Severe Water Stress Treatments Research Articles

Effects of water stress on starch synthesis and accumulation of two rice cultivars at different growth stages.

Rice is a water intensive crop and soil water conditions affect rice yield and quality. However, there is limited research on the starch synthesis and accumulation of rice under different soil water conditions at different growth stages. Thus, a pot experiment was conducted to explore the effects of IR72 (indica) and Nanjing (NJ) 9108 (japonica) rice cultivars under flood-irrigated treatment (CK, 0 kPa), light water stress treatment (L, -20 ± 5 kPa), moderate water stress treatment (M, -40 ± 5 kPa) and severe water stress treatment (S, -60 ± 5 kPa) on the starch synthesis and accumulation and rice yield at booting stage (T1), flowering stage (T2) and filling stage (T3), respectively. Under LT treatment, the total soluble sugar and sucrose contents of both cultivars decreased while the amylose and total starch contents increased. Starch synthesis-related enzyme activities and their peak activities at mid-late growth stage increased as well. However, applying MT and ST treatments produced the opposite effects. The 1000-grain weight of both cultivars increased under LT treatment while the seed setting rate increased only under LT3 treatment. Compared with CK, water stress at booting stage decreased grain yield. The principal component analysis (PCA) showed that LT3 got the highest comprehensive score while ST1 got lowest for both cultivars. Furthermore, the comprehensive score of both cultivars under the same water stress treatment followed the trend of T3 > T2 > T1, and NJ 9108 had a better drought-resistant ability than IR72. Compared with CK, the grain yield under LT3 increased by 11.59% for IR72 and 16.01% for NJ 9108, respectively. Overall, these results suggested that light water stress at filling stage could be an effective method to enhance starch synthesis-related enzyme activities, promote starch synthesis and accumulation and increase grain yield.

Effect of Water Deficit on Germination, Growth and Biochemical Responses of Four Potentially Invasive Ornamental Grass Species

Ornamental plant species introduced into new environments can exhibit an invasive potential and adaptability to abiotic stress factors. In this study, the drought stress responses of four potentially invasive ornamental grass species (Cymbopogon citratus, Cortaderia selloana, Pennisetum alopecuroides and P. setaceum) were analysed. Several seed germination parameters were determined under increasing polyethylene glycol (PEG 6000) concentrations. Additionally, plants in the vegetative stage were subjected to intermediate and severe water stress treatments for four weeks. All species registered high germination rates in control conditions (no stress treatment), even at high PEG concentrations, except C. citratus, which did not germinate at -1 MPa osmotic potential. Upon applying the water stress treatments, P. alopecuroides plants showed the highest tolerance, and C. citratus appeared the most susceptible to drought. Stress-induced changes in several biochemical markers (photosynthetic pigments, osmolytes, antioxidant compounds, root and shoot Na+ and K+ contents), highlighted different responses depending on the species and the stress treatments. Basically, drought tolerance seems to depend to a large extent on the active transport of Na+ and K+ cations to the aerial part of the plants, contributing to osmotic adjustment in all four species and, in the case of the most tolerant P. alopecuroides, on the increasing root K+ concentration under water deficit conditions. The study shows the invasive potential of all species, except C. citratus, in dry areas such as the Mediterranean region, especially in the current climate change scenario. Particular attention should be given to P. alopecuroides, which is widely commercialised in Europe as ornamental.

Effects of water stress on quality and sugar metabolism in ‘Gala’ apple fruit

Sugar plays an important role in apple fruit development, appearance and quality as well as contributing to a plant's water stress response. Trehalose and the trehalose biosynthetic metabolic pathways are part of the sugar signaling system in plants, which are important regulator of water stress response in apple. The effect of water stress treatments applied to apple trees and the corresponding effects of ABA on developmental fruit quality were examined for indicators of fruit quality during fruit development. The results indicated that the severe water stress treatment (W2) occurring after the last stage of fruit cell division caused a decrease in the color and size of fruit. The moderate water stress (W1) occurring after the last stage of fruit cell enlargement (S2) caused an increase in the content of fructose and sorbitol while the apple fruit shape was not affected. These changes in sugar are related to the activity of sugar metabolic enzymes. While the enzymatic activity of vacuolar acid invertase (vAINV) was higher, that of sucrose-phosphate synthase (SPS) was lower in water stress treated fruit throughout the developmental period. This indicates that enhanced sucrose degradation and reduced sucrose synthesis leads to an overall reduced sucrose content during times of drought. Thus, water stress reduced sucrose content. Whereas the content of endogenous trehalose and ABA were the highest in water stress treated fruit. A moderate water stress (W1) imposed on apple trees via water restriction (60%–65% of field capacity) after the fruit cell enlargement phase of fruit development yielded sweeter fruit of higher economic value.

