Mild Water Research Articles

Evaluation for Multiple Abiotic Stress Tolerance in Rice (Oryza Sativa) Genotypes

Abiotic stresses are the major constraints that affect the morphological, physiological and biochemical attributes of plants resulting in reduction of yield. Recently, combined occurrence of stresses has become a greater cause of concern in farmers’ fields. Hence, there is a need to identify genotypes that are tolerant to more than one stress. A study on physiological characterization for water and salinity stress was conducted in twenty rice genotypes during kharif 2022 at Regional Agricultural Research Station, Maruteru, Andhra Pradesh, India. Results showed that among all the treatments, root length, shoot length, root and shoot dry weight and chlorophyll content were greater under control followed by 1% mannitol, 2% mannitol and salinity stress. Visual scoring for water stress at seedling stage revealed that under mild water stress (1% M) in genotypes viz., CR4423-8, FL 478 and Pantara recorded 75-90% of survival and under severe water stress (2% M) 40-50% survival. Under salinity stress, the score 3 was recorded in FL 478 and 5 in Naveen, Pantara and CR 4423-75. For combined stresses, FL 478 and Pantara were identified as tolerant and can be suggested as donors.

Impact of Mild Water Stress During the Flowering Stage on Leaf Functional Traits and Yield of Selected Cowpea Varieties Grown in The Low Country Dry Zone of Sri Lanka

Impact of Mild Water Stress During the Flowering Stage on Leaf Functional Traits and Yield of Selected Cowpea Varieties Grown in The Low Country Dry Zone of Sri Lanka

The Effect of 6-Meter Underwater Diving Intervention on Recovery of Exercise-Induced Fatigue

Objective: To evaluate the effect of 6-meter underwater diving on recovery of exercise-induced fatigue and explore the potential mechanism. Method: Thirty-three male sophomores majored in physical education were included in this self-control, cross-over study. The fatigue was induced through programed swimming exercise at same intensity for both control and intervention groups. After exercise-induced fatigue, the subjects recovered through sitting on the floor and 6-meter underwater diving for 15 minutes in control and intervention groups respectively. The parameters observed included Heart Rate (HR), Critical Flicker Frequency (CFF), Simple Reaction Time (SRT) and Standing Long Jump (SLJ). Results: The HR was faster after exercise and recovery compared to that before exercise in both groups. SLJ was shorter after recovery compared to before exercise fatigue in both groups. After diving recovery, the CFF was lower than that before exercise fatigue, while the index of SRT was higher than that before exercise fatigue. Compared with the control group, the HR and SRT were significantly lower, but the SLJ and CFF were significantly higher in the intervention group than those of control group (HR, p<0.05; SRT, p<0.01, SLJ, CFF p<0.01). Conclusion: The fatigue recovery effect of 6m underwater environment is better than that of land recovery. The low temperature, mild hyperbaric oxygen, water pressure and buoyancy in under water environment may promote the repair of muscle and motor nerve after exercise and improve the exercise performance after intervention.

Hydrus-1D Model for Simulating Phosphorus Transport in Paddy Crop Irrigated with Alternate Wetting and Drying Practice

ABSTRACT The alternate wetting and drying (AWD) irrigation practice involves soil moisture stress-based irrigation scheduling which possibly affects the rice field’s phosphorus (P) transport and balance components. The focus of this study was to understand P-transport under AWD irrigation and estimate the associated balance components in rice using a solute transport model, Hydrus-1D. In this study, rice was cultivated in 30 lysimeter plots with three irrigation treatments (no soil water stress/NS, mild soil water stress/400 cm/MS, and severe soil water stress/750 cm/SS) and each treatment was replicated 10 times. The field experimental data were used to simulate P transport with the help of the Hydrus-1D model. The Hydrus-1D model was calibrated and validated for P transport within the soil matrix under AWD irrigation practice. The P distribution was mostly concentrated within the top puddled soil layer (0–20 cm) and did not move to the deeper soil layers. The simulated results indicate that the recommended dose of P with 3–5 cm ponding water depth will increase the P availability for rice and reduce the P leaching loss in AWD irrigation practice. The Hydrus-1D model can be used as a management tool to determine the appropriate P application rate and ponding water depth irrigated with AWD for which the required P nutrients are sufficiently available to rice and the P loss to the environment can be controlled for sustainable rice production.

