Levels Of Drought Stress Research Articles

Combined application of zinc and silicon alleviates terminal drought stress in wheat by triggering morpho-physiological and antioxidants defense mechanisms.

Wheat is an important global staple food crop; however, its productivity is severely hampered by changing climate. Erratic rain patterns cause terminal drought stress, which affect reproductive development and crop yield. This study investigates the potential and zinc (Zn) and silicon (Si) to ameliorate terminal drought stress in wheat and associated mechanisms. Two different drought stress levels, i.e., control [80% water holding capacity (WHC) was maintained] and terminal drought stress (40% WHC maintained from BBCH growth stage 49 to 83) combined with five foliar-applied Zn-Si combinations (i.e., control, water spray, 4 mM Zn, 40 mM Si, 4 mM Zn + 40 mM Si applied 7 days after the initiation of drought stress). Results revealed that application of Zn and Si improved chlorophyll and relative water contents under well-watered conditions and terminal drought stress. Foliar application of Si and Zn had significant effect on antioxidant defense mechanism, proline and soluble protein, which showed that application of Si and Zn ameliorated the effects of terminal drought stress mainly by regulating antioxidant defense mechanism, and production of proline and soluble proteins. Combined application of Zn and Si resulted in the highest improvement in growth and antioxidant defense. The application of Zn and Si improved yield and related traits, both under well-watered conditions and terminal drought stress. The highest yield and related traits were recorded for combined application of Zn and Si. For grain and biological yield differences among sole and combined Zn-Si application were statistically non-significant (p>0.05). In conclusion, combined application of Zn-Si ameliorated the adverse effects of terminal drought stress by improving yield through regulating antioxidant mechanism and production of proline and soluble proteins. Results provide valuable insights for further cross talk between Zn-Si regulatory pathways to enhance grain biofortification.

Assessment of biochemical compounds and antioxidant enzyme activity in barley and wheatgrass under water-deficit condition.

Wheatgrass and barley grass are freshly sprouted leaves of wheat and barley seeds and are rich sources of phytochemicals. This study was conducted to investigate the effects of drought stress on the biochemical compounds and antioxidant activities of barley grass and wheatgrass extracts. The grass was cultivated in an organic soil growing medium with different levels of drought stress (a control with 100% water holding capacity (WHC), mild drought stress with 75% WHC, moderate drought stress with 50% WHC, and severe drought stress with 25% WHC) in a growth chamber by controlling temperature (20/15 °C, day/night), light (12/12 h, light/dark; intensity 150 μmol m-2 s-1 with quantum dot light-emitting diodes), and relative humidity (60%) for 7 days. The drought stress showed increased levels of biochemical compounds, especially phenolics, flavonoids, and vitamin C, in both barley grass and wheatgrass extracts. The wheatgrass extracts showed 1.38-1.67 times higher phenolics, flavonoids, and vitamin C contents than the barley grass extracts did. The antioxidant (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity, and nitrite-scavenging activity) and antioxidant enzymes (guaiacol peroxidase, catalase, and glutathione reductase) were the highest under severe drought stress in both barley grass and wheatgrass extracts; and the wheatgrass extracts showed 1.20-5.70 times higher antioxidant enzyme activities than the barley grass extracts did. Proper drought-stress treatment of barley grass and wheatgrass may be a convenient and efficient method to increase biochemical compounds and antioxidants in our diet to exploit the related health benefits. © 2021 Society of Chemical Industry.

Impact of Drought Stress on Photosynthetic Response of Some Pear Species

To investigate photosynthetic response of some pear (Pyrus spp.) species to drought stress, a pot experiment was conducted using as factorial experiment based on completely randomized design (CRD) with three replication under greenhouse condition. The factors included five pear species including: P. biossieriana, P. communis, P. glabra, P. salicifolia and P. syriaca and three levels of drought stress [(100%, 60% and 30% of field capacity (FC)]. According to the obtained results, different levels of drought stress significantly restricted morphological and physiological responses in all studied species. Increasing drought stress intensity reduced leaf relative water content (RWC), net photosynthetic rate, stomatal conductance, transpiration rate and intercellular carbon dioxide concentration when compared to their values in control plants. However, root/shoot dry weight ratio, specific leaf weight and stomatal density per unit of area were increased. In P. glabra exposed to severe stress (30% of FC), the values of root/shoot dry weigh ratio (0.85 g), specific leaf weight (23 mg cm-2), stomata density per unit of area, relative water content (73%) and net photosynthetic rate (3.9 µmol CO2 m-2 s-1) were significantly higher than the other species. P. syriaca, P. salicifolia, P. biossieriana and P. communis were placed in the next ranks, respectively based on their response to drought. In conclusion, P. glabra is reported as a more effective species in mitigating the adverse effects of drought by boosting its protective mechanisms than the other pear species.

