Mild Water Stress Research Articles

Arbuscular Mycrorrhizal Fungi Inoculation and Applied Water Amounts Modulate the Response of Young Grapevines to Mild Water Stress in a Hyper-Arid Season.

Several factors may affect the success of a replanting vineyard. Given the current environmental conditions, an optimized irrigation schedule would still be one of the most desirable tools to improve crop productivity and fruit quality. On the other hand, the symbiosis of grapevines with arbuscular mycorrhizal fungi (AMF) is a key component of the vineyard production systems improving the vine growth, nutrient uptake, and berry quality. The aim of this study was to characterize the response of Merlot grapevines to AMF inoculation and two different irrigation amounts in their first productive year. The experiment was conducted on 2-year Merlot grapevines inoculated with AMF (I) or not-inoculated (NI) and subjected to two irrigation amounts, full irrigated (FI), where the amount of water was enough to maintain expansive growth and half irrigated (HI) where plants received the half of the amount of water of FI plants. Water status, gas exchange parameters, growth, mineral content, berry composition, and mycorrhizal colonization were monitored through the season. AMF inoculation improved the grapevine vegetative growth, water status, and photosynthetic activity, especially when vines were subjected to HI irrigation; however, no effect was observed on the leaf mineral content, must pH, total soluble solids, or total acidity. The main effects were observed on the flavonoid composition of berry skins at harvest. Irrigation amounts and mycorrhizal inoculation modified cyanidin and peonidin derivatives whereas flavonol composition was mainly affected by irrigation treatments. A strong relationship between the mycorrhizal colonization rate of roots and total quercetins, cyanidins, and peonidins was found. Findings support the use of a mycorrhizal inoculum and a better water management in a hyper-arid growing season; however, these results may be affected by edaphoclimatic characteristics and living microbiota in vineyard soils, which should be taken into account before making the decision of inoculating the vineyard.

Detecting Mild Water Stress in Olive with Multiple Plant-Based Continuous Sensors.

A comprehensive characterization of water stress is needed for the development of automated irrigation protocols aiming to increase olive orchard environmental and economical sustainability. The main aim of this study is to determine whether a combination of continuous leaf turgor, fruit growth, and sap flow responses improves the detection of mild water stress in two olive cultivars characterized by different responses to water stress. The sensitivity of the tested indicators to mild stress depended on the main mechanisms that each cultivar uses to cope with water deficit. One cultivar showed pronounced day to day changes in leaf turgor and fruit relative growth rate in response to water withholding. The other cultivar reduced daily sap flows and showed a pronounced tendency to reach very low values of leaf turgor. Based on these responses, the sensitivity of the selected indicators is discussed in relation to drought response mechanisms, such as stomatal closure, osmotic adjustment, and tissue elasticity. The analysis of the daily dynamics of the monitored parameters highlights the limitation of using non-continuous measurements in drought stress studies, suggesting that the time of the day when data is collected has a great influence on the results and consequent interpretations, particularly when different genotypes are compared. Overall, the results highlight the need to tailor plant-based water management protocols on genotype-specific physiological responses to water deficit and encourage the use of combinations of plant-based continuously monitoring sensors to establish a solid base for irrigation management.

Multi-seasonal water-stress memory versus temperature-driven dynamic structural changes in grapevine.