Ecological Water Requirement of Vegetation and Water Stress Assessment in the Middle Reaches of the Keriya River Basin

Desert oases are vital for maintaining the ecological balance in arid regions’ inland river basins. However, fine-grained assessments of water stress in desert oasis ecosystems are limited. In our study, we aimed to evaluate the water stress in desert oasis ecosystems in the middle reaches of the Keriya River Basin, with a specific focus on their ecological functions and optimizing water resource management. We hypothesized that evapotranspiration has significant effects on ecological water consumption. First, we estimated the actual evapotranspiration (ET) and potential evapotranspiration (PET) based on the SEBS (surface energy balance system) model and remote sensing downscaling model. Then, the ecological water requirement (EWR) and ecological water stress (EWS) index were constructed to evaluate the ecological water resource utilization. Finally, we explored the influencing factors and proposed coping strategies. It was found that regions with higher ET values were mainly concentrated along the Keriya River and its adjacent farmland areas, while the lower values were observed in bare land or grassland areas. The total EWR exhibited the sequence of grassland > cropland > forest, while the EWR per unit area followed the opposite order. The grassland’s EWS showed a distinct seasonal response, with severe, moderate, and mild water shortages and water plenitude corresponding to spring, summer, autumn, and winter, respectively. In contrast, the land use types with the lowest EWS were water areas that remained in a state of water plentitude grade (0.08–0.20) throughout the year. Temperature and vegetation index were identified as the primary influencing factors. Overall, this study provides a reliable method for evaluating the EWR and EWS values of basin scale vegetation, which can serve as a scientific basis for formulating water resource management and regulation policies in the region.

Hydrodynamic tearing of bacteria on nanotips for sustainable water disinfection

Water disinfection is conventionally achieved by oxidation or irradiation, which is often associated with a high carbon footprint and the formation of toxic byproducts. Here, we describe a nano-structured material that is highly effective at killing bacteria in water through a hydrodynamic mechanism. The material consists of carbon-coated, sharp Cu(OH)2 nanowires grown on a copper foam substrate. We show that mild water flow (e.g. driven from a storage tank) can efficiently tear up bacteria through a high dispersion force between the nanotip surface and the cell envelope. Bacterial cell rupture is due to tearing of the cell envelope rather than collisions. This mechanism produces rapid inactivation of bacteria in water, and achieved complete disinfection in a 30-day field test. Our approach exploits fluidic energy and does not require additional energy supply, thus offering an efficient and low-cost system that could potentially be incorporated in water treatment processes in wastewater facilities and rural communities.

Optimizing water and nitrogen management strategies to improve their use efficiency, eggplant yield and fruit quality.

With improvement in living standards, consumer preferences for vegetables are changing from quantity- to quality-oriented. Water and nitrogen supply, as two major determinants of vegetable crop yield and quality, can be optimally managed to improve the yield and quality. To evaluate the response in yield, fruit quality, and water and nitrogen utilization of eggplant to different water and nitrogen management strategies, a 2-year (2021 and 2022) field trial under mulched drip irrigation was conducted. The growth period was divided into seedling, flowering and fruit set, fruit development, and fruit ripening stages. Three irrigation levels were applied during the flowering and fruit set stage: W0, adequate water supply (70%-80% of field water capacity, FC); W1, mild water deficit (60%-70% FC); and W2, moderate water deficit (50%-60% FC). In addition, three nitrogen application rates were applied: N1, low nitrogen level (215 kg ha-1); N2, medium nitrogen level (270 kg ha-1); and N3, high nitrogen level (325 kg ha-1). The irrigation and nitrogen rates were applied in all combinations (i.e., nine treatments in total). Adequate water supply throughout the reproductive period in combination with no nitrogen application served as the control (CK). The yield of the W1N2 treatment was significantly increased by 32.62% and 35.06% in 2021 and 2022, respectively, compared with that of the CK. Fruit soluble protein, soluble solids, and vitamin C contents were significantly higher under W1 than W2. Fruit quality was significantly higher under the N2 rate compared with the other nitrogen rates. The W1N2 treatment showed the highest water productivity, with a significant increase of 11.27%-37.84% (2021) and 14.71%-42.48% (2022) compared with that under the other treatments. Based on the average water-deficit degree and nitrogen application rate, W0 and N1 had the highest partial factor productivity of nitrogen. Assessment of the results using the TOPSIS (technique for order preference by similarity to an ideal solution) method indicated that mild water deficit in combination with the medium nitrogen application rate (W1N2) was the optimal water and nitrogen management strategy for cultivated eggplant. The present findings contribute novel insights into the sustainable cultivation of eggplant in an oasis arid environment.

