The opportunity of using durum wheat landraces to tolerate drought stress: screening morpho-physiological components

Local genetic resources could constitute a promising solution to overcome drought stress. Thus, eight (8) durum wheat landraces and one improved variety were assessed for drought tolerance in pots under controlled conditions. Three water treatments were tested: control (100 % of the field capacity (FC)), medium (50 % FC) and severe (25 % FC) stress. The assessment was carried out at the seedling stage to mimic stress during crop set-up. Results showed that increased water stress led to a decrease in biomass and morpho-physiological parameters and an increase in antioxidant enzyme activities. Severe water stress decreased the chlorophyll fluorescence parameters, relative water content (RWC) and water potential of the investigated genotypes by 56.45, 20.58, 50.18 and 139.4 %, respectively. Besides, the phenolic compounds content increased by 169.2 % compared to the control. Catalase and guaiacol peroxidase activities increased 17 days after treatment for most genotypes except Karim and Hmira. A principal component analysis showed that the most contributed drought tolerance traits were chlorophyll fluorescence parameters, RWC and electrolyte conductivity. Unweighted pair group method with arithmetic mean clustering showed that the landraces Aouija, Biskri and Hedhba exhibited a higher adaptive response to drought stress treatments, indicating that water stress-adaptive traits are included in Tunisian landraces germplasm.

Soil Moisture Regulation under Mulched Drip Irrigation Influences the Soil Salt Distribution and Growth of Cotton in Southern Xinjiang, China

Water deficiency, together with soil salinization, has been seriously restricting sustainable agriculture around the globe for a long time. Optimal soil moisture regulation contributes to the amelioration of soil water and salinity for crops, which is favorable for plant production. A field experiment with five soil water lower limit levels (T1: 85% FC, T2: 75% FC, T3: 65% FC, T4: 55% FC, and T5: 45% FC, where FC is the field capacity) was conducted in southern Xinjiang in 2018 to investigate the responses of soil water-salt dynamics and cotton performance to soil moisture regulation strategies. The results indicated that in the horizontal direction, the farther away the drip irrigation belt, the lower the soil moisture content and the greater the soil salinity. In the vertical direction, the soil moisture and soil salinity increased first and then decreased with an increase in soil depth after irrigation, and the distribution was similar to an ellipse. Moreover, the humid perimeter of soil water and the leaching range of soil salt increased with a decrease in the soil moisture lower limit. Though more soil salt was leached out for the T5 treatment at the flowering stage due to the higher single irrigation amount, soil salinity increased again at the boll setting stage owing to the long irrigation interval. After the cotton was harvested, soil salt accumulated in the 0-100 cm layer and the accumulation amount followed T3 > T5 > T1 > T2 > T4. Moreover, with a decline of soil moisture lower limit, both plant height and nitrogen uptake decreased significantly while the shoot-root ratio increased. Compared with the yield (7233.2 kg·hm^-2) and water use efficiency (WUE, 1.27 kg·m^-3) of the T1 treatment, the yield for the T2 treatment only decreased by 1.21%, while the WUE increased by 10.24%. Synthetically, considering the cotton yield, water-nitrogen use efficiency, and soil salt accumulation, the soil moisture lower limit of 75% FC is recommended for cotton cultivation in southern Xinjiang, China.

Physiological and Biochemical Responses of Commercial Strawberry Cultivars under Optimal and Drought Stress Conditions

Improving the extent of adaptation and the choice of the most tolerant cultivar is the first step to mitigating the adverse effects of limited water, especially in susceptible plants such as strawberries. To address this issue, two commercial strawberry cultivars (Camarosa and Gaviota) were compared when irrigated to match 100, 75, 50, and 25% field capacity (FC) to simulate the control, slight, moderate, and severe drought stress conditions, respectively. Drought stress induced the reduction of total chlorophyll, carotenoid, relative water content, and phenolic content significantly, whereas the activity of antioxidant enzymes, electrolyte leakage, osmolyte accumulation, and oxidative markers upsurged progressively in drought severity-dependent behavior. Gaviota produced more proline, hydrogen peroxide as a marker of membrane lipid peroxidation and disposed of by higher electrolyte leakage, significantly. On the other hand, Camarosa having higher soluble carbohydrates as well as enzymatic and non-enzymatic antioxidants could be considered a drought-tolerant cultivar. Genotypic variation between these cultivars could be used in breeding projects to promote drought-tolerant strawberries in the future.

