Competitiveness of Bradyrhizobium japonicum inoculation strain for soybean nodule occupancy

The competitiveness of Bradyrhizobium japonicum inoculation strain against indigenous rhizobia was examined in a soil pot experiment. The effect of inoculation strain was evaluated under different soil conditions: with or without previously grown soybean and applied commercial inoculant. Molecular identification of inoculation strain and investigated rhizobial isolates, obtained from nodules representing inoculated treatments, was performed based on 16S rDNA and enterobacterial repetitive intergenic consensus (ERIC) sequencing. Inoculation strain showed a significant effect on the investigated parameters in both soils. Higher nodule occupancy (45% vs. 18%), nodule number (111% vs. 5%), nodule dry weight (49% vs. 9%), shoot length (15% vs. 7%), root length (31% vs. 13%), shoot dry weight (34% vs. 11%), shoot nitrogen content (27% vs. 2%), and nodule nitrogen content (9% vs. 5%) was detected in soil without previously grown soybean and applied commercial inoculant. Soil had a significant effect on the shoot, root and nodule nitrogen content, while interaction of experimental factors significantly altered dry weight and nitrogen content of shoots, roots and nodules, as well as number of nodules. Nodulation parameters were significantly related with shoot dry weight, shoot and nodule nitrogen content. Symbiotic performance of inoculation strains in the field could be improved through co-selection for their competitiveness and effectiveness.

Applying biostimulants boosts forage productivity without affecting soil biotic and abiotic parameters on a Central Coast California rangeland

There is increasing interest in using biostimulant products, such as microbial inoculants and humic substances, to help manage rangelands regeneratively. Understanding how plant and soil communities on rangelands respond to these products is therefore important. In this study, we examined the combined effects of a commercial inoculant and humic product that are currently on the market, and asked whether they influenced rangeland forage productivity and quality, soil microbial biomass and community composition, and abiotic soil parameters in Central Coastal California. We found that forage productivity and some metrics of forage quality responded positively to the foliar application of a commercial microbial inoculant and humic product, but that these benefits were not mirrored by changes belowground in the microbial community or abiotic parameters. Depending on the goals of using the products, this could be seen as a winning scenario and suggests microbial inoculants and humic products could warrant attention as a potential tool for regenerative stewardship of rangelands. While our study derives from one ranch and therefore requires confirmation of its ubiquity prior to broadscale adoption, our results provide new insights into the usefulness of this approach for managing rangeland productivity in California's Central Coast.

Soybean Response to Seed Coating with Chitosan + Alginate/PEG and/or Inoculation

Inoculated or coated soybean seeds are often sown in agricultural practice. These treatments play a different role depending on the chemical composition of the preparation. The aim of the field experiment was to demonstrate the effectiveness of the developed coating (chitosan + alginate/PEG) and commercial inoculant (HiStick® Soy) applied alone or in combination to soybean seeds. Uncoated (control) seeds were sown for comparison. The research was carried out in 2018–2020 using the cultivar ‘Mavka’. The experiment was located in Makowisko, Podkarpackie Province, Poland. Coating composition was developed in a laboratory belonging to the Łukasiewicz Research Network—Institute of Biopolymers and Chemical Fibers in Łódź, Poland. The main role of the coating is to protect soybean seeds from low temperatures. HiStick® Soy inoculant contains Bradyrhizobium japonicum bacteria which increase nodulation on the roots. The conducted research demonstrated that sowing only coated seeds was not very effective, because the suitable number of nodules had not developed on soybean roots. The application of the inoculant alone positively affected the assessed traits compared to control, however, plant population was lower than expected. The highest seed yield was obtained after sowing coated seeds in combination with the inoculant (4.32 t·ha−1) and only inoculated seeds (4.23 t·ha−1) compared to control (3.64 t·ha−1). The test of the novel seed-coating agent showed that it had an good effect and efficacy, but only in combination with the inoculation procedure.

Polymeric Formulations of Liquid Inoculants with Rhizobia Exopolysaccharides Increase Survival and Symbiotic Efficiency of Bradyrhizobium Strains with Cowpea and Soybean

We studied the survival of four elite strains of Bradyrhizobium in liquid inoculants with three formulations with EPS extracted from other rhizobia genera, and their symbiotic efficiency, with soybean and cowpea, in a greenhouse. For this purpose, we verified the utility of formulations for maintaining the cell viability of strains by counting the colony forming units (CFU) per milliliter of the liquid inoculants with formulations over 90 days. Survival of the soybean inoculant strains, 29W and CPAC15, in the PEPS formulation had the largest number of CFU (> 1010 mL− 1) after 90 days. For the cowpea inoculant strains, INPA3-1B and UFLA3-84, the formulations REPS1 had the largest number of CFU (> 1010 mL− 1) after 90 days. Symbiotic efficiency in soybean of the formulations PEPS and REPS2 was higher than that shown by the commercial inoculant. For cowpea, the three formulations with EPS showed symbiotic efficiency bigger than that of the commercial inoculant.

