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Soil microbes play a vital role in improving plant growth, soil health, ameliorate biotic/abiotic stress and enhance crop productivity. The present study was aimed to investigate a coordinated effect of compatible consortium [salt tolerating Rhizobium and rhizobacterium with 1-aminocyclopropane-1-carboxylate (ACC) deaminase] in enhancing plant growth promoting (PGP) traits, symbiotic efficiency, nutrient acquisition, anti-oxidative enzymes, grain yield and associated profitability in spring mungbean. We identified a non-pathogenic compatible Rhizobium sp. LSMR-32 (MH644039.1) and Enterococcus mundtii LSMRS-3 (MH644178.1) from salt affected areas of Punjab, India and the same were assessed to develop consortium biofertilizer based on salt tolerance, multifarious PGP traits, antagonistic defense activities and presence of nifH, acds, pqq, and ipdc genes. Indole Acetic acid (IAA), P-solubilization, biofilm formation, exo-polysaccharides, siderophore, salt tolerance, ACC deaminase activities were all found highly significant in dual inoculant (LSMR-32 + LSMRS-3) treatment compared to LSMR-32 alone. Under saline soil conditions, dual inoculant showed a higher seed germination, plant height, biomass, chlorophyll content and macro and micro-nutrient uptake, than un-inoculated control. However, symbiotic (nodulation, nodule biomass and leghaemoglobin content) and soil quality parameters (phosphatase and soil dehydrogenase enzymes) increased numerically with LSMR-32 + LSMRS-3 over Rhizobium sp. LSMR-32 alone. Dual bacterial inoculation (LSMR-32 + LSMRS-3) increased the proline content (2.05 fold), anti-oxidative enzymes viz., superoxide dismutase (1.50 fold), catalase (1.43 fold) and peroxidase (3.88 folds) in contrast to control treatment. Decreased Na+ accumulation and increased K+ uptake resulted in favorable K+/Na+ ratio through ion homeostasis. Co-inoculation of Rhizobium sp. LSMR-32 and Enterococcus mundtii LSMRS-3 significantly improved the grain yield by 8.92% and led to superior B: C ratio over Rhizobium sp. alone under salt stress. To best of our knowledge this is perhaps the first field report from Indian soils that largely describes dual inoculation of Rhizobium sp. LSMR-32 and Enterococcus mundtii LSMRS-3 and the same can be considered as a game-changer approach to simultaneously induce salt tolerance and improve productivity in spring mungbean under saline stress conditions.

Rising global temperatures due to climate change are affecting crop performance in several regions of the world. High temperatures affect plants at various organizational levels, primarily accelerating phenology to limit biomass production and shortening reproductive phase to curtail flower and fruit numbers, thus resulting in severe yield losses. Besides, heat stress also disrupts normal growth, development, cellular metabolism, and gene expression, which alters shoot and root structures, branching patterns, leaf surface and orientation, and anatomical, structural, and functional aspects of leaves and flowers. The reproductive growth stage is crucial in plants’ life cycle, and susceptible to high temperatures, as reproductive processes are negatively impacted thus reducing crop yield. Genetic variation exists among genotypes of various crops to resist impacts of heat stress. Several screening studies have successfully phenotyped large populations of various crops to distinguish heat-tolerant and heat-sensitive genotypes using various traits, related to shoots (including leaves), flowers, fruits (pods, spikes, spikelets), and seeds (or grains), which have led to direct release of heat-tolerant cultivars in some cases (such as chickpea). In the present review, we discuss examples of contrasting genotypes for heat tolerance in different crops, involving many traits related to thermotolerance in leaves (membrane thermostability, photosynthetic efficiency, chlorophyll content, chlorophyll fluorescence, stomatal activity), flowers (pollen viability, pollen germination, fertilization, ovule viability), roots (architecture), biomolecules (antioxidants, osmolytes, phytohormones, heat-shock proteins, other stress proteins), and “omics” (phenomics, transcriptomics, genomics) approaches. The traits linked to heat tolerance can be introgressed into high yielding but heat-sensitive genotypes of crops to enhance their thermotolerance. Involving these traits will be useful for screening contrasting genotypes and would pave the way for characterizing the underlying molecular mechanisms, which could be valuable for engineering plants with enhanced thermotolerance. Wherever possible, we discussed breeding and biotechnological approaches for using these traits to develop heat-tolerant genotypes of various food crops.

