Category Archives: Drought Stress

Separate or combined effects of soil compaction and/or drought on gas exchange, chlorophyll fluorescence and physiological traits of maize (Zea mays L.) hybrids

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In the natural environment, plants are subjected to simultaneous or sequential presence of various abiotic and/or biotic stresses, including soil compaction and soil drought. The effects of these stresses tested separately are relatively well understood, but still little is known about their simultaneous effects on plants. Our research involved four single hybrids of maize differing in their degree of susceptibility to soil compaction and drought. We investigated the effects of low and high soil compaction under optimal irrigation (LI, HI) and under three-week long soil drought (LD, HD), on the gas exchange (Pn, E, gS, Ci) and chlorophyll fluorescence parameters (F 0, F m, F v, F v/F m), total leaf area (LA), leaf greening (SPAD), leaf water deficit (WD), leaf water potential (ψ) and membrane injury (MI). The plants experiencing high soil compaction (HI) showed a decrease in all parameters of gas exchange (Pn, E, gS, Ci), leaf area (LA), leaf greening (SPAD) and the maximal quantum efficiency of PSII (F v/F m) in comparison with plants growing in non-compacted soil (LI). An increase was observed in the other fluorescence parameters, i.e., F 0, F m and F v and leaf WD, ψ and MI in HI vs. LI variants. In the plants exposed to drought (LD, HD), the changes in the measured traits were greater, especially for the sensitive hybrids P-8400 and NS-3023, than for the plants from LI treatment. A significant interaction between the degree of stress susceptibility and relative trait change was observed for practically all of the measured features. Moreover, in the short recovery period after the end of drought, the measured traits in LD and HD plants did not fully return to the control level, especially in the case of the sensitive hybrids (P-8400 NS-3023). The physiological reaction of maize hybrids to soil compaction and/or soil drought indicated the genetically determined variability of tolerance to those stresses. Significant correlation between RTC and stress susceptibility indexes (S-SI) provided suitable criteria for the hybrid selection. Also, our results showed the plasticity and capability of maize hybrids to respond to environmental conditions.

Cover crop water consumption: Analysing performance of the agrometeorological model for the calculation of actual evapotranspiration (AMBAV) in a container experiment

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Due to anthropogenic climate change, cover crop water consumption in winter could potentially increase drought stress for a succeeding crop. Simulation of cover crop evapotranspiration (ET) losses could be a tool for farmers to make smart management decisions. In Germany, the model AMBAV is used by the German Meteorological Service (DWD) to advise farmers in irrigation management. We compared measured ET of phacelia (Phacelia tanacetifolia), oilseed radish (Raphanus sativus var. oleiformis) and white mustard (Sinapis alba) cultivated in a container experiment with simulated data and conducted a sensitivity analysis to identify the meteorological and crop-specific parameters, which had the strongest effect on simulated ET. In general, measured ET exceeded simulated ET. Different statistical criteria showed that AMBAV performed best for the simulation of evaporation from a bare soil surface. Model performance was also strongly influenced by the irrigation regime in the container experiment. However, the sensitivity analysis showed that changes in irrigation hardly influenced simulated ET. We recommend optimization of the model for irrigated agriculture. Furthermore, we identified temperature and humidity as the most important meteorological and leaf area index as the most important crop-specific parameter for ET simulations with AMBAV. Since farmers' management decisions depend on the accuracy of ET simulations, they should be aware that even small regional deviations of meteorological conditions and soil cover can significantly affect model predictions.