Physiological, developmental and growth responses to desiccation induced stress in four seed coat colour varieties of Vigna unguiculata (L. Walp).

Cowpea (Vigna unguiculata L. Walp) is a widely grown leguminous crop in Ghana. This study was conducted using four varieties of cowpea based on the colour of the seed coat namely; red, brown, black and cream cowpea varieties, and were subjected to three different watering regimes, namely: Normal, moderate and severe water stress regimes. These different watering regimes were used as potential screening criteria to determine their drought tolerance ability. We monitored changes in physiological, morphological and yield traits due to the effects of four seed coat colour varieties and imposed water regimes. The effects of seed coat colour on relative water content (RWC) was significant (F = 13.15; p ≤ 0.05). Red variety recorded the highest RWC (60.14%) with the lowest RWC (50.71%) in the Black seed colour, all under severe water stress. The Red and Cream seed coats had a soil moisture content (SMC) of 62.61 and 48.70% respectively when the severe water stress treatment was considered. There was a decreasing trend in chlorophyll content for all four cowpea varieties. The Brown and Red varieties recorded the highest chlorophyll contents under moderate and severe water stress respectively. Proline concentrations were high with increasing drought severity. The Red cowpea variety recorded the maximum concentration of free proline (5.7 µg/g) under severe water stress. Mean seed weight in Red seed coat, subjected to severe water stress, was 0.48 g. Results in this experiment revealed that the Red seed coat colour appeared to be tolerant to severe water stress compared to Cream, Black and Brown seed coats. Key words: Cowpea, seed coat colour, water stress, relative water content, soil moisture content.

Nutrient Concentration of African Horned Cucumber (Cucumis metuliferus L) Fruit under Different Soil Types, Environments, and Varying Irrigation Water Levels

The nutrient concentration of most crops depends on factors such as amount of water, growing environment, sunlight, and soil types. However, the factors influencing nutrient concentration of African horned cucumber fruit are not yet known. The objective of the study was to determine the effect of different water stress levels, soil types, and growing environments on the nutrient concentration of African horned cucumber fruit. Freeze-dried fruit samples were used in the quantification of β-carotene and total soluble sugars. The results demonstrated that plants grown under the shade net, combined with severe water stress level and loamy soil, had increased total soluble sugars (from 8 to 16 °Brix). Under the shade-net environment, the combination of moderate water stress level and loamy soil resulted in increased crude protein content (from 6.22 to 6.34% °Brix). In addition, the severe water stress treatment combined with loamy soil, under greenhouse conditions, resulted in increased β-carotene content (from 1.5 to 1.7 mg 100 g−1 DW). The results showed that African horned cucumber fruits are nutrient-dense when grown under moderate water stress treatment on the loamy or sandy loam substrate in the shade-net and open-field environments.

Simulation of Canopy Cover, Soil Water Content and Yield Using FAO-AquaCrop Model under Deficit Irrigation Strategies