The Role of Nano-Silicon and Other Soil Conditioners in Improving Physiology and Yield of Drought Stressed Barley Crop

Abstract A field experiment was conducted in sandy soil to assess the effect of different sources of soil conditioners on barley (Hordeum vulgare L. cv. Giza 137) growth and its yield under drought stress. Plants were exposed to two levels of drought stress until grain maturity: (A) drought at 75% available water (AW) with NPK as control (treatment, T1); (B) mild drought stress at 50% AW with foliar spray of nano-silicon at 75 ppm (treatment, T2), foliar spray of nano-zeolite at 75 ppm (treatment, T3), perlite at 4 tons/h (treatment, T4), natural zeolite at 600 kg/ha (treatment, T5), bentonite at 4 tons/h (treatment, T6), and a combined treatment of T2+T3+T4+T5+T6 at the half amount of each material (T7). All the treatments received the recommended doses of organic matter. Vegetative growth and yield characters as well as anatomical characters were recorded. The physical and chemical soil properties were significantly improved by both foliar and soil conditioners application. The nutrients content of the barley crop were augmented under combined treatment (T7) as compared to other treatments. Under that treatment, barley crop chemical components, i.e. protein, ash, chlorophylls, amino acids, vitamins, and fibre were significantly higher compared to other treatments. In addition, gibberellic acid (GA3) and abscisic acid (ABA) content besides antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) activities were significantly affected by all treatments. The economical profits were achieved, as reflected by an investment factor value equal to or higher than 3, and this was achieved for all tested nanosilicon, zeolite, and soil conditioners indicated the effectiveness and profitability of studied treatments.

Physiological and Molecular Responses of 'Dusa' Avocado Rootstock to Water Stress: Insights for Drought Adaptation.

Avocado consumption is increasing year by year, and its cultivation has spread to many countries with low water availability, which threatens the sustainability and profitability of avocado orchards. However, to date, there is not much information on the behavior of commercial avocado rootstocks against drought. The aim of this research was to evaluate the physiological and molecular responses of ‘Dusa’ avocado rootstock to different levels of water stress. Plants were deficit irrigated until soil water content reached 50% (mild-WS) and 25% (severe-WS) of field capacity. Leaf water potential (Ψw), net CO2 assimilation rates (AN), transpiration rate (E), stomatal conductance (gs), and plant transpiration rates significantly decreased under both WS treatments, reaching significantly lower values in severe-WS plants. After rewatering, mild- and severe-WS plants showed a fast recovery in most physiological parameters measured. To analyze root response to different levels of drought stress, a cDNA avocado stress microarray was carried out. Plants showed a wide transcriptome response linked to the higher degree of water stress, and functional enrichment of differentially expressed genes (DEGs) revealed abundance of common sequences associated with water stress, as well as specific categories for mild-WS and severe-WS. DEGs previously linked to drought tolerance showed overexpression under both water stress levels, i.e., several transcription factors, genes related to abscisic acid (ABA) response, redox homeostasis, osmoprotection, and cell-wall organization. Taken altogether, physiological and molecular data highlight the good performance of ‘Dusa’ rootstock under low-water-availability conditions, although further water stress experiments must be carried out under field conditions.

