Relative Drought Tolerance Research Articles

Are Shade-Tolerant Plants Also Drought-Tolerant

This study examines the relationship between drought and shade tolerance in herbaceous plants, which is traditionally assumed to be mutually exclusive due to divergent resource allocation strategies. By collecting and analyzing relevant biochemical and morphological traits on a variety of plants native to grasslands in south eastern Ontario, a quantitative approach to analyzing the relationship between these two stress responses can be employed. This research aims to enhance our characterization of the interplay and relationship of drought and shade tolerance in relation to these plant species.

Screening New Mungbean Varieties for Terminal Drought Tolerance

Rainfed mungbean crops in Queensland Australia frequently experience terminal drought (drought stress in the final stages of reproductive development), highlighting the importance of drought-tolerant varieties for sustainable mungbean production. Given there is limited information on the relative drought tolerance of current mungbean varieties in Australia, the study of genetic variations and mechanisms of drought tolerance in summer mungbean can provide a basis for developing drought-tolerant mungbean varieties. This study evaluated the physiological, biochemical, and phenological traits underpinning yield attributes associated with drought tolerance in selected mungbean varieties. Four new mungbean varieties (AVTMB#1 to 4) and the Australian commercial line (Jade-AU) were grown in tall (75 cm) polyvinyl chloride (PVC) lysimeters where drought stress was imposed at the early flowering stage (R1) and maintained until maturity. Drought stress significantly impacted all the varieties. Averaged across all the varieties, drought stress was associated with a reduction in stomatal conductance (gs) and photosynthetic rate (Asat) by 78% and 86%, respectively, compared to well-watered plants. Internal carbon dioxide concentration (Ci), the effective quantum yield of photosystem II (ΦPSII) and maximum light-use efficiency of light-acclimated photosystem II (PSII) centres (Fv’/Fm’) were also decreased, while excitation pressure (1-qP) increased with drought treatment. A positive correlation (r = 0.60) existed between seed yield and ΦPSII assessed at R1, while a weak correlation with Fv’/Fm’ (r = 0.24) was observed. Excitation pressure (1-qP) at the R1 stage was negatively correlated with seed yield (r = −0.66). Therefore, leaf fluorescence measures, viz., 1-qP and ΦPSII, were recommended for use in screening mungbean varieties for drought tolerance. The varieties, AVTMB#1 and AVTMB#4, respectively achieved 39 and 38% greater seed yields relative to the commercial variety, Jade-AU, under terminal drought conditions.

Assessment of Drought and Zinc Stress Tolerance of Novel Miscanthus Hybrids and Arundo donax Clones Using Physiological, Biochemical, and Morphological Traits.

High-yield potential perennial crops, such as Miscanthus spp. and Arundo donax are amongst the most promising sources of sustainable biomass for bioproducts and bioenergy. Although several studies assessed the agronomic performance of these species on diverse marginal lands, research to date on drought and zinc (Zn) resistance is scarce. Thus, the objective of this study was to investigate the drought and Zn stress tolerance of seven novel Miscanthus hybrids and seven Arundo clones originating from different parts of Italy. We subjected both species to severe drought (less than 30%), and Zn stress (400 mg/kg-1 of ZnSO4) separately, after one month of growth. All plants were harvested after 28 days of stress, and the relative drought and Zn stress tolerance were determined by using a set of morpho-physio-biochemical and biomass attributes in relation to stress tolerance indices (STI). Principal component analysis (PCA), hierarchical clustering analysis (HCA) and stress tolerance indices (STI) were performed for each morpho-physio-biochemical and biomass parameters and showed significant relative differences among the seven genotypes of both crops. Heatmaps of these indices showed how the different genotypes clustered into four groups. Considering PCA ranking value, Miscanthus hybrid GRC10 (8.11) and Arundo clone PC1 (11.34) had the highest-ranking value under both stresses indicating these hybrids and clones are the most tolerant to drought and Zn stress. In contrast, hybrid GRC3 (-3.33 lowest ranking value) and clone CT2 (-5.84) were found to be the most sensitive to both drought and Zn stress.