The model was used to simulate tomato green canopy (CC), soil water (SWC) and final yield under deficit irrigation regimes as 1.25, 1.00, 0.75 and 0.50 percentages of crop evapotranspiration (ETc). The model was calibrated by used an experimental data and fine-tune to some conservative crop parameters. The NRMSEs in simulated CC and SWC in different treatments were 4.1–19.6 and 6.3–14.1%, respectively, that corresponds to overall averages of 0.92 and 0.84 for R2 in CC and SWC. In exception to severe water stress treatments, the model showed overestimation trend on biomass and yield, and proved satisfactory performance. The maximum simulated biomass and yield was 12.88 and 6.04 t/ha, respectively. The lower values in yield and biomass belong to less water applied treatments, that shows the model accuracy declines in high water deficiency. Simulated biomass WUEs varied from 2.26 to 3.73 kg/m3, likewise the yield WUEs varied from 1.06 to 1.71 kg/m3. The higher WUEs obtained in less water applied treatments, obviously, the WUE increases when applications of water decreased. The findings of water saving potential (WSP), recommended 0.75 of ETc to saved 25.09% of water with only 12.00 and 15.52% reduction in measured and simulated yield.

Effect of Mycorrhiza and Vermicompost on Drought Tolerance of Lime Seedlings (Citrus aurantifolia Cv. Mexican Lime)

ABSTRACT In order to investigate the effect of mycorrhizal arbuscular fungi (MAF) and vermicompost on drought tolerance of Mexican Lime seedlings (Citrus aurantifolia cv. Mexican Lime), a factorial experiment was conducted as a completely randomized design in greenhouse conditions. Factors included were water stress at three levels (100% ETc, 70% ETc and 40% ETc) and biofertilizers at three levels (0, 100 g mycorrhiza, 100 g vermicompost per pot) with four replications. Irrigation treatments were applied for two months on one year seedlings. The results showed that growth of leaf and root was significantly affected by drought stress and decreased, whereas the effect of drought stress on fresh and dry weight of stem was not statistically significant. According to the results, the rate of decrease in fresh and dry weight of leaves under severe water stress treatment compared to full irrigation was 35.38 and 31.79%, respectively. Also, the rate of decrease in fresh and dry weight of root in severe water stress treatments was 35.53 and 34.11%, respectively, compared to full irrigation. Inoculation of seedlings with bio-fertilizers especially 100 g mycorrhiza per pot significantly increased leaf fresh weight (19.94%), leaf dry weight (17.31%), stem fresh weight (26.7%), stem dry weight (26. 1%), root fresh weight (35.53%), root dry weight (14.82%), RWC (76.19%), enzyme activity, chlorophyll a (0.637 mg.g f.w.), b (0.372 mg.g f.w.) and carotenoid (11 mg.g f.w.) and reduced ion leakage (62.5%) compared to non-inoculated seedlings. Based on the results, it can be stated that application of 100 g bio-fertilizer could reduce adverse effects of drought stress on the Mexican Lime seedlings.

CONTROL OF DROUGHT STRESS IN TOMATO PLANTS USING SOME CULTURAL PRACTICES

In this study, tomato plants cv. Alisa were irrigated with three different amounts of water i.e. optimum amount which was the amount of water that added to raise soil field capacity (FC) from 70% (as re-irrigated tomato when FC drop to 70% is considered the most suitable irrigation regime) to 100% (T1), 66% (T2) and 33% (T3) of optimum water amount. Also, three different drought adaptable treatments were applied to tomato plants, i.e. drought pretreatment of seedlings (seedling priming), spraying plants with a reflecting antitranspirant (a suspension of calcium carbonate at concentration of 6%) or infected plants with arbuscular mycorrizal fungus, as well as control which was not treat with any of adaptable treatment. Decreasing amount of irrigation water applied decreased gradually plant height, fresh and dry weights of plant organs, leaflet area, No of days to the first anthesis (F50), fruit set percentage, relative water content (RWC), N, P and K and total carbohydrate contents in leaves, No of fruits/ plant, average fruit weight and early and total yields, than those of well-watered plants (T1). water deficit treatments (T2 & T3) enhanced root length, leaflet thickness, osmotic pressure (OP) in leaves, water use efficiency (WUE) and improved fruit quality i.e. increased vit. C, TSS, titratable acidity, and lycopene contents and fruit firmness in ripe fruits. In addition, water deficit treatments altered dry matter distribution in tomato plants as it enhanced dry mater partitioning to roots on the expense of above ground organs. All adaptable treatments used, often alleviated the detrimental effects of water deficit treated plants (T2&T3) as they promoted plant growth and productivity of both well watered and water stressed plants than those of untreated (control) plants. In most cases, spraying plants with the antitranspirant material gave the highest values of growth characteristics and yield and its components with well watered treatment (T1) and moderate water stress treatment (T2) but not with severe water stress treatment (T3). Using mycorrizal inoculation treatment gave the highest values of P content in leaves, and average fruit weight. Also it gave the second highest values (as average of the effect of the three water regimes) of plant growth, plant water relations and productivity characters alternately with drought pretreatment. In addition, mycorrizal treatment gave the highest total yield and highest total plant fresh and dry weights when combined with lowest water supply (T3) than those obtained by other two adaptable treatment.

