Evaluation of Symbiotic Association between Various Rhizobia, Capable of Producing Plant-Growth-Promoting Biomolecules and Mung Bean for Sustainable Production

To feed the increased world population, sustainability in the production of crops is the need of the hour, and exploration of an effective symbiotic association of rhizobia with legumes may serve the purpose. A laboratory-scale experiment was conducted to evaluate the symbiotic effectiveness of twenty wild rhizobial isolates (MR1–MR20) on the growth, physiology, biochemical traits, and nodulation of mung bean to predict better crop production with higher yields. Rhizobial strain MR4 resulted in a 52% increase in shoot length and 49% increase in shoot fresh mass, while MR5 showed a 30% increase in root length, with 67% and 65% improvement in root fresh mass by MR4 and MR5, respectively, compared to uninoculated control. Total dry matter of mung bean was enhanced by 73% and 68% with strains MR4 and MR5 followed by MR1 and MR3 with 60% increase in comparison to control. Rhizobial strain MR5 produced a maximum (25 nodules) number of nodules followed by MR4, MR3, and MR1 which produced 24, 23, and 21 nodules per plant. Results related to physiological parameters showed the best performance of MR4 and MR5 compared to control among all treatments. MR4 strain helped the plants to produce the lowest values of total soluble protein (TSP) (38% less), flavonoids contents (44% less), and malondialdehyde (MDA) contents (52% less) among all treatments compared to uninoculated control plants. Total phenolics contents of mung bean plants also showed significantly variable results, with the highest value of 54.79 mg kg−1 in MR—inoculated plants, followed by MR5- and MR1-inoculated plants, while the minimum concentration of total phenolics was recorded in uninoculated control plants of mung bean. Based on the results of growth promotion, nodulation ability, and physiological and biochemical characteristics recorded in an experimental trial conducted under gnotobiotic conditions, four rhizobial isolates (MR1, MR3, MR4, and MR5) were selected using cluster and principal component analysis. Selected strains were also tested for a variety of plant-growth-promoting molecules to develop a correlation with the results of plant-based parameters, and it was concluded that these wild rhizobial strains were effective in improving sustainable production of mung bean.

Lead-Tolerant Bacillus Strains Promote Growth and Antioxidant Activities of Spinach (Spinacia oleracea) Treated with Sewage Water

Irrigation with sewage-contaminated water poses a serious threat to food security, particularly in developing countries. Heavy metal tolerant bacteria are sustainable alternatives for the removal of wastewater contaminants. In the present study, four lead (Pb)-tolerant strains viz. Bacillus megaterium (N8), Bacillus safensis (N11), Bacillus sp. (N18), and Bacillus megaterium (N29) were inoculated in spinach and grown in sewage water treated earthen pots separately and in combination with canal water. Results showed that Pb-tolerant strains significantly improved plant growth and antioxidant activities in spinach and reduces metal concentration in roots and leaves of spinach plants irrigated with treated wastewater. Strain Bacillus sp. (N18) followed by B. safensis (N11) caused the maximum increase in shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, and leaf area compared to the uninoculated control of sewage water treated plants. These strains also improved antioxidant enzymatic activity including catalase, guaiacol peroxidase dismutase, superoxide dismutase, and peroxidases activities compared to the uninoculated control under sewage water conditions. Strain Bacillus sp. (N18) followed by B. safensis (N11) showed the highest reduction in nickel, cadmium, chromium, and Pb contents in roots and leaves of spinach compared to the uninoculated control plants treated with the sewage water. Such potential Pb-tolerant Bacillus strains could be recommended for the growth promotion of spinach after extensive evaluation under field conditions contaminated with wastewater.