Scientifically based agricultural interventions to improve vegetable productivity were carried out in four districts (Chikkamagalur, Raichur, Vijayapura and Tumkur) of Karnataka State in India, under the Government of Karnataka (GoK)-sponsored Bhoo Samruddhi project (improving the farm productivity and livelihood of smallholder farmers of Karnataka). The activities included, the demonstration of improved practices under protected cultivation (polyroof and shade nethouses), use of grafted seedlings in tomatoes, IPM methods to address tomato leaf miner damage, introduction of mungbean and vegetable cowpea as rotations or intercrops. As a postharvest strategy, we have demonstrated solar drying process and, good agricultural practices to reduce pesticide use & residues in chili. Our interventions have been successful not only in the target farms, the neighbouring farmers have also started adopting them and with the support of the Departments of Agriculture and Horticulture, GoK, the scaling up of these interventions has commenced.

Potassium (K), one of the essential elements required for plant growth and development, determines leaf quality in tobacco (Nicotiana tabacumL.). Potassium (K) levels are relatively high in black soils (vertisols), but K uptake is severely hindered by the presence of remarkably high levels of calcium and magnesium. Our major objective was to enhance potassium uptake in black soils, which cover the major tobacco growing regions of Andhra Pradesh, India. Among several agronomic inputs such as soil amendments, fertilizer application, and plant growth regulators, we found that foliar application of fulvic acid (FA), one of the most bioactive humate molecules, enhanced K levels in leaves. Using next-generation sequencing (NGS), we identified changes in expression levels of a number of genes related to metabolic pathways implicated in plant growth and nutrient uptake upon FA application. Interestingly, starch levels in leaves were reduced concomitant with an increase in K attributable to FA application. We attempt to provide plausible reasons for these observed FA-induced changes. Our results suggested that FA acts in a manner similar to the plant hormone auxin in tobacco, influencing expression of key genes encoding transporters and enzymes involved in K uptake and starch metabolism. While fulvic acid has beneficial effects on plant growth, its mechanism of action is still unclear. [ABSTRACT FROM PUBLISHER]

Global climate change will significantly increase the intensity and frequency of hot, dry days. The simultaneous occurrence of drought and heat stress is also likely to increase, influencing various agronomic characteristics, such as biomass and other growth traits, phenology, and yield-contributing traits, of various crops. At the same time, vital physiological traits will be seriously disrupted, including leaf water content, canopy temperature depression, membrane stability, photosynthesis, and related attributes such as chlorophyll content, stomatal conductance, and chlorophyll fluorescence. Several metabolic processes contributing to general growth and development will be restricted, along with the production of reactive oxygen species (ROS) that negatively affect cellular homeostasis. Plants have adaptive defense strategies, such as ROS-scavenging mechanisms, osmolyte production, secondary metabolite modulation, and different phytohormones, which can help distinguish tolerant crop genotypes. Understanding plant responses to combined drought/heat stress at various organizational levels is vital for developing stress-resilient crops. Elucidating the genomic, proteomic, and metabolic responses of various crops, particularly tolerant genotypes, to identify tolerance mechanisms will markedly enhance the continuing efforts to introduce combined drought/heat stress tolerance. Besides agronomic management, genetic engineering and molecular breeding approaches have great potential in this direction., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In the human diet, particularly for most of the vegetarian population, mungbean ( Vigna radiata L. Wilczek) is an inexpensive and environmentally friendly source of protein. Being a short-duration crop, mungbean fits well into different cropping systems dominated by staple food crops such as rice and wheat. Hence, knowing the growth and production pattern of this important legume under various soil moisture conditions gains paramount significance. Toward that end, 24 elite mungbean genotypes were grown with and without water stress for 25 days in a controlled environment. Top view and side view (two) images of all genotypes captured by a high-resolution camera installed in the high-throughput phenomics were analyzed to extract the pertinent parameters associated with plant features. We tested eight different multivariate models employing machine learning algorithms to predict fresh biomass from different features extracted from the images of diverse genotypes in the presence and absence of soil moisture stress. Based on the mean absolute error (MAE), root mean square error (RMSE), and R squared ( R 2 ) values, which are used to assess the precision of a model, the partial least square (PLS) method among the eight models was selected for the prediction of biomass. The predicted biomass was used to compute the plant growth rates and water-use indices, which were found to be highly promising surrogate traits as they could differentiate the response of genotypes to soil moisture stress more effectively. To the best of our knowledge, this is perhaps the first report stating the use of a phenomics method as a promising tool for assessing growth rates and also the productive use of water in mungbean crop., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Rane, Raina, Govindasamy, Bindumadhava, Hanjagi, Giri, Jangid, Kumar and Nair.)