Physiological response and secondary metabolites of three lavender genotypes under water deficit

Lavandula genus is a considerable medicinal plant in pharmaceutical and cosmetics industries. Considering increasing threat of drought in the world, it is important to identify genotypes which can tolerate drought. It is also important to characterize quantity and quality of essential oils, and tolerance indicators of these genotypes against drought stress. Therefore, an experiment was conducted in Gorgan University of Agricultural Sciences and Natural Resources, Iran, during 2017 and 2018, to investigate these factors. It was a factorial experiment based on randomized complete block design with two treatments, three genotypes (Lavandula angustifolia cv. Hidcote, Lavandula angustifolia cv. Munstead, and Lavandula stricta), and four levels of drought stress (irrigation regimes) (I1: 100–90% (control), I2: 80–70%, I3: 60–50% and I4: 30–40% of field capacity) which was done with three repetitions. Drought increased amount of proline in leaves, antioxidant activity, activity of catalase, peroxidase, ascorbate peroxidase, and superoxide enzymes, malondialdehyde content, total flavonoids, total phenol, total sugar and essential oil percentage. The PCA analysis of different irrigation regimes showed that in the first component, the best traits are antioxidant enzymes CAT, SOD, APX, while in the second component, only the trait Catalase is the best trait. The results of PCA analysis in lavender genotypes showed that L. stricta exhibits the most affected physiological changes while trying to adjust to changes in the water status of the environment, under the imposed conditions and shows the highest resistance. But it reduced dry weight of aerial parts, relative water content of leaves, and efficacy of essential oil. Lavandula stricta genotype had the highest amount of essential oil, but the highest dry weight of the aerial parts and essential oil yield were related to L. angustifolia cv. Hidcote and L. angustifolia cv. Munstead genotypes. In all evaluated genotypes, with increasing drought stress, monoterpene compounds were decreased and sesquiterpene compounds were increased. Totally it was shown that drought effect on evaluated traits depends on genotype and nature of traits; this indicates that by choosing drought-tolerant genotypes in breeding programs, high quantity and quality of essential oil, as well as tolerance to drought stress can be achieved.

Modeling the effect of moisture stress on the shift in optimal and maximum temperatures for germination of Malva parviflora L. seeds: Introducing a new hydrothermal time model

Introduction Seed germination is largely controlled by the temperature and moisture content of the seedbed. Therefore, hydrothermal time models have been widely used to describe seed germination patterns in response to temperature and water potential (Ψ) of the seedbed. The majority of these models assume a Normal distribution for base water potential (Ψb(g)) to describe the variation in time to germination. In some of these models, it is assumed that the thermoinhibition of germination induced by the shift in Ψb(g) to more positive values occur only at temperatures above the optimum (To) and that the To is independent of drought stress levels. In this study, the Weibull hydrothermal time was used to quantify the Ψb(g) changes in response to temperature and to model the effect of drought stress on the shift in the optimal (To(g)) and maximum (Tm(g)) temperatures for different germination fractions of malva parviflora seeds. Materials and methods The experiment was conducted at the Seed Technology Laboratory of Agricultural Sciences and Natural Resources University of Khuzestan in 2016. Germination test was performed at eight constant temperatures of 8, 12, 16, 20, 24, 28, 32 and 36 (± 0.2) °C in light/dark conditions (12 h/12 h). In each of the above temperature regimes, seed germination response to different levels of drought stress, i.e. osmotic solutions with concentrations of 0, -0.2, -0.4, -0.6, -0.8 and -0.1 MPa was evaluated. Germination test was performed with four replications (each Petri dish as one replicate). In each replicate, 50 seeds were placed on a layer of Whatman No 1 filter paper in a 9 cm glass Petri dish, and then moistened with 7 ml distilled water or other osmotic solutions. The number of germinated seeds was counted twice every day until germination stopped at each temperature regime (when no germination occurred for 5 consecutive days). All models, having been formulated into the hydrotime and then hydrothermal models, were fitted to data using PROC NLMIXED procedure of SAS software version 9.4. Results and discussion While Ψb(g) showed a linear increase in the temperature range between Tb (base temperature) and Tm(g), the hydrotime constant (θH) decreased nonlinearly in response to increasing temperature. Based on the relationship between Ψb(g) and θH, the shape of the germination rate (GR(g)) response to temperature in the hydrothermal time model was curvilinear. The model estimated the values of θHT (hydrothermal time constant), Tb, Ψbase (base water potential at Tb), and KT (slope of the Ψb(g) response to temperature) as 1800.04 MPa °C h, 4.20 °C, -2.46 MPa, and 0.064 MPa °C-1, respectively. Both To(g) and Tm(g) decreased proportionally with increasing drought intensity and became cooler for higher germination percentiles. For example, the estimated To(50) (optimal temperature for the median) for M. parviflora seeds germinated under no water stress (Ψ=0 MPa) was 23.38 °C but dropped to 15.59 °C as water availability became minimum (Ψ=-1.0 MPa). Similarly, it was estimated that 50% of seeds would be able to germination at (or below) 42.55 °C form zero osmotic potential (Tm(50) at Ψ=0 MPa) but to attain the same germination level at -1.0 MPa, temperature should never exceed 26.99 °C (Tm(50) at Ψ=-1.0 MPa). Conclusion The hydrothermal time model not only gave good fits to germination data but also showed some adaptive properties of M. parviflora seeds to different temperature and moisture environments. With the increasing severity drought, the To(g) and Tm(g) shifted to cooler values, which mean that the seeds were able to germinate at a narrower temperature range under drought conditions.