Effect of Rhizoctonia spp. on Polyphenol Oxidase Enzyme Activity in Alfalfa Seedling

Soil borne diseases cause significant losses on quantity and quality of many crop species annually. Rhizoctonia is a widespread and ecologically diverse soilborne fungus causing different types of diseases in many plant species including alfalfa (Medicago sativa). Rhizoctonia species have been traditionally identified based on the cell nuclear condition. Polyphenol oxidases (PPOs) are ubiquitous copper-containing enzymes that are widely occurring enzymes among plants. PPOs are involved in the oxidation of polyphenols into quinones (antimicrobial compounds) and lignification of plant cells that contribute to the formation of defense barriers against pathogens. The study was conducted with the aim to determine the effect of indigenous isolates of a multinucleate (Rhizoctonia solani AG-4) and nineteen isolates of binucleate Rhizoctonia on PPO activity in alfalfa (cv. Gea) seedling under in vitro conditions. The activity of PPO enzyme was determined in inoculated and uninoculated control alfalfa plants after ten days from inoculation. There was a significant increase in the activity of PPO after treatment of alfalfa seedling with isolates of Rhizoctonia. Among Rhizoctonia isolates, highest induction of PPO activity was recorded with pathogenic R. solani AG-4. In present study, increased amounts of PPO were also observed in plants that were challenged with Rhizoctonia spp. PPO has a role in catalyzing phenolic oxidation in limiting disease development. PPO may therefore be involved in induction of defense resistance against plant diseases.

Field Evaluation of Arbuscular Mycorrhizal Fungi in the Management of Orobanche: A Parasitic Weed in Tobacco (Nicotiana tabacum L.)

An investigation was carried out to evaluate the methods of application of AMF cultures in the management of Orobanche viz., planting of pre colonized tobacco seedling; soil application and the combination of both. The experiment was carried out in Orobanche infested soils of tobacco growing areas of Belagavi district. The results of the present investigations have revealed that the treatment received STD AMF had reduced the emergence of Orobanche (1.33 plot-1) compared to UASDAMFT (1.67 plot-1) and UASDAMFS (2.89 plot-1). The results with respect to different methods of applications of AMF on Orobanche numbers revealed that planting of pre colonized tobacco seedling plus soil application at the time of planting suppressed the Orobanche emergence (0.00 plot-1) compared to planting of pre colonized seedlings (1.67 plot-1) and direct soil application of AMF cultures at the time of planting (4.22 plot-1).The results pertaining to the interactive effect between mycorrhizal cultures in conjunction with the methods of application of AMF cultures significantly reduced the population of Orobanche with the treatment received planting of pre colonized seedling along with soil application of UASDAMFT, UASDAMFS and STD AMF recorded zero emergences of Orobanche at 60 DAP. However, the highest numbers of weeds were recorded in uninoculated control (68.67plot-1). Furthermore, mycorrhizal parameters like spore count and percent of root colonization were found to be the highest in the plots received mycorrhization in the form of pre-colonization and soil application with STD AMF at the time of transplanting in the main field compared to uninoculated control.

Salt-Tolerant Compatible Microbial Inoculants Modulate Physio-Biochemical Responses Enhance Plant Growth, Zn Biofortification and Yield of Wheat Grown in Saline-Sodic Soil

A wide range of root-associated mutualistic microorganisms have been successfully applied and documented in the past for growth promotion, biofertilization, biofortification and biotic and abiotic stress amelioration in major crops. These microorganisms include nitrogen fixers, nutrient mobilizers, bio-remediators and bio-control agents. The present study aimed to demonstrate the impact of salt-tolerant compatible microbial inoculants on plant growth; Zn biofortification and yield of wheat (Triticum aestivum L.) crops grown in saline-sodic soil and insight of the mechanisms involved therein are being shared through this paper. Field experiments were conducted to evaluate the effects of Trichoderma harzianum UBSTH-501 and Bacillus amyloliquefaciens B-16 on wheat grown in saline-sodic soil at Research Farm, ICAR-Indian Institute of Seed Sciences, Kushmaur, India. The population of rhizosphere-associated microorganisms changed dramatically upon inoculation of the test microbes in the wheat rhizosphere. The co-inoculation induced a significant accumulation of proline and total soluble sugar in wheat at 30, 60, 90 and 120 days after sowing as compared to the uninoculated control. Upon quantitative estimation of organic solutes and antioxidant enzymes, these were found to have increased significantly in co-inoculated plants under salt-stressed conditions. The application of microbial inoculants enhanced the salt tolerance level significantly in wheat plants grown in saline-sodic soil. A significant increase in the uptake and translocation of potassium (K+) and calcium (Ca2+) was observed in wheat co-inoculated with the microbial inoculants, while a significant reduction in sodium (Na+) content was recorded in plants treated with both the bio-agents when compared with the respective uninoculated control plants. Results clearly indicated that significantly higher expression of TaHKT-1 and TaNHX1 in the roots enhances salt tolerance effectively by maintaining the Na+/K+ balance in the plant tissue. It was also observed that co-inoculation of the test inoculants increased the expression of ZIP transporters (2–3.5-folds) which ultimately led to increased biofortification of Zn in wheat grown in saline-sodic soil. Results suggested that co-inoculation of T. harzianum UBSTH-501 and B. amyloliquefaciens B-16 not only increased plant growth but also improved total grain yield along with a reduction in seedling mortality in the early stages of crop growth. In general, the present investigation demonstrated the feasibility of using salt-tolerant rhizosphere microbes for plant growth promotion and provides insights into plant-microbe interactions to ameliorate salt stress and increase Zn bio-fortification in wheat.

