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The effects of water deficit on growth, nodulation, and several physiological and biochemical processes in six symbiotic combinations involving three Moroccan alfalfa (Medicago sativaL.) populations (Tafilalet1, Adis-Tata and Demnate2), an American Moapa variety and two rhizobial strains (RhL9 and RhL10) were studied. The experiment was conducted under greenhouse conditions. Seedlings were separately inoculated with the suspension of two rhizobial strains and grown under two irrigation regimes: 80% of field capacity (optimal irrigation) and 40% of field capacity (water deficit). The water stress was applied for five weeks and the agro-physiological and biochemical parameters related to water deficit tolerance were assessed. The results showed that the water deficit had significantly reduced the height of the plants, the dry biomass and nodulation. This constraint also negatively affected the relative water content of leaves, the membrane permeability, the stomatal conductance, the maximum quantum yield of photosystem II, the time to reach maximum fluorescence, the total chlorophyll content and the total nitrogen content. Comparison among the tested symbiotic combinations showed that their behaviors were significantly different. Under drought, oasis populations Ad and Ta maintained high PS II efficiency, membrane stability, relative water content, chlorophyll and nitrogen content in comparison to the mountain one Dm2 and the American Moapa variety. These parameters were maintained at adequate levels in the plants inoculated with the rhizobial strain RhL9 that showed a tolerance to water deficit conditions. [ABSTRACT FROM AUTHOR]

Asexual fungusNeotyphodiumspp. are often associated with aboveground parts of different grasses. Perennial ryegrass (Lolium perenneL.), dominant cool-season grass species in New Zealand, is frequently infected by endophytic fungus (Neotyphodium lolli). To evaluate the growth, nutrient status, and avoidance to dehydration stress, clones of diploid perennial ryegrass either infected withNeotyphodium loliiAR29 endophyte (E+) or not infected (E−) were grown in a potted Andisol with intermittent wetting-drying cycles in a controlled growth chamber. Results showed that endophyte infection (E+) significantly reduced plant height, tiller number, shoot and root dry weights, and root volume with an associated increase in root/shoot ratios of ryegrass. The E+ plants showed a greater shoot and lower root avoidance to dehydration stress than the E− plants. The negative values of relative interaction intensity index between the diploid ryegrass and AR29 endophyte association suggested that these host-endophyte associations were parasitic under intermittent soil wetting-drying cycles. While the nitrogen (N) and phosphorus (P) concentration, plant production index, and water-use efficiency were significantly greater in E+ plant than in E− plants, the N and P efficiency ratios were greater in E− plants than in E+ plants. Results suggested that the endophyte mediation may have synergistic or antagonistic effects which depend on particular host genotype-endophyte combinations and environmental conditions to promote drought tolerance in grasses for degraded land restoration or forage production. [ABSTRACT FROM AUTHOR]

This study was carried out to develop an efficient in vitro-selection system for water stress tolerance in Argania spinosa (L.). Calli were induced from nodal explants on Murashige and Skoog medium containing half-strength salts, supplemented with 1.0 mg l-1 α-naphthaleneacetic acid and 1.0 mg l-1 2,4-dichlorophenoxyacetic acid. Increasing concentrations (0, 5, 10, 20, 30, 40, 50, 60, 70, or 80 g l-1) of polyethylene glycol 6000 (PEG 6000) were used to study the effect of simulated water stress on the survival ability of A. spinosa calli. There was a significant reduction in callus growth with increasing concentrations of PEG 6000. Selection for water stress tolerance was achieved by exposing 1-month-old calli to 37.5 g l-1 PEG 6000 (-0.019 MPa) for 3 months. The mechanism(s) of tolerance in the selected calli were studied biochemically. After 8 d of water stress, K+ and Na+ ion concentrations were unaffected in PEG 6000-selected clones (n = 6). The selected calli also showed a significant increase in H2O2 concentration with increased tolerance to water stress compared to non-PEG 6000-selected calli. The activities of several important anti-oxidant enzymes were measured. The results showed important variations between the PEG 6000-selected and non-selected calli. PEG 6000-selected calli show significant increases in the activities of three important anti-oxidant enzymes involved in oxygen metabolism (catalase, peroxidase, and polyphenol oxidase), while superoxide dismutase activity was unchanged. Insignificant increases in malondialdehyde concentration were recorded in the PEG 6000-selected lines compared to the non-PEG 6000-selected calli. The in vitro system described here may be used for in vitro screening for A. spinosa calli that are more tolerant to water stress. Further studies on the performance of plants regenerated from the PEG 6000-stress-selected calli remain to be undertaken to verify the genetic stability of the tolerance induced. [ABSTRACT FROM AUTHOR]

