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.

Multi-trait PGP rhizobacterial endophytes alleviate drought stress in a senescent genotype of sorghum [Sorghum bicolor (L.) Moench].

Root-tissue colonizing bacteria demonstrated with multiple PGP traits from sorghum plants were identified as Ochrobactrum sp. EB-165, Microbacterium sp. EB-65, Enterobacter sp. EB-14 and Enterobacter cloacae strain EB-48 on the basis of 16S rRNA gene sequencing. Here, the in vivo experiments using ½-MS media and ½-MS media + 15% PEG 8000 (for inducing drought stress) indicated stress tolerance imparting ability of these rhizobacterial endophytes in a non-stay green and senescent genotype (R-16) of sorghum. In the experiment with sterile soilrite mix base, seed bacterization with these isolates showed improved plant growth specifically the roots, in terms of root length (~ 44.2 to 50.8% over controls), root dry weight (~ 91.3 to 99.8% over controls) and root surface area (~ 1 to 1.5 fold over controls) under drought stress. Rhizobacterial endophytes were successful, not only in providing better cellular osmotic adjustment in leaves (≥ 1-fold increase in proline accumulation over controls), but favorable physiological responses like Relative Water Content (RWC) and cell Membrane Stability Index (MSI) in the inoculated plants during the drought stress induction. Up-regulation of drought responsive genes like sbP5CS2 and sbP5CS1 was observed in these endophytes-treated plants as compared to untreated control and Escherichia coli DH5α (negative control)-treated plants. Interestingly, the stress imparting traits of rhizobacterial endophytes, including up-regulation of specific genes, were observed during sorghum seedling growth only under drought stresses. The results of this study lead to the conclusion that the potential endophytic rhizobacterial interactions can contribute to plant growth promotion as well as induced stress tolerance in sorghum.

Impact of carbon inputs on soil carbon fractionation, sequestration and biological responses under major nutrient management practices for rice-wheat cropping systems.

Major nutrient management systems for rice-wheat cropping were compared for their potential to credit organic carbon (C) to the soil, its fractionation into active (very labile, VLc; labile, Lc) and passive (less labile, LLc; non-labile, NLc) pools, and crop yield responses. A ten-year long experiment was used to study effects of: (i) no inputs (Control, O), (ii) 100% inorganic fertilizers (F) compared to reduced fertilizers inputs (55%) supplemented with biomass incorporation from (iii) opportunity legume crop (Vigna radiata) (LE), (iv) green manure (Sesbania aculeata) (GM), (v) farmyard manure (FYM), (vi) wheat stubble (WS), and (vii) rice stubble (RS). Maximum C input to soil (as the percentage of C assimilated in the system) was in GM (36%) followed by RS (34%), WS (33%), LE (24%), and FYM (21%) compared to O (15%) and F (15%). Total C input to soil had a direct effect on soil C stock, soil C fractions (maximum in VLc and LLc), yet the responses in terms of biological yield were controlled by the quality of the biomass (C:N ratio, decomposition, etc.) incorporated. Legume-based biomass inputs accrued most benefits for soil C sequestration and biological productivity.

Assimilates mobilization, stable canopy temperature and expression of expansin stabilizes grain weight in wheat cultivar LOK-1 under different soil moisture conditions.

BACKGROUND: Grain yield of wheat is primarily determined by both grain number and grain weight, which often influence each other in response to environmental stimuli. Some of the genotypes are capable of maintaining high single grain weight (SGW) across the environments. Understanding mechanisms and factors associated with the superiority of such genotypes over others is necessary to enhance productivity of wheat. RESULTS: Experiments were conducted to elucidate the physiological basis of high SGW of LOK-1, a wheat cultivar grown in dry and hot environments in the central and peninsular zones of India. SGW of LOK-1 was least affected by removal of spikelets indicating little competition between the grains within the spike for assimilates. Reduction in SGW due to defoliation was less and the contribution of stem reserves to the grain development was high in LOK-1 relative to other cultivars. It seems that high level of expression of genes such as expansin (TaExpA6) contributes to the high SGW of LOK-1. CONCLUSIONS: Source was not a limiting factor for grain growth of LOK-1 in contrast to other cultivars, whereas sink appeared to be a limiting factor in recently released/identified cultivars. Differences in the amounts of water soluble stem carbohydrate reserves translocated to grain could be one of the factors contributing to higher grain weight in LOK-1. High level expression of TaExpA6, one of the genes contributing to the elongation of endosperm, seems to be crucial for grain growth in wheat.

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.

Dietary Pyridoxine Protects against Stress and Maintains Immunohaematological Status in Chanos chanos Exposed to Endosulfan.

The amelioration effect of water-soluble vitamin pyridoxine against stress was evaluated in milkfish, Chanos chanos exposed to endosulfan. Two hundred and twenty-five fish were distributed randomly into five treatments, each with three replicates. Four isocaloric and isonitrogenous diets with graded levels of pyridoxine feed were as follows: normal water and fed with control diet (En0/PY0); endosulfan-treated water and fed with control diet (En/PY0); and endosulfan-treated water and fed with 50 (En/PY 50 mg/kg), 75 (En/PY 75 mg/kg) and 100 mg/kg (En/PY 100 mg/kg) pyridoxine-supplemented feed. The endosulfan in treated water was maintained at a level of 1/40th of LC50 (0.52 ppb). The effect of dietary pyridoxine supplementation was studied in terms of antioxidative enzymes (catalase, superoxide dismutase, glutathione-S-transferase), stress markers [heat-shock protein 70, caspase-3, cortisol, acetylcholine esterase (AChE), blood glucose], immunohaematological parameters (total protein, albumin, globulin and A/G ratio, nitroblue tetrazolium, RBC, WBC, Hb), gill histopathology and a subsequent challenge study with Vibrio parahaemolyticus. The antioxidative enzymes, stress markers, albumin and A/G ratio were significantly (p < 0.01) elevated, brain AChE and immunohaematological parameters were significantly (p < 0.01) decreased, and chromosome aberration and gill histopathology were also altered due to endosulfan exposure. The relative survival % was reduced due to the combined effect of endosulfan stress and bacterial challenge. Fish fed the diet supplemented with pyridoxine at 75 and 100 mg/kg was found to restore the studied parameter towards normal compared with control and indicated protection against endosulfan-induced stress significantly (p < 0.01). Results obtained in the present study indicate that the supplementation of 75 and 100 mg/kg of pyridoxine in the diet has a definitive role in the mitigation of the endosulfan-induced stress in milkfish, C. chanos fingerlings.