Effects of Bradyrhizobium japonicum on Nitrogen Content in Soybean Leaves and Seeds Cultivated on Acidic Soils

The legume-rhizobium symbiosis plays an important role in the nitrogen (N) assimilation of plants, more particularly in the humid tropical region where soils are deeply weathered and have poor electrochemical properties. On acidic soils of Haut-Katanga, DR Congo it is not clear how application of Bradyrhizobium japonicum affect N allocation among soybean organs (e.g., leaves, seeds). Here, we assessed the effect of Bradyrhizobium japonicum on N content of soybean leaves and seeds cultivated on acidic soils. We conducted two experiments using a split-plot setup with three replicates in two sites (i.e., Kasapa and Kanyameshi). The main plots included three strains of Bradyrhizobium plus the uninoculated control and four varieties of soybean in the subplot. We found that the different strains of Bradyrhizobium did not induce significant effects on the total N content of soybean leaves and seeds in the Kasapa site. In contrast, Bradyrhizobium affected significantly the N content of soybean leaves in the Kanyameshi site. We demonstrated that N content in the soil, which varies between the two sites, positively influences yield and nodulation. We conclude that that the efficiency of the soybean-Bradyrhizobium symbiosis and its influence on the allocation of N through soybean plants strongly depend on the chemical characteristics of the soil and particularly on the initial levels of N in the soils.

Stimulation of Soybean (Glycine max) growth and yield using Bradyrhizobium inoculants in the semi-arid environment of Botswana

Background: Crop yields in the semi-arid regions are low due to climatic and soil related constraints.Soybean as one of the most important legume crops grown worldwide, has a role to contribute nitrogen to improve nutrient poor soils in Africa. A study was conducted to examine the effects of Bradyrhizobium spp inoculations on the growth and yield of soybean varieties in a glasshouse.Method: The study was arranged in a randomized complete block factorial design, with factor A being two soybean varieties (Bimha and Status) while factor B was inoculation using four Bradyrhizobium strains and the uninoculated control. Results: Bradyrhizobium inoculation significantly (P less than 0.001)affected days to 50% flowering, days to emergence, nodule number, root dry weight and grain yield and yield traits. Parameters that were affected by both inoculant strain and variety included days to 50% flowering, days to emergence, number of pods per plant, pod weight and number of seeds per pod. The interaction effect of variety and Bradyrhizobium inoculant strain was observed only on number of pods per plants. Our study shows that soybean grows well when inoculated with Bradyrhizobium inoculants, in semi-arid conditions of Botswana.

