Moderate Water Deficit Research Articles

Exogenous ABA Induces Osmotic Adjustment, Improves Leaf Water Relations and Water Use Efficiency, But Not Yield in Soybean under Water Stress

Abscisic acid (ABA) plays a central role in the plant response to water deficit by inducing stomatal closure to conserve water when the soil dries. Exogenous ABA was applied at 45 days after sowing (DAS) as a soil drench, the physiological and seed yield response of soybean to exogenous ABA were examined as the soil was drying. Three experiments were conducted using the drought-tolerant soybean cultivar Jindou 19, grown in pots at the Yuzhong Experimental Station of Lanzhou University, China. In experiment 1, plants were exposed to progressive soil drying and leaf ABA concentration, leaf photosynthesis rate, leaf relative water content (RWC) and osmotic adjustment (OA) were measured. In experiment 2, plants were under progressive soil drying and lethal leaf water potential was measured. In experiment 3, flower production and abortion, and grain yield were measured in plants under well-watered (WW), moderate (MWD) and severe water deficits (SWD). Exogenous ABA application increased ABA accumulation in leaves and reduced the rate of soil drying. It also increased leaf photosynthetic rate, stomatal conductance and transpiration rate at 7–10 days after withholding water. The intrinsic and instantaneous water use efficiency (WUE) was consistently higher with exogenous ABA than without ABA as the soil dried. Exogenous ABA increased OA when the leaf relative water content (RWC) decreased at eight days after withholding water, lowering the lethal leaf water potential by 0.4 MPa. Exogenous ABA reduced water use, increased WUE for grain yield under WW and MWD, and had no effect on flower number, flower abortion or grain yield in any water treatment. We concluded that (1) exogenous ABA induced OA, improved leaf photosynthetic rate, leaf water relations and desiccant tolerance, but did not benefit grain yield in soybean under water deficits; (2) exogenous ABA improved the WUE at the leaf level as soil drying and WUE for grain yield under moderate water deficit.

Use of Reflectance Indices to Assess Vine Water Status under Mild to Moderate Water Deficits

The monitoring of vine water status is of interest for irrigation management in order to improve water use while optimizing both berry yield and quality. Remote-sensing techniques might provide accurate, rapid, and non-destructive estimates of vine water status. The objective of this study was to test the capability of the reflectance-based water index (WI) and the photochemical reflectance index (PRI) to characterize Vitis vinifera L. cv. Xarel·lo water status under mild to moderate water deficits. The study was conducted at the leaf level in irrigated potted plants and at the plant level on five commercial rain-fed vineyards in 2009 and 2010. In potted plants, the reflectance indices PRI and WI closely tracked variation in the leaf-to-air temperature difference (ΔT) with r2 = 0.81 and r2 = 0.83, for WI and PRI, respectively (p < 0.01). In addition, in potted plants, both PRI and WI showed significant relationships with light-use efficiency (LUE)—calculated as the ratio between net CO2 assimilation rate (An) and incident photosynthetic active radiation (PAR) at the leaf surface—with r2 = 0.92 and r2 = 0.74 for PRI and WI, respectively. At the canopy level, vine predawn water potential (Ψpd) was related to the canopy-to-air temperature difference (ΔTm) across years (r2 = 0.37, p < 0.05). In the years of study, the relationships between PRI and WI showed variable degrees of correlation against Ψpd and ΔTm. Across years, PRI and WI showed significant relationships with Ψpd, with r2 = 0.41 and r2 = 0.37 (p < 0.01), for WI and PRI, respectively. Indices formulated to account for variation in canopy structure (i.e., PRInorm and WInorm) showed similar degrees of correlation against Ψpd to their original formulations. In addition, PRI and WI were capable of differentiating (p < 0.01) between mild (Ψpd > −0.4 MPa) and moderate (Ψpd < −0.4 MPa) water deficits, and a similar response was observed when PRInorm and WInorm—formulated to account for variation in canopy structure—were considered. Thus, at the leaf level, our result suggest that WI and PRI can be used to adequately predict the diurnal dynamics of stomatal aperture and transpiration. In addition, at the canopy level, PRI and WI effectively differentiated vines under mild water deficits from those experiencing moderate water deficits. Thus, our results show the capability of WI and PRI in characterizing vine water status under mild to moderate water deficits.