Effect of naphthyl acetic acid foliar spray on the physiological mechanism of drought stress tolerance in maize (Zea Mays L.)

Owing to climate change, there has been an alarming increase in drought conditions, which has led to an expected increase in the loss of water in soil and water bodies. Moreover, the concomitant climatic disasters are causing severe crop losses worldwide. The designed experiment is aimed to determine the potential effect of naphthyl acetic acid (NAA) foliar spray and how it neutralizes the adverse effects of different drought stress levels (5d, 7d, 10d, 12d and 15d drought) on two maize varieties namely Pakhari and Jalal. A pot experiment was conducted in the Department of Botany, Bacha Khan University Charsadda, during the maize growing season in 2014. Results indicated that the drought-sensitive variety Pakhari is markedly affected, as observed from their reduced level of antioxidant enzymes including peroxidase, superoxide dismutase and catalase along with osmoprotectants including proline and sugar content at the lowest drought stress level of 5 days compared with that observed in the drought-tolerant variety Jalal. Furthermore, a marked decrease in the leaf water status 0.05–0.415 g−1, chlorophyll and carotenoid contents are associated with an increase in the accumulation of sugar, proline and antioxidant enzyme activities under drought stress. Analysis of variance between genotype, drought stress and NAA treatment was performed, and the results were considered significant at p<0.05, except for the germination rate index (GRI), total biomass (TB), carotenoid content (CC), seed vigor index (SVI-II), soluble protein content (SPT) and superoxide dismutase (SOD). Variance analysis was performed to examine the interactions between drought and NAA treatment,and the results were found to be significant at p < 0.05 for seed vigor index (SVI-I, SVI-II), root–shoot ratio (RSR), leaf area index (LAI), leaf area ratio (LAR), TB, chlorophyll ‘a’ (CA), chlorophyll ‘b’ (CB), CC, peroxidase (POD) and SOD content under high drought stress (15d) irrespective of SVI-I, CB, POD, SOD, RSR, CB, SSC and SPC under low drought (5d) conditions. It has been concluded from the obtained results that maize varieties exhibit tolerance when subjected to low levels of drought stress; however, high drought stress (15d) reduces crop yield via high osmotic potential, which poses an alarming threat to Pakistani agriculturists in the forthcoming climate change.

Metabolic effect of drought stress on the leaves of young oil palm (Elaeis guineensis) plants using UHPLC\u2013MS and multivariate analysis

The expansion of the oil palm in marginal areas can face challenges, such as water deficit, leading to an impact on palm oil production. A better understanding of the biological consequences of abiotic stresses on this crop can result from joint metabolic profiling and multivariate analysis. Metabolic profiling of leaves was performed from control and stressed plants (7 and 14 days of stress). Samples were extracted and analyzed on a UHPLC-ESI-Q-TOF-HRMS system. Acquired data were processed using XCMS Online and MetaboAnalyst for multivariate and pathway activity analysis. Metabolism was affected by drought stress through clear segregation between control and stressed groups. More importantly, metabolism changed through time, gradually from 7 to 14 days. The pathways most affected by drought stress were: starch and sucrose metabolism, glyoxylate and dicarboxylate metabolism, alanine, aspartate and glutamate metabolism, arginine and proline metabolism, and glycine, serine and threonine metabolism. The analysis of the metabolic profile were efficient to correlate and differentiate groups of oil palm plants submitted to different levels of drought stress. Putative compounds and their affected pathways can be used in future multiomics analysis.

