Jagadish Rane

Molecular investigations on grain filling rate under terminal heat stress in bread wheat ( Triticum aestivum L.)

Grain yield under post anthesis high temperature stress is largely influenced by grain filling rate (GFR). To investigate molecular basis of this trait, a set of 111 recombinant inbred lines (RILs) derived from Raj 4014, a heat sensitive genotype and WH 730, heat tolerant cultivar was phenotyped during 2009-2010 and 2010-2011 crop seasons, under field conditions. The difference in GFR (dGFR) between the timely and late sown conditions was used as a phenotypic parameter to find association with molecular markers, as parental lines exhibited significant difference for this trait. The mapping population showed clear-cut segregation pattern for differences in GFR between timely and late sown conditions. About 75% of the progenies showed no difference while 25% showed significant difference in GFR under high temperature stress created by late sown condition. To study the association of this trait with the markers, the parental lines were screened with 300 simple sequence repeat (SSR) microsatellite markers out of which 15% (45) were polymorphic between parental lines. These polymorphic markers were utilized for genotyping a subset, comprising of 43 RILs that had clear contrasting variation for dGFR. Regression analysis revealed significant association of dGFR of RILs with two markers viz., Xbarc04 and Xgwm314 with coefficients of determination (R2) values of 0.10 and 0.06, respectively. Keywords : Grain filling rate (GFR), simple sequence repeat (SSR), heat tolerance, wheat African Journal of Biotechnology Vol. 12(28), pp. 4439-4445

Comparative conventional and phenomics approaches to assess symbiotic effectiveness of Bradyrhizobia strains in soybean ( Glycine max L. Merrill) to drought

Symbiotic effectiveness of rhizobitoxine (Rtx)-producing strains of Bradyrhizobium spp. in soybean (cultivar NRC-37/Ahilya-4) under limited soil moisture conditions was evaluated using phenomics tools such as infrared(IR) thermal and visible imaging. Red, green and blue (RGB) colour pixels were standardized to analyse a total of 1017 IR thermal and 692 visible images. Plants inoculated with the Rtx-producing strains B. elkanii USDA-61 and USDA-94 and successive inoculation by B. diazoefficiens USDA-110 resulted in cooler canopy temperatures and increased canopy greenness. The results of the image analysis of plants inoculated with Rtx-producing strains were correlated with effective nodulation, improved photosynthesis, plant nitrogen status and yield parameters. Principal component analysis (PCA) revealed the reliability of the phenomics approach over conventional destructive approaches in assessing the symbiotic effectiveness of Bradyrhizobium strains in soybean plants under watered (87.41–89.96%) and water-stressed (90.54–94.21%) conditions. Multivariate cluster analysis (MCA) revealed two distinct clusters denoting effective (Rtx) and ineffective (non-Rtx) Bradyrhizobium inoculation treatments in soybean. Furthermore, correlation analysis showed that this phenotyping approach is a dependable alternative for screening drought tolerant genotypes or drought resilience symbiosis. This is the first report on the application of non-invasive phenomics techniques, particularly RGB-based image analysis, in assessing plant-microbe symbiotic interactions to impart abiotic stress tolerance.

Functional and phylogenetic diversity of cultivable rhizobacterial endophytes of sorghum [Sorghum bicolor (L.) Moench]

A diverse group of bacteria colonize the exo- and endo-rhizospheres of sorghum and play a critical role in its tolerance to drought and other abiotic stresses. Two hundred and eighty endophytic bacteria were isolated from the surface-sterilized roots of four sorghum cultivars that were grown on three soil types at three different phenological stages of growth. The isolates were subjected to in vitro screening for their plant growth promoting traits. Out of 280 isolates, 70 could produce Indole 3-Acetic Acid (IAA), 28 showed N-fixation, 28 could solubilize phosphate, 24 had ACC deaminase activity and 13 isolates were able to produce siderophores. Functional diversity grouping of the isolates indicated one isolate having five PGP traits and two isolates having four PGP traits; two and 29 isolates having three and two PGP traits, respectively. Among the thirty-four isolates that possessed multiple PGP traits, 19 and 17 isolates were able to produce significant quantities of IAA in the presence and absence of l-tryptophan, an inducer. Eight isolates possessed high levels of ACC deaminase activity. PCR–RFLP of the 16Sr RNA gene revealed a distinct clustering and considerable genetic diversity among these functionally characterized isolates. The 16S rRNA gene based identification of the isolates of single and multiple PGP traits revealed phylogenetic dominance of Firmicutes; Acinetobacter, Bacillus, Enterobacter, Geobacillus, Lysinibacillus, Microbacterium, Ochrobactrum, Paenibacillus and Pseudomonas were the major genera present in the endo-rhizosphere of sorghum. Results of this study are constructive in selection of effective rhizobacterial endophytes or consortia for drought stress alleviation in sorghum.