Effect of Water Stress on Photosynthesis, Chlorophyll Fluorescence Parameters and Water Use Efficiency of Common Reed in the Hexi Corridor

Water stress is the major environmental stress that affect agricultural production worldwide, especially in arid and semi-arid regions. This research investigated the effect of water stress on common reed (Phragmites australis (Cav.) Trin. ex Steud.) grown in the West Lake Wetland of Zhangye City, China. We designed with four water treatments (100, 95, 85 and 75% of water field capacity, i.e. CK (100%), mild (95%), moderate (85%) and severe (75%) water deficit regimes). The effect of water stress on photosynthesis and chlorophyll fluorescence parameters was investigated. There was a midday depression in net photosynthetic rate (Pn) for CK, mild and moderate drought, but not for severe drought. Stomatal limitation was dominant for mild treatment. But under severe drought stomatal limitation to photosynthesis was dominating in the morning and nonstomatal limitation was dominating in the afternoon. Compared with CK treatment, Pn, stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate (E) and water use efficiency (WUE) were always lower at drought stress. This result suggests that water stress caused the photosynthesis of common reed to be completely blocked and the common reed was a drought-sensitive plant. We found 75% is the moisture threshold for common reed. The decrease in Fm, Fv, Fv/Fm and increase F0 suggested that Rubisco activity reduced and PSII partially inactivated during the day under drought. However, part of this inactivation of PSII might be alleviated under mild or moderate drought, but severe drought cannot. Drought stress also affected the photosynthesis Pn-PAR response curve. Drought stress increased LCP, RD and decreased LSP, Pmax and AQY. This indicates that when common reed suffers from drought, the utilization range of light intensity become narrowed and photosynthetic ability or adaptability to light reduced.

Response of fruit yield, fruit quality, and water use efficiency to water deficits for apple trees under surge-root irrigation in the Loess Plateau of China

This study investigated the response of the fruit quality, fruit yield, and water use efficiency (WUE) to regulated deficit irrigation (RDI) during the different growth stages of apple trees (Malus pumila Mill) in the Loess Plateau of northern China. Different water deficit treatments were applied in 2016 and 2017 on a field planted with 5-year-old apple trees. The treatments included low (L), moderate (M), and severe (S) water deficit treatments during the bud burst to leafing (I), flowering to fruit set (II), and fruit growth (III) stages. Compared with full irrigation (FI), water deficit treatment during the different growth stages had significant effects on the fruit quality, fruit yield, and WUE of the apple trees. The L and M water deficit treatments during stage III significantly reduced the apple yield by 10.89% and 13.46% in 2016 and 3.66% and 10.10% in 2017, respectively. A water deficit during stage III decreased the single fruit weight, excellent-fruit percentage, and fruit water content by 2.79%–11.31%, 15.24%–20.36%, and 4.26%–10.07%, respectively, and increased fruit firmness, soluble solid content, and soluble reducing sugar content by 12.70%–21.31%, 13.83%–33.60%, and 10.13%–21.48%, respectively. The L and M water deficit treatments applied during stage I resulted in apple quality and yield that were similar to those resulting from the FI treatment, but the WUE was significantly higher in the L and M water deficit treatments than in the FI treatment. The optimal period for water deficit treatment is stage II, during which the highest yield and WUE were found. The L and M treatments during stage II increased the fruit yield by 13.93% and 13.28% in 2016 and 17.94% and 17.13% in 2017, respectively. The WUE of the apple trees was higher with the I I-L and I I-M treatments (greater than 7 kg m−3) than with other treatments. In addition, water deficit treatment during stage II caused a slight increase in fruit firmness and a slight decrease in fruit water content, which produces apples suitable for storage. Single fruit weight, excellent-fruit percentage, and soluble solid and soluble reducing sugar content were significantly improved, making the apples sweeter; thus, a water deficit during stage II had a significant positive effect on apple quality, with the I I-M treatment being optimal and the II-L treatment being second best. The optimal water deficit treatment of the II-M treatment enhances the fruit quality, yield, and WUE of apple trees in water-scarce environments.

