Assessing the effect of salinity on the oil quality parameters of Indian mustard (

High throughput phenotyping of functional traits and key indices for selection of salt tolerant Mustard [Brassica juncea (L.) Czern & Coss] genotypes

The current scanty knowledge about the salt tolerance mechanism underlying the ability of plants to tolerate salt stress hinders the potential production of numerous crops, including Indian mustard. To explore the traits and mechanism for salt tolerance, high throughput phenotyping of 250 stabilized F7:8 recombinant inbred lines (RILs) mapping population of Indian mustard were conducted under control and salinity (ECiw 12 dS m-1 ) for 54 morpho-physio-seed-quality traits. Most of the traits were reduced with variable percentages under salt stress. The stress tolerance index (STI) of YPP showed a significant negative association with Na+ concentration of root (RNa), indicating that RILs with low Na+ concentration have high seed yield and a positive significant association with STI of yield-related traits, photosynthesis rate (Pn), intrinsic water use efficiency (inWUE), fresh weight of upper leaf (USFW), fresh weight of branches (BrFW), fresh weight of basal leaf (BLFW), and fresh weight of middle leaf (MLFW) revealed that by improving these traits seed yield per plant (YPP) was improved. Based on principal component analysis (PCA) of 54 STI and new index composite selection index (CSI), RILs viz., R114, R150, R164, R170, and R206 were identified as stable performers which can be exploited for quantitative trait loci (QTLs)/gene discovery and serve as potential donors to combat salt stress. Our research will serve to determine the relative importance of different functional traits of salt tolerance mechanisms that can be used to screen colossal germplasm.

Synergistic action of Pseudomonas fluorescens with melatonin attenuates salt toxicity in mustard by regulating antioxidant system and flavonoid profile

Salt stress is an alarming abiotic stress that reduces mustard growth and yield. To attenuate salt toxicity effects, plant growth-promoting rhizobacteria (PGPR) offers a sustainable approach. Among the various PGPR, Pseudomonas fluorescens (P. fluorescens NAIMCC-B-00340) was chosen for its salt tolerance (at 100 mM NaCl) and for exhibiting various growth-promoting activities. Notably, P. fluorescens can produce auxin, which plays a role in melatonin (MT) synthesis. Melatonin is a pleiotropic molecule that acts as an antioxidant to scavenge reactive oxygen species (ROS), resulting in stress reduction. Owing to the individual role of PGPR and MT in salt tolerance, and their casual nexus, their domino effect was investigated in Indian mustard under salt stress. The synergistic action of P. fluorescens and MT under salt stress conditions was found to enhance the activity of antioxidative enzymes and proline content as well as  promote the production of secondary metabolites. This led to reduced oxidative stress following effective ROS scavenging, maintained photosynthesis, and improved growth. In mustard plants treated with MT and P. fluorescens under salt stress, eight flavonoids showed significant increase. Kaempferol and cyanidin showed the highest concentrations and are reported to act as antioxidants with protective functions under stress. Thus, we can anticipate that strategies involved in their enhancement could provide a better adaptive solution to salt toxicity in mustard plants. In conclusion, the combination of P. fluorescens and MT affected antioxidant metabolism and flavonoid profile that could be used to mitigate salt-induced stress and bolster plant resilience.

Salt Removal through Residue-Filled Cut-Soiler Simulated Preferential Shallow Subsurface Drainage Improves Yield, Quality and Plant Water Relations of Mustard (Brassica juncea L.)

Soil salinity and the use of saline groundwater are two major constraints in crop production, which covers a ~1.0 billion ha area of arid and semi-arid regions. The improved drainage function of soil can modify the salty growing environment for higher agricultural production. The present study evaluated the effectiveness of cut-soiler-constructed rice residue-filled preferential shallow subsurface drainage (PSSD) to improve the drainage function and its effect on the yield, quality and plant–water relations of mustard over 2019–2021. Cut-soiler-simulated drains were made in a semi-controlled lysimeter (2 × 2 × 3; L*W*H m) as the main plot treatment in a double replicated split–split experiment with two soil types (subplot) and three irrigation water salinities (4, 8 and 12 dS m−1) as the sub-sub-plot treatment. The drainage volume of variable salinity (EC), dependent on the total water input, was substantially higher in the rainy season (April to October), i.e., 16.6, 7.76 and 12.0% during 2018, 2019 and 2020, with 1.7, 0.32 and 0.77 kg salt removal per lysimeter, compared to the post-rainy season. The mustard seed, straw and biological yields were improved by 31.4, 14.41 and 18.08%, respectively, due to a positive effect on plant–water relations. The mustard seeds produced in the cut-soiler-treated plots recorded higher oil, crude fiber and protein contents and a lower erucic acid content. The increase in salt load, by higher-salinity irrigation water, was also efficiently managed by using cut-soiler PSSD. It was found that the saline irrigation water up to 12.0 dS m−1 can be used under such PSSD without any extra salt loading. The present study showed the potential of cut-soiler PSSD in root zone salinity management by improving drainage in salt-affected arid regions.