Genetic variation in physiological responses of mungbeans (Vigna radiata (L.) Wilczek) to drought

Mungbean is a relatively drought tolerant leguminous crop with a short life cycle. Using leaf water loss (LWL) as a screen for drought tolerance, two mungbean genotypes exhibiting more than two–fold variation in leaf water loss were explored for the genetic variation in their physiological and molecular responses to drought. Efficient stomatal regulation together with better photosynthetic capacity constituted an important trait combination for drought adaptation in water saving low LWL genotype. The stomatal closure under drought was accompanied with a concomitant down-regulation of farnesyl transferase gene. However, cooler canopy temperature, a well branched root system coupled with a relatively higher proline accumulation in water spending high LWL genotype constituted another set of adaptive traits operating when exposed to deficit soil moisture conditions. We report drought induced down-regulation of proline dehydrogenase and the presence of 118 base pair intron in this gene. The high seed yield of low LWL genotype despite a hotter canopy might be attributed to higher net assimilation and quantum yield recorded under drought in this genotype. Thus, these interlinked features contribute to adaptive mechanisms of mungbeans which is widely grown in harsh environments exposed to drought and high temperatures.

Virus Induced Gene Silencing Approach: A Potential Functional Genomics Tool for Rapid Validation of Function of Genes Associated with Abiotic Stress Tolerance in Crop Plants

Virus-induced gene silencing (VIGS) is a versatile tool for functional characterization of plant genes using gene transcript suppression. With increased identification of differentially expressed genes employing high-throughput transcript profiling under various abiotic stresses, functional elucidation of stress-responsive genes is crucial to understand their role in stress tolerance. In recent past, VIGS has been successfully used as reverse genetic elegant tool for gene function analysis in various model plants and also in crop plants. Viral vector-based silencing of gene of interest and studying the gene knockdown plants under stress can be one of the potential options for assessing functional significance of stress-responsive genes. This review provides an overview of how VIGS is used in different crop plants to characterize genes responsive to various kinds of abiotic stresses, viz., drought stress, salinity stress, heat stress, cold stress, and oxidative and nutrient-deficiency stresses. This review also documents examples from studies where abiotic stress-responsive genes have been functionally characterized using VIGS. In addition, we also summarize improvement in abiotic stress tolerance, seed yield, and seed quality traits in crop plants. This review also describes advantages of VIGS over other functional genomics tools, improvement and limitations of VIGS approach, and future prospects of VIGS as efficient tool for studying adaptation and tolerance in crop plants to various kinds of abiotic stresses. In this review, we have also discussed the mechanism of VIGS and novel ways for application of VIGS to carry out functional elucidation of abiotic stress-responsive genes in a wide range of crops.

RNAi Approach: A Powerful Technique for Gene Function Studies and Enhancing Abiotic Stress Tolerance in Crop Plants

RNA interference (RNAi) is a versatile tool frequently used for gene function studies in plants. RNAi phenomenon involves small interfering RNA (siRNA) or short hairpin or microRNA (miRNA) to suppress the expression of sequence-specific gene at posttranscriptional or translational level. This technology has been used to study functional relevance of genes, enhancing crop yield, improving nutritional quality, and increasing crop productivity through suppression of expression of genes responsive to abiotic stress, involved in biomass and grain yield. Here, we describe mechanism of RNAi-mediated gene silencing and application of RNAi technique involving siRNA, shRNA, and microRNA for elucidating function of genes responsive to abiotic stress in crops and also for improving abiotic stress tolerance in crop plants.

Inculcating Resilience to Agriculture Under Abiotically Stressed Environments: Way Forward

Several transformative changes like growing population, changing lifestyles, expanding urbanisation, accelerated land degradation and climate change-induced abiotic stresses are challenging the future food and nutritional security world over especially the low-income countries. All these changes necessitate development of a strategic framework for agricultural innovations which can ensure inclusive and sustainable agricultural growth especially in harsh agroecosystems afflicted by abiotic stresses. A multidisciplinary and holistic approach to manage the stressed environments should aim at characterisation of abiotically stressed environments; reoriented, novel and scaled-up natural resource management (NRM) technologies for stress mitigation; improved adaptation to stressed environments; and task-oriented capacity building. Augmentation, integration and promotion of the best available tools, approaches and technologies should involve investments and incentives for breeding protocols, regional networks for exploring synergies and dynamic policy support. Several leads for policy support towards successful mitigation and adaptation have been listed for meeting the future challenges of abiotic stresses.