ENHANCING DROUGHT TOLERANCE OF TOMATO PLANTS GROWN UNDER DIFFERENT IRRIGATION REGIMES BY SOME CULTURAL PRACTICES

Water scarcely is a common problem especially in arid and semi-arid areas of the world like the Mediterranean region. Therefore, enormous efforts directed to improve the adaptation of plants to use less irrigation water by increasing their tolerant and resistant to water deficit by different means. In this study, tomato plants cv. Alisa were irrigated with three different amounts of water i.e. optimum amount which was the amount of water that added to raise soil field capacity (FC) from 70% (as re-irrigated tomato when FC drop to 70% is considered the most suitable irrigation regime) to 100% (T1), 66% (T2) and 33% (T3) of optimum water amount. Also, three different drought adaptable treatments were applied to tomato plants, i.e. drought pretreatment of seedlings (seedling priming), spraying plants with a reflecting antitranspirant (a suspension of calcium carbonate at concentration of 6%) or infected plants with arbuscular mycorrizal fungus, as well as control which was not treat with any of adaptable treatment. Decreasing amount of irrigation water applied decreased gradually relative water content (RWC), No of fruits/ plant, average fruit weight and early and total yields, than those of well-watered plants (T1). The reduction in total yield was mainly due to the reduction of both fruit weight and fruit number. However, water deficit treatments (T2 & T3) enhanced water use efficiency (WUE) and improved fruit quality i.e. increased vit. C, TSS, titratable acidity, and lycopene contents and fruit firmness in ripe fruits. The increase in fruit quality traits by water stress could be interpreted on the base that plants grown under such conditions react by stimulate the secondary metabolism which increasing plant defense, the secondary metabolites involved sugars, organic acids, vitamins, carotenoids and etc. All adaptable treatments used, often alleviated (even partly) the detrimental effects of water deficit treated plants (T2&T3) as they promoted plant productivity of both well watered and water stressed plants than those of untreated (control) plants. The increase in total yield resulted from using adaptable treatments was mainly due to the increase in average fruit weight, and to lesser extent fruit number. Adaptable treatments also enhanced plant water relation (RWC &WUE) compared to those of untreated control, but they considerably reduced fruit quality traits. In most cases, spraying plants with the antitranspirant material gave the highest values of yield and its components particularly when combined with well watered treatment (T1) and moderate water stress treatment (T2) but not with severe water stress treatment (T3). Using mycorrizal inoculation treatment gave the highest values of average fruit weight, also it gave the second highest values of plant water relations and productivity characters alternately with drought pretreatment. In addition, mycorrizal treatment gave the highest total yield when combined with lowest water supply (T3) than those obtained by other two adaptable treatments.

Performance of potato (Solanum tuberosum) advanced hybrid MS/6-1947 under high temperature stress and water deficit conditions