Anaesthetic effect of clove basil (Ocimum gratissimum L.) essential oil on the giant river prawn (Macrobrachium rosenbergii, De Man 1879) exposed to different water pHs

The increasing concern for invertebrate welfare has led to improvements in management procedures and protective legislation; under discussion is the use of anaesthetic agents to improve the welfare of farmed prawns. In parallel, the aquatic environments present changes in their physical and chemical characteristics, like the acidification of waters. With this perspective, our study analysed the effectiveness of Ocimum gratissimum essential oil (EO-OG) as a natural anaesthetic for Macrobrachium rosenbergii at different concentrations and water pHs. Juvenile M. rosenbergii were exposed to five different EO-OG concentrations (0, 100, 200, 300, and 400 μL L−1) and vehicle control (ethanol), at two water pHs (8.08 ± 0.10 and 6.42 ± 0.15). Induction time was EO-OG concentration-dependent regardless of water pH; i.e. the time required for sedation and anaesthesia decreased with the increase of EO-OG concentration. No correlation was found between recovery time and EO-OG concentration. The most effective EO-OG concentration was 400 μL L−1, with prawn sedation in 2.0–2.5 min, anaesthesia in 3.5–4.1 min, and full recovery in 16 min, regardless of water pH. The different tested water pHs influenced sedation time; i.e. sedation time was higher in mild acidic water than in mild alkaline water. Anaesthesia induction and recovery times were similar at both water pHs. Survival rates were 100% in all experimental groups. In summary, EO-OG is effective as a sedative and anaesthetic for juvenile M. rosenbergii in routine procedures, at the recommended concentration of 400 μL L−1, with mild alkaline water.

Narrow root cone angle promotes deeper rooting, cooler canopy temperatures and higher grain yield in a rice (Oryza sativa L.) recombinant inbred line population grown under different water availabilities in aerobic production systems

Rice crops are one of the world’s major consumers of irrigation water. With water becoming more limited, water-saving aerobic production (AP) systems may provide an alternative to traditional flooded culture. Genotypes with narrow root cone angle (RCA) and subsequently deeper rooting systems are hypothesised as key for AP adaptation ensuring water uptake at depth. Using a recombinant inbred line (RIL) population and differential genotypes (narrow and wide RCA groups) derived from a Sherpa/IRAT109 cross, a glasshouse experiment and four field experiments with different water inputs in well-watered (WW, in two seasons), mild water deficit (MWD), and intermittent water deficit (IWD) conditions were carried out to characterise the relationship of RCA with grain yield (GY) and key physiological traits. Significant genotypic variation and group differences were found in root traits, canopy temperature and GY. Expression of genotypes with narrow RCA were found to be consistent across experiments and water availability conditions. Genotypes in the narrow RCA group produced a greater proportion of roots below 20 cm (7.4–17.7%), longer total root length (69.7%), cooler canopies (0.3–1.0 °C) and higher GY (14–62%) compared with wide RCA group. Two promising RILs were identified which expressed high GY in WW (12.0–13.4 t/ha) conditions while maintaining GY in IWD (up to 9.4 t/ha). Higher GY was obtained in genotypes with cooler canopies (r = −0.72) and narrow RCA (r = −0.39) in IWD. Narrower RCA was associated with higher total root length (r = −0.70) and higher stomatal conductance (r = −0.71) in the glasshouse and proportion of deep roots (r = −0.65) and cooler canopies (r = 0.66) in the field. To our knowledge, this was one of the foremost studies exploring and demonstrating such relationships in rice AP systems. Root traits determined in the field were congruent with the other root-related traits driving differences between RCA groups measured in the glasshouse providing confidence with the field phenotyping methods. This work demonstrated the advantage conferred by the development of narrow RCA in aerobic conditions, presented improved physiological understanding of RCA and with genomics assisted breeding, is considered valuable for the development of AP-adapted, sustainably produced rice.