Perennial plants perpetually adapt to environmental changes in complex and yet insufficiently understood manner. We aimed to separate the intra-seasonal temperature effects on structure and function from perennial and annual water stress effects. This study focused on grapevine (Vitis vinifera L. 'Cabernet Sauvignon') petioles, which being a continuously produced organ, represent the current status of the plant. Field-grown mature plants subjected to multi-annual irrigation treatments (severe water stress, mild water stress and non-stressed) throughout the growing season were compared with greenhouse-grown plants under three temperature regimes (22, 28 and 34 °C). Physiological and functional anatomy parameters were measured. A generalized additive model (GAM) based on meteorological and lysimeter-based field data was applied to determine the relative influence of various meteorological parameters on evapotranspiration (ETc) during the growing season in the field experiment. At the beginning of the growing season, in May, petioles in the severe stress treatment showed a stress-related structure (decreased length, safer hydraulic structure and increased lignification), though having high values of stem water potential (SWP). As the season progressed and temperatures increased, all water availability treatments petioles showed similar changes, and at the end of season, in August, were structurally very similar. Those changes were independent of SWP and were comparable to high temperature-induced changes in the greenhouse. In contrast, stems hydraulic structure was strongly influenced by water availability. Regression analyses indicated a relationship between petioles xylem structure and stomatal conductance (gs), whereas gs (but not SWP) was temperature-dependent. The GAM showed that ETc was mainly dependent on temperature. Our results indicate a perennial water-stress memory response, influencing the petiole structure at the beginning of the following season. Intra-seasonally, the petiole's structure becomes independent of water status, whereas temperature drives the structural changes. Thus, ongoing climate change might disrupt plant performance by purely temperature-induced effects.

Plant-atmosphere and soil-atmosphere temperature differences and their impact on grain yield of super hybrid rice under different irrigation conditions.

Continued drought during the late growth stage of super hybrid rice (SHR) markedly reduces yield, and management practices that use water more efficiently can contribute greatly to high and stable yields from SHR. The absolute temperature differences (ATDs) between the rice plant and the atmosphere and between the soil and the atmosphere are believed to be important determinants of grain yield. However, it has not previously been determined whether these ATDs have any effect on SHR yields under water-saving cultivation. A two-year field experiment involving two SHR varieties, Liangyoupeijiu (LYPJ) and Y-Liangyou 9000 (YLY900), evaluated the effects of reducing water supply from mid-booting to maturity on grain yield, canopy relative humidity (CRH), leaf area index (LAI), and ATDs between the ambient temperature and the leaf surface, panicles, canopy, and soil. Grain yield increased significantly under shallow water irrigation (SW), by 8.84% (YLY900) and 12.26% (LYPJ), but decreased significantly under mild water stress (MS, -20 to -30 kPa), by 14.36% (YLY900) and 9.47% (LYPJ), as well as severe water stress (SS, -40 to -50 kPa), by 35.06% (YLY900) and 28.74% (LYPJ). As water supply decreased, so did the CRH and the ATDs, with significant decreases under MS and SS. The temperature differences were significantly and positively correlated with grain yield (P < 0.01) in both cultivars. LAI was increased under SW conditions, but was significantly decreased under MS and SS. Our study suggests that the dual goal of saving water while maintaining high yield can be achieved by applying SW irrigation from mid-booting to maturity and by adopting cultivation measures that maintain high CRH and high plant-atmosphere and soil-atmosphere ATDs in order to alleviate water stress. YLY900 has a higher yield potential than LYPJ under SW conditions, suggesting that its wide cultivation may help achieve this dual goal.

The Influences of Different Irrigation Water on Spatial Distribution of Cotton Bolls and Yields

Takeing the jujube orchard intercropping cotton as experimental material In southern Xinjiang to study the influences of different irrigation water on spatial distribution of cotton bolls and yields. Setting the moderate water stress W1 (250 m3/667m2), mild water stress W2(300 m3/667m2), the appropriate moisture W3(350 m3/667m2), the sufficient water supply W4(400 m3/667m2), in total four different irrigation water processing. The results show that : (1) The cotton boll’ shedding rate in different water processing in order W4 > W1 > W3 > W2,the shedding rate of upper and lower is much higher than the middle fruit spur.(2)the effective boll of cotton are mainly in the middle part. (3)The total boll weight of cotton middle fruit spur greater than the total boll weight of fruit spur in the upper and lower. And the lower part’ weight is slightly higher than the upper.(4) The boll weight of upper fruit spur have bigger fluctuations than the lower,each part of the cotton boll weight as W2 > W3 > W4 > W1. (5) Four water treatment have a little effect on lint percent, seed cotton and ginned cotton showed the same trend as W2 > W3 > W4 > W1. Comprehensive consideration in many aspects, the drop irrigation amount 300-350m3/667m2 could as the reference standard of this locality jujube orchard intercropping.