A greenhouse experiment (5 × 2 × 2 factorial arranged in randomized-complete-design with three replicates) was conducted to assess the combined effects of nickel (Ni) and drought stress on growth and yield parameters of canola (Brassica napusL. var. Talaye) grown on two calcareous soils of loamy and sandy clay textures. Treatments consisted of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni kg−1soil) and two levels of water status 100% and 60% field capacity (FC and 0.6FC, respectively). Growth parameters and yield components of plants decreased at drought-stress conditions. Almost all of the studied growth/yield parameters of canola grown on loamy soil were significantly more than those of the sandy clay soil, probably due to the increased capability of loamy soil for supplying the plant water/nutrient requirements. Nickel could positively affect some of the mean growth and yield parameters (e.g., grain yield) over both of the water status conditions. Nevertheless, some of the traits not only increased by Ni fertilization but also decreased compared to that of the control. The positive responses of canola was observed with higher amounts of applied Ni in the sandy clay soil than in loamy soil, e.g., the maximum grain yields of canola grown on loamy and sandy clay soils were obtained with applications of 0.5 and 1 mg Ni kg−1, respectively. Generally, results demonstrated that Ni could not mitigate the negative effects of drought stress on canola growth or yield components. [ABSTRACT FROM AUTHOR]

The study aimed at determining the root dynamics of cactus pear following a soil-water gradient and to characterize some root types of the speciesO. ficus-indica(L.) Miller (cultivar Morado–green cladode) andO. robustaWendl. (cultivar Monterey–blue cladode). One-year-old plants, planted in pots (210 mm diameter and 550 mm deep soil) and grown in the greenhouse at day/night temperatures of 25–30/15–18°C, were investigated. The water treatments applied were 0–25%, 25–50%, 50–75%, and 75–100% depletion of plant available soil water. The impact of water stress was quandtified in terms of root and cladode mass, root length, water-use efficiency (WUE: dry weight gain for roots and/or cladodes per unit water used–evapotranspiration), and water needed to fill up a cladode. Root mass decreased and root length increased significantly for both species with water stress. The root mass and length ofO. ficus-indicawere for all water treatments higher (p <0.05) than that ofO. robusta. By contrast, the root length/root mass ratio was higher4 forO. robustathanO. ficus-indica. Roots ofO. ficus-indicaandO. robusta, on average for all water treatments, comprised only 8.6% and 8.9% of the total plant biomass (dry weight), respectively. Root WUE decreased significantly (p <0.05) with water stress for both species. A water application of only 12 to 14 mm is needed to fill up the cladodes of the twoOpuntiaspecies with water stress. Given water shortages on arid lands and climate change, more development attention needs to be given toOpuntiaspecies. [ABSTRACT FROM PUBLISHER]

Nonstructural carbohydrate (NSC) accumulation in submergence tolerant rice cultivars (cv) was studied in six Indica rice [Oryza sativa (L.)] cv under control and simulated submerged conditions. Tolerant cultivars accumulated greater contents of NSC compared to the susceptible cultivars. Starch and total NSC content showed significant positive association with survival percentage. On the other hand, elongation due to submergence was significantly a negative association with survival. The CO2 photosynthetic rate, chlorophyll content, maximum photochemical efficiency of PS II (Fv/Fm), and activities of Rubisco were not significantly different between tolerant and susceptible cv under control condition. The ADP glucose pyrophosphorylase (AGPPase) activity was significantly higher in the tolerant cv and was a positive association with starch/NSC, whereas Fructose 1,6-diphosphatase (FDPase) activity was significantly higher in susceptible cv compared to tolerant cv and was a negative association with starch/NSC. Greater activities of AGPPase along with lower activities of FDPase might facilitate greater accumulation of NSC in tolerant rice cultivars. [ABSTRACT FROM AUTHOR]