Response of Water Stress and Bacterial Fertilizer Addition to the Structure of Microbial Flora in the Rhizosphere Soil of Grapes Under Delayed Cultivation

ABSTRACT The objectives of this study were to reveal the soil microbial structures in the rhizosphere soil of the delayed cultivation and to evaluate the effects of water stress and bacterial fertilizer on major bacteria. The experiment was conducted in 2019 in Yongdeng County, Gansu Province. Three treatments of water regulation were set, including the moderate water stress, mild water stress and adequate water supply treatment with the bacterial fertilizer added at the levels of no addition (0 g), small addition (75 g) and large addition (150 g), respectively. The results showed that the relative abundance of dominant species of soil microorganisms was significantly higher under sufficient water supply and mild water stress treatment than under moderate water stress treament. Under the mild water stress condition, the relative abundance of the most dominant species in each classification level sequentially decreased with the bacterial fertilizer added increasingly. Adding a small amount of bacterial treatment fertilizer to moderate water stress can improve the overall abundance of soil microbial communities during the growth period of new shoots. It was found that Proteobacteria, Bacteroidetes, Gemmatimonadetes, Actinobacteria, Firmicutes, Acidobacteria, Chloroflexi, Planctomycetes, Thaumarchaeota, Verrucomicrobia, and the other bacteria were the major bacterial phyla in the rhizosphere soil of delayed cultivation grapes, among, which Proteobacteria were the most dominant group. Therefore, adding a small amount of bacterial fertilizer under the mild water stress treatment can not only improve the diversity and richness of soil microorganisms during the fruit expansion period, but also significantly save water resources compared with the traditional irrigation regimes.

Organ-specific responses during acclimation of mycorrhizal and non-mycorrhizal tomato plants to a mild water stress reveal differential local and systemic hormonal and nutritional adjustments

Main conclusionTomato plant acclimation to a mild water stress implied tissue-specific hormonal and nutrient adjustments, being the root one of the main modulators of this response.Phytohormones are key regulators of plant acclimation to water stress. However, it is not yet clear if these hormonal responses follow specific patterns depending on the plant tissue. In this study, we evaluated the organ-specific physiological and hormonal responses to a 14 day-long mild water stress in tomato plants (Solanum lycopersicum cv. Moneymaker) in the presence or absence of the arbuscular mycorrhizal fungus Rhizoglomus irregulare, a frequently used microorganism in agriculture. Several physiological, production, and nutritional parameters were evaluated throughout the experiments. Additionally, endogenous hormone levels in roots, leaves, and fruits at different developmental stages were quantified by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC–MS/MS). Water deficit drastically reduced shoot growth, while it did not affect fruit production. In contrast, fruit production was enhanced by mycorrhization regardless of the water treatment. The main tissue affected by water stress was the root system, where huge rearrangements in different nutrients and stress-related and growth hormones took place. Abscisic acid content increased in every tissue and fruit developmental stage, suggesting a systemic response to drought. On the other hand, jasmonate and cytokinin levels were generally reduced upon water stress, although this response was dependent on the tissue and the hormonal form. Finally, mycorrhization improved plant nutritional status content of certain macro and microelements, specially at the roots and ripe fruits, while it affected jasmonate response in the roots. Altogether, our results suggest a complex response to drought that consists in systemic and local combined hormonal and nutrient responses.