Rising global temperatures are proving to be detrimental for the agriculture. Hence, strategies are needed to induce thermotolerance in food crops to sustain the food production. GABA (γ-aminobutyric acid), a non-protein amino acid, can partially protect plants from high-temperature stress. This study hypothesises that declining GABA concentrations in the cells of heat-stressed mungbean plants increases the heat-sensitivity of reproductive function. Mungbean plants were grown in a natural, outdoor environment (29.3/16.1 ± 1 °C as mean day/night temperature, 1350-1550 µmol m -2 s -1 light intensity, 60-65% as mean relative humidity) until the start of the reproductive stage. Subsequently, two temperature treatments were imposed in a controlled environment-control (35/23 °C) and heat stress (45/28 °C)-at about 800 µmol m -2 s -1 light intensity and 65-70% as mean relative humidity, until pod maturity. In heat-stressed (HS) plants, endogenous GABA concentrations in leaf and anther samples had declined by 49 and 60%, respectively, and to a much lesser degree in the plants, exogenously supplemented with 1 mM GABA. The reproductive function of GABA-treated heat-stressed plants improved significantly in terms of pollen germination, pollen viability, stigma receptivity and ovule viability, compared to untreated HS controls. In addition, GABA-treated heat-stressed plants had less damage to membranes, photosynthetic machinery (chlorophyll concentration, chlorophyll fluorescence, RuBisCO activity were functionally normal) and carbon assimilation (sucrose synthesis and its utilisation) than the untreated HS controls. Leaf water status improved significantly with GABA application, including enhanced accumulation of osmolytes such as proline and trehalose due to increase in the activities of their biosynthetic enzymes. GABA-treated heat-stressed plants produced more pods (28%) and seed weight (27%) plant -1 than the untreated controls. This study is the first to report the involvement of GABA in protecting reproductive function in mungbean under heat stress, as a result of improved leaf turgor, carbon fixation and assimilation processes, through the augmentation of several enzymes related to these physiological processes.

Experimental evidence is presented to show that the 18O enrichment in the leaf biomass and the mean (time-averaged) transpiration rate are positively correlated in groundnut and rice genotypes. The relationship between oxygen isotope enrichment and stomatal conductance (g(s)) was determined by altering g(s) through ABA and subsequently using contrasting genotypes of cowpea and groundnut. The Peclet model for the 18O enrichment of leaf water relative to the source water is able to predict the mean observed values well, while it cannot reproduce the full range of measured isotopic values. Further, it fails to explain the observed positive correlation between transpiration rate and 18O enrichment in leaf biomass. Transpiration rate is influenced by the prevailing environmental conditions besides the intrinsic genetic variability. As all the genotypes of both species experienced similar environmental conditions, the differences in transpiration rate could mostly be dependent on intrinsic g(s). Therefore, it appears that the delta18O of leaf biomass can be used as an effective surrogate for mean transpiration rate. Further, at a given vapour pressure difference, delta18O can serve as a measure of stomatal conductance as well.