DIFFERENT SOURCES AND CONCENTRATIONS OF CALCIUM ALTERD GRAIN YIELD, OSMOTIC COMPONENTS AND SOME PHYSIOLOGICAL TRAITS IN MAIZE UNDER DROUGHT STRESS

Lack of sufficient water around the world, is the most important factor to reducing the growth and yield of crops. The use of nutrient elements such as calcium can partially prevent its adverse effects on plants. Therefore, this experiment performed to study the effect of sources and different concentrations of calcium (C1=control, C2= 1.5, C3= 3g/l calcium chloride, C4= 1.5 and C5= 3 g/l calcium silicate) on maize under drought stress (W1= 8 (control), W2= 12 and W3= 16 days irrigation interval). The results showed that by increasing drought level from W1 to W3, grain yield, biomass, the weight of thousand seeds and the number of seed per plant were reduced. Application of calcium, especially 3 g/l calcium silicate improved them. Drought stress decreased the amount of chlorophyll “a”, relative water content (RWC), and increased electrolyte leakage, soluble carbohydrate and proline in leaf tissues. In the absence of drought stress, calcium silicate had a better effect than on maize plant. At the highest level of drought stress (W3), also application of 3 g/l calcium silicate improved the grain yield by reducing the amount of electrolyte leakage, increasing the synthesis of proline and soluble carbohydrates and also improving the yield components compared to calcium chloride. Therefore, it can be stated that calcium silicate at drought stress conditions has a greater effect than calcium chloride on maize plant.

The Effect of Foliar Application of Melatonin on Changes in Secondary Metabolite Contents in Two Citrus Species Under Drought Stress Conditions.

Plant secondary metabolites are compounds that play an important role in plant interactions and defense. Persian lime and Mexican lime as the two most important sour lime varieties with high levels of secondary metabolites, are widely cultivated in tropical and subtropical areas. Melatonin is a pleiotropic molecule that plays a key role in protecting plants against drought stress through regulating the secondary metabolite biosynthesis pathway. This study was performed as a factorial experiment consisting of three factors in a completely randomized design (CRD), including four concentrations of melatonin (0, 50, 100, and 150 μM), three levels of drought stress [100% (control), 75% (moderate stress), and 40% (severe stress) field capacity (FC)], and two Citrus cultivars. The experiment was conducted for 60 days in a greenhouse condition. Based on the results of this study under severe drought stress, melatonin-treated crops had higher total flavonoid and total phenolic contents than the untreated crops. The highest level of essential oils components was observed on 100 μM foliar application of melatonin under severe drought stress in both varieties. The main component of the essential oil was limonene in both Citrus species. Moreover, based on the analysis of the results, hesperidin was the main polyphenol in both varieties. Since the use of melatonin often increases the production of secondary metabolites, this study can be considered as a very effective method for controlling the adverse effects of drought stress in citrus for both industrial and horticultural aims.

Silicon mitigates the effects of moderate drought stress in cover crops

AbstractCover crops are important components of sustainable agricultural systems under no‐till conditions. However, in the Brazilian Cerrado region, plant growth and straw production on the soil surface have been hampered by insufficient soil water availability during off‐season. A pot experiment was conducted to investigate the effect of silicon fertilization on the morphological and physiological characteristics of cover crops under drought stress conditions. We hypothesized that silicon could mitigate the adverse effects of drought stress because of its role in improving the photosynthetic process and antioxidant defence mechanisms of plants. Thus, two silicon fertilizer levels (0 and 180 mg/kg of Silicon), three grass cover crops (Urochloa brizantha cv. BRS Piatã, U. brizantha cv. Marandu and Pennisetum glaucum cv. ADR 300) and three drought stress levels (100% pot capacity (PC): well‐watered conditions, 50% PC: moderate water stress and 25% PC: severe water stress) were laid out as a randomized block design in a factorial arrangement and replicated four times. Morphophysiological characteristics were recorded after 22 days of exposure to drought stress. Drought stress decreased the growth rate, leaf area (LA), net CO2 assimilation rate and stomatal conductance of the three cover crops. However, with the application of silicon fertilizer, a portion of the negative effects caused by water restriction could be mitigated, even though there were differences in the responses to silicon fertilization and water stress levels among the cover crop species. Silicon application potentiated the tillering and plant growth rate and increased the photosynthetic rate and water use efficiency of U. brizantha (cv. Marandu and cv. BRS Piatã) plants grown under moderate drought stress conditions.