Efficient depolymerization of alkali lignin to monophenols using one-step synthesized Cu–Ni bimetallic catalysts inlaid in homologous biochar

The efficient depolymerization of lignin for the production of high-value chemicals is essential for the development of a sustainable and competitive biorefinery. In this study, we report the preparation of homologous biochar-supported inlaid Cu–Ni catalysts (CuxNiy/BC) using a one-step method, and their application for lignin depolymerization in mild water without the need for external hydrogen, additives, or co-catalysts. The Cu1Ni3/BC (0.05 g catalyst, 8 h, 280 °C, and 18 mL water) showed exceptional catalytic activity, with a monophenol yield of 94.35 ± 2.92 mg/g, bio-oil yield of 68.98 ± 1.42%, and a lignin conversion rate of 92.36 ± 1.99%, which outperformed both the biochar support and monometallic catalysts. The outstanding catalytic performance of Cu1Ni3/BC was attributed to its strong metal-support interaction, alloy sites, and well-dispersed nanoparticles. Reusability experiments demonstrated that the Cu1Ni3/BC exhibited relatively good stability for up to four reuses, with only a 2.32% reduction in catalytic activity per cycle. Mechanism investigation revealed that the Cu1Ni3/BC, with its abundant mesoporous structure and enhanced acid sites, displayed excellent deoxygenation ability, enabling effective cleavage of C–O/C–C bonds and the production of G-type phenols. This approach provides new insights into the large-scale utilization of lignin for the production of high-value chemicals.

Plant Photosynthesis and Dry Matter Accumulation Response of Sweet Pepper to Water–Nitrogen Coupling in Cold and Arid Environment

In order to optimize the water and nitrogen management mode and realize the efficient scale production of sweet pepper, from 2021 to 2022, field experiments on sweet pepper cultivation with different water and nitrogen coupling modes were conducted in the Hexi Oasis irrigation areas. The regulation effects of the water–nitrogen coupling mode on the dry matter accumulation characteristics, photosynthesis, yield, and water–nitrogen utilization efficiency of sweet pepper were further discussed. Irrigation was set for full irrigation (W1, 75–85% FC [field capacity]), mild (W2, 65–75% FC), and moderate (W3, 55–65% FC) water deficit levels. Three levels of nitrogen were applied, high (N1, 300 kg·ha−1), medium (N2, 225 kg·ha−1) and low (N3, 150 kg·ha−1), with full irrigation and no nitrogen application used as the control (CK). The results showed that the appropriate water–nitrogen coupling mode could enhance the photosynthetic rate, increase dry matter accumulation and the accumulation rate, advance the days of a maximum rate of dry matter accumulation, and improve yield and water–nitrogen utilization efficiency. N1W1 had the greatest dry matter accumulation, the mean rate and the maximum increase rate of dry matter accumulation in sweet pepper, which was not a significant difference from N2W2, but significantly increased by 19.61%, 19.67%, and 23.45%, respectively, compared with CK. Water deficit significantly advanced the days of a maximum rate of dry matter accumulation. The days of a maximum rate of dry matter accumulation appeared 1.18–5.79 days earlier at W3 than at W2 and W1, and the maximum rate appeared gradually later with increasing irrigation. The net photosynthetic rate, the transpiration rate, and stomatal conductance of N2W2 sweet pepper showed the best performance at all growth stages, significantly increasing by 23.87%, 27.71%, and 27.39%, respectively, compared with CK. Moreover, the Intercellular CO2 concentration was significantly reduced by 14.77% in N2W2 compared to CK. The N2W2 had the highest yield, water use efficiency, and irrigation water use efficiency of sweet pepper, significantly increasing 26.89%, 33.74%, and 31.22% compared to CK. Excessive water and nitrogen dosage reduced nitrogen partial factor productivity, while an appropriate increase in irrigation under reduced nitrogen conditions facilitated the water nitrogen potential. Passage path analysis further showed that water–nitrogen coupling promotes plant biomass formation and distribution by increasing photosynthetic assimilation capacity, ultimately increasing yield. Therefore, the N2W2 treatment (65–75% FC, 225 kg·ha−1) is the ideal water and nitrogen mode for obtaining higher yields and water and nitrogen use efficiency of sweet pepper in a cold and arid environment.