Abscisic Acid Coordinates Dose-Dependent Developmental and Hydraulic Responses of Roots to Water Deficit.

Root water uptake is influenced by root system architecture, which is determined by root growth and branching and the hydraulics of root cells and tissues. The phytohormone abscisic acid (ABA) plays a major role in the adaptation of plants to water deficit (WD). Here we addressed at the whole-root level in Arabidopsis (Arabidopsis thaliana) the regulatory role of ABA in mechanisms that determine root hydraulic architecture. Root system architecture and root hydraulic conductivity (Lpr) were analyzed in hydroponically grown plants subjected to varying degrees of WD induced by various polyethylene glycol (PEG) concentrations. The majority of root traits investigated, including first- and second-order lateral root production and elongation and whole-root hydraulics, had a bell-shaped dependency on WD, displaying stimulation under mild WD conditions (25 g PEG L-1) and repression under more severe conditions. These traits also showed a bell-shaped dependency on exogenous ABA, and their regulation by WD was attenuated in genotypes altered in ABA biosynthesis and response. Thus, we propose that ABA acts as a coordinator and an integrator of most root responses to mild and moderate WD, whereas responses to strong WD (150 g PEG L-1) are largely ABA independent. We also found that roots exhibit different growth responses to both WD and ABA depending on their rank and age. Taken together, our results give further insights into the coordinated water acquisition strategies of roots deployed in relation to WD intensity.

Adaptation of photosynthesis to water deficit in the reproductive phaseof a maize (Zea mays L.) inbred line

Photosynthesis is sensitive to water deficit (WD) stress. Maize (Zea mays L.) yield is vulnerable to water stress, especially if it occurs during the reproductive stage. In this study, the expression patterns of photosynthesis-related genes, together with photosynthetic gas-exchange and fluorescence parameters were investigated in a maize inbred line exposed to 50% of field water capacity (moderate WD) for 15 d after tassel emergence. The results demonstrated that WD down-regulated expression of psbA, psbB, psbC, psbP, psaA, psaB, and cab, especially at later periods of WD stress. Besides, with the increased WD stress, the steady decline in the value of photosynthesis performance index, maximum quantum yield of primary photochemistry, quantum yield for electron transport, quantum yield for the reduction of end acceptors of PSI per photon absorbed, and the efficiency of an electron beyond QA- that reduced PSI acceptors, and a clear increase in the J-step and I-step, K-band as well as L-band were observed. The results suggested that WD might restrict light-harvesting and electron transport. Interestingly, leaf transcript levels of rbcL and rbcS were up-regulated at the later stage of water stress in maize inbred line, which helped repair injury to PSII centers and maintain PSII activity (increased quantum yield of dissipation and effective antenna size of an active reaction center) under 15-d lasting WD.

UV Light Acclimation Capacity of Leaf Photosynthetic and Photochemical Behaviour in Near-isohydric and Anisohydric Grapevines in Hot and Dry Environments

The photosynthetic and photochemical adaptation of grapevine leaves to high UV radiation, under hot and dry summer conditions, was investigated in near-isohydric Cannonau (syn. Grenache) and nearanisohydric Bovale grande (syn. Carignan). From pea-size stage until harvest, vines with mild to moderate water deficit were subjected to UV-blocking treatment (–UV) and compared to a control exposed to sunlight (C). Canopy light and thermal microclimate, growth and density, maximum leaf gas exchange, primary photochemistry (PSII) and phenols were monitored. Average increments in canopy temperature under –UV tunnels during day-time and night-time were 3.3°C and 0.8°C in Bovale grande and 2.6°C and 1.1°C in Cannonau. Cultivars reached similar leaf area, intrinsic water-use efficiency and stem water potential under C and –UV. Cannonau showed lower stomatal conductance, maximum net assimilation and transpiration rates, but also faster recovery of PSII under heat and moderate water stress. UV radiation induced a stronger and longer impact on leaf assimilation, but the duration of elevated temperatures under −UV induced higher photoinhibition and lower photochemical efficiency. A similar degree of correlation between leaf temperature and gas exchange was found among cultivars and treatments. In Cannonau, leaf anthocyanin decreased due to heat-induced long-lasting PSII photoinactivation under C. Conversely, Bovale grande showed higher phenolic content stability, thus higher photoprotection and recovery of PSII functional units. Agronomical practices affecting leaf phenolic accumulation influence canopy acclimation to heat and high sunlight. Vineyard management must avoid excessive canopy sun exposure and duration of elevated temperatures to favour high assimilation, while reducing photoinactivation and heat damage.

