Potentials of Lactic Acid Bacteria in Enhancing Nodulation of Bradyrhizobium daqingense and Yield in Soybean

Background: The ferments of lactic acid bacteria (LAB) are used since decades in agricultural practice to control diseases, to promote plant growth and also to improve soils. However the functional roles of LAB in phytomicrobiome need to be discovered, which would result in understanding of the symbiotic relationship between LAB and plants and that could be exploited to improve agricultural production. Methods: In this study, the scientific investigation was carried out for pot culture evaluation of six efficient LAB isolates from soybean rhizosphere, on nodulation and yield of soybean in green house condition, which were proven positive for IAA and GA production and PGPR traits. Result: Among the eight different treatment combination with Bradyrhizobium daqingense the treatment which received consortium of all six LAB isolates had significant impact on plant growth characters viz. plant height, root length, number of branches and chlorophyll content at 30 and 60 DAS. The LAB consortia also showed significantly high nodule number (47.67), nodule dry weight (117 mg plant-1) and leg haemoglobin content (6.27 mg g-1 fresh nodule) at 30 DAS. The yield and yield related traits was also highest in consortium treated plants. The property of plant to produce more nodules and healthy root growth can be attributed to IAA producing ability of inoculated LAB isolates.

PGPR Characteristics of Rhizospheric Bacteria to Understand the Mechanisms of Faba Bean Growth

Rhizobacteria play an important role in maintaining soil balance. Among these bacteria, there are those taht have shown their ability to promote the growth of plants, known as Plant Growth Promoting Rhizobacteria (PGPR). In our work, we are interested in characterizing 110 bacterial strains isolated in the field in the region of Ben Badis (Constantine Algeria) from 5 varieties of faba bean. Phenotypic and biochemical characterization showed that most of the isolates are cream-colored, slightly raised, flat and opaque, Gram−, catalase+ and oxidase−, and Bacillus form. PCA analysis allowed us to select 40 isolates with a high degree of variability to continue our work. The results obtained have directed us towards different taxonomic groups (rhizobium, Pseudomonas, Bacillus etc.). The evaluation of the PGPR potential of bacteria (phytostimulation, biofertilization and biocontrol), showed that 100% of bacteria are able to produce auxin at different concentrations, with the highest concentration (177.77 µg/mL) for the isolate 6, and that more than 50% of isolates are capable of producing nitrogen, ammonia and phytate mineralization. These PGPR traits have a direct effect on plant growth of five varieties of the faba bean and can be used to select the best performing bacteria for inoculation tests.

Response of Different Cultivars of Wheat Plants (Triticum aestivum L.) to Inoculation by Azotobacter sp. under Salinity Stress Conditions

Salinity is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Therefore, cope with this problem we should be develop strategies to enhance salinity tolerance in different crops. One of these modern strategies is to use plant growth promoting rhizobacteria (PGPR) which can help plants to withstand under harsh environmental conditions. The present study was evaluated six isolates of Azotobacter sp. (Az1-Az6) which tested in vitro for growth, PGPR traits such as indole-3 acetic acid (IAA) production and nitrogen fixation, germination indicators for different wheat cultivars i.e. Misr 1, Gemmiza 12 and Sakha 95 under different levels of NaCl. Also, the efficacy of inoculation with two superior isolates in different wheat cultivars in a Gnotobiotic Sand System and greenhouse experiment for improving growth dynamics, physiological attributes, nutrient uptake and antioxidant enzymes under different levels salinity of sandy soil (0, 4, 8 and 12 dS m-1). Out of 6 isolates, two isolates (Az2 and Az6) could show salinity tolerance and exhibited PGPR traits as well as improvement germination tests. Both the bacteria could promote growth in 3 cultivars of wheat tested in terms of increase in fresh weight, dry weight, root and shoot length as well as root colonization compared to uninoculated control under Gnotobiotic Sand System experiment. Under greenhouse experiment conditions, inoculation treatment with Az6 showed a significant increase of vegetative growth, physiological and biochemical parameters of different wheat cultivars under different salinity stress treatments. Also, Az6 treatment recorded the highest N% from wheat plants attained 2.64, 2.51 and 2.43% at 4 dS m-1 for Misr1, Sakha 95 and Gemmiza 12 cultivars, respectively but the highest K+, K+/Na+% and the lowest Na+% were obtained from plants that grown in soil salinized with 8 and 12 dS m-1. The same trend was observed for antioxidant enzymes. Thus, inoculation with Azotobacter isolates Az2 and Az6 could be efficiently used to partially or completely eliminate the effects of salt stress on growth of different wheat cultivars.