Hormesis Responses of Photosystem II in Arabidopsis thaliana under Water Deficit Stress.

Since drought stress is one of the key risks for the future of agriculture, exploring the molecular mechanisms of photosynthetic responses to water deficit stress is, therefore, fundamental. By using chlorophyll fluorescence imaging analysis, we evaluated the responses of photosystem II (PSII) photochemistry in young and mature leaves of Arabidopsis thaliana Col-0 (cv Columbia-0) at the onset of water deficit stress (OnWDS) and under mild water deficit stress (MiWDS) and moderate water deficit stress (MoWDS). Moreover, we tried to illuminate the underlying mechanisms in the differential response of PSII in young and mature leaves to water deficit stress in the model plant A. thaliana. Water deficit stress induced a hormetic dose response of PSII function in both leaf types. A U-shaped biphasic response curve of the effective quantum yield of PSII photochemistry (ΦPSII) in A. thaliana young and mature leaves was observed, with an inhibition at MiWDS that was followed by an increase in ΦPSII at MoWDS. Young leaves exhibited lower oxidative stress, evaluated by malondialdehyde (MDA), and higher levels of anthocyanin content compared to mature leaves under both MiWDS (+16%) and MoWDS (+20%). The higher ΦPSII of young leaves resulted in a decreased quantum yield of non-regulated energy loss in PSII (ΦNO), under both MiWDS (-13%) and MoWDS (-19%), compared to mature leaves. Since ΦNO represents singlet-excited oxygen (1O2) generation, this decrease resulted in lower excess excitation energy at PSII, in young leaves under both MiWDS (-10%) and MoWDS (-23%), compared to mature leaves. The hormetic response of PSII function in both young and mature leaves is suggested to be triggered, under MiWDS, by the intensified reactive oxygen species (ROS) generation, which is considered to be beneficial for activating stress defense responses. This stress defense response that was induced at MiWDS triggered an acclimation response in A. thaliana young leaves and provided tolerance to PSII when water deficit stress became more severe (MoWDS). We concluded that the hormesis responses of PSII in A. thaliana under water deficit stress are regulated by the leaf developmental stage that modulates anthocyanin accumulation in a stress-dependent dose.

Determination of Water Stress in Wheat Crops by Thermal Images Under Mediterranean Conditions

ABSTRACT Canopy temperature is used as an indicator of plant water stress. In recent years, technological advances have allowed improved applications in agriculture from temperature sensors clamped on leaves to short-range remote-sensing, such as infrared thermometry and thermal imaging. There are many scientific studies on the use of thermal imaging to determine crop water stress; however, no study on wheat crops has been found in the literature. Therefore, this study aimed to determine the detectability of water stress in wheat by using thermal images. In the experiment, drainage-type, weighable lysimeters were used to make precise irrigations and obtain components of the water budget for calculating the plant water consumption. Wheat crops were grown under four different irrigation levels including no water stress as control (I100), mild water stress (I75), moderate water stress (I50), and severe water stress (I25). When the thermal images were examined, it can be seen that pre-irrigation images reflect water stress conditions better than post-irrigation. The warm color distribution was more evident under severe water stress, whereas cold colors were dominant under no water stress. During the experimental period, the plant leaf temperatures varied from 17.5 to 34.2°C, while the spike temperatures ranged from 26.6°C to 36.3°C. The lowest plant leaf and spike temperature values were observed under control, whereas the highest values were obtained under severe water stress. It can be said that thermal cameras that provide fast and contactless data acquisition have the potential to be used in detecting water stress in wheat crops.