A precise and accurate knowledge of the effects of plant water stress is crucial to framing strategies for improving agricultural productivity in regions of agricultural water (water required for agricultural and allied operations such as field preparation, seeding, irrigation, drainage, livestock production, and dairying) shortage. Success would depend upon the reliability, precision, and accuracy of the techniques used for creating water stress. This paper reports a simple, inexpensive, reproducible, and eco-friendly laboratory technique that essentially consists of a specially designed potometer for creating plant water stress. In this technique, the mode of step-by-step root-zone water stress development resembles in situ field water deficit, exhibiting parallel physiological responses to stress and, at the same time, it takes care of the anomalies, deficiencies, and difficulties generally inherent in other techniques of creating water stress at the whole-plant level. This new technique is superior to the other available ones being used by researchers working for enhancing crop productivity under deficit irrigation and dryland agriculture. [ABSTRACT FROM PUBLISHER]

This study aims at estimating trends in spring phenology from vegetation index and air temperature at 2 m height. To this end, we have developed a methodology to infer spring phenological dates from Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI) time-series, which are then extrapolated to the period 1948-2006 with the help of Reanalysis data, using its 2 m height air temperature parameter. First, yearly NDVI is fitted to a double-logistic function for the whole extent of the GIMMS database (1981-2003). This fitting procedure allows us to describe, on a yearly basis, the NDVI evolution for each pixel through the estimation of six parameters which include the spring date. Retrieved spring date time-series are then upscaled to Reanalysis database resolution and compared to degree-day amounts. Those degree-day amounts are estimated for various thresholds in order to determine the best thresholds for their calculations on a pixel-by-pixel basis. Once the correct thresholds are identified by correlation with corresponding GIMMS spring date time-series, spring dates are estimated for the whole extent of the Reanalysis database (1948-2006). Finally, Mann-Kendall trend tests are conducted on degree-day-retrieved spring date time-series and trends are estimated only for those pixels that show statistically significant trends. These trends in spring occurrence have an average value of -0.03 days per year, but range between -0.9 and +0.9 days per year, depending on the considered areas. Since the approach is based only on air temperature, retrieved spring dates for vegetation whose growth is limited by water are unreliable, as correlation analysis confirms. The obtained spring date trends show good coherence with previous studies and could be used for climate change impact studies, especially in polar and temperate areas, where the model is more reliable. [ABSTRACT FROM AUTHOR]

A fruit thinning strategy is introduced for 'Conference' pear to mitigate water stress and to maximise yield. Three irrigation and four thinning treatments were applied. The three irrigation treatments were: full irrigation (FI); deficit irrigation, receiving 50% of the water in FI (DI-50); and deficit irrigation receiving 20% of the water in FI (DI-20). The four fruit thinning treatments were: no thinning (NT); light thinning (LT), leaving more than 80% of the crop load; medium thinning (MT) leaving 50% of the crop load; and heavy thinning (HT) leaving 20% of the crop load. All thinning treatments were combined with DI-20, but only NT and MT were combined with FI and DI-50. Fruit thinning improved fruit size in FI and DI-50, but is not recommended because of the high labour cost and reduction in total fresh-market yield. For DI-20, thinning increased the midday stem water potential (Ψstem), improved yield (with LT), and increased fruit size (with HT). A three-dimensional regression model was developed to optimise fresh-market yield by fruit thinning, and showed the impact of Ψstem. Using the model, it was also possible to choose, for each value of Ψstem, a suitable crop load to maximise the fresh-market yield. [ABSTRACT FROM AUTHOR]

We describe the development of a water-use strategy for horticulture in England and Wales. Data were gathered from a literature review as well as from industry and grower surveys, and combined with information from interviews with key informants, in order to assess current practices and underlying trends in water-use within seven horticultural sectors. The spatial distribution of horticultural holdings relative to water availability and stress were mapped for both direct abstraction and mains water supplies. From this, a strategy was developed to define the key priorities at grower and industry levels, and the actions required, including research, communication, and knowledge transfer, to improve water-use efficiency and to reduce environmental water impacts. The key priorities identified included: improving our knowledge of the impacts of irrigation on diffuse pollution, including leaching of nitrate, phosphate, and pesticides; the need to improve grower understanding of water regulation; and quantifying the links between poor uniformity of irrigation, crop production, and profitability. [ABSTRACT FROM AUTHOR]