Variation in Seed Germination and Amylase Activity of Diverse Carrot [Daucus carota (L.)] Germplasm under Simulated Drought Stress

Drought is one of the major environmental challenges constraining the production of agricultural crops, including carrot. Seed germination is the initial and most critical stage of crop establishment, and it is very sensitive to drought stress because water scarcity affects the enzymatic solubilization of stored metabolites in seeds that provide energy for the growth of germinating embryo. Few studies evaluating the effect of drought stress on carrot seed germination of more than a few cultivars grown under stress have been published. Therefore, the present study was designed to define the appropriate osmotic potential for evaluating drought tolerance of carrot, evaluate the response of diverse carrot germplasm to drought stress during seed germination to identify drought-tolerant accessions that may be used by plant breeders, and evaluate the relation between amylase activity and germination rate of drought-tolerant and drought-sensitive accessions. To identify an appropriate screening osmotic potential, two commercial cultivars and two United States Department of Agriculture inbreeds were evaluated at six osmotic potentials (00, −0.30, −0.51, −0.58, −0.80, and −1.05 MPa); −0.58 MPa was identified as the optimal osmotic potential for screening the drought tolerance of carrot seed. Cultivated and wild carrot plant introductions (PIs) (n = 200 and n = 50, respectively) from the National Plant Germplasm System were evaluated for drought tolerance under nonstress and simulated drought stress conditions (00 MPa and −0.58 MPa, respectively) by calculating the absolute decrease (AD) in percent germination, inhibition index (II), relative drought tolerance (RDT), and drought tolerance index (DTI). All measurements of drought tolerance identified significant differences among accessions; the AD in seed germination ranged from 0.0% to 69.3%, II ranged from 0.0% to 80.2%, RDT ranged from 0.2 to 1.0, and DTI ranged from 0.13 to 1.47. All wild carrot accessions displayed low levels of drought tolerance, but PI 652387 and PI 177381 (both from Turkey) and PI 274297 (Pakistan) were most drought-sensitive, whereas cultivated accessions PI 643114 (United States), PI 652208 (China), and PI 502347 (Uzbekistan) were most drought-tolerant. Tolerant accessions displayed much higher α-amylase activity under nonstress conditions than sensitive accessions, and α-amylase activity of tolerant accessions was also reduced less with seed germination under increasing osmotic potential (range, 0.0 to −1.05 MPa) than sensitive accessions over 24, 48, and 72 hours of seed germination. This is the first evaluation of drought stress tolerance during seed germination and the enzymatic response of diverse carrot germplasms under simulated drought stress.

Provenances from introduced stands of Northern Red Oak (Quercus rubra L.) outperform those from the natural distribution

Northern Red Oak (Quercus rubra L.), which is native to North America, covers over 350.000 ha in Europe and is currently the most common non-native deciduous tree species in Germany. Due to its high growth potential and higher drought tolerance in relation to native oak species, its valuable ecological characteristics and the versatile use of its wood for lumber or furniture it is one of the potential alternative tree species in a future warmer climate.In this study, growth performance of Q. rubra (particularly basal area [m2 ha-1] at age 33) is analysed, using data from a provenance trial established in 1991 with three test sites located in North, East and Central Germany. We focus on 12 common provenances, six of North American origin and six sourced from introduced stands from Germany, to evaluate patterns of provenance-environment interaction (P × E). Using effect size statistics, we found a significant percent gain in productivity of German compared to North American provenances on two humid sites. Two provenances from South-west Germany further convince with a good stem form. North American provenances from Canada show an equivalent growth to those from Germany on a drier test site, while provenances from the United States show poor growth in all environments. We assessed the provenance sensitivity across the tested environments by characterising growth differences with the joint regression analysis (JRA), which confirmed a significant P × E and the growth superiority of German provenances. The application of the Weighted Average of the Absolute Scores (WAAS) as a stability parameter enables the classification of provenances into generalists and specialists. While the German provenances can be assumed to be generalists with above average performance (4 provenances) or specialists with a high productivity on humid sites (2 provenances) and therefore seem suitable for recommendations, those from Canada performed well in the dry environment, which could be promising if planted at sites with decreasing precipitation regimes. All of these aspects shall contribute to a broader use of Northern Red Oak especially in Germany in the process of forest restoration.