Normalization of the crop water stress index to assess the within-field spatial variability of water stress sensitivity

This paper presents a novel methodology for identifying homogeneous areas within high-frequency drip-irrigated orchards and for defining the most sensitive and resistant areas of the field to water stress. The methodology proposed here is based on the assessment of water status at the tree level during mild water stress using remote sensing derived indicators which provide valuable information about the spatial distribution of the response to water stress within an orchard. The areas more resistant to water stress will maintain a good water status, while those prone to water stress will develop initial symptoms of water deficit. The study was performed over three different peach orchards that were evaluated from 2 to 3 years. Water status was monitored using high-resolution thermal imagery acquired before and after the onset of water stress. The Thermal Sensitivity Index (TSI), derived from the difference of the CWSI and the cumulated reference evapotranspiration between the two dates, demonstrated to be well related to the increase of stem water potential. The spatial distribution of TSI enables the identification of sensitive areas within a peach orchard, a first step for establishing precision drip irrigation programs.

Postveraison Deficit Irrigation Effects on Fruit Quality and Yield of "Flame Seedless" Table Grape Cultivated under Greenhouse and Net.

Lack of color in the skin of red table grape varieties is a serious problem in areas of warm climate. This problem is often addressed by the application of ethylene release products such as ethephon. Strict regulation in the use of this product in EU forces European grape producers to look for suitable alternatives. With the aim to increase red skin color, we applied regulated deficit irrigation (RDI) strategies from veraison until harvest on “Flame Seedless” table grape vines cultivated under nets and under a plastic greenhouse in South East Spain, and compared yield and fruit quality with vines fully irrigated under the same net and plastic greenhouses. Our results show a modest improvement in the percentage of commercial clusters with better skin color, probably because the short duration of the deficit irrigation period only caused a slight decrease in soil water content and a mild water stress in RDI vines. Larger differences were observed under the more limiting conditions of the plastic greenhouse for light environment, especially when berry skin color was measured by CIRG (color index of red grape). More noticeable effect of RDI was noted on fruit earliness. Water savings were also remarkable. Negative effects of RDI on berry size or total soluble solid content were not perceived. Our results suggest that RDI is a suitable strategy to save irrigation water without substantial negative effects on yield and berry size. However, the effects on skin color were insufficient in the trial conditions.

Effect of Water Stress on Reproduction and Colonization of Podosphaera aphanis of Strawberry

In a number of pathosystems involving the powdery mildews (Erysiphales), plant stress is associated with decreased disease susceptibility and is detrimental to pathogen growth and reproduction. However, in strawberry, anecdotal observations associate severe powdery mildew (Podosphaera aphanis) with water stress. In a 2017 survey of 42 strawberry growers in Norway and California, 40 growers agreed with a statement that water-stressed strawberry plants were more susceptible to powdery mildew compared with nonstressed plants. In repeated in vitro and in vivo experiments, we found that water stress was consistently and significantly unfavorable to conidial germination, infection, and increases in disease severity. Deleterious effects on the pathogen were observed from both preinoculation and postinoculation water stress in the host. Soil moisture content in the range from 0 to 50% was correlated (R2 = 0.897) with germinability of conidia harvested from extant colonies that developed on plants growing at different levels of water stress. These studies confirm that P. aphanis fits the norm for biotrophic powdery mildews and hosts under stress. Mild water stress, compared with a state of optimal hydration, is likely to decrease rather than increase susceptibility of strawberry to P. aphanis. We believe it is possible that foliar symptoms of leaf curling due to diffuse and inconspicuous infection of the lower leaf surfaces by P. aphanis could easily be mistakenly attributed to water stress, which we observed as having a nearly identical leaf curling symptom in strawberry.

How does water and salt stress affect the germination and initial growth of Brazilian soya bean cultivars?