Agriculture Drought Management Options: Scope and Opportunities

Drought is one of the recurring features of Indian agriculture especially in the rainfed areas. Severity of its impacts depends upon its nature (chronic and contingent), its duration and frequency, and the extent of area afflicted. Drought not only impacts production at farm level vis-a-vis national food security but also causes miseries to human life and livestock. The present drought management strategies, however, are skewed toward crisis management rather than risk management. The latter needs enhanced insight into even the minute features of the agroecologies for viable solutions to mitigate drought stress. These solutions are determined by capacity to reduce soil moisture deficit, minimizing the impact of drought and accelerating the recovery. However, the key technologies for drought proofing are watershed management, in situ water conservation, and integrated farming systems that include resilient crops, contingent crop plans, etc. Drought stress management further needs shaping through modern tools for characterization of agroecosystem, stress mitigation options, and genetic modification of crops for drought tolerance. In this context, the present review attempts to look at various options being offered by advances in drought management.

Abiotic Stresses in Agriculture: An Overview

Agriculture production and productivity are vulnerable to abiotic stresses. These stresses emerge due to drought, temperature extremes (heat, cold chilling/ frost), radiation (UV, ionizing radiation), floods in addition to edaphic factors which include chemical (nutrient deficiencies, excess of soluble salts, salinity, alkalinity, low pH/acid sulfate conditions, high P and anion retention, calcareous or gypseous conditions, low redox, chemical contaminants—geogenic and xenobiotic), physical (high susceptibility to erosion, steep slopes, shallow soils, surface crusting and sealing, low water-holding capacity, impeded drainage, low structural stability, root-restricting layer, high swell/shrink potential), and biological (low or high organic contents) components. These stresses are the major challenges for production of crops, livestock, fisheries, and other commodities. Only 9% of the world’s agricultural area is conducive for crop production, while 91% is under stresses which widely occur in combinations. While losses to an extent of more than 50% of agricultural production occur due to abiotic stresses, their intensity and adverse impact are likely to amplify manifold with climate change and over exploitation of natural resources. Fragile agroecosystems like the dryland areas are highly vulnerable to such disastrous impact. To mitigate the effects/impact of multiple stressors, proposed strategies include improved agronomic management, while the breeding of stress tolerant genotypes can enhance capacity for adaptation to stress environments. However, a holistic integrated multidisciplinary approach in systems perspectives is a need of the hour to get the best combination of technologies for a particular agroecosystem. Therefore, this compendium through different comprehensive chapters conveys relevant updates on trends in abiotic stresses and their impact in addition to scientific interventions for stress management through mitigation and adaptation options. The compendium also explains scope for modern science to mitigate abiotic stresses and improve adaptation through genetic improvement and some of the policy support endeavors. The way forward includes information on implementation of existing technologies and gaps to be filled through future research for abiotic stress management.

Abiotic Stress Management for Resilient Agriculture

Agriculture production and productivity are vulnerable to abiotic stresses. These stresses emerge due to drought, temperature extremes (heat, cold chilling/ frost), radiation (UV, ionizing radiation), floods in addition to edaphic factors which include chemical (nutrient deficiencies, excess of soluble salts, salinity, alkalinity, low pH/acid sulfate conditions, high P and anion retention, calcareous or gypseous conditions, low redox, chemical contaminants—geogenic and xenobiotic), physical (high susceptibility to erosion, steep slopes, shallow soils, surface crusting and sealing, low water-holding capacity, impeded drainage, low structural stability, root-restricting layer, high swell/shrink potential), and biological (low or high organic contents) components. These stresses are the major challenges for production of crops, livestock, fisheries, and other commodities. Only 9% of the world’s agricultural area is conducive for crop production, while 91% is under stresses which widely occur in combinations. While losses to an extent of more than 50% of agricultural production occur due to abiotic stresses, their intensity and adverse impact are likely to amplify manifold with climate change and over exploitation of natural resources. Fragile agroecosystems like the dryland areas are highly vulnerable to such disastrous impact. To mitigate the effects/impact of multiple stressors, proposed strategies include improved agronomic management, while the breeding of stress tolerant genotypes can enhance capacity for adaptation to stress environments. However, a holistic integrated multidisciplinary approach in systems perspectives is a need of the hour to get