Estimation of drought tolerance of spring barley samples in their initial period of development on an osmotic solution

Development of drought-tolerant spring barley varieties is one of the important breeding directions for resistance to abiotic stress factors. In order to solve this problem successfully, it is necessary to use in hybridization the varieties and lines with the highest tolerance. The main purpose of the current study was to estimate the effect of osmotic stress of different concentrations on seed germination and to evaluate the relative drought tolerance of spring barley varieties and lines. The study was carried out in the laboratory for plant physiology in 2018–2020. The estimation of drought tolerance of spring barley samples was carried out on 26 varieties and lines, bred in the ARC “Donskoy”, in the initial period of development. The laboratory experiments on the ability of spring barley seeds to germinate on a sucrose solution (imitation of a lack of moisture in the soil) make it possible to estimate drought tolerance of samples at the early stages of their development. There was studied an effect of a sucrose solution with an osmotic pressure of 3, 8, 10, 12, 14 atmospheres on the ability of seed germination. When increasing a concentration of the solution, there was a seed germination decrease in all genotypes. As a result of the study, there were the largest statistically significant differences (P > 0.95) of the samples under the concentration of the osmotic sucrose solution of 8 atmospheres, in comparison with the options of 3, 10, 12 and 14 atmospheres. There have been obtained the data on the relative drought tolerance of spring barley varieties and lines. The maximum indicators of seed germination under osmotic pressure of 8 atmospheres were registered among the samples ‘Zernogradsky 1716’ (91.1 %), ‘Zernogradsky 1717’ (85.9 %), ‘Zernogradsky 1719’ (84, 1%), ‘12545/18’ (80.2 %), ‘Zernogradsky 1701’ (78.9 %), ‘12551/18’ (72.9%), ‘12487/18’ (72.4%), ‘Zernogradsky 1724’ (70.6 %), ‘Zernogradsky 1721’ (69.8 %), ‘12525/18’ (69.2 %) in comparison with the standard variety ‘Ratnik’ (43.6 %). The identified samples can be used for further study of drought tolerance in the field.

Using δ<sup>13</sup>C and hydroscapes for discriminating cultivar specific drought responses

Measurement of carbon isotope discrimination in berry juice at maturity (δ13C) provides an integrated assessment of vine water status and water use efficiency (WUE) during the period of berry ripening, and when collected over multiple seasons, can provide an indication of drought stress responses. Berry juice δ13C measurements were carried out on 48 different varieties planted in a common garden experiment in Bordeaux, France from 2014 through 2020 and found important differences across this large panel of varieties. Cluster analysis showed that δ13C values are likely affected by the differing phenology of each variety, resulting in berry ripening of different varieties taking place under different conditions of soil water availability within the same year. Accounting for these phenological differences, the cluster analysis created a classification of varieties that corresponds well to our current empirical understanding of their relative drought tolerance. In addition, using measurements of predawn and midday leaf water potential measurements collected over four seasons on a subset of six varieties, a hydroscape approach was used to develop a list of metrics indicative of the sensitivity of stomatal regulation to water stress (i.e., an/isohydric behaviour). Key hydroscape metrics were also found to be well correlated with some δ13C metrics. A variety’s water potential regulation as characterized by a minimum critical leaf water potential as determined from hydroscapes was strongly correlated to δ13C values under well-watered conditions, suggesting that the latter may be a useful indicator of drought stress response.

Overexpression of Pennisetum purpureum CCoAOMT Contributes to Lignin Deposition and Drought Tolerance by Promoting the Accumulation of Flavonoids in Transgenic Tobacco.