Current status of global rice water use efficiency and water‐saving irrigation technology recommendations

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Rice has a high water requirement, but water use efficiency (WUE) in rice has always been low, and the status of rice WUE and the factors influencing it in various countries around the world is currently unclear. Therefore, this paper collected 56 articles from 2000 to 2022, through which WUE data from different countries and different provinces in China were collated, and the effects of various water-saving irrigation technologies on WUE of rice and irrigation water use were analysed using the method of Meta-analysis. The results of this paper show that rice WUE is low in most countries, with the lowest WUE of 0.28 kg/m3 in Thailand and the highest WUE of 1.25 kg/m3 in Bangladesh among the countries included in this study, and flood irrigation is used in most countries. Compared to flood irrigation, all water-saving irrigation involved can increase rice WUE and reduce irrigation water input, alternate wet and dry irrigation (W1), and controlled irrigation (W2) were able to increase the WUE of rice by 49.86%, 84.74%, and reduce the irrigation water input by 36.55%, 39.55% respectively. Among the six types of water-saving irrigation input, dry cultivation (W3) had the most significant effect on increasing WUE and reducing irrigation water, reaching 2.02 times and 67.53%, respectively. Based on the annual rainfall (R) and the application of water-saving irrigation in Asia, sub-regionally applicable water-saving irrigation technologies are recommended. W3 is recommended when R <200 mm, W2 is recommended when 200 mm < R < 800 mm, and W1/W2/shallow alternate wet and dry irrigation (W5) is recommended when R >800 mm. According to the data collected in this paper, W1, W2, W3, and W5 can save 3.40 × 1011 m3, 3.78 × 1011 m3, 2.52 × 108 m3, 2.22 × 1011 m3 of irrigation water, respectively. Based on the calculations in this paper, different water-saving irrigation techniques can save 3.50 × 1011 m3 of water in Asia according to the recommendations. To promote water-saving irrigation technology, countries need to formulate policies to ensure the development of water-saving irrigation technology, raise farmers' awareness of water conservation, and provide training and financial support. Promoting the use of different water-saving irrigation technologies for different regions can significantly reduce irrigation water and increase the WUE of rice, which is important in addressing the challenges of global water scarcity.

Screening of barley germplasm for drought tolerance based on root architecture, agronomic traits and identification of novel allelic variants of HVA1

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Drought is a major constraint for barley production as it is normally cultivated in rainfed and marginal areas lacking optimum productivity. The domestication bottleneck and further selection pressure have resulted in reduced genetic diversity in barley. Genebank germplasm holds a huge potential for identifying new alleles for stress tolerance. In the present study, a diverse set of 214 accessions from Indian National Genebank were screened for drought tolerance in hydroponics and field conditions. Analysis of variance revealed a significant effect of drought on root architecture, relative water content, membrane stability index, chlorophyll content, plant height, and yield attributes. Cumulative stress response in terms of better root phenotype, physiological and agronomic traits showed accessions IC113045, EC578521, IC582699, EC492318, EC578711, EC667420, IC393980 and IC594943 as most promising donors for breeding programmes in drought-prone areas. Further allelic variation of candidate gene, Hordeum vulgare aleurone 1 (HVA1), and its promoter sequence was studied in a subset of drought-tolerant and -susceptible accessions. The HVA1 gene showed six SNPs and one indel in the genic regions whereas three SNPs and one indel in promoter. Two alleles of HVA1 gene, one in exotic and other in indigenous accession, were found to be associated with drought tolerance. These results were confirmed by qRT-PCR analysis exhibiting significant increase in transcript abundance of HVA1 in drought-tolerant accessions in comparison with susceptible accessions, thereby highlighting its possible role in imparting drought tolerance. The study helped identify genetic resources for drought tolerance in barley and unravelled new alleles of HVA1.

Genotypic responses of rice to alternate wetting and drying irrigation in the Mekong Delta

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In the Vietnamese Mekong Delta (VMD), alternate wetting and drying (AWD) in rice (Oryza sativa L.) production during the dry season has the potential to reduce greenhouse gas emission and freshwater use. However, its effect on yield compared with continuously flooded systems can vary. To evaluate the effect of AWD on yield and yield-forming processes on genotypes commonly grown in the VMD, field trials over two consecutive dry seasons were conducted at the Loc Troi Group's agricultural research station in the VMD. We observed a significant yield reduction, 7% on average, across all varieties grown under AWD. Analysis of yield components showed that under AWD, genotypes on average produced more tillers, but fewer spikelets, suffered greater spikelet sterility and had a lower 1000 grain weight. The size of this effect differed between dry seasons. Accordingly, we were able to identify and characterize genotypes better suited to AWD. We also could relate shifts in sink-source relationships to the overlap of drying events and key phenological stages other than flowering. Our study shows how successful implementation of AWD requires adaptation to both environment and genotype.