Soil salinity under climate change: Challenges for sustainable agriculture and food security

Soil salinity is one of the major and widespread challenges in the recent era that hinders global food security and environmental sustainability. Worsening the situation, the harmful impacts of climate change accelerate the development of soil salinity, potentially spreading the problem in the near future to currently unaffected regions. This paper aims to synthesise information from published literature about the extent, development mechanisms, and current mitigation strategies for tackling soil salinity, highlighting the opportunities and challenges under climate change situations. Mitigation approaches such as application of amendments, cultivation of tolerant genotypes, suitable irrigation, drainage and land use strategies, conservation agriculture, phytoremediation, and bioremediation techniques have successfully tackled the soil salinity issue, and offered associated benefits of soil carbon sequestration, and conservation and recycling of natural resources. These management practices further improve the socio-economic conditions of the rural farming community in salt-affected areas. We also discuss emerging reclamation strategies such as saline aquaculture integrated with sub surface drainage, tolerant microorganisms integrated with tolerant plant genotypes, integrated agro-farming systems that warrant future research attention to restore the agricultural sustainability and global food security under climate change scenarios.

Differential response of Indian mustard (Brassica juncea L., Czern and Coss) under salinity: photosynthetic traits and gene expression

To explore the effect of salt stress on photosynthetic traits and gene expression in Indian mustard, four genotypes CS 54 (national check for salinity), CS 52-SPS-1-2012 (salt tolerant mutant), CS 614-4-1-4-100-13 (salt sensitive mutant) and Pusa bold (high yielding variety) were evaluated under irrigation water salinity (ECiw 12, and 15 dS m-1). Results suggest genotype CS 52-SPS-1-2012 followed by CS 54 performed better under imposed salt stress due to differential regulation of Na+ accumulation in the roots and main stem, restriction of Na+ influx from root to shoot, maintaining higher net photosynthetic traits under saline stress compared to CS 614-4-1-4-100-13 and Pusa bold. Further, overexpression of antiporters (SOS1, SOS2, SOS3, ENH1 and NHX1) and antioxidant (APX1, APX4, DHAR1 and MDHAR) genes in salt tolerant genotypes CS 52-SPS-1-2012 and CS 54 demonstrated their significant role in imparting salt tolerance in Indian mustard.

Near-infrared reflectance spectroscopy calibrations for assessment of oil, phenols, glucosinolates and fatty acid content in the intact seeds of oilseed Brassica species

BACKGROUND

Very few near-infrared reflectance spectroscopy (NIRS) calibration models are available for non-destructive estimation of seed quality traits in Brassica juncea. Those that are available also fail to adequately discern variation for oleic acid (C_18:1 )_, linolenic (C_18:3 ) fatty acids, meal glucosinolates and phenols. We report the development of a new NIRS calibration equation that is expected to fill the gaps in the existing NIRS equations.

RESULTS

Calibrations were based on the reference values of important quality traits estimated from a purposely selected germplasm set comprising 240 genotypes of B. juncea and 193 of B. napus. We were able to develop optimal NIRS-based calibration models for oil, phenols, glucosinolates, oleic acid, linoleic acid and erucic acid for B. juncea and B. napus. Correlation coefficients (RSQ) of the external validations appeared greater than 0.7 for the majority of traits, such as oil (0.766, 0.865), phenols (0.821, 0.915), glucosinolates (0.951, 0.986), oleic acid (0.814. 0.810), linoleic acid (0.974, 0.781) and erucic acid (0.963, 0.943) for B. juncea and B. napus, respectively.

CONCLUSION

The results demonstrate the robust predictive power of the developed calibration models for rapid estimation of many quality traits in intact rapeseed-mustard seeds which will assist plant breeders in effective screening and selection of lines in quality improvement breeding programmes. © 2018 Society of Chemical Industry.

Elucidating the role of osmotic, ionic and major salt responsive transcript components towards salinity tolerance in contrasting chickpea (Cicer arietinum L.) genotypes

The growth of chickpea (Cicer arietinum L.) is extremely hampered by salt stress. Understanding of physio-biochemical and molecular attributes along with morphological traits contributing to the salinity tolerance is important for developing salt tolerant chickpea varieties. To explore these facts, two genotypes CSG8962 and HC5 with contrasting salt tolerance were evaluated in the salinity stress (Control and 120 mM NaCl) conditions. CSG8962 maintained lower Na/K ratio in root and shoot, trammeled Na translocation to the shoots from roots compared to HC5 which ascribed to better exclusion of salt from its roots and compartmentation in the shoot. In chickpea, salt stress specifically induced genes/sequences involved at several levels in the salt stress signaling pathway. Higher induction of trehalose 6 phosphate synthase and protein kinase genes pertaining to the osmotic and signaling modules, respectively, were evident in CSG8962 compared to HC5. Further transcripts of late embryogenesis abundant, non-specific lipid transfer protein, HI and 219 genes/sequences were also highly induced in CSG8962 compared to HC5 which emphasizes the better protection of cellular membranous network and membrane-bound macromolecules under salt stress. This further suppressed the stress enhanced electrolyte leakage, loss of turgidity, promoted the higher compatible solute accumulation and maintained better cellular ion homoeostasis in CSG8962 compared to HC5. Our study further adds to the importance of these genes in salt tolerance by comparing their behavior in contrasting chickpea genotypes.