Impression of foliar-applied folic acid on coriander (Coriandrum sativum L.) to regulate aerial growth, biochemical activity, and essential oil profiling under drought stress

Drought is one of the major environmental limitations in the crop production sector that has a great impact on food security worldwide. Coriander (Coriandrum sativum L.) is an herbaceous angiosperm of culinary significance and highly susceptible to rootzone dryness. Elucidating the drought-induced physio-chemical changes and the foliar-applied folic acid (FA; vitamin B9)-mediated stress tolerance mechanism of coriander has been found as a research hotspot under the progressing water scarcity challenges for agriculture. The significance of folic acid in ameliorating biochemical activities for the improved vegetative growth and performance of coriander under the mild stress (MS75), severe stress (SS50), and unstressed (US100) conditions was examined in this study during two consecutive seasons. The results revealed that the plants treated with 50 mM FA showed the highest plant fresh biomass, leaf fresh biomass, and shoot fresh biomass from bolting stage to seed filling stage under mild drought stress. In addition, total soluble sugars, total flavonoids content, and chlorophyll content showed significant results by the foliar application of FA, while total phenolic content showed non-significant results under MS75 and SS50. It was found that 50 mM of FA upregulated the activity of catalase, superoxide dismutase, and ascorbate peroxidase enzymes in MS75 and SS50 plants compared with untreated FA plants. Thus, FA treatment improved the overall biological yield and economic yield regardless of water deficit conditions. FA-accompanied plants showed a decline in drought susceptibility index, while it improved the drought tolerance efficiency, indicating this variety to become stress tolerant. The optimum harvest index, essential oil (EO) percentage, and oil yield were found in MS75 followed by SS50 in FA-supplemented plants. The gas chromatography-mass spectrometry analysis revealed a higher abundance of linalool as the major chemical constituent of EO, followed by α-terpeniol, terpinene, and p-Cymene in FA-treated SS50 plants. FA can be chosen as a shotgun tactic to improve drought tolerance in coriander by delimiting the drastic changes due to drought stress.

In-Situ Estimation of Soil Water Retention Curve in Silt Loam and Loamy Sand Soils at Different Soil Depths

The soil water retention curve (SWRC) shows the relationship between soil water (θ) and water potential (ψ) and provides fundamental information for quantifying and modeling soil water entry, storage, flow, and groundwater recharge processes. While traditionally it is measured in a laboratory through cumbersome and time-intensive methods, soil sensors measuring in-situ θ and ψ show strong potential to estimate in-situ SWRC. The objective of this study was to estimate in-situ SWRC at different depths under two different soil types by integrating measured θ and ψ using two commercial sensors: time-domain reflectometer (TDR) and dielectric field water potential (e.g., MPS-6) principles. Parametric models were used to quantify θ—ψ relationships at various depths and were compared to laboratory-measured SWRC. The results of the study show that combining TDR and MPS-6 sensors can be used to estimate plant-available water and SWRC, with a mean difference of −0.03 to 0.23 m³m⁻³ between the modeled data and laboratory data, which could be caused by the sensors’ lack of site-specific calibration or possible air entrapment of field soil. However, consistent trends (with magnitude differences) indicated the potential to use these sensors in estimating in-situ and dynamic SWRC at depths and provided a way forward in overcoming resource-intensive laboratory measurements.