Classification of soybean genotypes during the seedling stage in controlled drought and salt stress environments using the decision tree algorithm

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Soybean is one of the most important oilseed crops grown worldwide. However, abiotic stresses such as drought and salinity can seriously affect soybean production, especially in tropical climate conditions. To evaluate the adaptability and stability of soybean genotypes under abiotic stress conditions, some studies have proposed a multitrait tool to select stress-tolerant soybean genotypes through a multitrait stability index (MTSI). This index can be used under stressful environmental conditions to quantify the genotypic stability of soybean cultivars. Our study is based on an unprecedented approach, where we propose to use a machine learning algorithm called ‘Random Forest’ to obtain a classification model based on a decision tree algorithm. The decision tree data structure can be used even by nonexperts facilitating the decision-making process for genotype selection. The proposed model evaluated the importance of six shoot and root morphological variables and predicted from which controlled growth environment the soybean plants originated. Using this model more than 73% of the genotypic patterns were learned correctly. Besides that, this model can also predict and rank the most critical variables in the development of soybean genotypes, having obtained results very similar to recent field research. The research is important for plant breeders who seek an early selection of soybean seedlings for drought and saline stresses.

Does the plant growth regulator paclobutrazol enhance root growth of maize exposed to drought stress during flowering?

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Due to climate change, crop production will increasingly be affected by water limitation, causing remarkable decreases in grain yields of cereals. Plant growth regulators such as paclobutrazol (PAC) have been shown to protect plants from detrimental impacts of drought stress, and improvement of root growth and antioxidant activity were identified as main reasons for their positive effect. A container experiment was conducted with two maize (Zea mays L.) cultivars, Galactus and Fabregas, to investigate how PAC application affects root growth and grain yield under stress conditions. At growth stage V8, the plants were treated once with PAC (0, 2, or 3 mg PAC per plant), and concomitantly reduction in soil water content commenced until 30–35% of the maximum water-holding capacity (WHC) was achieved. The plants were exposed to this drought condition for three weeks during flowering as the critical period for kernel setting. Both factors, PAC application and drought stress, caused decreases in plant height, whereas total leaf area was unchanged and transpiration rate was significantly reduced by water limitation only. Flowering was almost unaffected by PAC treatment; yet, drought stress significantly delayed start of silking. The straw yield was decreased due to PAC and drought stress, and an improvement of the harvest index was obtained for drought-stressed Galactus plants with PAC application. Grain yield was unaffected by PAC application, whereas drought stress caused significant decreases by 15% on average of both cultivars. The kernel number of drought-stressed Galactus plants was increased after PAC treatment, but concurrently smaller kernels were produced. Water limitation generally decreased kernel number. Drought-stressed Fabregas plants consumed less water after PAC treatment, resulting in significant improvements of water-use efficiency (WUEgrain) during silking and thus most likely alleviating stress intensity. For both cultivars, PAC treatment and water limitation showed almost no significant impact on root dry matter, root length density, and root surface area, either determined for different soil layers down to 80 cm or on a per-plant basis. It is concluded that grain yield performance of maize plants, exposed to water limitation during flowering, was not source-limited but sink-limited. Consequently, even if PAC can cause improvement of antioxidant activity and photosynthesis, due to sufficient availability of assimilates in the maize kernels a positive effect on grain yield is improbable. Considering source–sink relationships during flowering and kernel set, enhanced root growth due to PAC treatment did apparently not occur.