Impact of soil salinity on the cowpea nodule-microbiome and the isolation of halotolerant PGPR strains to promote plant growth under salinity stress

Four soil samples (SS-1—SS-4) isolated from semi-arid soils in Punjab, Pakistan were used as inocula for cowpea (Vigna unguiculata L.) grown under salinity stress to analyze the composition of bacteria in the rhizosphere and within nodules through cultivation-dependent and cultivation-independent methods. Two cowpea varieties, 603 and the salt-tolerant CB 46, were each inoculated with four different native soil samples, and data showed that plants inoculated with soil samples SS-2 and SS-4 grew better than plants inoculated with soil samples SS-1 and SS-3. Bacteria were isolated from both soils and nodules, and 34 of the 51 original isolates tested positive for PGPR traits in plate assays with many exhibiting multiple plant growth-promoting properties. A number of isolates were positive for all PGPR traits tested. For the microbiome studies, environmental DNA (eDNA) was isolated from SS-1 and SS-4, which represented the extremes of the Pakistan soils to which the plants responded, and by 16S rRNA gene sequencing analysis were found to consist mainly of Actinobacteria, Firmicutes, and Proteobacteria. However, sequencing analysis of eDNA isolated from cowpea nodules established by the trap plants grown in the four Pakistan soils indicated that the nodule microbiome consisted almost exclusively of Proteobacterial sequences, particularly Bradyrhizobium. Yet, many other bacteria including Rhizobium, Mesorhizobium, Pseudomonas, as well as Paenibacillus, Bacillus as well as non-proteobacterial genera were isolated from the nodules of soil-inoculated cowpea plants. This discrepancy between the bacteria isolated from cowpea nodules (Proteobacteria and non-Proteobacteria) versus those detected in the nodule microbiome (Proteobacteria) needs further study.

Polyamine Modulation by antagonistic bacteria Bacillus subtilis in chickpea during Fusarium oxysporum f. sp. ciceri interaction

Chickpea (Cicer arietinum L.) is pivotal source of protein for vegetarian diet, however, its productivity is adversely affected by wilt disease. Non pathogenic rhizospheric microorganism’s leads to induce resistance and are found to be effective in management of this disease. The polyamines (PAs) content and its metabolism are the key in plant microbial interaction, so the alteration in PAs viz. spermidine (SPD), spermine (SPM) and putresine (PTR) in chickpea by Bacillus substilis isolate K18 (BS-K18) effective antagonist (75%) of Fusarium oxysporum f. sp. ciceri (Foc) and having PGPR traits was analyzed under Foc stress. The higher PAs content was reported in resistant variety (WR-315) compared to susceptible variety (JG-62). The PTR was dominant PA present in chickpea, further overall root tissue reported higher PA content as compared to leaves tissue. The PA content was constitutively improved by B. subtilis seed treatment in resistant and susceptible varieties. The Foc stress leads to induction of PA content in leaves and root tissue, where its content was higher in resistant variety as compared to susceptible variety. The BS-K18 seed treatment under Foc stress leads to induction of PA content as compared to both treatments alone, the SPD and SPM were more induced in leaves and root tissue of susceptible variety whereas PTR was more induces in resistant variety. Overall, polyamines were induced up to 3 DAT then after decline suggest their early role in plant defence mechanism, further PTR was found to be dominating polyamine during chickpea-Foc interaction under BS-K18 treatment. The Bacillus subtilis seed treatment leads to improve wilt tolerance in susceptible var. JG-62 through modulation of PAs, the same mechanism also helped to enhanced effectiveness of resistant var. WR-315.

Molecular diversity of stress-tolerant PGPR rhizobia nodulating clusterbean (Cyamopsis tetragonoloba L.) grown in hyper-arid zone of Rajasthan

A total of 81 rhizobia were retrieved from nodules of clusterbean grown in hyper-arid zone of Rajasthan. Twenty one rhizobial isolates showed combined drought tolerance of 40% concentration of polyethylene glycol 6000 and temperature tolerance at 45°C. All the stress-tolerant rhizobia were authenticated by plant infectivity test and further showed the presence of nitrogen fixation nifH gene. Most of the stress-tolerant rhizobia harbour multiple PGPR traits. The molecular diversity among stress-tolerant rhizobia was accomplished through RFLP of 16S rDNA using restriction enzymes MspI and HaeIII. Dendrogram data showed that all 21 isolates were distributed into two major clusters. Total of 20 genotypes were formed but 13 biotypes were constituted at 80% level of similarity. Out of these, biotype 10 was found to be the most prevalent biotype of hyper-arid zone. Moreover, isolates from same nodule were not 100% similar. It indicated that vast diversity was present among stress-tolerant clusterbean rhizobial isolates.

Production and Metabolism of Indole Acetic Acid in Root Nodules and Symbiont (Rhizobium undicola) Isolated from Root Nodule of Aquatic Medicinal Legume Neptunia oleracea Lour.

Indole acetic acid is a phytohormone which plays a vital role in plant growth and development. The purpose of this study was to shed some light on the production of IAA in roots, nodules, and symbionts of an aquatic legume Neptunia oleracea and its possible role in nodular symbiosis. The symbiont (N37) was isolated from nodules of this plant and identified as Rhizobium undicola based on biochemical characteristics, 16S rDNA sequence homology, and DNA-DNA hybridization results. The root nodules were found to contain more IAA and tryptophan than root; however, no detectable amount of IAA was found in root. The IAA metabolizing enzymes IAA oxidase, IAA peroxidase (E.C.1.11.1.7), and polyphenol oxidase (E.C.1.14.18.1) were higher in root than nodule but total phenol and IAA content were reversed. The strain N37 was found to produce copious amount of IAA in YEM broth medium with tryptophan and reached its stationary phase at 20 h. An enrichment of the medium with mannitol, ammonium sulphate, B12, and 4-hydroxybenzaldehyde was found to promote the IAA production. The presence of IAA metabolizing enzymes and IAA production with PGPR traits including ACC deaminase activity of the symbionts was essential for plant microbe interaction and nodule function.