Variability among Young Table Grape Cultivars in Response to Water Deficit and Water Use Efficiency

Climate change will lead to higher frequencies and durations of water limitations during the growing season, which may affect table grape yield. The aim of this experiment was to determine the variability among 3-year old table grape cultivars under the influence of prolonged water deficit during fruit development on gas exchange, growth, and water use efficiency. Six own rooted, potted table grape cultivars (cv. ‘Muscat Bleu’, ‘Fanny’, ‘Nero’, ‘Palatina’, ‘Crimson Seedless’ and ‘Thompson Seedless’) were subjected to three water deficit treatments (Control treatment with daily irrigation to 75% of available water capacity (AWC), moderate (50% AWC), and severe water deficit treatment (25% AWC)) for three consecutive years during vegetative growth/fruit development. Water deficit reduced assimilation, stomatal conductance, and transpiration, and increased water use efficiencies (WUE) with severity of water limitation. While leaf area and number of leaves were not affected by treatments in any of the tested cultivars, the response of specific leaf area to water deficit depended on the cultivar. Plant dry mass decreased with increasing water limitation. Overall, high variability of cultivars to gas exchange and water use efficiencies in response to water limitation was observed. ’Palatina’ was the cultivar having a high productivity (high net assimilation) and low water use (low stomatal conductance) and the cultivar ‘Fanny’ was characterized by the highest amount of total annual dry mass as well as the highest total dry mass production per water supplied during the experiment (WUEDM). Hence, ‘Fanny’ and ‘Palatina’ have shown to be cultivars able to cope with water limiting conditions and should be extensively tested in further studies.

Growth and nutrition of cowpea (Vigna unguiculata) under water deficit as influenced by microbial inoculation via seed coating

AbstractDrought can drastically reduce cowpea [Vigna unguiculata (L.) Walp.] biomass and grain yield. The application of plant growth‐promoting rhizobacteria and arbuscular mycorrhizal fungi can confer resistance to plants and reduce the effects of environmental stresses, including drought. Seed coating is a technique which allows the application of minor amounts of microbial inocula. Main effects of the factors inoculation and water regime showed that: severe or moderate water deficit had a general negative impact on cowpea plants; total biomass production, seed weight and seed yield were enhanced in plants inoculated with P. putida; inoculation of R. irregularis significantly increased nitrogen (N) and phosphorus (P) shoot concentrations; and R. irregularis enhanced both chlorophyll b and carotenoids contents, particularly under severe water deficit. Plants inoculated with P. putida + R. irregularis had an increase in shoot P concentration of 85% and 57%, under moderate and severe water deficit, respectively. Singly inoculated P. putida improved potassium shoot concentration by 25% under moderate water deficit. Overall, in terms of agricultural productivity the inoculation of P. putida under water deficit might be promising. Seed coating has the potential to be used as a large‐scale delivery system of beneficial microbial inoculants.

Regulated Deficit Irrigation at Special Development Stages Increases Sugar Beet Yield