Effect of combination of light and drought stress on physiology and oxidative metabolism of rice plants

The realized productivity of crop plants is generally lower than the potential productivity due to the influence of one or more external stresses (biotic and abiotic). Simultaneous occurrence of combination of abiotic stresses, which is more common under field condition, results in compounded effect on functional processes. Main focus of the present work is the combined effect of drought and light (irradiance) on rice plants. Potted seedlings of four selected rice lines (viz., IR36, N22, CRD40 and Bhootmuri) were exposed to three different levels of drought stress (50%, 25%, 12.5% of water) along with control (100%) in combination with three different light intensities (high, medium and low) during experimental period. After 7 days of stress, plant height and relative water content (RWC) were relatively low while root length increased with increasing water stress level and light intensity. Protein content increased with increasing water stress and light intensity, while chlorophyll level was higher at higher light intensities. Malondialdehyde (MDA) content, indicative of lipid peroxidation, increased with water stress only at high light intensities. Superoxide dismutase (SOD), peroxidase (POX) and ascorbate peroxidase (APX) activities increased with combined drought and light stress level, whereas catalase (CAT) activity was higher at higher light intensities. On the other hand, superoxide (O2.-) production, but not hydrogen peroxide (H2O2) production was higher with increasing water stress and light intensity. It appears that light-induced ROS (O2.-) production under drought condition provoked oxidative stress, though a potential mechanism of tolerance was apparent through antioxidant system.

Physiological and biochemical responses of almond rootstocks to drought stress

Water availability is a very important factor for the growth and development of plants, which limits the plant production capacity. Rootstocks are widely utilized to improve plants tolerance to various biotic and abiotic stresses. In this study, physiological and biochemical responses of fifteen almond rootstock candidates to drought stress were investigated under in vitro conditions. The shoot tips from fifteen almond rootstock candidates were cultured in MS medium containing 1.0 mg/L BAP, 0.01 mg/L IBA, 30 g/L sucrose and 7 g/L agar. Plantlets were exposed to 0%, 1% and 2% polyethyleneglycol (PEG) as drought stress levels during four weeks. At the end of the stress period, the genotypes were evaluated in terms of total number of shoots per explant, the proline, chlorophyll, total phenolics, total flavonoids and total protein contents, and the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) enzyme activities of the shoots were determined. The results showed that the drought stress increased total flavanoids, phenolic compounds and proline contents, while it reduced the number of shoots, chlorphyll a, b and total chlorophyll contents. Moreover, the drought stress increased the activities of APX, CAT and SOD enzymes in all genotypes. On the other hand, it decreased the protein content in six genotypes but increased the protein content in the nine genotypes. Based on the results, it was observed that the almond genotypes were generally tolerant to the drought. However, it was determined that the genotypes numbered 9, 29 and 185 showed more tolerant to the drought as compared to the other genotypes. These results suggest that improving the antioxidant system can enhance the drought tolerance of rootstocks.

Insight into the thiourea-induced drought tolerance in two chickpea varieties: Regulation of osmoprotection, reactive oxygen species metabolism and glyoxalase system