AbstractThe effects of water and salt stress on rate of germination and seedling growth were investigated under laboratory conditions in 46 soya bean genotypes from Central‐West region of Brazil to verify how these stresses may limit crop establishment during the initial growth stage and also to identify the most tolerant genotypes to drought and salinity. Mild water and salt stresses were imposed by seed exposure to –0.20 MPa iso‐osmotic solutions with polyethylene glycol—PEG 6000 (119.57 g/L) or NaCl (2.357 g/L) for 12 days at 25°C. The germination percentage, seedling length and seedling dry matter were measured, and then, salt or drought tolerance indexes were calculated. The “NS 5909 RG,” “NS 7000 IPRO,” “NS 7338IPRO,” “FPS Solimões RR,” “NS 5151 IPRO,” “SYN 13610 IPRO,” “LG 60177 IPRO,” “NS 6909 IPRO” and “BMX Desafio RR” were identified as the most drought‐tolerant genotypes, whereas under salinity conditions, the genotypes “5D 615 RR,” “BMX Desafio RR,” “5D 6215 IPRO” and “BMX Ponta IPRO” were identified as tolerant. The “BMX Desafio RR” is the genotype most adapted to both stress conditions and, therefore, should be used under conditions of water shortage and excess salt in the soil at sowing time.

Maize lateral root developmental plasticity induced by mild water stress. II: Genotype-specific spatio-temporal effects on determinate development.

Maize lateral roots exhibit determinate growth, whereby the meristem is genetically programmed to stop producing new cells. To explore whether lateral root determinacy is modified under water deficits, we studied two maize genotypes (B73 and FR697) with divergent responses of lateral root growth to mild water stress using an experimental system that provided near-stable water potential environments throughout lateral root development. First-order laterals of the primary root system of FR697 exhibited delayed determinacy when grown at a water potential of -0.28 MPa, resulting in longer and wider roots than in well-watered (WW) controls. In B73, in contrast, neither the length nor width of lateral roots was affected by water deficit. In water-stressed FR697, root elongation continued at or above the maximum rate in WW roots for 3 days longer, and was still 45% of maximum when WW roots approached their determinate length. Maintenance of root elongation was associated with sustained rates of cell production. In addition, kinematic analyses showed that reductions in tissue expansion rates with aging were delayed in the longitudinal, radial and tangential planes throughout the root growth zone. Thus, this study reveals large genotypic differences in the interaction of water stress with developmental determinacy of maize lateral roots.

Carbon dioxide fertilization effect on plant growth under soil water stress associates with changes in stomatal traits, leaf photosynthesis, and foliar nitrogen of bell pepper (Capsicum annuum L.)

Understanding the processes and mechanisms of crops in response to elevated CO2 concentration and water stress is critical for accurately projecting the potential risk of climate change on global agriculture productivity. We examined effects of elevated CO2 concentration on plant growth, stomatal traits, leaf gas exchange, and biochemistry of bell peppers under water stresses with environmental growth chambers controlling CO2 concentration at ambient (400 μmol mol−1) or elevated (800 μmol mol−1) CO2 level along a soil water gradient including full irrigation (75–85 % FC), mild water stress (65–75 % FC), moderate water stress (55–65 % FC), and severe water stress (45–55 % FC). We found that rising atmospheric CO2 concentration dramatically enhanced the plant biomass of bell peppers through the strong CO2 fertilization effect even under the mild and moderate water stresses. The CO2 fertilization effect on plant growth under water stress was directly confirmed by the boosted leaf photosynthesis, which can be attributed to the increased stomatal number and the larger stomatal openness as well as the more regular spatial distribution patterns of bell pepper plants grown at high CO2 concentration and water stress. As a result, the leaf-level water use efficiency was enhanced due to the stimulated leaf photosynthesis and the reduced leaf transpiration under high CO2 concentration, even for these bell pepper plants are suffering water stresses. Nevertheless, this CO2 fertilization effect on plant growth and leaf photosynthesis were generally decreased along the soil water gradients, indicating that the CO2 fertilization effect may partially be mitigated or even offset by water availability as evidenced by the little impact of high CO2 concentration on the total biomass of pepper plants under severe water stress. Our results suggest that water stress may lower the CO2 fertilization effect on plant growth of bell pepper plants, thus current ecological processes models based on the strong CO2 fertilization effect may overestimate the benefits of plants from future rising CO2 concentration, and meanwhile underestimate the potential risk of climate change on global agricultural productivity, where elevated CO2 concentration is usually accompanied by regional drought events.