Core Ideas Different growth stages of drip‐irrigated sugar beet can bear different water deficit level. The canopy development stage is the most water‐sensitive period of the sugar beet. Regulated deficit irrigation could increase beet yield and reduce the consumption of water resources in arid land. ABSTRACTThe shortage of water resources promotes the development of water saving irrigation in arid land. Regulated deficit irrigation (RDI), as one of the water‐saving irrigation technologies through applying a certain amount of water stress to the crops to promote the distribution of the photosynthate of crops to the needs of the tissues and organs, can save water and may increase yield. Our study evaluated the effect of the RDI on the sugar beet (Beta vulgaris L. cv. Beta356). Seven irrigation treatments were applied based on the growth stages of sugar beet (canopy development, storage root development, and sugar accumulation) and water deficit levels (30, 50, and 70% of field capacity [FC]). The yield, quality, sugar yield, irrigation water use efficiency (IWUE), and agronomic physiological traits of sugar beet were evaluated. Moderate water deficit (50% of FC) during canopy development increased sugar yield by 27% compared with the control (70% of FC during the whole growth stages). Severe (30% of FC) water deficit increased sugar yield by 45% during storage root development, and by 55% during sugar accumulation. The RDI during canopy development and storage root development inhibited leaf growth but did not affect yield. Malondialdehyde content and relative conductivity increased significantly when soil water content dropped to the irrigation threshold levels (i.e., 30% and 50% of FC) before rehydration during canopy development. After rehydration, there were significant increases in peroxidase activity and proline content (indicators of antioxidant defense and osmotic stress). Our results indicated that RDI increased yield at 30% and 50% of FC during three growth stages (canopy development, storage root development, and sugar accumulation) of sugar beet, which reduced irrigation water requirements. RDI could be applied as a strategic action for crop sustainability and water saving in arid land.

The effect of strobilurin on ethylene production in flowers, yield and quality parameters of processing tomato grown under a moderate water stress condition in Mediterranean area

This research was conducted in Southern Italy over two growing seasons to evaluate the effect of strobilurin application on the ethylene production of flowers (EF) and on the yield and quality parameters of processing tomato grown under moderate water deficit conditions. The following two irrigation regimes were applied: IR100, full irrigation that restores 100% of the maximum crop evapotranspiration (ETc) and IR75, which is 75% of the amount of water of IR100. Furthermore, from the beginning of flowering two fungicide treatments were applied three times: fungicide treatment without strobilurin (ST0) and strobilurin fungicide with an azoxystrobin based product (STaz). At full flowering, ethylene production in the flowers (EF) was determined. At harvest, the main yield and qualitative parameters were evaluated. The strobilurin treatment caused a significant decrease of EF, which was less evident in the first warmer year than in the second. This result was presumably because of the interference of high temperatures on the inhibition of ethylene synthesis described for the strobilurin. In contrast, the decrease of EF due to strobilurin treatment was more evident under IR75 than under IR100. Finally, the decrease in the number of marketable fruits with respect to the EF increase was lower under strobilurin treatment presumably because of the protective effect of this molecule on the flower drop. Further studies are needed to investigate this hypothesis in greater detail.

Drought priming during the vegetative stage can enhance post-anthesis drought tolerance by improving photosynthetic capacity in winter wheat

Drought stress during the reproductive period of cereal crops leads to significant yield reductions, therefore, exploring effective methods to improve tolerance to post-anthesis drought is necessary. Pot experiment was carried out to investigate the effects of pre-drought priming on physiological characteristics and grain yield with drought stress at post-anthesis. Moderate water deficits (60–65% of the field capacity) were imposed to prime wheat plants during either the tillering or jointing stages, while severe drought stress (40–45% of the field capacity) was applied during the grain filling stage. The priming treatments significantly improved grain yield resulting in higher biomass. Compared to the control, the grain yield and biomass of the non-priming, tillering priming, and jointing priming treatments were reduced by 15.7, 9.1, and 9.3% and by 11.1, 6.1, and 10.5%, respectively. The primed plants exhibited higher adaptability to subsequent severe drought stress during grain filling, showing higher photosynthetic capacities and light use efficiencies with higher leaf water potentials, soluble protein contents, and Rubisco contents and enhanced enzymatic antioxidant systems. The tillering stage is more responsive to drought priming based on the observed grain yield. These results indicate that moderate drought during the vegetative period is conducive to the development of water-saving agriculture to cope drought stress during grain-filling in wheat.

Does the Introgression of Bt Gene Affect Physiological Cotton Response to Water Deficit?