Irrigation Scheduling Based on Wireless Sensors Output and Soil-Water Characteristic Curve in Two Soils

Data-driven irrigation planning can optimize crop yield and reduce adverse impacts on surface and ground water quality. We evaluated an irrigation scheduling strategy based on soil matric potentials recorded by wireless Watermark (WM) sensors installed in sandy loam and clay loam soils and soil-water characteristic curve data. Five wireless WM nodes (IRROmesh) were installed at each location, where each node consisted of three WM sensors that were installed at 15, 30, and 60 cm depths in the crop rows. Soil moisture contents, at field capacity and permanent wilting points, were determined from soil-water characteristic curves and were approximately 23% and 11% for a sandy loam, and 35% and 17% for a clay loam, respectively. The field capacity level which occurs shortly after an irrigation event was considered the upper point of soil moisture content, and the lower point was the maximum soil water depletion level at 50% of plant available water capacity in the root zone, depending on crop type, root depth, growth stage and soil type. The lower thresholds of soil moisture content to trigger an irrigation event were 17% and 26% in the sandy loam and clay loam soils, respectively. The corresponding soil water potential readings from the WM sensors to initiate irrigation events were approximately 60 kPa and 105 kPa for sandy loam, and clay loam soils, respectively. Watermark sensors can be successfully used for irrigation scheduling by simply setting two levels of moisture content using soil-water characteristic curve data. Further, the wireless system can help farmers and irrigators monitor real-time moisture content in the soil root zone of their crops and determine irrigation scheduling remotely without time consuming, manual data logging and frequent visits to the field.

QsMYB1 expression is modulated in response to heat and drought stresses and during plant recovery in Quercus suber

Cork oak is an economically important forest species showing a great tolerance to high temperatures and shortage of water. However, the mechanisms underlying this plasticity are still poorly understood. Among the stress regulators, transcription factors (TFs) are especially important since they can control a wide range of stress-inducible genes, which make them powerful targets for genetic engineering of stress tolerance. Here we evaluated the influence of increasing temperatures (up to 55 °C) or drought (18% field capacity, FC) on the expression profile of an R2R3-MYB transcription factor of cork oak, the QsMYB1. QsMYB1 was previously identified as being preferentially expressed in cork tissues and as having an associated alternative splicing mechanism, which results in two different transcripts (QsMYB1.1 and QsMYB1.2). Expression analysis by reverse transcription quantitative PCR (RT-qPCR) revealed that increasing temperatures led to a gradual down-regulation of QsMYB1 transcripts with more effect on QsMYB1.1 abundance. On the other hand, under drought condition, expression of QsMYB1 variants, mainly the QsMYB1.2, was transiently up-regulated shortly after the stress imposition. Recovery from each stress has also resulted in a differential response by both QsMYB1 transcripts. Several physiological and biochemical parameters (plant water status, chlorophyll fluorescence, lipid peroxidation and proline content) were determined in order to monitor the plant performance under stress and recovery. In conclusion, this report provides the first evidence that QsMYB1 TF may have a putative function in the regulatory network of cork oak response to heat and drought stresses and during plant recovery.

Soil residue analysis and degradation of saflufenacil as affected by moisture content and soil characteristics

BACKGROUND

Saflufenacil dissipation in soils under different moisture conditions is not available in the scientific literature. The objective of this study was to evaluate saflufenacil degradation and persistence in soils from rice regions under field capacity (non-flooded) and saturated (flooded) conditions.

RESULTS

The accelerated solvent extraction (ASE) residue analytical method developed to conduct the study resulted in recovery greater than 80% for the combinations of soils and moisture conditions. Saflufenacil degradation was faster at field capacity for all soils, except for Morey soil. Herbicide half-life was 28.6, 15.0 and 23.1 days under field capacity treatments and 58.8, 36.9 and 79.7 under saturated conditions for Nada, Crowley and Gilbert soils respectively. A half-life no longer than 80 days was observed for the combination of soils and moisture treatments.

CONCLUSION

An ASE method was developed and used to extract saflufenacil from soil samples. Half-life averaged among soils was 59 and 33 days for saturated and field capacity respectively. Saflufenacil persistence in the environment was 2-3 times longer under flooded conditions for most of the soils studied.