Maize production is affected by water and nitrogen (N) deficit either separately or joined, but this fact is not completely defined. The aim was to evaluate the fate of N in maize fertilized and subjected to water stress in controlled conditions. A greenhouse experiment was carried out at the University of Buenos Aires campus. The design was a 2 × 2 factorial with four replications. The factors were N: 70 and 140 kg N ha-1 as labeled urea (15N), and water: 100% or 50% of the potential evapotranspiration. The harvest of aerial and root biomass was carried out at R1 stage. Nitrogen in plants, soils nitrate, ammonia volatilization, and 15N percentage were determined. Obtained results only partially agree with previous research. Water stress depressed aerial biomass production independently of N doses. When water was limiting, the uptake of N from fertilizer was independent of N. When water was not limiting, N uptake increased with the higher N doses. Volatilization losses were 3.7 to 7.8% of N applied as fertilizer. Plant N recovers was around 45% of the N applied, except in treatment water stressed with high N rate (19%). Nitrate-N from the fertilizer in the soil at harvest and accumulated N from the fertilizer in plant were lineally related (r2 = 0.54; p < 0.001). Important destinations of N were accumulation in plant, volatilization and incorporation into soil organic matter. However, residual nitrate was a main fate in heavily fertilized and water deficit treatment. This process could lead to the eventual nitrate leaching. [ABSTRACT FROM AUTHOR]

Response of plant growth and essential oil yield of rose-scented geranium (Pelargonium capitatum x P. radens 'Rose') to withholding irrigation at different times of regrowth cycles was investigated at Hatfield Experimental Farm of the university of Pretoria, South Africa, from 2004 to 2007. No-stress (control), and 1-month withholding irrigation periods during the 2nd, 3rd, or 4th month of regrowth were applied as treatments. Herbage yield showed a significant reduction when the water stress period was imposed during the 3rd or 4th month of regrowth. A remarkable essential oil yield loss was observed only when the plants were stressed during the 4th month of regrowth. Essential oil content (% oil on fresh herbage mass basis) apparently increased in the stressed treatments, but total oil yield dropped as a result of lower herbage mass. Essential oil composition changes in response to irrigation withholding treatments were not consistent. Water-use efficiency was not significantly affected by withholding irrigation in the 2nd or 3rd month of regrowth. With a marginal oil yield loss, c. 330-460 m³ of water/ha per regrowth cycle could be saved by withholding irrigation during the 3rd month of the regrowth cycles. The overall results highlighted that, in water scarce regions, withholding irrigation during either the 2nd or 3rd month of regrowth could improve water productivity in rose-scented geranium. [ABSTRACT FROM AUTHOR]

Sticky fleabane, Inula viscosa , a wild perennial Asteracea widespread in the Mediterranean area, is characterized by high tolerance to water deficiency. In this study, plants of I. viscosa obtained from seedlings were grown in a controlled environment and irrigated from transplanting to flowering with salinized water at seven different NaCl concentrations (ECi = 0.5 to 52.1 dS m -1 ), in order to evaluate the salinity tolerance and the ion content (Na, Cl, N, P, K, Ca and Mg, as mg kg -1 of dry weight) within plant tissues (roots, basal stems, medium stems, apical stems, lateral shoots, basal and apical leaves). Data obtained showed for I. viscosa a marked tolerance to salt stress. A K/Na concentration ratio of 0.1 was in the tissues of the basal leaves, suggesting a mechanism of Na exclusion from the younger leaves and the apical stems. The results in the first growing year indicate that I. viscosa can grow and flower in saline conditions up to ECi = 52.1 dS m -1 , even if it shows a marked reduction of fresh and dry weight; although Inula viscosa cannot be defined an halophyte plant as Inula crithmoides , it can be considered suitable for programs of desertification control, considering its high fresh biomass production also in high salinity conditions. [ABSTRACT FROM AUTHOR]