ABSTRACT: Water deficit may affect the expression of lepidoptera-controlling proteins in cotton. However, it is unknown if there is a differential response of conventional and Bt cotton cultivars to water deficit, what could potentially affect the plant competition with weeds. The objective of this work was to investigate the response of Bt cotton cultivars to water deficit compared with their conventional near-isolines. The experiment was conducted in a greenhouse, where the cotton cultivars FMT 705, FMT 709 and IMACD 8276, with and without the Bt gene, were grown under two water regimens: 100% and 50% (moderate water deficit) of available soil water. Cotton phenology was severely affected by moderate water deficit, with a reduction in shoot and root dry matter production, root length and diameter, plant height and leaf area. No effect of the Bt gene was observed. Water deficit during cotton flowering decrease stomatal conductance, net assimilation of CO2 and transpiration rates. The leaf water potential is lower in plants exposed to a moderate water deficit compared with non-stressed plants. However, the introgression of the Bt gene does not modify cotton physiological and phenotypic response to water deficit.

Effects of exogenous application of salicylic acid on drought performance of medicinal plant, Fritillaria przewalskii Maxim

This study investigated the effects of salicylic acid (SA) foliar application on Fritillariaprzewalskii under drought stress condition. Plants were subjected to three irrigation regimes, 75-80% control (CK), 60-65% medium stress (M) and 40-45% severe stress (S) of the field capacity and three levels of SA, 0.0, 0.5 and 1.0 mM. Relative water content (RWC), proline content, total soluble carbohydrates, chlorophyll “a” (Chl a), chlorophyll “b” (Chl b), chlorophyll “a + b” (Chl a + b), carotenoids contents, malondialdehyde (MDA) contents and activities of several antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR) and ascorbate peroxidase (APX) activity were measured. RWC, soluble carbohydrates, Chl b, Chl a + b, MDA content and activities of antioxidant enzymes (SOD, POD, CAT, GR and APX) were significantly affected by water deprivation without SA. Exogenous SA significantly increased the content of RWC, total leaf soluble carbohydrates, leaf proline and Chl b at moderate water deficit and severe water deficit. MDA content was decreased significantly by exogenous SA. The activities of antioxidant enzymes (SOD, POD, CAT, GR and APX) were also significantly affected by exogenous SA. However, the content of Chl a, Chl a + b, and carotenoids were not significantly affected by exogenous SA.

CHLORIMURON-ETHYL IN CONVENTIONAL AND TRANSGENIC SOYBEAN CULTIVARS UNDER WATER DEFICIT STRESS

ABSTRACT Water deficit is a limiting factor for the soybean yield; it triggers different physiological and anatomical adaptations that have deleterious effects on the plants and can affect the selectivity of herbicides, causing production losses. In this context, the objective of this work was to evaluate the action of the chlorimuron-ethyl herbicide when applied at different stages of soybean plants, using conventional and transgenic cultivars, and different soil water potentials. A rate of 20 g ha-1 of the chlorimuron-ethyl herbicide was applied to two soybean cultivars (MG/BR46-Conquista - conventional, and BRS-Valiosa-RR - transgenic) at two phenological stages (V2 - first fully expanded trifoliate leaves, and V4 - third fully expanded trifoliate leaves), using three soil water potentials (-0.03 MPa, -0.07 MPa, and -0.5 MPa). Phytotoxicity, and plant height were evaluated at 3, 7, 14, and 21 days after the herbicide application. The shoot dry weight, root dry weight, and root system nodulation were evaluated. The soybean plants had lower phytotoxicity when subjected to application of chlorimuron-ethyl under water deficit conditions. The use of chlorimuron-ethyl reduced the growth and biomass of soybean plants and affected the plants' root system nodulation. The transgenic cultivar (BRS-Valiosa-RR) presented better performance when subjected to a moderate water deficit (-0.07 MPa), which contributes to biological nitrogen fixation.