De Novo Assembly and Characterization of Stress Transcriptome in a Salinity-Tolerant Variety CS52 of Brassica juncea

Oilseed mustard, Brassica juncea, exhibits high levels of genetic variability for salinity tolerance. To obtain the global view of transcriptome and investigate the molecular basis of salinity tolerance in a salt-tolerant variety CS52 of B. juncea, we performed transcriptome sequencing of control and salt-stressed seedlings. De novo assembly of 184 million high-quality paired-end reads yielded 42,327 unique transcripts longer than 300 bp with RPKM ≥1. When compared with non-redundant proteins, we could annotate 67% unigenes obtained in our study. Based on the mapping to expressed sequence tags (ESTs), 52.6% unigenes are novel compared to EST data available for B. juncea and constituent genomes. Differential expression analysis revealed altered expression of 1469 unigenes in response to salinity stress. Of these, 587, mainly associated with ROS detoxification, sulfur assimilation and calcium signaling pathways, are up regulated. Notable of these is RSA1 (SHORT ROOT IN SALT MEDIUM 1) INTERACTING TRANSCRIPTION FACTOR 1 (RITF1) homolog up regulated by >100 folds in response to stress. RITF1, encoding a bHLH transcription factor, is a positive regulator of SOS1 and several key genes involved in scavenging of salt stress-induced reactive oxygen species (ROS). Further, we performed comparative expression profiling of key genes implicated in ion homeostasis and sequestration (SOS1, SOS2, SOS3, ENH1, NHX1), calcium sensing pathway (RITF1) and ROS detoxification in contrasting cultivars for salinity tolerance, B. juncea and B. nigra. The results revealed higher transcript accumulation of most of these genes in B. juncea var. CS52 compared to salt-sensitive cultivar even under normal growth conditions. Together, these findings reveal key pathways and signaling components that contribute to salinity tolerance in B. juncea var. CS52.

Proteomic analysis of canola root inoculated with bacteria under salt stress

Plant-growth promoting bacteria can ameliorate the negative effects of salt stress on canola. To better understand the role of bacteria in canola under salt stress, salt-sensitive (Sarigol) and salt-tolerant (Hyola308) cultivars were inoculated with Pseudomonas fluorescens and protein profiles of roots were compared. Bacterial inoculation increased the dry weight and length of canola roots under salt stress. Using a gel-free proteomic technique, 55 commonly changed proteins were identified in Sarigol and Hyola308 roots inoculated with bacteria under salt stress. In both canola cultivars, proteins related to amino acid metabolism and tricarboxylic acid cycle were affected. Hierarchical cluster analysis divided the identified proteins into three clusters. Proteins related to Clusters II and III, which were secretion-associated RAS super family 1, dynamin-like protein, and histone, were increased in roots of both Sarigol and Hyola308 inoculated with bacteria under salt stress. Based on pathway mapping, proteins related to amino acid metabolism and the tricarboxylic acid cycle significantly changed in canola cultivars inoculated with or without bacteria under salt stress. These results suggest that bacterial inoculation of canola roots increases tolerance to salt stress by proteins related to energy metabolism and cell division.

BIOLOGICAL SIGNIFICANCE

Plant-growth promoting bacteria as an emerging aid can ameliorate the negative effect of salt stress on canola. To understand the role of bacteria in canola under salt stress, salt sensitive Sarigol and tolerant Hyola308 cultivars were used. Dry weight and length of canola root were improved by inoculation of bacteria under salt stress. Using gel-free proteomic technique, 55 commonly changed proteins identified in Sarigol and Hyola308 inoculated with bacteria under salt stress. In both canola cultivars, the number of proteins related to amino acid metabolism and tricarboxylic acid cycle was more than other categories with higher change in protein abundance. Hierarchical cluster analysis divided into 3 clusters. Cluster II including secretion-associated RAS super family 1 and dynamin-like protein and Cluster III including histones H2A were increased by bacterial inoculation in both cultivars. Furthermore, pathway mapping highlighted the importance of S-denosylmethionine synthetase and malate dehydrogenase that decreased in canola inoculated with bacteria under salt stress. These results suggest that bacterial inoculation helps the canola to endure salt stress by modulating the proteins related to energy metabolism and cell division.