0.89) were higher than those for SLA (0.31 to 0.88) and yield (0.12 to 0.65). A positive but small genetic correlation coefficient (rg) (0.26) was found between HI and yield, and low to moderate rg (0.14 to 0.55) were observed between HI and SLA. A relative high negative genetic correlation rg (-0.81 to -0.57) was found between δ13C and yield. In theory, the high heritability and no G×E interaction for δ13C make it possible a surrogate that can be used to assess drought tolerance in peanut breeding. [ABSTRACT FROM AUTHOR]

Canopy temperature difference (CTD) is used to selectwheat(Tr/f/'cumaesf/VumL.)varietiestolerant to drought and heat stresses. As CTD reflects the stomatal conductance and transpiration of wheat leaves, and root-synthesized cytokinin has been shown to be distributed into the aerial parts by the transpiration stream, we therefore investigated the associations of CTD with trans-zeatin (Z) and trans-zeatin riboside (ZR) concentration and tolerance of a leaf to high light and high temperature (HLHT) stresses in the flag leaf of different wheat genotypes in field trials. The measurements at 14 d postanthesis (DPA) in 2009 and at 7, 14, 21, and 28 DPA in 2010 showed that Z plus ZR level increased as canopy temperature decreased. This could be at least partially explained by the fact that the flag leaves of low canopy temperature (LT) genotypes received higher delivery rates per unit leaf area of Z plus ZR from the roots and had lower cytokinin oxidase activities than those of high canopy temperature (HT) genotypes. The flag leaves of LT genotypes also exhibited longer photosynthetic durations, higher activities of antioxidant enzymes, and stronger tolerance to HLHT stresses than those of HT genotypes, especially at the late grain filling stage. Hence, CTD shows the potential to be an index for selecting wheat with high cytokinin level of the flag leaf favorable for longer photosynthetic duration and stronger tolerance to HLHT stresses. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) grown in marginal soils may frequently be subjected to water deficit conditions. The study was designed to determine physiological response, cell wall components, and expression of genes involved in cell wall biosynthesis of switchgrass under short-term drought stress and recovery. Grasses were exposed to drought for 4 d in 2007 (Exp. 1) and 7 d in 2008 (Exp. 2) in a greenhouse and then rewatered for 1 d in both experiments, respectively. Drought stress reduced tissue water content, leaf dry weight, and chlorophyll fluorescence and increased total carotenoid concentration and electrolyte leakage, and the values of these parameters returned to those of the control levels after rewatering. Reductions in leaf hemicellulose and total plant hemicellulose concentrations and increases in stem and total plant lignin concentrations were observed in Exp. 1; however, LH and TH were not recovered after rewatering. The concentration of leaf acid detergent fiber increased under drought stress and was back to the control level after recovery while leaf neutral detergent fiber remained unchanged under drought stress but decreased after recovery. The transcript levels of CesA1, CesA6, and CesA12 encoding cellulose synthesis and CslHl encoding hemicellulose were suppressed by drought stress but the suppressions were reversed by rewatering. These candidate genes can be used for further studying the mechanisms that regulate cell wall biosynthesis in switchgrass. [ABSTRACT FROM AUTHOR]

Water deficit is increasingly becoming a limiting factor for peanut production in the Virginia-Car-olina (VC) peanut growing region. Even though extensive research efforts have been made worldwide to improve drought tolerance in pea-nut, performance of genotypes largely depends on the environment in which they grow and no such information is available for the VC area. The objective of this study was to determine the variability for CO₂ assimilation rate (A), stomatal conductance (gs), transpiration efficiency (A:gs), specific leaf area (SLA), chlorophyll content esti-mate (soil plant analysis development [SPAD] meter readings), stomata number per square centimeter and per leaf, and canopy tempera-ture depression (CTD) of 18 peanut (Arachis hypogaea L.) virginia-type cultivars and breed-ing lines grown in rain-fed plots in southeastern Virginia. The relationship between physiological and agronomic traits was then analyzed. Geno-type had a significant effect on all physiological traits. Excepting CTD, year also had a significant effect on all physiological characteristics. The genotype x year interaction was not significant for A, gs, A:gs, SPAD, and SLA suggesting domi-nant controlling factors for these traits. Under water stress in both years, pod yield was con-sistently associated with A (higher A results in higher yield) and SPAD (greener leaves results in higher yield). These results suggest that devel-opment of cultivars with greener leaves and higher A when gs is low may ensure better yields under rain-fed conditions in the VC region. [ABSTRACT FROM AUTHOR]