Differential expression between drought-tolerant and drought-sensitive sugarcane under mild and moderate water stress as revealed by a comparative analysis of leaf transcriptome.

Sugarcane contributes 80% of global sugar production and to bioethanol generation for the bioenergy industry. Its productivity is threatened by drought that can cause up to 60% yield loss. This study used RNA-Seq to gain a better understanding of the underlying mechanism by which drought-tolerant sugarcane copes with water stress. We compared gene expression in KPS01-12 (drought-tolerant genotype) and UT12 (drought-sensitive genotype) that have significantly different yield loss rates under drought conditions. We treated KPS01-12 and UT12 with mild and moderate water stress and found differentially expressed genes in various biological processes. KPS01-12 had higher expression of genes that were involved in water retention, antioxidant secondary metabolite biosynthesis, and oxidative and osmotic stress response than UT12. In contrast, the sensitive genotype had more down-regulated genes that were involved in photosynthesis, carbon fixation and Calvin cycle than the tolerant genotype. Our obtained expression profiles suggest that the tolerant sugarcane has a more effective genetic response than the sensitive genotype at the initiation of drought stress. The knowledge gained from this study may be applied in breeding programs to improve sugarcane production in drought conditions.

Evaluation of Deficit Irrigation and Water Quality on Production and Water Productivity of Tomato in Greenhouse

This study deals with the evaluation of the effects of deficit irrigation (DI) and water quality (WQ) on the vegetative and productive response of greenhouse-grown tomatoes (Lycopersicon esculentum Mill. cv. Izmir). A pot-based experiment was carried out over two growing seasons. Three WQ: (groundwater, recycled wastewater and a mix of both) were applied in four irrigation scenarios which targeted soil moisture content (SMC) maintaining at 60%, 70%, 80% and 100% of field capacity (FC). Results showed that both DI and WQ had significant effects on crop development, yield and water productivity. The highest values of plant height (186.0 ± 0.58 cm) and stem diameter (23.40 ± 0.02 mm) were found at 100% FC (control). Total yield ranged from 2.33 ± 0.03 kg/plant (60% FC) to 4.05 ± 0.06 kg/plant (control). However, mild water stress (SMC maintaining at 80% FC) showed a positive effect on irrigation water use efficiency (IWUE) without significant yield reduction compared to control. IWUE was at its maximum (31.77 ± 0.47 kg/m3) at 80% FC. A DI regime based on 80% FC could be an efficient irrigation strategy particularly in water-limiting condition. Recycled wastewater was superior among the three WQ for achieving a better crop growth, yield and water productivity at same DI level.

Soil water status triggers CO2 fertilization effect on the growth of winter wheat (Triticum aestivum)

Understanding the key processes and potential mechanisms of crops in response to elevated atmospheric CO2 concentration and drought may further shed lights on the impacts of climate change on the global agriculture ecosystems. This study examined the effects of elevated atmospheric CO2 concentration on the growth of winter wheat under different soil water conditions (full irrigation, mild water stress, moderate water stress, and severe water stress) with growth chambers where the CO2 concentration was controlled at 400 and 800 µmol mol−1, respectively. We found a very strong CO2 fertilization effect on the growth of winter wheat under full irrigation condition, whereas this CO2 fertilization effect declined and eventually vanished with soil water stress, as evidenced by the decreased plant biomass and leaf photosynthesis of winter wheat independent of CO2 concentration. This adverse impact of water stress on the CO2 fertilization effect for plant growth may attribute to the changes in morphological characteristics of individual stoma and spatial distribution pattern of stomata as well as the non-structural carbohydrates of winter wheat. These results suggested that water stress may lower the CO2 fertilization effect on plant growth through altering stomatal traits, leaf photochemical processes, and biochemical compositions of winter wheat. Therefore, many current climate models based on earlier “double-CO2” experiment may overestimate the CO2 fertilization effect on crops, and meanwhile underestimate the impacts of climate change on global agriculture production when the elevated atmospheric CO2 concentration confounded with drought stress under future climate change.

