Metabolomic, photoprotective, and photosynthetic acclimatory responses to post-flowering drought in sorghum

Climate change is globally affecting rainfall patterns, necessitating the improvement of drought tolerance in crops. Sorghum bicolor is a drought-tolerant cereal capable of producing high yields under water scarcity conditions. Functional stay-green sorghum genotypes can maintain green leaf area and efficient grain filling in terminal post-flowering water deprivation, a period of ~10 weeks. To obtain molecular insights into these characteristics, two drought-tolerant genotypes, BTx642 and RTx430, were grown in control and terminal post-flowering drought field plots in the Central Valley of California. Photosynthetic, photoprotective, water dynamics, and biomass traits were quantified and correlated with metabolomic data collected from leaves, stems, and roots at multiple timepoints during drought. Physiological and metabolomic data was then compared to longitudinal RNA sequencing data collected from these two genotypes. The metabolic response to drought highlights the uniqueness of the post-flowering drought acclimation relative to pre-flowering drought. The functional stay-green genotype BTx642 specifically induced photoprotective responses in post-flowering drought supporting a putative role for photoprotection in the molecular basis of the functional stay-green trait. Specific genes are highlighted that may contribute to post-flowering drought tolerance and that can be targeted in crops to maximize yields under limited water input conditions.

Drought Stress Induces Morpho-Physiological and Proteome Changes of Pandanus amaryllifolius

Drought is one of the significant threats to the agricultural sector. However, there is limited knowledge on plant response to drought stress and post-drought recovery. Pandanus amaryllifolius, a moderate drought-tolerant plant, is well-known for its ability to survive in low-level soil moisture conditions. Understanding the molecular regulation of drought stress signaling in this plant could help guide the rational design of crop plants to counter this environmental challenge. This study aimed to determine the morpho-physiological, biochemical, and protein changes of P. amaryllifolius in response to drought stress and during recovery. Drought significantly reduced the leaf relative water content and chlorophyll content of P. amaryllifolius. In contrast, relative electrolyte leakage, proline and malondialdehyde contents, and the activities of antioxidant enzymes in the drought-treated and recovered samples were relatively higher than the well-watered sample. The protein changes between drought-stressed, well-watered, and recovered plants were evaluated using tandem mass tags (TMT)-based quantitative proteomics. Of the 1415 differentially abundant proteins, 74 were significantly altered. The majority of proteins differing between them were related to carbon metabolism, photosynthesis, stress response, and antioxidant activity. This is the first study that reports the protein changes in response to drought stress in Pandanus. The data generated provide an insight into the drought-responsive mechanisms in P. amaryllifolius.

Response of potato (Solanum tuberosum L.) cultivars to drought stress under in vitro and field conditions

Background Potato (Solanum tuberosum L.), the world’s third most important crop, is frequently thought to be sensitive to moderately sensitive to drought, and yield has fallen considerably over consecutive stress periods. Drought produces a wide range of responses in potato, from physiological alterations to variations in growth rates and yield. Knowledge about these responses is essential for getting a full understanding of drought-tolerance mechanism in potato plants which will help in the identification of drought-tolerant cultivars. Results A set of 21 commercial potato cultivars representing the genetic diversity in the Middle East countries market were screened for drought tolerance by measuring morpho-physiological traits and tuber production under in vitro and field trials. Cultivars were exposed to drought stress ranging from no drought to 0.1, 0.2 and 0.3 mol L−1 sorbitol in in vitro-based screening and 60, 40 and 20% soil moisture content in field-based screening. Drought stress adversely affected plant growth, yield and cultivars differed for their responses. Shoots and roots fresh weights, root length, surface area of root, no. of roots, no. of leaves, leaf area, plant water content %, K+ content, under in vitro drought treatments and shoots fresh and dry weights, no. of tubers and tuber yield under field drought treatments were examined and all decreased due to drought. The stress tolerance index decreased with increasing drought in examined cultivars; nevertheless, it revealed a degree of tolerance in some of them. Grouping cultivars by cluster analysis for response to drought resulted in: (i) a tolerant group of five cultivars, (ii) a moderately tolerant group of 11 cultivars, and (iii) a sensitive group of five cultivars. Furthermore, stress-related genes, i.e., DRO, ERECTA, ERF, DREB and StMYB were up-regulated in the five cultivars of the tolerant group. Likewise, the stomatal conductance and transpiration explained high correlation with the tuber yield in this group of cultivars. Conclusion The diversity in germplasm indicated that potato cultivars can be developed for production under certain degrees of drought. Some cultivars are good candidates to be included in drought-tolerant breeding programs and recommended for cultivation in drought-stricken regions. Graphical Abstract