The sulfhydryl bioregulator thiourea (TU) is effective in ameliorating the negative impact of different abiotic stresses in plants. To explore the significant performance of TU (5 mM TU, as foliar spray) in conferring mild (25% depletion of water from field capacity, FC), moderate (50% depletion from FC) and severe (75% depletion from FC) drought stress (applied at 25 days after sowing), physiological and biochemical responses of two chickpea (Cicer arietinum L.) cultivars (cv. BARI Chola-7 and BARI Chola-9) were investigated in the current study. Shoot fresh weight, dry weight, chlorophyll content and leaf relative water content reduced noticeably in mild, moderate and severe drought stresses over control. A sharp increase of H2O2 accumulation, thiobarbituric acid reactive substances and proline content were noticed at any level of drought stress which further declined in TU-treated drought-stressed plants. Thiourea-foliar application also increased ascorbate and glutathione contents and upregulated antioxidant enzyme activities, compared to drought-stressed plants alone. Thiourea-induced increased glyoxalase I and glyoxalase II activities are the indications of upregulated methylglyoxal detoxification system. Enhancement of antioxidant defense and glyoxalase system, osmoregulation and protection of photosynthetic pigments by TU improved growth, imparted oxidative stress tolerance, ameliorated ROS toxicity and improved physiology of chickpea plants under drought stress.

​Screening of Chickpea (Cicer arietinum L.) Genotypes for Germination and Early Seedling Growth under PEG 6000 Induced Drought Stress

Background: Drought stress at germination and early growth stages hinders the seedling establishment in chickpea which ultimately affects the economic yield. Such adverse affects of drought can be mitigated by screening and identifying the tolerant genotypes of chickpea which is commonly cultivated under rain-fed conditions during post-rainy season. Methods: Effect of drought stress on germination and early seedling growth of thirty three chickpea genotypes was studied under four different concentrations of PEG 6000 (-0.3, -0.6, -0.9 and -1.2 MPa) along with control and hydration under laboratory conditions during 2018-19. Result: Significant variation was observed among the genotypes for germination, root length, shoot length and seedling vigour index under different concentrations of PEG 6000. Complete inhibition of germination was observed in most of the genotypes at -1.2 MPa. Based on the results obtained, JG 11 and NBeG 3 were considered as tolerant since they showed comparatively higher germination, root length, shoot length and seedling vigour even at -1.2 MPa, while NBeG 723 and NBeG 833 were considered as susceptible genotypes because of their poor germination and seedling growth even at lower levels of drought stress.

Influence of deficit irrigation in enhancing the Postharvest quality of vegetables

Deficit irrigation (DI) is an agricultural water management strategy by which crops are exposed to a level of drought stress either during a certain period of time or during the entire growing season. DI in peppers (Capsicum annuum L.) reduces the fresh weight of the harvested fruits. However, the results also proved that DI from flower initiation to fruit harvest lead to better water use efficacy of pepper cultivars, particularly Cv. Marconi Rosso. Further, the results proved that the postharvest quality, importantly the health-benefitting properties of peppers can be enhanced through the water-stress treatment. It leads to more accumulation of sugars as a mechanism to reduce the osmotic potential of the water-stressed plants. Similarly, the phenolic content, reported to have number of health benefitting properties, was also increased in all three cultivars of peppers with the deficit irrigation practice, under glass house condition.

Tolerance to salinity and drought stresses in pistachio (Pistacia vera L.) seedlings inoculated with indigenous stress-tolerant PGPR isolates

Salinity and drought are two major abiotic stresses that limit plant growth and productivity through their adverse effects on diverse physiological processes in plants, especially their photosynthetic capacity. Application of indigenous stress-tolerant plant growth-promoting rhizobacteria (PGPR) is among the eco-friendly strategies employed to ameliorate the harmful effects of salinity/drought stresses on plants. The present study was carried out to investigate the effects of stress-tolerant PGPR isolates on vegetative growth, nutritional, and photosynthetic parameters of pistachio (Pistacia vera L.) seedlings (cv. Badami-Riz–e-Zarand) under salinity and drought conditions. A factorial greenhouse experiment was conducted as a completely randomized design with three replications for 28 weeks in 2019. The treatments consisted of PGPR inoculations (control: non-inoculated, and inoculation with Staphylococcus sciuri, Zobellella denitrificans, and Arthrobacter endophyticus), three salinity levels (0, 1000 and 2000 mg NaCl kg−1 soil), and three irrigation intervals (C: irrigated every two days; D1: four days and D2: six days). The results indicated that, under high levels of salinity and drought stresses (2000 mg NaCl kg−1 soil + six-day irrigation intervals), separate inoculation of pistachio seedlings with Arthrobacter endophyticus, Zobellella denitrificans and Staphylococcus sciuri significantly enhanced the shoot and root dry weight, leaf area, leaf number, shoot and root K+ concentration and relative water content (RWC), which were accompanied by decreases in shoot and root Na+ concentrations. Moreover, the combined salinity and drought stresses had a greater effect on reducing total chlorophyll (TChl), carotenoids, chlorophyll fluorescence index (Fv/Fm), net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and water use efficiency (WUE), whereas application of the stress-tolerant PGPR isolates significantly increased these photosynthetic parameters compared to the non-inoculated seedlings at the corresponding stress levels. According to the results, the indigenous stress-tolerant PGPR isolates effectively improved the growth, physiological and photosynthetic parameters in pistachio seedlings subjected to salinity and drought stresses, which could be attributed to the local adaptation of the PGPR isolates as well as their plant growth-promoting properties that were unraveled in our in vitro studies, e.g. production of auxin, ACC-deaminase, siderophore, exopolysaccharides along with P/Zn solubilization activities.