Drought and elevated temperature often occur alone or in combination in many areas, limiting cool-season grass growth. Rising atmospheric CO2 concentration may affect plant adaptation to drought and high temperature. The objective of this study was to investigate the effectiveness of elevated CO2 in mitigating the negative effects of drought or elevated temperature alone or a combination of these stresses on physiological processes in a perennial grass species. The effects of these treatments on water relations, photosynthesis, and respiration were determined in tall fescue (Festuca arundinacea Schreb. cultivar Rembrandt). Grass plants were subjected to the following treatments in growth chambers: heat stress (30°C or 5°C above the optimal level of 25°C), drought stress by maintaining soil water content at 50% of field capacity, or the combined two stresses for 28 d. Stressed and unstressed control plants were exposed to a constant level of either ambient CO2 (400 µL L-1) or elevated CO2 (800 µL L-1). At ambient CO2 concentration, drought and the combined stress for 28 d caused significant decline in leaf relative water content (RWC), photochemical efficiency (ratio of variable to maximum fluorescence [Fv:Fm]), net photosynthetic rate {A), stomatal conductance (gs, maximal ribulose- 1,5-bisphosphate carboxylase oxygenase (Rubisco)- limited rate of photosynthesis (Vcmax), and maximal electron transport-limited rate of photosynthesis (Jmax) but increased membrane electrolyte leakage (EL) and dark respiration rate (Rd). Elevated temperature to 5°C above the optimal level resulted in the increases in gs, EL, and Rd but had no significant effects on the other physiological parameters. Drought stress for 28 d was more detrimental than increasing temperature by 5°C for tall fescue and the combined stress was more detrimental than either stress alone. Elevated CO2 mitigated the degree of change in all physiological factors under drought or heat stress and resulted in increases in A (162%) and RWC (19%) and a reduction in EL (21%) under the combined stress. These results suggest that elevated CO2 could improve tall fescue tolerance to drought and elevated temperature by enhancing plant water status, cellular membrane stability, and photosynthesis capacity and by suppressing gs for water loss and C consumption through lowering respiration rate. [ABSTRACT FROM AUTHOR]

Salinity and drought are two of the major abiotic stresses that affect rice {Oryza sativa L.) production especially in Asia. Quantitative trait loci (QTL) for salt tolerance (ST) at seedling stage and drought tolerance (DT) at reproductive stage were identified using 77 BC2F8 advanced backcross introgression lines (ILs) derived from a cross of Teqing × Binam in Teqing background. Ten ST QTL were identified governing days to seedlings survival (DSS), score on salt toxicity symptoms on leaves (SST), shoot K+ concentration (SKC), and shoot Na+ concentration (SNC) at seedling stage, and 23 QTL were identified under reproductive stage drought and irrigated conditions for panicle number per plant (PN), thousand grain weight (TGW), seed fertility (SF), plant height (PH), and grain yield per plant (GYP). Most QTL detected at reproductive stage showed obvious differential expression to drought stress. In addition, another eight QTL were detected by trait ratio of the stress to the irrigation; the alleles at all loci except QSf3 showed increasing trait values to be associated with Binam, indicating Binam alleles at these loci could improve DT under drought stress. Upon comparison of identified ST and DT QTL we found 14 QTL shared the same genome regions with similar gene actions, clearly suggesting that genetic overlap existed between the two abiotic stress tolerances. Pyramiding of favorable alleles from Binam into Teqing background should allow us to develop superior ILs with higher levels of ST and DT. [ABSTRACT FROM AUTHOR]

Plant tolerance to drought and heat stress may be interrelated. The study was designed to examine whether improved heat tolerance through drought preconditioning is associated with changes in lipid and protein content and antioxidant enzyme activities. Kentucky bluegrass (Poa pratensis L.) (cv. Brilliant) plants were well watered (non-preconditioned control) or exposed to drought without irrigation for 12 d (drought preconditioning) and then exposed to heat stress (35°C/30°C) for 25 d in growth chambers. Compared to the non-preconditioned control, preconditioned plants had higher turf quality and chlorophyll content, and lower leaf electrolyte leakage and lipid peroxidation under heat stress. Lipid saturation level increased under heat stress due to decreases in the content of linolenic (C18:3) and increases in linoleic (C18:2) and palmitic (C16:0) acids. Total fatty acid content and the content of C18:3 were significantly higher and C16:0 content was lower in preconditioned than in non-preconditioned plants at 15 d of heat stress. The activity of superoxide dismutase increased in preconditioned plants at the initiation of heat stress, but it decreased in non-preconditioned plants under heat stress. Preconditioned plants had higher catalase and ascorbate peroxidase activities than non-preconditioned plants under heat stress. Drought preconditioning accelerated the up-regulation of chaperonin and heat shock protein 90, inhibited the down- regulation of proteins for amino acid metabolism, and induced the expression of lipoxygenase. These results imply that drought-preconditioning-enhanced heat tolerance was associated with the promotion of antioxidant activities and chaperoning protein expression, protecting plants from cellular damages from heat stress. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) is one of the important food crops drastically affected by drought. Considering the low heritability of grain yield under water stress, several secondary traits associated with drought tolerance have been used, but the success achieved in deriving cultivars with high yield potential under stress is less compared to irrigated conditions. Hence, objective of the experiment was to estimate heritability for grain yield under lowland stress and select for grain yield per se using wild species Oryza meridionalis Ng and also to identify physio-morphological traits responsible for withstanding water stress. A population derived from O. sativa cv. IR58025B × O. meridionalis (BC2F3) was evaluated under control and stress conditions. Variability observed for yield and component traits indicated O. meridionalis to be a good source of useful alleles for drought tolerance. Broad-sense heritability (h2) of grain yield under stress, although only 33.1%, was comparable to control 59.4%, indicating direct selection for grain yield per se can be practiced. Twenty high-yielding selected lines and 40 random lines were evaluated under control and stress conditions to estimate selection response. Yield of selected lines outperformed random lines and checks under stress. Furthermore, 10 lines (5 high yielding and 5 low yielding) selected from the population were characterized for root morphological traits. Maximum root length (MRL) and root volume (RV) of selected high-yielding lines recorded maximum compared with checks and low-yielding lines indicating positive influence of drought avoidance root traits on grain yield under stress. Hence, O. meridionalis can be a good source of root traits contributing to stress tolerance and selection for grain yield under stress is an effective strategy in deriving drought tolerant lines in rice. [ABSTRACT FROM AUTHOR]