Chlorophyll fluorescence was used to study the effect of a hardening treatment on aspects of desiccation tolerance in the moss Atrichum androgynum. Mosses were hardened by reducing the relative water content of apical stem segments to 0.5 for 3 days, followed by storing the material fully hydrated for 1 day. Desiccation tolerance was assessed by storing plants over silica gel for 16 h, and then monitoring the recovery of photosystem II during rehydration. Hardening decreased the efficiency of photosystem II before desiccation, particularly at saturating light intensities. During rehydration, photosystem II activity recovered faster in hardened plants. Hardening also considerably increased non-photochemical quenching during the first few hours of rehydration. Previous data had shown that photophosphorylation, but not carbon fixation, is starting at this time, suggesting that the moss needs strong protection from excess light. Increased non-photochemical quenching was the result of greater thylacoidal-based or fast-relaxing quenching (qE), rather than reaction centre-based or slow-relaxing quenching (qI). Slow-relaxing quenching was similar in hardened and non-hardened mosses, and was only important during the early stages of rehydration when the need for photoprotection was greatest. In A. androgynum hardening apparently shifts the photosynthetic apparatus from a 'high efficiency' state to a less efficient but 'photoprotected' state. [ABSTRACT FROM AUTHOR]

Gametophytes from six populations of the moss Philonotis fontana (Hedw.) Brid. were grown under two lightand two water regimes in order to assess the effects of these environmental factors on gametophytic architecture and leaf and leaf-cell dimensions. Both light and water affected growth, but the light treatments had a greater effect, and on more characters, than did the water treatments. Significant population effects under common garden conditions point to genetic variation for several traits, and population × environmental treatment interactions demonstrated genetic variation for patterns of phenotypic plasticity, i.e. plants differed in their 'norms of reaction'. Variation among populations in leaf dimensions tended to have a strong genetic component (20–30% of the total variation), whereas cell dimensions showed relatively little genetic variation (<10% of the total). [ABSTRACT FROM AUTHOR]

The experiment was conducted using uniform 9 year-old plants of ber (Ziziphus mauritiana L.) 'Mundia' on loamy sand soil at the Horticultural Research Farm, Asalpur, Jobner, (Jaipur-Rajasthan), India. The experiment continued for 2 years from June to March 1995-96 and 1996-97. The experiment consisted of 24 treatment combinations of three water regimes, four mulches and two kaolin treatments. A split-plot design used the irrigation treatments on the main plots, with sub-plots of mulch and kaolin treatments, with four replications having two trees per unit. Increasing levels of water significantly increased growth and productivity. Among various mulches, black polythene (M1) resulted in maximum growth and productivity. In contrast, kaolin improved only the productivity. The treatment combination of I2 (15 cm depth of irrigation) + M1 (black polythene) + K1 (6% kaolin spray) gave the highest fruit yield (13.1 t ha-1). [ABSTRACT FROM AUTHOR]

Pot experiments with split-root plants and two years of field experiments with manipulation of soil water content have shown that partial rootzone drying (PRD) does not affect yield in raspberries, Rubus idaeus L. ’Glen Ample’ and ’Glen Prosen’. In some cases PRD can reduce stomatal conductance, thus reducing water loss. This results in a higher water use efficiency. Partial rootzone drying may be an efficient irrigation strategy where raspberries are produced under shelter. [ABSTRACT FROM AUTHOR]