Comparing Hydraulics Between Two Grapevine Cultivars Reveals Differences in Stomatal Regulation Under Water Stress and Exogenous ABA Applications.

Hydraulics of plants that have different strategies of stomatal regulation under water stress are relatively poorly understood. We explore how root and shoot hydraulics, stomatal conductance (gs), leaf and root aquaporin (AQP) expression, and abscisic acid (ABA) concentration in leaf xylem sap ([ABA]xylemsap) may be coordinated under mild water stress and exogenous ABA applications in two Vitis vinifera L. cultivars traditionally classified as near-isohydric (Grenache) and near-anisohydric (Syrah). Under water stress, Grenache exhibited stronger adjustments of plant and root hydraulic conductances and greater stomatal sensitivity to [ABA]xylemsap than Syrah resulting in greater conservation of soil moisture but not necessarily more isohydric behavior. Correlations between leaf (Ψleaf) and predawn (ΨPD) water potentials between cultivars suggested a “hydrodynamic” behavior rather than a particular iso-anisohydric classification. A significant decrease of Ψleaf in well-watered ABA-fed vines supported a role of ABA in the soil-leaf hydraulic pathway to regulate gs. Correlations between leaf and root AQPs expression levels under water deficit could explain the response of leaf (Kleaf) and root (Lpr) hydraulic conductances in both cultivars. Additional studies under a wider range of soil water deficits are required to explore the possible differential regulation of gs and plant hydraulics in different cultivars and experimental conditions.

Special issue in honour of Prof. Reto J. Strasser - Origin rather than mild drought stress influenced chlorophyll a fluorescence in contrasting silver fir (Abies alba Mill.) provenances

The performance of PSII photochemistry in five Central European provenances of silver fir differing in the altitude of origin (250-1,300 m a.s.l.) were studied using the chlorophyll a fluorescence parameters derived from the JIP-test. Measurements were performed on two dates in 2016: at the start and at the peak of growing season. Within this period, mild water stress was recorded, allowing us to monitor changes in photochemistry under drought conditions. Our results confirmed that silver fir is generally resistant to water deficit at the PSII level. However, the differences in photochemistry between provenances originating from different climatic conditions were observed. The high-altitude provenances (from wetter and colder localities) achieved higher PSII efficiency, which was also supported by clear trends along the climatic and geographic gradients of the provenance origins. After the drought, comparable PSII efficiency for low-altitude provenances and even higher for these originating in higher altitudes was observed.

Influence of Foliar-Applied Humic Acid and Some Key Growth Regulators on Sugar Beet (Beta vulgaris L.) Under Drought Stress: Antioxidant Defense System, Photosynthetic Characteristics and Sugar Yield

To assess the impact of humic acid and three potential growth regulators as salicylic acid (SA), gibberellic acid (GA3) and ascorbic acid (AsA) on sugar beet under drought stress, a field experiment as a split plot based on completely randomized block design was performed. The main plots comprised three watering regimes, well-watered, 60% field capacity (mild water stress) and 45% field capacity (severe water stress). Foliar application of humic acid, SA, GA3 and AsA was allocated into sub-plots. Both drought stress regimes caused a decline in root yield, sugar content, chlorophyll content, relative water content and leaf area index. In contrast, drought stress resulted in a marked rise superoxide dismutase, peroxidase and catalase activities as well as the levels of proline, glycine betaine, malondialdehyde and hydrogen peroxide in sugar beet plants. However, foliar application of humic acid, SA, GA3 and AsA reasonably increased the activities/levels of enzymatic and non-enzymatic antioxidants and vita organic osmolytes. The current findings suggest that exogenous application of humic acid is effective in tailoring the sugar plants to thrive well on drought-prone areas.