Increased leaf appearance rate (LAR) could reduce preanthesis water use of sorghum [Sorghum bicolor (L.) Moench] by restricting plant size via reduced tillering. The aim of this paper was to assess LAR as a potential pathway for adaptation to postanthesis drought stress. Four hybrids with different LAR were grown in four semicontrotled experiments under well-watered conditions or postanthesis drought stress and in two irrigated field experiments. Observations included leaf area dynamics, transpiration, transpiration efficiency (TE), leaf N, biomass, and grain yield. ATx642 hybrids (0.0306 leaf °C d') had significantly greater LAR than AQL39 hybrids (0.0279 leaf °C d1) and this increased early main shoot vigor. Under low plant density, this reduced tiller number and hence leaf area and biomass around anthesis. As hybrids had similar TE and differed little in phenology, this can reduce preanthesis water use. Water availability at flag leaf determined grain number per plant (adjusted R2 0.80, p < 0.01) and hence grain yield. However, the effect of increased LAR on reduced plant size was temperature dependent. Under high temperature, genotypic differences in tillering were reduced and main shoot leaf number increased more in hybrids with greater LAR. This increased responsiveness of leaf number could increase plant size and water use at anthesis. Hence, greater LAR may confer drought adaptation only in specific environments unless it is also associated with critical aspects of biomass partitioning. [ABSTRACT FROM AUTHOR]

Drought responsive turfgrass cultivars are becoming increasingly important in water conservation. Eight cultivars of bermudagrass [Cynodon dactylon (L.) Pers.], one cultivar of buffalo grass [Buchioe dactyloides (Nutt.) Engelm.], and two root-zone depths were evaluated for drought response and recovery during consecutive 60-d drought and 60-d recovery periods over 2 yr. Individual cultivar responses to drought and post-drought recovery time were quantified through digital image analysis as the number of days to decrease to or increase to 50% green ground cover, respectively. No grass survived the 60-d drought when planted on the restricted 10-cm soil depth in 2006 or 2007, while all entries survived when planted on the unrestricted native soil depth. Both study years provided unique conditions for investigating drought response as the mean time to reach 50% green ground cover differed by 17 d between the 2 yr of study. Some cultivars lost 50% green ground cover in 20 d while other cultivars lasted the entire 60-d drought period without losing 50% green ground cover. Post-drought turfgrass recovery responses differed by as much as 45 d in achieving 50% green ground cover. Documenting individual cultivar responses to drought and recovery may provide perspective on individual grass cultivars that may initiate poor irrigation management behavior due to early leaf firing as well as refine consumer expectations following drought conditions. [ABSTRACT FROM AUTHOR]

As water resources become restricted for use on amenity turfgrass systems, the inability for consumers to delineate incremental drought stress relating to plant health can result in the misuse of water resources during drought conditions. Seven cultivars of St. Augustinegrass (SA) [Stenotaphrum secundatum (Walt.) Kuntze] and two root zone depths were evaluated for drought response and recovery during consecutive 60-d drought and 60-d recovery periods over 2 yr. Using digital image analysis, drought response and recovery were quantified as the number of days to decrease or increase to 50% green ground cover, respectively. Both study years provided unique conditions for investigating drought response as the mean time to reach 50% green ground cover differed by 24 d between the 2 yr of study. Some SA cultivars lost 50% green ground cover in 23 d while other cultivars lasted the entire 60 d drought period without losing 50% green ground cover. Floratam provided the most consistent drought response and recovery compared to other SA cultivars. Once water was no longer limited, cultivars demonstrated up to a 52 d difference in attaining 50% green ground cover. Results could significantly impact home consumer irrigation behaviors and influence consumer expectations of turfgrass following drought conditions. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) yield is substantially diminished by drought during the initial phase of kernel development. To advance our understanding of the mechanisms underlying this response, we determined the timing of sucrose, glucose, starch, and abscisic acid (ABA) accumulation in apical (inferior) and basal (superior) kernels during water deficit (3-8 d after pollination) and recovery. While net flux of material was nearly zero into both apical and basal kernels during stress, growth resumed after rewatering only in basal kernels. In bulk tissues of pedicelplacenta, pericarp, or endosperm, basal kernels did not have higher glucose, sucrose, or starch concentrations than apical kernels. However, glucose and sucrose concentration in the pedicel-endosperm interface where phloem terminates was maintained at control concentrations in basal kernels, while it was depleted in apical kernels. Kernel set in basal versus apical kernels was also associated with lower levels of ABA in the pedicel-placenta tissue of basal kernels after rewatering. These findings support a model of interacting influences of carbohydrate and ABA, and suggest that this interaction might be a good target for future efforts to genetically improve maize drought tolerance. [ABSTRACT FROM AUTHOR]