Arbuscular mycorrhizae alleviate water deficit stress and improve antioxidant response, more than nitrogen fixing bacteria or chemical fertilizer in the evening primrose

We treated the evening primrose grown under moderate or severe water deficit with an arbuscular mycorrhizal fungus (Glomus mosseae), and nitrogen fixing bacteria (Azospirillum lipoferum), or with a chemical fertilizer (urea + triple superphosphate). The experiment was conducted at an arid and a semi-arid experimental station with plants grown in the field, after greenhouse propagation. Experiments were conducted in a split factorial layout within a randomized complete block design with three replications, at each location. Our results show that under physiological stress conditions caused by water deficit, the evening primrose adopts typical strategies to reduce the negative impact of water deficit stress. Some of these strategies include antioxidant enzyme synthesis, which protect from reactive oxygen species, a decrease in overall growth, but relative increase in root, and an increase in plant antioxidant pigments. Water deficit significantly reduced plant total biomass and chlorophyll a (especially in the arid region), but it increased the root to shoot ratio, chlorophyll b, carotenoid, anthocyanin, proline, the antioxidant enzymes peroxidase, polyphenol oxidase, superoxide dismutase, malondialdehyde and hydrogen peroxide (especially in the arid region). The application of the chemical fertilizers and biological inoculants in all conditions decreased H2O2 and antioxidant enzymes activity. The arbuscular mycorrhizae alleviated the physiological stress response more than the nitrogen fixing bacteria or chemical fertilizer by increasing anti-oxidant pigments concentration, total biomass and root to shoot ratio of evening primrose under water deficit stress. Therefore, arbuscular mycorrhizae should be considered an essential component of evening primrose cultivation in arid or semi-arid climates to alleviate moderate to severe water deficit.

Inoculation with mycorrhizal fungi on the growth and tolerance to water deficit of coffee plants

ABSTRACT Water stress can be alleviated in plants inoculated with arbuscular mycorrhizal fungi compared to that experienced by those without mycorrhizae. The objective of this study was to evaluate the growth of coffee plants colonized by arbuscular mycorrhizal fungi under different soil moisture conditions. Seeds of the coffee cultivar Catuaí Vermelho IAC 99 and three fungal inoculants (Rhizophagus clarus, Claroideoglomus etunicatum and Dentiscutata heterogama) were used in this study. The soil moisture contents tested were 40, 60, 80, and 100% of field capacity. Seedlings in the matchstick stage were inoculated with mycorrhizae, and then later planted in plastic pots when they developed four to five pairs of definitive leaves. Both the extent of mycorrhizal colonization and increases in leaf area were related to soil moisture content in a quadratic manner for plants inoculated with all three mycorhizzal fungi (R. clarus, C. etunicatum, and D. heterogama), as well as for non-inoculated ones. The highest value of colonization of coffee by mycorrhizae was 39%, which occurred in association with R. clarus at 71% of field capacity. The leaf areas of plants inoculated with fungi increased more than those of non-inoculated plants, regardless of the type of inoculum used. Plants inoculated with D. heterogama at 100% field capacity produced 21% more root dry mass than non-inoculated plants did. Inoculation with arbuscular mycorrhizal fungi and higher soil moisture increased the growth of coffee seedlings. The plants inoculated with R. clarus, C. etunicatum, and D. heterogama were tolerant to moderate water deficits (i.e. lower soil water contents). Mycorrhizal colonization was highest for plants in soils with moisture levels close to 75% of field capacity.

Nitrogen-mediated alleviation of photosynthetic inhibition under moderate water deficit stress in rice (Oryza sativa L.)

High nitrogen (N) application improves the acclimation of plant photosynthesis to water deficit stress, however, the metabolic details for this are not yet fully understood. Using hydroponics, we found that moderate water deficit simulated with 10% PEG 6000 inhibited rice photosynthetic rate by 17.2% in low N condition (LN, 0.71 mM) versus 7.9% in moderate N condition (MN, 2.86 mM). Plants grown at MN had an increased photorespiratory serine metabolism and glycerate recycling under water stress, which was in accordance with the enhancement of glutathione concentration and ascorbate-glutathione cycle, indicating that the serine metabolism plays a significant role in improving antioxidant capacity. Additionally, the up-regulation of GS2 facilitated the re-assimilation of NH3 released in photorespiration. Aspartate aminotransferase (AspAT)- and glutamate:glyoxylate aminotransferase (GGAT)-mediated glutamate transamination and phosphoenolpyruvate carboxylase (PEPC)-mediated anaplerotic reaction provided a carbon skeleton, 2-oxoglutarate, for NH3 assimilation, which reduced the depletion of sugars. Sugars therefore can be stored and used for the regeneration of RuBP through the pentose phosphate pathway to maintain CO2 assimilation. In contrast, water deficit stress-induced protein degradation, down-regulation of N assimilation, and depletion of carbohydrates in LN-supplied plants, as well as the failure of the ascorbate-glutathione cycle due to reduced glutathione biosynthesis, perturbed the function of chloroplasts. We conclude that high N supply preserves the biochemistry of photosynthesis through coordinated regulation of the C and N metabolism to facilitate the acclimation of rice photosynthesis to water deficit stress.