In present investigation, potato (Solanum tuberosum L.) advanced stage hybrid MS/6-1947 was evaluated along with controls under high temperature and water stress regimes for three successive winter crop seasons. Under high temperature at Modipuram, MS/6-1947 (13.3 t/ha) showed yield enhancement of 20, 9 and 11% over the controls Kufri Bahar, Kufri Pukhraj and Kufri Surya. It also exhibited at par tolerance to hopper with Kufri Surya and damages due to mite burn were lower than Kufri Bahar and Kufri Pukhraj. The hybrid possessed 18% tuber dry matter. Results ondrought toleranceat Modipuram revealed superior performance of MS/6-1947 under normal irrigation, mild water and severe water stress conditions as compared to best control Kufri Pukhraj as yield reduction was comparatively lower under mild and severe water stress treatments. Drought tolerance index (DTI) values were maximum in MS/6-1947 (1.02 and 0.79) followed by Kufri Pukhraj (0.86 and 0.51) and Kufri Bahar (0.72 and 0.58) under mild and severe water deficit treatments, respectively. Drought tolerance studies at Jodhpur revealed better performance of MS/6-1947 under normal and mild water stress conditions as compared to the controls Kufri Pukhraj and Kufri Surya as yield reduction was comparatively lower under mild water stress conditions. DTI values were maximum in MS/6-1947 (1.08) followed by Kufri Puhkraj (1.01) and Kufri Surya (0.41) under mild water deficit treatment. Tuber dry matter content increased under water stress over normal irrigation at both the locations. MS/6-1947 is suitable for table potatoes. MS/6-1947 may be a better option for integrating in cereal based crop sequences, for exploiting its yield potential in early season and for attaining sustainable productivity in areas where high temperature and lower water availability are constraint for raising the successful potato crop.

Leaf physiological and anatomical responses of Lantana and Ligustrum species under different water availability

Understanding the plant characteristics that support tolerance to water stress is important in choosing plants in arid or semi-arid environments, such as the Mediterranean. In particular, leaf characteristics can affect the response of plants to water stress. In order to understand how plants with different leaf features can overcome water stress, four water regimes were adopted on two species that are widespread in the Mediterranean environment, Lantana camara and Ligustrum lucidum. The four treatments were: control (C), in which the pot substrate moisture was maintained close to water container capacity (WCC), light deficit irrigation (LDI) irrigated at 75% of WCC, moderate deficit irrigation (MDI) at 50% of WCC, and severe deficit irrigation (SDI) at 25% of WCC. To better understand the action mechanisms, the trial was repeated twice (from January to May, and from May to September). Morphological, anatomical and physiological data were measured to identify the action mechanisms. Water deficit significantly decreased the biomass accumulation in both species during the experimental growth period. In Lantana, significant variations in total leaf area and leaf number were registered between C and SDI, while in Ligustrum, the differences were significant only for total leaf area. The water deficit treatments reduced the leaf thickness especially in Ligustrum. In both species, photosynthesis reduction was related to stomatal closure. Ligustrum showed a higher variability among treatments indicating a faster and more efficient response to water limitations compared to Lantana, as also demonstrated by the lower biomass reduction in the most severe water stress treatment.

Modulation of Brassica napus source–sink physiology through film antitranspirant induced drought tolerance amelioration that is dependent on the stress magnitude

AbstractIncrease in drought conditions during the oilseed rape (OSR) reproductive phase is predicted to occur more often in the temperate zone, leading to significant yield losses. Crop management solutions such as film antitranspirant (AT) applied at key drought‐sensitive growth stages on both wheat and oilseed rape have recently been shown to alleviate drought‐induced yield losses. However, there is a lack of information regarding potential AT effectiveness to reduce drought damage on OSR plants at different soil moisture regimes. Therefore, two similar experiments were performed in a computer‐controlled glasshouse/phenotyping centre to investigate the physiological responses of OSR to well‐watered (WW), moderate water stress (MWS), water stress (WS) and severe water stress (SWS) conditions. Stress treatments were imposed at the initiation of flowering and treated with an AT or water onto the leaf canopy. Stress limited the gas‐exchange and increased leaf temperature, leaf‐to‐air temperature, bud‐to‐air temperature and ABA concentrations which increased with stress intensity in all tissues analysed. Yield components were significantly reduced by WS and SWS treatments when compared to the WW plants. Application of AT counteracted the detrimental effect of WS and SWS by decreasing water use over the first few days of stress application thus improving relative water content and leaf water‐use efficiency, decreasing ABA accumulation in leaf and all the reproductive organs analysed (buds, flowers and pods) and avoiding bud‐to‐air temperature increases. AT application sustained pod formation and seed production under WS but only seed production under SWS conditions. These data suggest that leaf‐canopy application of AT at key phenological stages under particular magnitudes of soil moisture deficit may sustain OSR reproduction and reduce yield losses.