Perennial grasslands provide numerous agroenvironmental benefits due to continuous soil cover. In Mediterranean areas, chronic summer drought is expected to increase as a result of climate changes. Plant adaptations that protect meristematic tissues include dehydration delay, dehydration tolerance, and summer dormancy. Summer dormancy can only be reliably tested in plants not subjected to water deficit. Under summer irrigation, complete dormancy is manifested by cessation of growth in association with full senescence of foliage and induced dehydration of leaf bases. Incomplete dormancy occurs when leaf growth is partially constrained and associated with moderate levels of foliage senescence. Summer dormancy is under hormonal control and is induced under increasing photoperiod and temperature. Recent results show that drought cannot induce summer dormancy under early-spring short days, although a water deficit under late-spring long days reinforces it and could enhance drought survival. Dehydration tolerance and dormancy are independent phenomena. Summer dormancy has been correlated with superior survival after severe summer droughts in many perennial grass species. This trait has potential for improving cultivars able to meet agronomic and environmental goals. [ABSTRACT FROM AUTHOR]

The significantly lower annual rainfall experienced in Australia over the past decade together with projections of long-term climate change has placed increased emphasis on the use of pasture plants with superior tolerance to environmental stress, particularly drought, to ensure persistence for the grazing industries. Summer dormancy is one of the more important traits that grasses have to adapt to environments where there is little, variable, or no summer rainfall. In this article, the role that the summer dormancy trait has played in enhancing the survival of temperate perennial grasses in Australia is reviewed with special reference to orchardgrass (cocksfoot; Dactylis glomerata L.) and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. The performance of cultivars and populations with this trait is assessed in comparison to germplasm without the trait. Other major factors such as the contribution of rooting depth to stress tolerance and their possible relationship with summer dormancy are documented and evaluated. Current knowledge of the physiological basis by which summer dormancy improves survival of summer drought is also summarized. [ABSTRACT FROM AUTHOR]

Growing warm-season legumes during fallow periods associated with traditional continuous systems of winter wheat (Triticum aestivum L.) in the southern Great Plains (SGP) can provide supplemental forage, biological N, and protection from soil erosion, provided the legumes can tolerate drought stress and not deplete the available water in the soil profile. Our objective was to quantify water use by five species of pulse legumes {pigeon pea [(Cajanus Cajan (L.) Millsp.) cv. GA-2], guar [Cyamopsis tetragonobloba (L.) Taub., cv. Kinman], cowpea [Vigna unguiculata (L.) Walp., cv. Chinese red], mung bean [Vigna radiate (L.) Wilcz., cv. Berkins], and soybean [Glycine max (L.) Merr., cv. Hutcheson (the control)]). Seeds were inoculated and planted after wheat harvest in mid-June 2003 through 2006. The amount of water in the upper 65 cm of the soil profile was measured on nine dates [from 45 d before planting legumes to 195 d since planting (DSP)]. Significant (P < 0.01) differences in soil water were recorded among treatments, dates, and years. Differences in soil water among fallow, cowpea, and mung bean were less following the 2003 and 2004 summer seasons and most noticeable in 2005 and 2006. Mung bean, guar, soybean, and pigeon pea used the greatest amounts of water in 2005, the wettest season, while cowpea and mung bean used the least in 2003. Mung bean, cowpea, and guar generated smaller water deficits and used less soil water, in three of four years, and could be effective in wheat-summer legume rotations in the SGP. [ABSTRACT FROM AUTHOR]

Dry bean (Phaseolus vulgaris L.) is highly susceptible to drought stress, and drought affects 60% of global bean production. We evaluated elite exotic dry bean germplasm derived from the Mesoamerican gene pool for drought tolerance, yield, and adaptation to western Nebraska during 2006 and 2007 at three research sites. Seven tropical lines were evaluated with two great northern cultivars (Matterhorn and Beryl-R) and one pinto cultivar (Bill-Z) serving as checks. Adjacent nonstressed (NS) and drought-stressed (DS) blocks were evaluated. Within each block, the selected lines were assigned to experimental units using a randomized complete block design with four replications at each location. On average, yield was 60% less, 100-seed weight was 19.2% lower, and maturity occurred 4 d earlier under DS than under NS conditions. Beryl-R, SER 22, and Matterhorn had the greatest average yield under both NS (3564, 3347, and 3440 kg ha-1, respectively) and DS (1701, 1773, and 1584 kg ha-1, respectively). These genotypes were also the most drought tolerant based on the drought susceptibility index (0.9, 0.8, and 0.9, respectively) and geometric mean (2462, 2436, and 2335, respectively). Based on these results, Matterhorn, Beryl-R, and SER 22 show the most promise for use in breeding for drought tolerance. [ABSTRACT FROM AUTHOR]