Characterization of Root-Endophytic Actinobacteria From Cactus (Opuntia Ficus-Indica) for Plant Growth Promoting Traits

The present study is the first report of isolation and characterization of endophytic actinobacteria from cactus (Opuntia ficus-indica). A total of 179 morphologically distinct endophytic actinobacterial isolates were purified from the roots of two different genetic accessions of cactus. All these isolates were screened for their plant growth promotion traits namely growth on N-free medium, P-solubilization, siderophore production, ACC deaminase activity and IAA production. A majority of the endophytic actinobacterial isolates (85%) exhibited the potential for plant growth promotion under in vitro conditions. Ten among the isolates were selected based on their multi-PGP traits and were identified as Streptomyces sp. based on the 16S rRNA gene sequencing and phylogenetic analysis. Plant growth promoting potential of these selected endophytic Streptomyces was studied in wheat seedlings. All these selected isolates significantly enhanced the growth parameters like seedling length and rootlets number compared to the uninoculated control. The wheat seeds inoculated with Streptomyces tuirus VL-70-IX exhibited maximum number of rootlets (6.33) compared to uninoculated control (3.67). The inoculation of endophytic actinobacteria Streptomyces pseudogriseolus VL-70-XII caused maximum seedling length (20.53 cm) and root length (8.26 cm) while the inoculation of S. radiopugnans HV-VIII resulted in highest shoot length (12.33 cm). These endophytic actinobacteria isolated from the roots of cactus accessions showed potential PGP traits. This work lays foundation for characterization and selection of endophytic actinobacteria from the under-exploited, drought tolerant species such as cactus with potential cross-compatibility for the improvement of plant growth of field crops especially under abiotic stress conditions..

Improved growth of bell pepper (Capsicum annuum) plants by inoculating arbuscular mycorrhizal fungi and beneficial rhizobacteria

Background: Plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) are an alternative for sustainable management of pepper crops. Objective: To investigate the beneficial effects of PGPR and AMF inoculation on the growth of bell pepper plants. Methods: Two PGPR strains were used (Pseudomonas tolaasii P61 and Bacillus pumilus R44) as well as their mixture, and an uninoculated control. In addition, bacterial treatments were combined with an AMF-consortium (Funneliformis aff. geosporum and Claroideoglomus sp.). A 4×2 factorial experiment [four levels for the bacterial inoculation and two levels of AMF-inoculation (non-AMF and AMF)] was performed with eight treatments, at greenhouse conditions for 80 days after inoculation. AMF inoculation was done at sowing and PGPR after 15 days of seedling emergence. Results and Conclusions: Uninoculated control showed lower growth responses than plants inoculated with PGPR and AMF, alone or in combination. Overall, inoculation of the strain P61 or the combination of R44+AMF increased plant growth. AMF improved the photochemical efficiency of PSII in comparison to either control plants or plants inoculated with R44 or with the bacterial mix. Both PGPR and AMF improved growth and vigor of bell pepper plants.

EFFECTS OF PATHOGENIC FUNGAL INFECTION ON THE NUTRIENT AND ANTI-NUTRIENT CONSTITUENTS OF POST HARVEST Irvingia gabonensis (OGBONO) SEEDS

Effects of pathogenic fungal infection on the nutrient and anti-nutrient constituents of post-harvest Irvingia gabonensis seeds were evaluated. The fungi pathogens isolated from partially rotted seeds of I. gabonensis seeds include Rhizopus stolonifer, Aspergillus flavus, Aspergillus niger and Penicillium italicum. These fungi were used as test fungi to inoculate healthy I. gabonesis seeds aseptically. The results of the proximate analysis in (%w/w)/100g of seeds inoculated with test fungi and uninoculated (control) seeds carried out revealed that there was a significant increase (p<0.05) in Moisture, Ash and Lipid content of seeds inoculated with the test fungi, relative to uninoculated (control) seeds. While fiber carbohydrate and protein content decreased in fungi inoculated seeds relative to uninoculated seeds. There was a significant difference (p<0.05) in mineral content evaluated. Calcium, Phosphorus and Iron increased in seeds inoculated with the test fungi relative to the uninoculated, while Potassium, Soduim and Magnesium decreased in seeds inoculated with the test fungi. Anti-nutrient (phytochemical) content; Tannin, Saponin, Total oxalate and Cynogenic glucoside increased in the fungi inoculated seeds relative to uninoculated seeds. Significant differences also existed among the test fungi. Apparently, Penicillium italicum induced more changes in the anti-nutrient (Phytochemical) content measured. Hence higher values were recorded by Penicillium italicum in Tannim, Saponin, Total oxalate and Cynogenic glucoside, Keywords: Irvingia gabonensis, Nutrient, Anti-nutrient, Fungi, Inoculated