Many vegetable production regions in the southwestern US are strictly regulated on water use. In addition, demand for high quality and nutritious vegetables has increased. This study was performed to explore the effects of deficit irrigation on yield, fruit quality, lycopene content, vitamin C and sugar composition of red-fleshed diploid and triploid watermelon (Citrullus lanatus (Thunb) Matsum & Nakai) cultivars. Irrigation treatments were 1.0, 0.75 and 0.5 evapotranspiration (ET) rates. Cultivars used were ’Summer Flavor 710’, ’RWM 8036’, ’Allsweet’, ’Sugarlee’, and ’SWD 7302’ (diploids) and ’Summer Sweet 5244’, ’SWT 8706’, ’Sugar Time’, and ’Tri X Sunrise’ (triploids). Total water applied through a subsurface drip system was 395, 298 and 173 mm, for the 1.0, 0.75 and 0.50 ET rates, respectively. Total yields were highest at 1.0 ET (53.9 t ha-1) compared with 0.5 ET (26.8 t ha-1). Triploids had a 34% higher total yield and fewer culls (2%) compared with diploid cultivars (25%). Highest yields were obtained for ’Tri X Sunrise’, ’SWT 8706’, and ’SWD 7302’. ’Sugar Time’ had the highest soluble solids content (13.4%) of all cultivars (range 9.7–11.0%). Triploid cultivars had firmer flesh compared to diploids (12.0 v 9.9. N). Lycopene content increased slightly with maturity (55.8 to 60.2 µg g fw), and was significantly higher at 0.75 ET and 1.0 ET. Lycopene content averaged over all treatments was 60–66 µg g-1 fw for triploids and 45 to 80 µg g-1 fw for diploid fruits. Overall, lycopene and vitamin C content did not decrease with deficit irrigation at 0.75 ET. There was genetic variability for lycopene, vitamin C, and sugar composition, primarily fructose, among diploids and triploids. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the effect of partial rootzone drying (PRD) in comparison to conventional irrigation (CI) at both 0.8 and 0.4 crop evapotranspiration (ETc) on water relations, vegetative growth, yield, and fruit composition of mature Sauvignon blanc grapevines (Vitis vinifera L.) in the San Joaquin Valley of California, USA. Soil moisture decreased quickly on the dry side and was restored quickly on the wet side of PRD-treated vines after switching. There was no yield reduction while vegetative growth was reduced at 0.4 ETc. However, in contrast to published studies assuming and emphasizing the role of PRD, this study demonstrated that only an irrigation amount of 0.4 ETc reduced stomatal conductance, transpiration, pruning weight, number of lateral shoots, number of active growing points, and fruit titratable acidity (TA). It appears that the irrigation amount, not PRD, is the determining factor inducing water stress and reducing transpiration and vegetative growth. With vine water relations only occasionally affected and no improvement in vine performance and vine water use at the same irrigation amount, PRD is not recommended for winegrape production with Sauvignon blanc under similar climatic conditions and cultural practices as in this study. Commercial implementation of PRD as described in previous studies should not be recommended until PRD is proven advantageous over CI at the same irrigation amount. [ABSTRACT FROM AUTHOR]

Tree development, yield and quality characteristics of fresh fruit and oil were evaluated under different water regimes for five years. The olive cultivars Ascolana Tenera, Kalamata, Nocellara del Belice, Maiatica and Itrana were tested in a factorial combination of four irrigation regimes: a rainfed control (To) and three treatments (T1, T2, and T3) irrigated daily with a restitution of 33, 66, and 66% of crop evapotranspiration (ETc). In all years the lowest values of soil water content and xylem potential were detected in September and early October in To, during the phenological phase of rapid enlargement of fruit cells, while values were near field capacity during the irrigation season in treatment T3. Growth parameters such as canopy, trunk cross section area and pruned wood showed little differences between the rain-fed control and the lowest irrigation level and between treatment T2 and T3 while differences were evident between the control and treatment T2. Yield, fruit size, pulp-stone ratio and dry-matter content of fruit peaked at an irrigation depth of 66% of ETc, while higher volumes did not significantly increase yield, suggesting that complete replacement of water loss by the crop is not recommended. Only ’Kalamata’ showed a higher yield of T3 over T2. Irrigation regimes did not affect the oil content calculated on dry-weight basis and the increase in oil per hectare was explained according to the increase in fruit dry matter content and number of fruit for ’Kalamata’. The fatty acid composition, sugar and acid content of the oil were not affected by irrigation, while the total polyphenol decreased up to treatment T2. In the most irrigated treatment bitterness and pungency of the oil slightly decreased as compared with the rainfed control, while fruiting was unaffected by irrigation. [ABSTRACT FROM AUTHOR]

Evaluates the growth, yield and quality of shallot under three levels of irrigation and nitrogen fertilization, on a clay soil in the sub-humid tropical climate of eastern Ethiopia from 1999 to 2002. Bulb yield and mean bulb weight; Highest total weight and rotting losses of bulbs; Increase in the mean bulb weight with nitrogen.

Considers the effect of irrigation and air humidity on the water relations and root and shoot growth of Rhamnus alaternus L. during the nursery phase. Evaluation of the resulting degree of hardening; Reduction of all shoot growth parameters with low air humidity and water deficit.