Elephant grass (Pennisetum purpureum) is a fast-growing and low-nutrient demand plant that is widely used as a forage grass and potential energy crop in tropical and subtropical regions of Asia, Africa, and the United States. Transgenic tobacco with the PpCCoAOMT gene from Pennisetum purpureum produces high lignin content that is associated with drought tolerance in relation to lower accumulation of reactive oxygen species (ROS), along with higher antioxidant enzyme activities and osmotic adjustment. In this study, transgenic tobacco plants revealed no obvious cost to plant growth when expressing the PpCCoAOMT gene. Metabolomic studies demonstrated that tobacco plants tolerant to drought stress accumulated flavonoids under normal and drought conditions, which likely explains the observed tolerance phenotype in wild-type tobacco. Our results suggest that plants overexpressing PpCCoAOMT were better able to cope with water deficit than were wild-type controls; metabolic flux was redirected within primary and specialized metabolism to induce metabolites related to defense to drought stress. These results could help to develop drought-resistant plants for agriculture in the future.

Stress indices based on cane and sugar yields: Implications in selection of sugarcane varieties for drought tolerance

Drought is a major cause of yield loss for many important crops including sugarcane. Due to increasing demand for sugar by a growing world population, it is needed to accelerate the selection of sugarcane clones/varieties that are resistant/tolerant and productive under water stress conditions. This study was conducted to assess the relative drought tolerance of diverse sugarcane clones/varieties evaluated under water stress (E2) and normal (E2) conditions for sugar and cane yields. Analysis of variance revealed significant differences among tested clones/varieties under both the water regimes. Per cent cane and sugar yield reduction in comparison to normal (E1) situation was assessed that ranged from 16.66–47.89 and 25.54–62.54 per cent, respectively under stressed (E2) conditions. Since, water deficit is the single largest abiotic stress affecting sugarcane productivity and the development of water use efficient and drought tolerant cultivars is an imperative, eleven stress indices were worked out from cane and sugar yields recorded under normal and stress conditions as reported earlier to see their effectiveness in sugarcane crop. Study is suggestive that lower score values for seven stress and stability indices viz. stress susceptibility index (SSI), stress tolerance index (STI), yield stability index (YSI), yield index (YI), drought resistance index (DI), relative drought index (RDI) and modified stress tolerance index (K1STI and K2STI) higher score for stress tolerance (TOL), mean productivity and geometric mean productivity (MP and GMP) and stress susceptibility percentage index (SSPI) categorized the clones/varieties as tolerant ones and vice versa. Further association studies showed that all the indices exhibited significant positive interaction with cane and sugar yields (CY and SY) under stress conditions except SSI and SSPI. Also inter association with different level of magnitude and significance among/between different indices were observed indicating their importance for selection of clones under drought stress situations. YI and DI had a positive correlation with RDI, GM, MP, K1 & K2 and between themselves for both cane and sugar yields indicating that they are a better predictor of potential cane and sugar yields under a stress conditions and can be useful for sugarcane researchers. Besides, clones and varieties reported in study with lowest score for SSI, STI, YSI, YI, DI, RDI and (K1STI and K2STI) and highest score for TOL, MP, GMP and SSPI be categorized for enhanced tolerance to water stress in present global warming situation in terms of their resilience to stress and production capacity to have better cane and sugar yields.

Evaluation of the drought resistance of pea (<i>Pisum sativum</i> L.) from the VIR collection