Modulation in Plant Growth and Drought Tolerance of Wheat Crop upon Inoculation of Drought-tolerant-Bacillus Species Isolated from Hot Arid Soil of India

Drought is one of the most detrimental environmental stressors to plants with the potential to decrease crop yields and affect agricultural sustainability. Native bacteria with beneficial traits enhance plant growth and help avoid and reverse the effects of drought in plants to a greater extent. In the present study, we aimed to ( i ) isolate drought-tolerant Bacillus isolates from the rhizosphere soil of wheat crop grown at different locations in Jaisalmer district, Rajasthan state and (ii) further evaluate their ability to enhance plant growth and induce drought tolerance in wheat ( Var. HD-2967) grown under drought stress conditions. Of more than 100 isolates, two putative Bacillus isolates capable of tolerating 30 % polyethylene glycol-6000 (PEG-6000) [equivalent to -9.80 MPa (Megapascal)] were identified as Bacillus altitudinis DT-89 and Bacillus paramycoides DT-113. These isolates exhibited different plant growth promoting (PGP) attributes such as phosphate solubilization, and production of siderophore, exopolysaccharide, ammonia, indole acetic acid and cytokinin at low osmotic stress of 10% PEG-6000 but shown variable response at higher osmotic stress particularly at 30% PEG-6000. However, they did not show any antifungal activity and one isolate was negative for phosphate solubilization. Of two strains, B. altitudinis DT-89 function more prominently with respect to plant growth promotion and drought tolerance to plant in the early stage but protective traits of B. paramycoides DT-113 was more prominent after 75 days as evident by increased EPS (164%), root dry weight (144.44%), chlorophyll content (90.26%), SOD (389%) and proline (99.3%). The results support both the strains as a potential candidate to alleviate drought stress and enhance plant growth in the drought regions.

Antioxidant Response and Calcium-Dependent Protein Kinases Involvement in Canola (Brassica napus L.) Tolerance to Drought

Canola is an important temperate oil crop that can be severely affected by drought. Understanding the physiological and molecular mechanisms involved in canola tolerance to water deficit is essential to obtain drought-tolerant productive cultivars. To investigate the role of antioxidant response and the possible involvement of calcium-dependent protein kinases (CDPKs) in canola tolerance to drought, we analyzed four genotypes with different sensitivity to water stress. Leaf relative water content, canopy temperature, PSII efficiency, electrolyte leakage index and lipid peroxidation were used as indicators to classify the cultivars as drought-tolerant or drought-sensitive. Antioxidant enzymes superoxide dismutase, guaiacol peroxidase and catalase displayed significantly higher activities in drought-tolerant than in drought-sensitive cultivars subjected to water deficit, suggesting that the efficiency of the antioxidant response is essential in canola drought tolerance. The increased expression of genes BnaCDPK6 and BnaCDPK14 under drought conditions, their differential expression in drought-tolerant and drought-sensitive genotypes, and the presence of multiple cis-acting stress-related elements in their promoter regions suggest that CDPKs are part of the signaling pathways that regulate drought response in canola. We propose the BnaCDPK genes and their regulator elements as potential molecular targets to obtain drought-tolerant productive canola cultivars through breeding or genetic transformation.

Drought Tolerant Near Isogenic Lines of Pusa 44 Pyramided With qDTY2.1 and qDTY3.1, Show Accelerated Recovery Response in a High Throughput Phenomics Based Phenotyping