The presence of biologically active substances (BAS) in biosolids may enhance plant stress tolerance and growth, but the underlying mechanisms are not well understood. This greenhouse study investigated the effects of untreated biosolids, containing 2.1 μg indole-3-acetic acid (IAA) g-1, and tryptophan-treated biosolids, containing 15.4 μg IAA g-1, on tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] drought resistance. Treatments included a fertilizer control, indole3-butyric acid (IBA) at 2 μM (hormone control), treated biosolids (2.95 g kg-1 soil), and untreated biosolids (2.97 g kg-1 soil). Nitrogen availability was equalized among treatments, and tall fescue physiological responses were measured under well-watered or moisture stress conditions. Treated biosolids improved turfgrass quality and root mass under both soil moisture regimes and delayed leaf wilting under moisture stress. At the end of the second drought cycle (2 February), treated biosolids improved quality and photochemical efficiency by 18 and 26% relative to the control. Treated biosolids increased leaf IAA by 122 and 52%, respectively, and trans-zeatin riboside by 100 and 189%, respectively, during each of two maximum drought periods. Leaf tissue increases of IAA and cytokinin were associated with greater content of these hormones in the soil. The data suggest that biosolids application may alter growth hormone (IAA and cytokinin) content and improve plant drought resistance. [ABSTRACT FROM AUTHOR]

An efficient and accurate detection of dry matter (DM) yield of legume-grass mixtures can facilitate a targeted and site-specific management of legume-based swards. The major objective of this study was to examine the relationship between spectral signatures of legume-grass swards and DM yield across a wide range of legume species (white clover [Trifolium repens U, red clover [T. pratense L.], alfalfa [Medicago sat/va L.], birdsfoot trefoil [Lotus corniculatus U), legume proportion (0-100% of DM), and growth stage (beginning of tillering to end of flowering). Modified partial least squares (MPLS) regression, stepwise multiple linear regression (SMLR), and the vegetation indices (Vis), simple ratio, normalized difference vegetation index, enhanced vegetation index, and red edge position were used for analysis of the hyperspectral data set (350-2500 nm). Compared to common calibrations, legume-specific models achieved better results, indicating that each legume species had its own spectral characteristics. Modified partial least squares and SMLR gave the best R² values, ranging in cross validation from 0.74 to 0.92 with a standard error below 92 g DM m-2. The DM yield prediction by VIs resulted in unsatisfactory accuracies. Prediction accuracy for MPLS and SMLR models were still acceptable even with a reduced spectral data set (630-1000 nm), a finding that could facilitate an application of field spectroscopy in practice. [ABSTRACT FROM AUTHOR]

Plants may survive drought stress by altering photosynthetic metabolism. This study was designed to investigate stomatal and metabolic changes associated with photosynthetic responses to drought for bermudagrass. A hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy, cv. Tifway] and a common bermudagrass (C. dactylon, cv. C299) were subjected to drought by withholding irrigation in growth chambers. Tifway maintained higher relative water content and lower electrolyte leakage than C299 under drought. Net photosynthetic rate (Pn) and stomatal conductance (gs) decreased, with more rapid decline in C299, but Pn was significantly greater in Tifway than in C299, while gs did not differ between the two genotypes during 14 d of drought. Photochemical efficiency, ribulose-1 ,5bisphosphate carboxylase:oxygenase (Rubisco) activity, and activation state declined during drought stress, but were higher in Tifway than in C299 within 14 d of treatment. Electrophoretic analysis revealed that at 14 and 18 d of drought, pyruvate orthophosphate dikinase (98 kDa) and Rubisco protein (49 kDa) exhibited severe degradation in C299 but to a lesser extent in Tifway. These results indicated that the superior drought resistance in Tifway could be attributed to higher photosynthetic capacity through the maintenance of higher metabolic activities, as manifested by more active Rubisco enzyme and Rubisco activase and more stable photosynthetic proteins. [ABSTRACT FROM AUTHOR]

Cuphea (Cuphea viscosissima Jacq. × C. Ianceolata W.T. Aiton) may be prone to drought stress, yet little is known about the yield response of this new oilseed crop to irrigation. A field study was conducted in western Minnesota on a Barnes loam soil (fine-loamy, mixed, superactive, frigid Calcic Hapludolls) in 2002 and 2003 to compare yield and water use of irrigated and nonirrigated cuphea. Nonirrigated cuphea received only precipitation, while irrigated plants received supplemental watering to maintain soil water content near field capacity during the study. Crop drought stress was assessed by measuring photosynthesis, stomatal conductance, leaf water potential, and δ13C (13C/12C stable isotope composition). In 2002, soil water content was similar for irrigated and nonirrigated plants throughout the growing season owing to timely rains, and seed yield was similar between treatments (873 kg ha-1). During 2003, irrigation resulted in a 2.7-fold increase in seed yield and greater harvest index than nonirrigated plants, while water use efficiency (WUE) of seed production for both treatments was similar (2.4 kg ha-1 mm-1). Drought conditions occurred in 2003; by mid-August, leaf photosynthesis and leaf water potential of nonirrigated plants were 83 and 56% less, respectively, than for irrigated cuphea. Moreover, δ13C measurements of seed further confirmed that nonirrigated cuphea suffered significant drought stress. Our results indicate that cuphea is drought sensitive and that regions or soils prone to water deficits will likely require supplemental irrigation to increase seed yield. [ABSTRACT FROM AUTHOR]