Background. As a result of global warming, climate change is now taking place, increasing the frequency and duration of droughts. Therefore, the development of new varieties with an increased drought resistance and adaptation to certain environmental conditions is of primary importance. The aim of this work was to modify the express method of drought resistance evaluation in peas at an early stage of plant growth and development, and to apply this method to test 50 accessions from the VIR global collection.Materials and methods. Drought resistance studies involved garden pea accessions of different eco-geographic origin, which had been previously characterized in field tests in conditions of the Krasnodar Territory in 2017-2019. The roll-ups protocol was used for evaluating early drought resistance in the accessions. The stress intensity was modified by varying the concentration of sucrose in the solution used for growing of pea seedlings. To select an appropriate concentration, an osmotic pressure of 0.5 and 0.7 MPa was applied. As a result, the osmotic pressure of 0.5 MPa was chosen. The diagnostic criterion of the method is the radicle length index (RLI), that is, the ratio of the average radicle length of seedlings against a provocative background to the control values.Results. The osmotically active solution led to significant reduction in the radicle length of pea seedlings. The studied accessions exhibited considerable genetic variability for early drought tolerance, the RLI value varied from 0.28 to 0.88. Sources of high drought resistance during the period of seedling growth have been identified. The correlation analysis showed the absence of a reliable relationship between the RLI and the crop structure indicators (correlation coefficients from r = +0.17 to r = -0.24).Conclusion. By using the method of determining the relative drought tolerance at early stages of pea accessions development, one highly resistant (k-9333 from Morocco) and 10 resistant accessions (k-1495, k-9372, k-9401, k-9418, k-9733, k-9909, k-9934, k-9938, k-10072, and k-10116.) have been identified.

СРАВНИТЕЛЬНАЯ ОЦЕНКА ФИЗИОЛОГО-БИОХИМИЧЕСКИХ ПАРАМЕТРОВ НЕКОТОРЫХ ВИДОВ И СОРТОВ FICUS В УСЛОВИЯХ ЛЕТНЕГО ДЕФИЦИТА ВЛАГИ НА ЮЖНОМ БЕРЕГУ КРЫМА

The physiological and biochemical parameters of 6 genotypes of genus Ficus species leaves, associated with drought tolerance during the periods of the summer drought on the Southern coast of Crimea were determined. The specific features of the water regime of the species F. carica, F. palmata, F. virgata under the influence of drought factors were revealed. The species F. virgata turned out to be the most sensitive to insufficient water supply. Weak ability to retain moisture and insufficient turgidity was observed in the leaves of the varieties Krymskiy Cherniy and Opylitel Nikitskiy. Leaves of the species F. palmata are characterized by reduced water cut, good water-holding ability and restore tissue turgor at a high level. Protective and adaptive reactions to water stress of the leaves of the Sabrutsiya Rozovaya and Sary Stambulskiy varieties are manifested in the economical use of moisture and protects tissues from excessive dehydration, which ensures a sufficient level of repair for normal physiological processes. It was established that at different periods of the summer season, the biochemical parameters of the studied genotypes at different stages of the experiment varied differently. At the beginning of the summer period, in most of the studied genotypes, the content of proline decreased under full leaves watering, with the restoration of turgidity, it increased, and at the end of the summer, the opposite changes occurred. The activity of peroxidase during restoration of tissue turgor at the beginning of the summer period increased and decreased to a minimum at the end of summer. Catalase activity at the beginning of the summer period decreased with watering the leaves and increased with wilting but at the end of the summer demonstrated no changes with watering and wilting of the leaves and varied in different directions when the turgor was restored. The activity of polyphenol oxidase at the beginning of the summer period at the stage of complete watering and restoration of turgor increased in most genotypes, changed in different directions when wilting, and in late summer it decreased during watering and restoration of turgor and increased after wilting. Despite the amplification of the drought factors, at the end of the summer period the leaves of the studied genotypes preserved the possibility to carry out normal metabolic processes to a greater extent. It was revealed that the proline content, the activity of peroxidase and polyphenol oxidase contribute significantly to the adaptation to drought of the studied genus Ficus species. Analysis of the obtained data allows suggesting that the varieties Sabrutsiya Rozovaya, Sary Stambulskiy and the species F. palmata, which have good water-holding abilities, a high degree of repair after critical dehydration and the ability of the antioxidant system to quickly respond to extreme conditions display the highest adaptive ability to the hydrothermal stress effects, which indicates their relative drought tolerance.

Salt Marsh Elevation Drives Root Microbial Composition of the Native Invasive Grass Elytrigia atherica.