Willow bark proanthocyanidins with potential for water treatment: Chemical characterization and zinc/bisphenol A removal

This study investigates the chemical structure of proanthocyanidin-rich crude extracts from willow bark and these materials were tested initially as adsorbents for artificial (waste)water treatment. The crude extracts were obtained through mild water extraction and the colorant fractions were further chromatographically fractionated to understand the chemical structure of the willow bark proanthocyanidins. The chemistry of crude extracts and purified fractions were investigated using nuclear magnetic resonance (NMR) and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Both NMR (liquid and solid-state) and UPLC-MS/MS suggest that the crude extracts constitute of interflavan linked flavan-3-ols, i.e. proanthocyanidins with both procyanidin (PC)-type and prodelphinidin (PD)-type subunits, with the PC/PD ratio of approximately 2.3–2.5. PD-type proanthocyanidins were detected from the purified colorant fractions only with UPLC-MS/MS. Both the UPLC-MS/MS and size exclusion chromatography suggest that the crude extracts have an average oligomerization degree of roughly 5–6 flavan-3-ol units. Adsorption experiments showed that the activated foams made of crude extracts were effective in removing both zinc and Bisphenol A (BPA) with removal efficiencies of roughly 80–90% and thus these willow bark-derived proanthocyanidins are promising in water treatment. The significance of this study suggests the upgrading use of crude extracts for water treatment could significantly improve the value of willow bark.

Comparative analysis of drought-responsive biochemical and transcriptomic mechanisms in two Dendrobium officinale genotypes

Drought stress is one of the most sever natural disaster, threatening to plant growth and global crop security. Dendrobium officinale is a drought-tolerance crop with effective defense mechanisms against drought stress, as well as an important economic plant for medicinal, cosmetic, or ornamental purposes. Revealing the regulatory mechanisms conferring drought resistance upon D. officinale is thus crucial for genetic breeding and water-saving agriculture. In this study, the biochemical and transcriptomic profiles of two D. officinale genotypes were comprehensively analyzed under three drought stress conditions. The M genotype has a relative weaker drought tolerance, as shown by withered leaves, rapidly accumulated malondialdehyde, and severely repressed expression of photosynthesis-related genes under water deficit. In the O genotype (drought-tolerant genotype), proline content, ascorbate peroxidase and catalase activities significantly increased with intensifying drought stress, showing a higher level than that in the M genotype, especially under severe drought stress. By contrast, superoxide dismutase and peroxidase activities were higher in the M genotype under moderate and severe water deficient. Transcriptome analysis demonstrated that mild water deficit initiated the plant hormone signal transduction pathway, while severe drought stress launched the flavonoid biosynthesis pathway in both D. officinale genotypes. Notably, high expression of most protein phosphatases type 2 C in the M genotype, a negative regulator of abscisic acid signaling, may partially explain the relative weaker drought tolerance of the M genotype. Moreover, the higher flavonoid content corresponding with the highly expressed PAL and DFR in the O genotype than in the M genotype, may confer a stronger drought tolerance upon the O genotype under water deficit. Additionally, the biased expression pattern of heat shock proteins, late embryogenesis abundant proteins, and dehydrins may also be linked to the different drought responses of the two D. officinale genotypes. Our results provide a theoretical basis for drought-tolerant crops breeding and water-sparing agriculture.

Some physio-biochemical traits of sunflower (<em>Helianthus annuus</em> L.) as affected by arbuscular mycorrhizal fungi inoculation under different irrigation treatments

Plant-arbuscular mycorrhizal (AM) fungi association is one of the oldest symbiotic relationships between organisms. This relationship may be more important under stress conditions such as drought and can help the host plant tolerate drought. This study was conducted in 2016 and 2017 at the Agricultural Research Farm of Razi University, Kermanshah, Iran to evaluate the effect of AM fungi (AMF) inoculation (with either Funneliformis mosseae or Rhizophagus intraradices) on some physio-biochemical traits of three sunflower cultivars under different soil irrigation treatments (severe water deficit stress, mild water deficit stress and well-watered). In both years, water deficit conditions significantly reduced leaf relative water content (RWC), chlorophyll concentrations (a, b and total) and shoot phosphorus concentration (SPC) while simultaneously increasing shoot proline levels and malondialdehyde (MDA) concentrations. AMF inoculation had positive effects on RWC, chlorophyll concentrations and SPC irrespective of sunflower cultivar and irrigation treatment. Shoot proline concentration and MDA reduced more in AM than non-AM plants. In most cases F. mosseae performed better than R. intraradices in terms of plant performance. Moreover, the improvements caused by AM fungi were more evident under water deficit than well-watered condition. It may be concluded that AM inoculation can alleviate the negative effects of water deficit stress on some important physio-biochemical traits of sunflower grown in the field, and can be considered as a practical and economical approach to improve crop performance in environments exposed to water limitations.