Drought is a worldwide constraint to dry bean (Phaseolus vuigaris L.) production. The objective of this research was to determine the response of three dry bean landraces and 13 cultivars evaluated under non-stressed (NS) and intermittent drought-stressed (DS) environments at Kimberly, Idaho in 2003 and 2004. The NS received seven irrigations in 2003 and five in 2004, and DS only four in 2003 and two in 2004. Most water use occurred within the top 0.5 m soil in both the NS and DS. Drought reduced biomass and seed yield, harvest index, and seed weight. Maturity was delayed in severe drought, but was similar or shortened by 1 to 6 d under moderate drought. Mean seed yield was reduced by 62% in 2003 and by 27% in 2004. Common Red Mexican and CO 46348 had high seed yield in both NS and DS environments, whereas ‘Matterhorn’ and ‘Othello’ yielded comparatively high under DS but moderately in NS environment. Drought resistance was inadvertently reduced from Common Red Mexican landrace to intermediate levels in ‘NW-63’ and ‘UI 239’ released in 1979 and 1993, respectively, and more recently released ‘LeBaron’ (1999) and ‘U1259’ (1996) were susceptible. Conversely, drought resistance was increased in newer pinto (Othello 1986; CO 46348) and great northern (Matterhorn 1998) releases compared to the landraces and older cultivars tested for those market classes. Seed yield in NS and DS was positively correlated. Seed yield was also correlated with harvest index in DS and NS. All early maturing cultivars except Othello (e.g., U159, US 1140, Common Pinto, Topaz, UI 320, and LeBaron) were susceptible. Common Red Mexican did not have any reduction in seed weight due to drought stress. Drought resistant genotypes should be used for determining irrigation frequency, amount of water to be applied, and mechanisms of resistance and for identifying, mapping, and pyramiding favorable genes for dry-land and irrigation-assisted sustainable production systems. [ABSTRACT FROM AUTHOR]

The key to an efficient screening method is the ability to screen large amounts of plant material in the shortest time possible. 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 hirsumm L.) seedlings. Twenty-one converted race stocks (CRS) and two cultivars were evaluated for seedling drought tolerance (SDT) on an individual plant basis. Genotypes were evaluated October-November 2004 and February-March 2005 under greenhouse conditions. Seedlings were subjected to three sequential cycles of drought at 15 d after planting (DAP). Drought cycles consisted of withholding water until the moisture content of indicator ‘Deltapine 491’ (DP 491) plants had an average volumetric water content of 0.07. Plants then were watered to saturation and allowed to drain to field capacity and percent survival recorded after 48 h. 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. The drought tolerance of the CRS was similar to that of ‘Acala 1517–99’. CRS M-9044-0165 was the most stable genotype, according to an analysis of the difference in percentage of survival for each genotype across the two experiments. [ABSTRACT FROM AUTHOR]

Field research conducted in 2003 and 2004 evaluated hyperspectral radiometry as a tool to detect localized dry spots on creeping bentgrass (Agrostis stolonifera L.) putting greens. Discriminant analysis identified 14 wavebands between 861 and 887 nm that distinguished drought severity. An overall accuracy of 85% was achieved using these wavebands with low-stressed greens correctly classified 91%. High-stressed greens were correctly classified 100% of the time with individual wavebands between 905 and 992 nm using 2003 data as a training model to cross-validate 2004 data. These results suggest these individual wavebands are highly sensitive to early season drought-stress in creeping bentgrass greens and could be considered a more stable portion of the spectrum over time concerning high-stressed creeping bentgrass putting greens. A significant relationship (p = 0.034) was established between average reflectance values of wave-bands between 1480 and 1530 nm and volumetric soil water content (VWC). Although not highly correlated, this relationship demonstrated that as VWC increased, reflectance decreased. Data collected in late spring/early summer may be the optimal time to detect areas of putting greens most susceptible to drought stress before unfavorable growth conditions occur. [ABSTRACT FROM AUTHOR]

Future climate changes are expected to increase risks of drought, which already represent the most common stress factor for stable barley (Hordeum vulgare L.) production in Mediterranean areas. It is important, therefore, to evaluate if there are needs of specific adaptive measures in selecting genotypes for these more stressful environments. Our objective was to study diversity of yield performance under rainfed (R) and irrigated (I) conditions in 89 barley genotypes of different origin, growth habit, and year of release, representing a sample of cultivars grown in Europe. The experiment was conducted at Foggia (southern Italy) for 3 yr. For each trial, a water stress index (WSI) was calculated on the basis of the daily potential and actual evapotranspiration in the growing season, estimated by Thornthwalte's method. The WSI explained most of the variation in yield (R² = 0.89**) among years and treatments. We examined, using the yield vs. WSI regression, the behavior of a given genotype across trials. The intercept and slope values were used as measures of yield potential and adaptability under drought, respectively. Several cultivars showing high yield potential and minimal genotype × environment (GE) interaction were identified. Notably, they were characterized by a high slope of the yield vs. WSI regression. Furthermore, within the range of water stress here examined, high yield potential played a preeminent role in the performance of these barley genotypes. This explains why, in this specific context, a selection based on minimum yield decrease under stress with respect to favorable conditions failed to identify the best genotypes. [ABSTRACT FROM AUTHOR]