Some growth and chlorophyll fluorescence parameters of black and hybrid poplar clones under water stress

The effects of water stress on some growth and chlorophyll a fluorescence parameters were investigated in two native black poplar (Populus nigra L.) clones (Kocabey and Gazi) and in two hybrid poplar (Populus × euramericana (Dode) Guinier) clones (I-214 and I-45/51) to determine which among the four clones is the best adapted to water-stress conditions. The potted seedlings were grown under three watering regimes. As a result of the applied watering regimes, the predawn water potential (ψ pd) of seedlings was maintained at about -0.3, -0.9, and -1.6 MPa in control, moderate, and severe water-stress treatments during the experiment, respectively. Drought treatment had significant effects on the morphology and growth characteristics of the clones but had generally insignificant effects on survival and the photochemical activity of photosystem II (PSII). Results obtained from the present study demonstrate that I-214 was the most successful in terms of its higher root/shoot ratio (Rs), maximum fluorescence yield (Fm), maximum quantum efficiency of PSII (Fv/Fm) values, and lower number of leaves among the examined four poplar clones under drought stress conditions. Consequently, the I-214 poplar clone may have the potential to be used in drought areas.

Identification of loci contributing to maize drought tolerance in a genome-wide association study

Genome-wide association studies (GWAS) have been used widely to analyze the genetic control of complex traits in crops. In the present study, seven related phenotypic traits were analyzed in combination to study their association with 41,101 SNPs in 201 maize inbred lines that had been evaluated in seven environments (year/location combinations) under water-stressed (WS) or well-watered (WW) regimes. By comparing the association signals with a fixed P value, GWAS showed that the number of association signals identified varied among traits and in different environments. Data that were missing under the severe water stress treatment had a great impact on the results of this GWAS. A total of 206 significant SNPs were associated with 115 candidate genes for drought tolerance and related traits including final grain yield, total number of ears per plot, kernel number per row, plant height, anthesis-silking interval, days to anthesis (DtA), and days to silking (DtS). Among these, four genes were associated with at least two different related traits, and six genes associated with traits were detected in at least two environments under water stress. Nine candidate QTL identified by GWAS were also discovered, three of which co-located to a consensus QTL region meta-analyzed by linkage mapping for drought tolerance. Some regulatory genes related to abiotic stress responses might also make a strong contribution to drought tolerance. The comprehensive information presented here regarding consensus QTL combined with candidate genes derived from GWAS provides an important reference tool for improving maize drought tolerance.

Physiological and growth responses of pomegranate tree (Punica granatum (L.) cv. Rabab) under partial root zone drying and deficit irrigation regimes

This study evaluated the effects of full irrigation (FI, 100% ETC), partial root zone drying and deficit irrigation with mild (75%ETC) and severe (50% ETC) water stress on the physiological and growth behavior of pomegranate trees in southern Iran in 2011 and 2012. The experiment was set up as a split plot design in completely randomized blocks design with three replications. Results showed that the stem water potential (ψstem) was directly related to the soil water deficit (SWD), and it varied from −2.07 to −3.27MPa in 2011 and −1.67 to −3.23MPa in 2012. In all times of measurements, higher values of stomatal conductance (gs), net photosynthesis (An) and leaf scale transpiration (Tr) were obtained in FI and mild water stress treatments (An: 3.15–12.64μmolm−2s−1, gs: 0.032–0.129molm2s−1 and Tr: 2.72–9.48mmolm2s−1) in comparion with those obtained in the severe water stress treatments (An: 2.11–11.81μmolm−2s−1, gs: 0.021–0.11molm2s−1 and Tr: 1.89–7.58mmolm2s−1). Results generally showed low values of gs in the Rabab cultivar in the studied arid area. Furthermore, the hydraulic signaling (ψstem) in response to the water stress and weather conditions controlled the seasonal variation of gs. Transpiration efficiency (TE) increased with increasing the degree of water stress and PRD showed higher TE (1.17–1.18μmolmmol−1) than that in DI strategies (1.06–1.07μmolmmol−1). Furthermore, the value of intrinsic water use efficiency (IWUE) in FI (85μmolmol−1) was statistically lower than that obtained in mild (PRD75, DI75) and severe (PRD50, DI50) water stress treatments (87.8–89.9μmolmol−1). Different irrigation strategies did not significantly affect the fruit growth rate, and its maximum values occurred at about 170 DAB (0.27–0.35mmd−1) in all irrigation strategies. The LAI values in FI and mild water stress strategies were significantly different compared with those in the severe water stress treatments. For all irrigation strategies, the maximum LAI values occurred at flowering stage (68 DAB), and was 6.09 and 6.15 (FI), 5.97 and 6.04 (DI75), 6.33 and 6.64 (PRD75), 4.60 and 4.82 (DI50) and 4.91 and 5.03m2m−2 (PRD50) in 2011 and 2012, respectively. In conclusion, PRD75 is the recommended, applicable water-saving strategy and good alternative with respect to FI among other irrigation managements when water resources are limited in order to increase TE and IWUE while other physiological and growth parameters are maintained at an acceptable level.