Elytrigia atherica is a native invasive plant species whose expansion on salt marshes is attributed to genotypic and phenotypic adaptations to non-ideal environmental conditions, forming two ecotypes. It is unknown how E. atherica–microbiome interactions are contributing to its adaptation. Here we investigated the effect of sea-water flooding frequency and associated soil (a)biotic conditions on plant traits and root-associated microbial community composition and potential functions of two E. atherica ecotypes. We observed higher endomycorrhizal colonization in high-elevation ecotypes (HE, low inundation frequency), whereas low-elevation ecotypes (LE, high inundation frequency) had higher specific leaf area. Similarly, rhizosphere and endosphere bacterial communities grouped according to ecotypes. Soil ammonium content and elevation explained rhizosphere bacterial composition. Around 60% the endosphere amplicon sequence variants (ASVs) were also found in soil and around 30% of the ASVs were ecotype-specific. The endosphere of HE-ecotype harbored more unique sequences than the LE-ecotype, the latter being abundant in halophylic bacterial species. The composition of the endosphere may explain salinity and drought tolerance in relation to the local environmental needs of each ecotype. Overall, these results suggest that E. atherica is flexible in its association with soil bacteria and ecotype-specific dissimilar, which may enhance its competitive strength in salt marshes.

Significance of root hairs for plant performance under contrasting field conditions and water deficit.

Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experimentally elucidate some of the impacts that root hairs have on plant performance on a field scale. A field experiment was set up in Scotland for two consecutive years, under contrasting climate conditions and different soil textures (i.e. clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Root hair length, density and rhizosheath weight were measured at several growth stages, as well as shoot biomass, plant water status, shoot phosphorus (P) accumulation and grain yield. Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions, although significant variations were found between soil textures as the growing season progressed. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance resulting in a less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot P accumulation. Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. Selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder's dilemma of trying to simultaneously enhance both productivity and resilience. Therefore, the maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

Crambe (Crambe abyssinica Hochst): A Non-Food Oilseed Crop with Great Potential: A Review

Crambe (Crambe abyssinica Hochst) is an oilseed crop in the Brassicaceae family. Crambe’s ability to survive in diverse environmental conditions, its unique oil composition, the high oil content, suitability for the production of slip agents for plasticizers, the capacity to be easily included in common crop rotations, and its adaptability to equipment used for small grain cultivation has renewed the interest in this emerging crop. Crambe is considered one of the main sources of erucic acid, which can be up to 60% of its seed oil content. Erucic acid (C22:1) is a fatty acid with industrial importance since it is used to produce erucamide, key ingredient in the plastic industry. Inclusion of crambe into crop rotations can be beneficial because of its short life cycle, low fertility requirements, resistance to pest and diseases, and relative drought tolerance. Currently high erucic acid rapeseed (Brassica napus L.) (HEAR) is the principal source for erucic acid. However, the risk of contaminating food quality rapeseed (i.e., canola) by cross-pollination and the negative impact on climate, due to high inputs, are potential limitations to expand HEAR cultivation. Crambe has thus great potential to, at least, partially replace HEAR as a source of erucic acid, if the current knowledge-gap in agronomic management and crop improvement (seed yield and quality) can be addressed. Seed yield needs to be increased to be able to compete with HEAR. In addition, reducing glucosinolates and fiber in crambe meal may increase its inclusion in monogastrics rations. The objective of this review was to compile and summarize new and existing information on agricultural practices in crambe production and management to identify gaps in knowledge and areas for future research to increase the cultivation of crambe.

Effect of deficit irrigation on physiology and forage yield of forage sorghum, pearl millet, and corn