Carbon-13 discrimination (Δ) and water use efficiency (WUE) have been largely ignored in turfgrass. Turfgrass performance under drought may be improved by selecting for low Δ, which has been shown to be negatively correlated with WUE. The objectives of this 2-yr greenhouse study were (i) to compare Δ and WUE in 12 genotypes of Kentucky bluegrass (Poa pratensis L.) with evapotranspiration (ET) and rooting for assessing turf performance under drought, and (ii) to determine the relative importance of ET in drought resistance by comparing diverse ET genotypes (6 low and 6 high) during drydown. Clipping dry weight to ET ratio (WUE) was evaluated with sandfilled weighing lysimeters (20-cm diam. by 65-cm depth) during two 4-d periods (Days 1 to 4 and 5 to 8) in 2002 and 2003. Carbon (13C/13C) analysis of leaf clippings was used to derive Δ values. Time domain reflectometry (TDR) was used to measure changes in volumetric soil moisture content (VSMC) at the 8.25-, 17.5-, 35.0-, and 52.5-cm depths to indicate moisture uptake and rooting activity. Drought resistance was visually assessed as wilt and leaf-firing symptoms. Low- and high-ET genotypes were similar in wilt and leaf firing, suggesting low ET may not be relevant in drought survival. Deep rooting at the 52.5-cm depth and higher ET as soils dried were associated with less leaf firing. The WUE at Days 5 to 8 was comparable in some years with rooting. The Δ was not always reliable in assessing WUE, but turf performance under drought was correlated with Δ. Low Δ values were associated with less wilt (r = 0.59, P ≤ 0.05) and leaf firing (r = 0.58, P ≤ 0.05), suggesting that Δ may be a useful selection criterion for superior performance under limiting soil moisture. [ABSTRACT FROM AUTHOR]

Kentucky bluegrass (Poa pratensis L.; KBG) has good turf quality with adequate irrigation, but moderate to low drought resistance. Interspecific hybridization of Kentucky bluegrass with Texas bluegrass (Poa arachnifera Torr.; TBG), a drought resistant grass native to Texas, has been made to transfer genes of drought resistance from TBG to KBG. The objectives of this study were (i) to investigate whether the hybrids have improved drought resistance compared with either TBG or KBG by examining physiological responses to drought stress; and (ii) to determine major physiological factors associated with recuperative ability of those plants from drought stress. Plants were exposed to drought stress by withholding irrigation for 42 d in a greenhouse. The experiment consisted of 29 fourth-generation backcrossed hybrids, one third-generation hybrid (BDF), two KBG parents ('C-74', 'Midnight'), and one TBG parent. The genotypes classified into three cluster groups of drought resistance (high, moderate, and low) based on the responses of relative water content (RWC), electrolyte leakage (EL), and photochemical efficiency (Fv/Fm) to drought stress. The RWC and Fv/Fm declined with drought stress, but were maintained at higher levels in the high resistance group than the other group, while EL increased during drought and was lower in the high resistance group. Texas bluegrass, Midnight KBG, and two hybrids were ranked highest in drought resistance. Other hybrids varied in drought resistance, with more hybrids of BDF × Midnight ranked in the high drought resistance group than the hybrids of BDF × C-74. Among all physiological parameters examined, EL was the most sensitive indicator to drought stress, as demonstrated by its most rapid increase in response to the stress. High Fv/Fm and retaining of green leaves during drought stress contributed to fast recovery from drought stress following rewatering. [ABSTRACT FROM AUTHOR]

Drought and heat are two major factors limiting growth of cool season grasses. Rapid recovery from the combination of those stresses is important for the persistence of perennial turfgrasses. The study was designed to examine physiological factors associated with the persistence and recovery of Kentucky bluegrass (Poa protensis L.) exposed to combined drought and heat stress following rewatering and/or temperature drop. Two cultivars differing in drought and heat tolerance, 'Midnight' (tolerant) and 'Brilliant' (sensitive), were exposed to drought and heat stress (35°C) simultaneously in a growth chamber until most plants became brown and completely desiccated (14 d). Plants were then subjected to three recovery treatments: (i) rewatered but exposed to heat stress (rewatering); (ii) returned to optimum temperature (20°C) but unwatered (cooling), and (iii) rewatering and cooling. Leaf photochemical efficiency (Fv/Fm), chlorophyll content, and activities of superoxide dismutase (SOD) and catalase (CAT) declined, while electrolyte leakage (EL) and lipid peroxidation increased rapidly during the combined stress. The adverse impact of the combined stress was more severe for Brilliant than for Midnight. Following rewatering or in combination with cooling, all parameters except chlorophyll content fully recovered for Midnight. However, for Brilliant, most of the parameters did not recover completely; Fv/Fm recovered partially. There was no recovery for any parameters of either cultivar when plants were returned to the optimum temperature but still unwatered. The results suggested that simultaneous drought and heat stress could cause permanent physiological damage for Kentucky bluegrass, particularly for the stress-sensitive cultivar. Rewatering was essential for physiological recovery from the combined stress, regardless of temperature conditions. Rapid resumption of Fv/Fm, cell membrane stability, and antioxidant activities were important factors contributing to the recovery of Kentucky bluegrass. [ABSTRACT FROM AUTHOR]