Reproductive stage drought stress (RSDS) is a major challenge in rice production worldwide. Cultivar development with drought tolerance has been slow due to the lack of precise high throughput phenotyping tools to quantify drought stress-induced effects. Most of the available techniques are based on destructive sampling and do not assess the progress of the plant’s response to drought. In this study, we have used state-of-the-art image-based phenotyping in a phenomics platform that offers a controlled environment, non-invasive phenotyping, high accuracy, speed, and continuity. In rice, several quantitative trait loci (QTLs) which govern grain yield under drought determine RSDS tolerance. Among these, qDTY2.1 and qDTY3.1 were used for marker-assisted breeding. A set of 35 near-isogenic lines (NILs), introgressed with these QTLs in the popular variety, Pusa 44 were used to assess the efficiency of image-based phenotyping for RSDS tolerance. NILs offered the most reliable contrast since they differed from Pusa 44 only for the QTLs. Four traits, namely, the projected shoot area (PSA), water use (WU), transpiration rate (TR), and red-green-blue (RGB) and near-infrared (NIR) values were used. Differential temporal responses could be seen under drought, but not under unstressed conditions. NILs showed significant level of RSDS tolerance as compared to Pusa 44. Among the traits, PSA showed strong association with yield (80%) as well as with two drought tolerances indices, stress susceptibility index (SSI) and tolerance index (TOL), establishing its ability in identifying the best drought tolerant NILs. The results revealed that the introgression of QTLs helped minimize the mean WU per unit of biomass per day, suggesting the potential role of these QTLs in improving WU-efficiency (WUE). We identified 11 NILs based on phenomics traits as well as performance under imposed drought in the field. The study emphasizes the use of phenomics traits as selection criteria for RSDS tolerance at an early stage, and is the first report of using phenomics parameters in RSDS selection in rice.

Genetic Variation in Drought-Tolerance Traits and Their Relationships to Growth in Pinus radiata D. Don Under Water Stress

The selection of drought-tolerant genotypes is globally recognized as an effective strategy to maintain the growth and survival of commercial tree species exposed to future drought periods. New genomic selection tools that reduce the time of progeny trials are required to substitute traditional tree breeding programs. We investigated the genetic variation of water stress tolerance in New Zealand-grown Pinus radiata D. Don using 622 commercially-used genotypes from 63 families. We used quantitative pedigree-based (Genomic Best Linear Unbiased Prediction or ABLUP) and genomic-based (Genomic Best Linear Unbiased Prediction or GBLUP) approaches to examine the heritability estimates associated with water stress tolerance in P. radiata. Tree seedling growth traits, foliar carbon isotope composition (δ13C), and dark-adapted chlorophyll fluorescence (Y) were monitored before, during and after 10 months of water stress. Height growth showed a constant and moderate heritability level, while the heritability estimate for diameter growth and δ13C decreased with water stress. In contrast, chlorophyll fluorescence exhibited low heritability after 5 and 10 months of water stress. The GBLUP approach provided less breeding value accuracy than ABLUP, however, the relative selection efficiency of GBLUP was greater compared with ABLUP selection techniques. Although there was no significant relationship directly between δ13C and Y, the genetic correlations were significant and stronger for GBLUP. The positive genetic correlations between δ13C and tree biomass traits under water stress indicated that intraspecific variation in δ13C was likely driven by differences in the genotype’s photosynthetic capacity. The results show that foliar δ13C can predict P. radiata genotype tolerance to water stress using ABLUP and GBLUP approaches and that such approaches can provide a faster screening and selection of drought-tolerant genotypes for forestry breeding programs.

Effects of Two Varieties and Fertilization Regimes on Growth, Fruit, and Silymarin Yield of Milk Thistle Crop

Milk thistle is an alternative crop to winter cereals for southern Europe as this species is drought tolerant and its fruits contain silymarin. The aim of this study was to assess the impact of two varieties and fertilization regimes (sheep manure and inorganic fertilizer) on crop productivity. A two-factor experiment was conducted in a randomized split-plot design with three replicates. The varieties were Palaionterveno and Spata, while the fertilization treatments were control, sheep manure, and calcium ammonium nitrate applied at 75 and 125 kg N ha−1. Variety and fertilization significantly affected plants development and productivity, as well as oil and silymarin yield. The use of manure and inorganic nitrogen fertilizer increased rosette diameter, oil and silymarin yield, above-ground biomass, and fruit yield. The influence of inorganic fertilization, regardless of the application dose, was more apparent than organic fertilization. Moreover, variety significantly affected plants growth and silymarin content, as well as silymarin composition. The variety Spata had the greatest silymarin content, reaching 4.40%, and a high silybin B concentration. In conclusion, the selection of a suitable variety is important for achieving high fruit and silymarin yields, while inorganic nitrogen fertilization can maximize the productivity of the milk thistle crop.