Growth of Pelargonium sidoides DC. in response to water and nitrogen level

Water stress is the most limiting factor in agricultural productivity in arid and semi-arid regions and causes very high losses in crop yield. Regulation of growth and stomatal conductance are the main mechanisms by which plants respond to water stress. Pelargonium sidoides is a medicinal plant that grows in South Africa and is used for the treatment of upper respiratory ailments. Cultivation has been considered as a viable means of reducing the pressure on natural populations of this species, but little to no information is available in this regard. Water and nitrogen supply are two of the most important factors that affect growth and yield of plants. This study therefore aimed at investigating the physiological and morphological response, in relation to growth, of P. sidoides to soil water and nitrogen levels. To achieve this objective, P. sidoides plants were grown under a rainshelter and exposed to three irrigation levels (well watered control, moderate water stress, and severe water stress treatment) and four nitrogen levels (0, 50, 100, and 150kg · N · ha−1). Nitrogen and water level had no significant interaction effect on measured parameters. Water stress significantly reduced stomatal conductance, while nitrogen had no significant effect on it. The well watered control had a significantly higher leaf area index, plant height, leaf area, and fresh root yield compared to the water stressed treatments. Nitrogen level had a significant effect on number of leaves, where 100kg · N · ha−1 had a significantly higher number of leaves compared to other nitrogen treatments. The study provides a first report on the response of P. sidoides to water and nitrogen and showed that the plant responds to water stress by closing its stomata and employing other morphological strategies like reducing plant growth.

Phytochemical and physiological changes in Ashwagandha (Withania somnifera Dunal) under soil moisture stress

Ashwagandha, commonly known as the Indian Ginseng (Withania somnifera) is an ingredient in many herbal preparations used for healing various ailments. It is cultivated in semi-arid regions of India as rain-fed crop. The response of this crop (cv. JA-134) to progressive soil moisture deficit on growth, physiology and content of phytochemicals was studied. At the end of treatment period, soil water potential (Ψw) decreased to -10.93, -1.15 MPa at 30 cm depth, predawn leaf water potentials were reduced to -0.62 and -0.51 MPa in the severe and moderate stress. Leaf area was reduced by 27.4% and 34.4% in moderate and severe water stress treatment compared to control. Chlorophyll content was reduced by 60% in the severe water stress. Changes in the steroidal alkaloids and lactones that are the major medicinal active principles derived from root extracts of this plant species was also analyzed. A reduction of 52.6% in net photosynthesis was noticed under severe stress. At the end of the treatment period, moderate and severe stress treatments had 0.751 and 0.714 mg g-1 12-deoxywithastramonolide (12-DWS) content in the roots respectively. The content of 12-DWS and withanolide were at 77% and 93% of the control in the moderate and severe stress, respectively, while yield of these compounds were at 65% and 78% of control in mild and severe stress. Thus, preferential partitioning of biomass in roots leads to higher root yield in moderate stress. Higher root yield partially offset the loss of bioactive compounds under soil moisture stress.