Exogenous β-Aminobutyric Acid (BABA) Improves the Growth, Essential Oil Content, and Composition of Grapefruit Mint (Mentha suaveolens × piperita) under Water Deficit Stress Conditions

Grapefruit mint, Mentha suaveolens × M. piperita, belonging to the Lamiaceae family, is an important medicinal plant with applications in the cosmetic, pharmaceutical, food, and nutraceutical industries. Environmental factors such as cold, salinity, and water deficit significantly impact the quantity and quality of the active compounds of medicinal plants. To examine the effects of drought stress and β-aminobutyric acid (BABA) as an elicitor on the biochemical characteristics and essential oil (EO) profile of grapefruit mint, a factorial experiment was conducted in a completely randomized design (CRD) with two factor and three replications under greenhouse conditions. The first factor included field moisture capacity (FC) as the control (100% FC), mild (75% FC), moderate (55% FC), and severe water deficit stress (35% FC), while the second factor consisted of 0 (control plants without BABA), 0.8, 1.6, and 2.4 mM of BABA foliar application. Water stress and BABA application significantly affected the EO content and composition of grapefruit mint. The highest content of EO was observed in mild drought stress and BABA spraying at 1.6 to 2.4 mM, which increased by about 140% compared with the control condition. The EO components were identified using GC-FID and GC-MS analysis. Linalool (33.7–47.3%) and linalool acetate (31.2–52%) were the most abundant compounds. The highest content of linalool acetate was observed in severe drought stress (35% FC) with foliar application of BABA (1.6 mM), which increased by 33.86% compared with the control condition. However, the highest content of linalool was observed under normal irrigation with foliar application of 0.8 to 1.6 mM BABA. Based on the results, severe drought stress reduced the total chlorophyll and carotenoids by 81.76 and 64.6% compared with the control condition, respectively. Water stress and the foliar application of BABA significantly affected the activity of antioxidant enzymes (ascorbate peroxidase, APX; guaiacol peroxides, GPX; and superoxide dismutase, SOD). The application of 1.6 mM BABA significantly increased the activity of antioxidant enzymes under water stress conditions. Finally, our results showed that the application of BABA (mainly at 1.6 mM) can improve the grapefruit mint yield and EO profile under water stress conditions.

Cumulative response of Tempranillo vines to the crop forcing technique and pre-forcing and post-veraison water stress in terms of yield and grape and wine quality

Elevated temperatures during berry ripening are detrimental to grape quality. The crop forcing technique (summer pruning that ‘forces’ the vine to start a new cycle) increases must acidity and malic acid concentration at harvest by delaying the date of veraison. However, little information is available on the sensitivity to water stress of forced vines. A 3-year trial was conducted to test three irrigation strategies in forced vines: a minimum threshold of mid-day stem water potential (Ψs) of −0.75 MPa before forcing (DI), a minimum Ψs threshold of −1.2 MPa only after veraison (RDI), and the combination of both treatments (DI + RDI). Results were compared to a non-forced treatment with a minimum Ψs threshold of −1.2 MPa after veraison (C-RDI). Must acidity increased, and pH decreased in the forced treatments. However, yield was reduced by 35% and irrigation requirements increased by 20% when comparing forced and unforced treatments. As a result, water use efficiency was reduced in forced treatments. Only after a dry spring did the, DI (11%) and DI + RDI (30%) treatments, save water compared to the C-RDI treatment. Moreover, although Ψs before forcing never fell below −0.75 MPa, a significant negative correlation (R2 = 0.76) was found between the integral of water stress before the vines were forced and the number of forced bunches per vine. Post-veraison water stress in forced vines reduced the polyphenol content of the wine. Our findings suggest that forced vines are extremely sensitive to even mild water stress.