Moisture deficits can depress cotton (Gossypium hirsutum L.) lint yield in all cotton production regions. However, most cotton physiological drought stress research has been conducted in arid production regions, growth chambers, or greenhouses. The objective of this research was to document the effects of moisture deficit stress on the physiology of cotton grown in the humid southeastern USA. Field studies were conducted under dryland and irrigated conditions from 1998 to 2001 with eight genotypes, including an okra-normal leaftype near-isoline pair and transgenic lines paired with their recurrent parents. Dry matter partitioning, light interception, canopy temperature, leaf water potential, gas exchange, chlorophyll (Chl) fluorescence, and leaf Chi content data were collected. Genotypes responded similarly to both soil moisture regimes. Drought stress reduced overall plant stature with a 35% leaf area index (LAI) reduction, prompting an 8% reduction in solar radiation interception. Dryland leaves had 6% greater CO2 exchange rates (CER) and 9% higher light-adapted photosystem II (PSII) quantum efficiency than irrigated leaves during the morning. However, as water potential of the dryland plants became more depressed during the afternoon, the CER and light adapted PSII quantum efficiency of the dryland plants became inhibited and was 6 and 10% lower, respectively, than irrigated leaves. A 19% greater Chi content for the dryland leaves contributed to their higher CER during the morning. This polarity of photosynthesis throughout the day for the dryland plants relative to irrigated plants may explain some of the irrigation yield response inconsistencies in the southeastern USA. [ABSTRACT FROM AUTHOR]

Many different approaches have been used for the simulation of drought stress in pot studies. An ideal technique should (i) maintain uniform soil water content within the rooting zone, (ii) allow the rate at which stress develops to be precisely controlled, regardless of differences in plant size or variations in environmental conditions, (iii) permit a range of physiologically distinct stress levels to be imposed and maintained indefinitely, and (iv) provide a means of accurately quantifying the stress level. In the present study, a computer automated null-balance lysimeter was evaluated against these criteria. Separate experiments were conducted with soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) growing in 2.5-L pots. Single plant water use was quantified gravimetrically by frequent, automated recording of pot weights, and transpired water was replaced by a computer controlled watering system such that relative soil water content (RSWC) was maintained within a narrow range. In this way, pots were held at four RSWC levels ranging from 20 to 75%. Despite the frequent additions of small amounts of water at the tops of the pots, soil water distribution within the pots was found to be remarkably uniform, suggesting that bulk RSWC was a suitable indicator of the soil water deficit experienced by the roots. Measurements of whole plant water use indicated that the four RSWC levels represented four statistically distinct levels of water stress. It is concluded that null balance lysimetry is a useful approach to simulating drought stress in greenhouse experiments, with specific advantages over other available techniques. [ABSTRACT FROM AUTHOR]

Investigates the heat and drought responses of the wild wheat relative Aegilops geniculata Roth. Variation in leaf temperature; Chlorophyll content; Water-status related traits.

Examines if drought preconditioning and tolerance to heat stress affect osmotic adjustment and root growth in Kentucky bluegrass. Grass quality and relative water content of leaves; Osmotic adjustment; Solute accumulation.

Examines the role of nodule size in soybean in the fixation of nitrogen during droughts. Nodule gas exchange; Nodule water content; Carbon 14 labeling.

Examines drought-stress effects on branch and mainstem seed yield and yield components of determinate soybean. Comparison of the effects on branch vegetative and reproductive development with mainstem development; Determination of total seed yield of soybean; Importance of good branch vegetative growth in soybean cultivars; Effects of late planting of soybean.

Presents results of a quantitative trait locus analysis of drought tolerance in the soybean, Glycine max. Seasonal evapotranspiration rate; Season-specific water-use efficiency; Meteorological conditions; Effect of irrigation treatments on plant transpiration and growth; Genotype-water interaction.

Examines the impact of drought on pasture plants in the United States. Comparison of the conditions of perennial ryegrass, white clover and tall fescue following a drought; Analysis of carbohydrate and water contents of the plants.

Discusses the use of the water potential index (WPI) as a measure of the total water stress experienced by any crop in a given environment for a specific time interval. Derivation of the index; Usefulness of the WPI in evaluations of field-grown bread wheat and faba bean genotypes of contrasting characteristics.

Dicusses rooting characteristics and its contribution to drought avoidance in turfgrasses. How plants can avoid drought; Evaluation of interspecific differences in turfgrass rooting; Uses of soil water depletion; Methodology and results of the study.

Information about several papers discussed at the First International Workshop on Summer Dormancy in Grasses: Coping With Climate Change is presented. Topics include the perennial cool-season grass species, dormancy of grasses and the effects of human-inflicted droughts to the grasses. The symposium talks about plant traits, genetics and grass breedings.