Improved tolerance of wheat plants (Triticum aestivum L.) to drought stress and rewatering by the arbuscular mycorrhizal fungus Glomus claroideum: effect on growth and cell membrane stability

The aim of this paper was to investigate the contribution of the arbuscular mycorrhizal fungus Glomus claroideum to drought stress tolerance in wheat plants grown under controlled conditions in a growth chamber, and subjected to moderate or severe water stress and rewatering. Water stress tolerance was determined through total dry weight, leaf relative water content, leakage of solutes and leaf chlorophyll and protein concentrations in mycorrhizal and non-mycorrhizal wheat plants. Total dry weight and leaf chlorophyll concentrations were significantly higher in mycorrhizal plants after moderate or severe water stress treatments compared with non-mycorrhizal ones. Electrolyte leakage was significantly lower in water-stressed inoculated plants. Compared to non-inoculated plants, leaf relative water content and total protein concentration of inoculated individuals increased only under severe water stress. When irrigation was re-established, mycorrhizal plants increased their total dry weight and leaf chlorophyll concentration, and recovered cell membrane permeability in leaves compared with non-mycorrhizal plants. In conclusion, root colonization by G. claroideum could be an adequate strategy to alleviate the deleterious effects of drought stress and retard the senescence syndrome in wheat.

Leaf and canopy level photosynthetic responses of French prune (Prunus domestica L. ‘French’) to stem water potential based deficit irrigation

SummaryThe effects of full irrigation and two levels of water stress on tree physiology were investigated in a French prune orchard. The control treatment received approximately 100% of the estimated seasonal crop water requirements throughout the season. The moderate and severe water stress treatments were managed to decline from a fully watered status in late spring to a midday stem water potential of –1.5 and –2.0 MPa, respectively, by harvest. Water stress caused a clear reduction in stem water potential throughout the daylight period, as well as reductions in leaf conductance and photosynthesis, and all of these reductions were more severe with increasing water stress. In a moderate and severe stress treatment, the photosynthetic rate of fully exposed leaves was reduced to 90% and 81% respectively, of the control treatment. There was a linear decline in light saturated photosynthesis with a decline in stem water potential. However, the stress treatments also influenced leaf orientation and the resulting incident light distribution on leaves within the canopy, such that light was more uniformly distributed in canopies under water deprivation than it was under full irrigation. The overall effect of water stress was that the moderate and severe stress treatments had 101% and 93% respectively of calculated canopy photosynthesis compared with the control. This may account for the observed tolerance of prune production to deficit irrigation. A midday depression in assimilation was observed on most days in all treatments, but was not associated with feedback inhibition resulting from carbohydrate accumulation in leaves.

Effect of Drought Stress on Leaf and Whole Canopy Radiation Use Efficiency and Yield of Maize

Drought stress reduces yield of maize (Zea mays L.) and other grain crops by (i) reducing canopy absorption of incident photosynthetically active radiation (PAR), (ii) reducing radiation use efficiency (RUE), and (iii) reducing harvest index (HI). The primary objective of this work was to quantify yield losses attributable to each of these components for maize exposed to drought stress in a 2‐yr field study. A second objective was to examine the relationship between RUE at the single leaf level (estimated using chlorophyll fluorescence techniques) and RUE at the whole crop level. Two levels of soil water deficit and a control treatment were established using drip tape irrigation, and dry matter harvests were taken at midseason and at physiological maturity. Mild and severe water stress treatments reduced final grain yield by 63 and 85%, respectively, in 2000, and by 13 and 26%, respectively, in 2001. Reduction of intercepted PAR (IPAR) was generally a very minor yield loss component. Yield losses attributable to reduced RUE and reduced HI were of similar magnitude. Weekly chlorophyll fluorescence measurements were used to estimate the average quantum efficiency of photosystem II at a photosynthetic photon flux density of 1200 μmol m−2 s−1 (ΦII1200) for each plot. Crop dry matter accumulation was not linearly related to IPAR, due to decreased RUE in the water stress treatments. However, the linear relationship was restored when daily IPAR was multiplied by the current estimate of ΦII1200, suggesting that ΦII1200 can be used as an indicator of whole‐crop RUE.