High Heterogeneity of Root Carbon Allocation Affects Root Turnover Rate and Production of Bothriochloa ischaemum Under Drought Stress

The mechanism that causes the difference in carbon (C) turnover rate in root populations is unclear. The carbon utilization strategy is assumed to be the main causal factor responsible for differences in root turnover rate. In this study, we determined the correlations between root turnover rate, production, and proportions of C allocated to roots using 13CO2 as a labeling gas in a 13C pulse labeling experiment. The proportions of δ13C were measured in various organs of the grass Bothriochloa ischaemum sampled 0, 6, 24, 48, 216, and 360 h after labeling in three treatments: control (CK), mild water stress (MS), and serious water stress (SS). We found that drought stress increased short-term C allocation to belowground. Fine roots have stronger C demand than coarse root under drought condition. The amount of 13C gradually decreased in leaves and increased in soil with time after 13C pulse labeling. Stem 13C increased with the level of stress and peaked at 24 h, while both fine- and coarse-root 13C peaked at 216 h. 13C distributed to fine roots in MS was significantly higher than in the other treatments at 216 h. The fine-root turnover rate in SS treatment was positively correlated with root biomass but not the amount of 13C. Larger C allocation to roots increased fine-root mass in MS, stimulated rapid fine-root turnover, and increased C input to both the rhizosphere and soil. The fine-root turnover in CK was significantly positively correlated with both 13C amount and biomass, which indicated that increasing short-term C input accelerated turnover in the fine-root pool. The C allocation difference between the fine roots and coarse roots may be a key cause of the different turnover rate in the root population.

Rapid On-Site Phenotyping via Field Fluorimeter Detects Differences in Photosynthetic Performance in a Hybrid-Parent Barley Germplasm Set.

Crop productivity can be expressed as the product of the amount of radiation intercepted, radiation use efficiency and harvest index. Genetic variation for components of radiation use efficiency has rarely been explored due to the lack of appropriate equipment to determine parameters at the scale needed in plant breeding. On the other hand, responses of the photosynthetic apparatus to environmental conditions have not been extensively investigated under field conditions, due to the challenges posed by the fluctuating environmental conditions. This study applies a rapid, low-cost, and reliable high-throughput phenotyping tool to explore genotypic variation for photosynthetic performance of a set of hybrid barleys and their parents under mild water-stress and unstressed field conditions. We found differences among the genotypic sets that are relevant for plant breeders and geneticists. Hybrids showed lower leaf temperature differential and higher non-photochemical quenching, resembling closer the male parents. The combination of traits detected in hybrids seems favorable, and could indicate improved photoprotection and better fitness under stress conditions. Additionally, we proved the potential of a low-cost, field-based phenotyping equipment to be used routinely in barley breeding programs for early screening for stress tolerance.

Composition variation of the essential oil from Ocimum basilicum L. cv. Genovese Gigante in response to Glomus intraradices and mild water stress at different stages of growth

In this study, a factorial experiment was carried out to investigate the effect of AMF (arbuscular mycorrhizal fungi) and water stress on the quality of fresh plants (through the analysis of essential oil composition) and also on the morphological characteristics (in terms of biomass) of basil (Ocimum basilicum L. cv. Genovese Gigante). The factors included an arbuscular mycorrhizal fungus inoculation (Glomus intraradices), irrigation level (mild water stress, 60% Field capacity) and the interaction of both AMF and water stress. In addition, the effects of harvesting at two different developmental stages were assessed with respect to the plants tolerance to abiotic stress and the quality of the fresh plant. The main essential oil (EO) constituents for this cultivar were eugenol, which varied between 7.1 and 50.8%, and linalool, 17.0–54.7%, in all the samples. The highest relative amount of eugenol (50.8%) was obtained during the vegetative stage in plants under water stress whereas samples from the control presented 16.2% for this compound. The samples which were significantly different from the control samples were the WS (water stress) samples from the vegetative stage. Additionally, this study suggests that AMF plants offset the adverse effect of water stress. In this context, and since the interaction of AMF and water stress did not significantly change the fresh plant quality, i.e. the essential oil profile in both stages of development, it is worthwhile considering this method of production. Finally, this experiment permitted an understanding of the stressor thresholds of the species used and also that, compensatory responses occur at different time scales, including between generations and also during development (developmental plasticity).