Root distribution patterns of reticulatus and inodorus melon (Cucumis melo L.) under subsurface deficit irrigation

Information on root growth patterns is crucial to understand cultivar adaptations to deficit irrigation, particularly for subsurface drip-irrigated crops, where root systems are more confined than furrow or sprinkler systems. A 2-year field experiment evaluated the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on root growth of melon (Cucumis melo L.) cultivars (Mission, Da Vinci, and Super Nectar) on a mollisol soil in southwestern Texas, USA. Root length intensity (La; mm cm−2), and root length density (RLD; cm cm−3) were measured at different growth stages using the minirhizotron and soil core methods, respectively. A higher La was recorded in 2012 than in 2011 (3.71 mm cm−2 vs. 0.50 mm cm−2), due to differences in temporal distribution of rainfall between years. Overall, deficit irrigation increased La as compared to 100% ETc, but significant effects occurred at depth (> 40 cm below the soil surface and > 25 cm below the subsurface drip tape). In 2012, moderate water deficit promoted deep root growth at the fruit setting stage but not in 2011, while root growth responses to cumulative deficit varied with cultivar. In 2012, deficit irrigation enhanced root growth in cv. Mission (cantaloupe; reticulatus) throughout the season, it was maintained in cv. Da Vinci (Tuscan; reticulatus), while it decreased in cv. Super Nectar (honeydew; inodorus) at the final harvest stage. Thus, the reticulatus melon cvs. Mission and Da Vinci can better adjust to moderate water-deficit conditions as compared to the inodorus melon cv. Super Nectar. Minirhizotron data provided useful information on root growth dynamics in deeper soil layers in a non-destructive way, which makes it a valuable tool in screening cultivars for water deficit adaptation.

Grapevine leafroll disease alters leaf physiology but has little effect on plant cold hardiness.

Foliar sugar accumulation in grapevines with leafroll disease was correlated with lower photosynthesis, likely due to feedback inhibition. However, cold acclimation of dormant tissues remained unaffected by the virus status. Grapevine leafroll-associated viruses (GLRaV) contribute to losses in fruit yield and quality worldwide. Visually, leafroll disease symptoms appear similar to those associated with an imbalance in source/sink relations and a concomitant feedback inhibition of photosynthesis, which is often caused by an impasse in sugar translocation. In order to test this potential relationship and related physiological responses, leaf water status, gas exchange, non-structural carbohydrates, and dormant tissue cold hardiness were examined over 2years in healthy and GLRaV-3-infected, field-grown Merlot grapevines. Diurnal and seasonal changes in leaf water status and gas exchange were dominated by variations in water availability, temperature, and leaf age, while GLRaV-3 infection contributed less to the overall variation. By contrast, foliar carbohydrates increased markedly in infected plants, with starch accumulating early in the growing season, followed by soluble sugar accumulation, leaf reddening, and declining gas exchange. Photosynthesis correlated negatively with leaf sugar content. However, dormant-season cold hardiness of buds and cane vascular tissues was similar in healthy and infected vines. These findings support the idea that visible symptoms of grapevine leafroll disease are a consequence of carbohydrate accumulation which, in turn, may lead to feedback inhibition of photosynthesis. In addition, this study provided evidence that GLRaV-3 infection is unlikely to alter the susceptibility to moderate water deficit and winter damage in mature Merlot grapevines.