Adaptive plasticity in plant traits increases time to hydraulic failure under drought in a foundation tree.

The viability of forest trees, in response to climate change-associated drought, will depend on their capacity to survive through genetic adaptation and phenotypic plasticity in drought tolerance traits. Genotypes with enhanced plasticity for drought tolerance (adaptive plasticity) will have a greater ability to persist and delay the onset of hydraulic failure. By examining populations from different climate-origins grown under contrasting soil water availability, we tested for genotype (G), environment (E) and genotype-by-environment (G×E) effects on traits that determine the time it takes for saplings to desiccate from stomatal closure to 88% loss of stem hydraulic conductance (time to hydraulic failure, THF). Specifically, we hypothesized that: (i) THF is dependent on a G×E interaction, with longer THF for warm, dry climate populations in response to chronic water deficit treatment compared with cool, wet populations, and (ii) hydraulic and allometric traits explain the observed patterns in THF. Corymbia calophylla saplings from two populations originating from contrasting climates (warm-dry or cool-wet) were grown under well-watered and chronic soil water deficit treatments in large containers. Hydraulic and allometric traits were measured and then saplings were dried-down to critical levels of drought stress to estimate THF. Significant plasticity was detected in the warm-dry population in response to water-deficit, with enhanced drought tolerance compared with the cool-wet population. Projected leaf area and total plant water storage showed treatment variation, and minimum conductance showed significant population differences driving longer THF in trees from warm-dry origins grown in water-limited conditions. Our findings contribute information on intraspecific variation in key drought traits, including hydraulic and allometric determinants of THF. It highlights the need to quantify adaptive capacity in populations of forest trees in climate change-type drought to improve predictions of forest die-back.

Resilience of oilseed rape plants to drought stress after exogenous application of AM1, an ABA-mimicking ligand

AM1 (ABA-mimicking ligand) is a newly identified signaling molecule for plants during drought tolerance. To investigate the potential role of AM1 in response of rapeseed to drought stress, we conducted experiments by growing rapeseed plants under different levels of drought stress with or without applying AM1 or ABA in a rain shelter. The results indicated that drought significantly inhibited rapeseed growth by damaging the photosynthesis system, increasing active oxygen accumulation, destroying the oxidative system, and worsening membrane lipid peroxidation. Exogenously applied AM1 and ABA both relieved the damage to rapeseed that was induced by drought stress. Compared with the drought-treated rapeseed, the AM1 treatment significantly improved plant height, number of green leaves, root collar thickness, leaf area, dry matter weight, and root cap ratios of rapeseed. In addition, Pn, Gs, Ci, Tr were significantly increased by the AM1 treatment. The AM1 treatment also alleviated the drought-induced reductions in Fv/Fm, ΦPSII, qN and ETR; induced an increase in NPQ; and resulted in decreased active oxygen accumulation and membrane lipid peroxidation. Although the ABA treatment relieved photosynthetic fluorescence and antioxidation system parameters to some extent, the effect was inferior to AM1 treatment. Yield under AM1 treatment was higher than that under ABA treatment but was still far lower than that of normal water supply control. In summary, AM1 is functionally similar to ABA in terms of drought relief and regulation, moreover has a better effect.