AbstractThe declining Ogallala aquifer in the Texas High Plains may no longer meet the irrigation requirement to produce high water‐demanding forage crops like silage corn (Zea mays L.) to support a large number of beef and dairy enterprises. Forage sorghum (Sorghum bicolor L.) and pearl millet (Pennisetum glaucum L.) can be viable alternatives to silage corn due to their relative drought tolerance than silage corn. A field experiment was conducted at New Deal, TX to assess and compare the physiology, forage yield, and nutrient composition of the brown midrib (BMR) forage sorghum, BMR pearl millet, and corn under deficit irrigation in 2018 and 2019. The experiment was conducted in a split‐plot design with three irrigation levels (I0 [50 mm], I1 [200 mm], and I2 [350 mm]) as main‐plot and five cultivars (P1498AM [corn], AF7401 and Silo700D [BMR sorghum], and Epic and Exceed [BMR pearl millet]) as sub‐plot with four replications. The higher leaf water potential (LWP), stomatal conductance, and leaf area index resulted in greater biomass assimilation in I2 compared to I1 and I0 irrigation treatments in both years. Sorghum and pearl millet cultivars showed lower water status through lower LWP and canopy‐air temperature difference compared to corn cultivar. However, sorghum cultivars yielded greater fresh biomass than pearl millet and corn in both years. Lower lignin concentration and higher digestible energy were observed in corn, followed by pearl millet and sorghum. These results suggest that under water‐stress conditions BMR sorghum can produce higher forage yield with acceptable nutritive value.

Differential responses of antioxidants and dehydrin in two Switchgrass (Panicum virgatum L.) cultivars contrasting in drought tolerance

Abstract Drought stress is a major limiting factor for plant growth and development in many regions of the world. This study was designed to investigate antioxidant metabolism and dehydrin expression responses to drought stress in two switchgrass cultivars (drought tolerant Alamo, and drought sensitive Dacotah) contrasting in drought tolerance. The plants were subjected to well-watered [100% evapotranspiration (ET)] or drought stress (30%-50% ET) conditions for up to 24 d in growth chambers. Drought stress decreased leaf relative water content (RWC), increased leaf electrolyte leakage (EL), leaf malondialdehyde (MDA) content in two cultivars, but Alamo exhibited higher leaf RWC level, lower leaf EL and MDA when compared to Dacotah at 24 d of drought treatment. Drought stress also increased superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities in two cultivars, Alamo had relatively higher SOD, CAT and APX activities and greater abundance of SOD and APX isozymes than Dacotah at 24 d of drought treatment. Alamo had higher abundance of 55 KDa and 18 KDa dehydrin accumulation than Dacotah under drought treatment. Relative genes expression level of PvCAT1, PvAPX2, PvERD and PvPIP1;5 in Alamo were significantly higher than Dacotah at 24 d of drought treatment. These results suggest that increase in antioxidant enzymes and accumulation of dehydrin were highly related with switchgrass drought tolerance. Antioxidant enzyme activity, isozyme expression and dehydrin abundance could provide a useful screening tool to identify relative drought tolerance in switchgrass cultivars.

THE IMPACT OF WATER AND TEMPERATURE STRESSES ON GERMINATING ABILITY OF WINTER DURUM WHEAT SEEDS YIELDED IN THE YEARS WITH VARIOUS WEATHER CONDITIONS

The study was conducted in 2016–2018. The objects were three commercial varieties developed by the FSBSI “Agricultural Research Center “Donskoy”, one of which was the standard variety “Donchanka” in the SVT system in the Rostov Region. The purpose of the research was to comprehensively estimate winter durum wheat seeds yielded in the years with various weather conditions due to their resistance to moisture deficit and heat. According to the results of laboratory study, the current paper has presented indicators of relative drought tolerance and heat resistance. The germinating ability of the studied varieties of winter durum wheat “Lazurit” and “Oniks” was better than that of the standard variety “Donchanka” in all concentrations of the solution. Using an osmotic solution with a concentration of 12 and 14 atm all varieties possessed great germinating ability and belonged to the first resistance group. At a critical concentration of osmotic pressure (16 atm), the number of germinated seeds ranged from 69.4% (“Lazurit”) to 63% (“Donchanka”). It has been established that the seeds of the studied winter durum wheat varieties were characterized by little germinating ability under an increasing water stress, while the seeds of different years of reproduction had a different response to water stress. It has been identified that the seeds of the studied varieties significantly varied in their germinating ability after heating. The variety “Oniks” was the most resistant to temperature stress with a germination rate of 86.7% (1-st resistance group) that is on 14% higher than the control variety “Donchanka”. The variety “Lazurit” with a germination rate of 80.2% also belonged to the first resistance group and exceeded the control variety by only 8%. According to the degree of depression in the accumulation of dry sprouts mass under the high temperature impact (thermal testing at +54 °С), the variety “Oniks” was the best with the depression degree of 8.2%. In 2016 the variety “Lazurit” was the most stable, in 2017 and 2018 it was the variety “Oniks”.