Plant photosynthetic responses under drought stress: Effects and management

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Balanced photosynthesis is essential for improved plant survival and agricultural benefits in terms of biomass and yield. Photosynthesis is the hub of energy metabolism in plants; however, drought stress (DS) strongly perturbs photosynthetic efficiency due to biochemical and diffusive limitations that reduce key photosynthetic components and close stomata. This review describes photosynthetic responses, chloroplast retrograde signalling, and genetic imprints that curtail DS damage to photosynthetic machinery. While stomatal closure, disrupted photosynthetic systems, over-reduced electron transport rates (ETR), partial hindrance of the Calvin cycle, and reduced pigment contents strongly affect the repertoire of photosynthetic processes under DS, chloroplast retrograde signalling also has a plausible role in preserving photosynthetic capacity. Progress in agronomic, genetic engineering approaches and isoprene regulation would help to rescue photosynthetic apparatus under DS.

The effect of silicon fertilizers on agronomic performance of bread wheat under drought stress and non‐stress conditions

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Drought is one of the major constraints of wheat production, especially in rainfed wheat production systems. The objective of this study was to evaluate the effects of different silicon fertilizer formulations on the agronomic performance of diverse wheat genotypes under drought-stressed conditions. Twenty wheat genotypes were evaluated in field and greenhouse environments under non-stressed and drought-stressed and two silicon fertilizer formulations (granular and liquid potassium silicate) and untreated control. The four-way interaction involving genotype, environment, water regime and silicon formulation had a significant effect (p < .05) for aboveground biomass, productive spike number, hundred seed weight and grain yield. Granular silicon application was the most effective treatment both under non-stressed and drought-stressed conditions compared to the liquid and control treatments. Under field and drought conditions, the highest yielding genotype was MC18, which exhibited a mean grain yield of 4.17 t ha−1 with granular silicon, 2.56 t ha−1 with liquid silicon and 2.18 t ha−1 without silicon. The yield of genotype MC18 improved by 91.3% using granular silicon under drought-stressed and by 44.6% under non-stressed conditions compared with the untreated control. Granular silicon positively affected the drought stress tolerance indices compared to the liquid silicon and untreated control. The principal component biplot analysis revealed that liquid and granular silicon positively impact yield response for all test genotypes under drought-stressed and non-stressed conditions compared with the control. Silicon application reduced genotype variation for agronomic traits and enhanced agronomic trait relationships under drought-stressed conditions. Drought stress tolerance indices are influenced by silicon application. The effect of silicon has a direct and indirect effect on yield and yield components. Silicon fertilization can be considered as a mitigation measure to cope with the adverse effect of drought stress on wheat.

Genotypic stability in root system architecture and aboveground biomass revealed diverse adaptability of peanut (Arachis hypogaea L.) to moderate water deficit

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Many crop species, including cultivated peanut (Arachis hypogaea L.), modify their above- and below-ground growth to cope with water deficit stress. This acclimation to water deficit often triggers a biomass partitioning shift—allocating more biomass to the roots, to increase the accessibility of roots to water resources. However, additional carbon partitioning to roots may not always translate into increased water use and maintenance of aboveground biomass (ABM) and yield. Therefore, selecting an efficient root system architecture (RSA) should aim to sustain a high ABM production under a water deficit scenario. To better understand the associations of above and belowground biomass partitioning under moderate water deficit, this study evaluated the genotypic stability of 40 peanut genotypes in ABM and RSA in greenhouse experiments and further assessed genotypic differences in 4 site-year field experiments. Our results suggested that higher ABM-producing genotypes generally had high plasticity when subjected to water deficit whereas the low ABM-producing genotypes had relatively high stability. Hierarchical clustering analysis further revealed that genotypes with a high root-to-shoot ratio potentially had increased genotypic stability in ABM underwater deficit. Interestingly, genotypes that maintained the highest ABM underwater deficit did not have the highest total root biomass and length. Instead, these genotypes had the highest root length in the top layer of soil (0–0.3 m) and relatively fewer roots in the deeper layer of soil (0.3–1 m). Greenhouse-screened stable genotypes exhibited minimal yield reduction when subjected to mid-season water deficit in some of the field validation experiments, but it also happened to some plastic genotypes, indicating that further validation of controlled environment screenings for genotypic water-deficit tolerance in the field is necessary.