A comparison of Sitka spruce x white spruce hybrid families as an alternative to pure Sitka spruce plantations in upland Britain

The heavy reliance of British forestry on Sitka spruce (Picea sitchensis (Bong.) Carr.) presents a risk in a time of changing climate and increasing incidence of pests and diseases. Three experiments were established in 1987 to examine alternative species including hybrids of Sitka spruce and white spruce (Picea glauca (Moench) Voss.) (SS x WS). After 29 years, the height and diameter growth of the best-performing hybrid families was as good as that of unimproved Queen Charlotte Islands (Haida Gwaii) Sitka spruce at two sites, with slightly reduced diameter growth being the only difference at the third site. The SS x WS hybrid families also outperformed white spruce and Engelmann spruce. Performance of the hybrid families was variable and strongly associated with parentage; selection of both female and male parents should be an important consideration in any future research and breeding programmes. There was no evidence that the hybrid families performed disproportionately well at the drier of the three sites and further work would be required to investigate relative drought tolerance. The results show that the SS x WS hybrid families could be an alternative to Sitka spruce and contribute to increasing forest diversity to develop more resilient forests.

Evaluation of four medicinal herb species under conditions of water-deficit stress

Abilities of four commercial herb species namely, Chlorophytum borivilianum, Stevia rebaudiana, Withania somnifera, and Andrographis paniculata were tested for relative drought tolerance under poly house conditions. The findings based on the quantum of data collected for growth, yield of economic parts and physiological traits reveal differential relative potential to sustain performance and cope with the conditions of water stress. Comparative performance of four herb species under stress (50% water deficit) for stress duration of 10, 20 and 30 days revealed significant adverse effects of water-deficit stress as well as stress durations. Out of the four herb species studied, adverse impact of 50% water deficit up to 30 days of stress on growth, yield, rate of photosynthesis, canopy temperature depression and chlorophyll fluorescence (Fv/Fm) ratio was significantly higher in S. rebaudiana and A. paniculata in comparison to C. borivilianum and W. somnifera. In this study, C. borivilianum and W. somnifera have exhibited greater relative drought tolerance as compared to A. paniculata and S. rebaudiana.

Canopy temperature depression at grain filling correlates to winter wheat yield in the U.S. Southern High Plains

Wheat breeding has improved drought tolerance over the years. However, our knowledge on drought tolerance in relation to the diurnal pattern of canopy temperature (CT) and grain yield is limited. A three-season wheat field study ending 2012, 2015, and 2016 was conducted at Bushland, Texas to investigate the relationship between canopy temperature depression (CTD) and yield during the grain filling period. For each season, 20 elite wheat genotypes were grown under dryland conditions, and CT was measured by Smart Crop wireless IRT sensors every 15min continuously for 12–15days during mid-grain filling (∼10–25days after flowering). There was a genotypic variation for CTD regardless of time of the day; however, the variation was more evident during the day time (10:00–18:00h), with the smallest CTD (i.e., warmer canopy) at 14:00–15:00h. In a dry season of 2012, TAM 304, TAM 112, Dumas, and Hatcher had greater CTD (i.e., cooler canopy) than other genotypes. In two wet/near normal seasons (2015 and 2016) Duster, TAM 111, TAM 110, TAM 112, and TAM 105 had greater CTD. There was a significant (P<0.05) positive linear relationship between grain yield and day-time CTD. Hence, a cooler plant canopy during the mid-grain filling in winter wheat appears to be an important indicator of greater drought tolerance and yield under dryland condition. This knowledge may help breeders to conduct high-throughput field phenotyping in large breeding populations.