Application of Selected Inoculant Producing Antifungal and Fibrinolytic Substances on Rye Silage with Different Wilting Time

This research was conducted to determine the effects of selected inoculant on the silage with different wilting times. The ryes were unwilted or wilted for 12 h. Each rye forage was ensiled for 100 d in quadruplicate with commercial inoculant (Lactobacillus plantarum sp.; LPT) or selected inoculant (Lactobacillus brevis 100D8 and Leuconostoc holzapfelii 5H4 at 1:1 ratio; MIX). In vitro dry matter digestibility and in vitro neutral detergent fiber digestibility were highest in the unwilted MIX silages (p < 0.05), and the concentration of ruminal acetate was increased in MIX silages (p < 0.001; 61.4% vs. 60.3%) by the increase of neutral detergent fiber digestibility. The concentration of ruminal ammonia-N was increased in wilted silages (p < 0.001; 34.8% vs. 21.1%). The yeast count was lower in the MIX silages than in the LPT silages (p < 0.05) due to a higher concentration of acetate in MIX silages (p < 0.05). Aerobic stability was highest in the wilted MIX silages (p < 0.05). In conclusion, the MIX inoculation increased aerobic stability and improved fiber digestibility. As a result of the wilting process, ammonia-N in silage decreased but ruminal ammonia-N increased. Notably, the wilted silage with applied mixed inoculant had the highest aerobic stability.

Commercial arbuscular mycorrhizal fungal inoculant failed to establish in a vineyard despite priority advantage

Background Arbuscular mycorrhizal (AM) fungi associate with most plants and can increase nutrient uptake. As a result, commercial inoculants called “biofertilizers” containing AM fungi have been developed and marketed to increase plant performance. However, successful establishment of these inoculants remains a challenge, and may be negatively impacted by competition with fungi already present (priority effects). Perennial agriculture may be more amenable if inoculants can be successfully established on crops prior to field planting. Methods Here, we inoculate grapevine (Vitis vinifera) with a commercial inoculant in three treatments designed to manipulate the strength and direction of priority effects and quantified the abundance of the fungal strain before and after introduction using droplet digital PCR (ddPCR). Results We found that the introduced strain did not establish in any treatment, even with priority advantage, and inoculated vines did not differ in performance from non-inoculated vines. Fungal abundance was not greater than in pre-inoculation soil samples during any of the five years sampled and may have been impaired by high available phosphorus levels in the soil. This study highlights the need to understand and evaluate how the management of the agricultural system will affect establishment before introduction of “biofertilizers”, which is often unpredictable.

Phenotypic diversity of bacteria in root nodules of Dalbergia ecastaphyllum (L.) Taub. (Fabaceae)

Many species belonging to family Fabaceae are able to establish symbiotic relationships with nitrogen-fixing bacteria. Studies developed with Dalbergia ecastaphyllum (L.) Taub., for example, have demonstrated the symbiotic potential of this species. In this sense, this study aimed to analyze the phenotypic characteristics of rhizobia isolated from D. ecastaphyllum and to identify whether these bacterial isolates are capable of establishing symbiotic relationships with Vigna unguiculata (L.) Walp. D. ecastaphyllum seeds were sown in soil samples collected in Japaratinga, Alagoas, Brazil, in three zones located at different distances from the high tide line. At 60 days after the emergence of the plants, nodulation in the roots of D. ecastaphyllum was analyzed and the bacteria were isolated. Subsequently, the phenotypic characterization of the bacteria was carried out based on some criteria (growth time, type of pH, colony color, type of mucus and amount of mucus). For the nodulation test, the species V. unguiculata was used. In total, 17 phenotypic types of bacterial isolates were identified, of which 8 are fast-growing and 9 are intermediate-growth. Regarding the type of pH, 7 phenotypes are acidic pH, 8 are neutral pH and 2 are alkaline pH. As for the coloring of the bacterial colonies, 5 are yellow, 7 white and 5 pink. It was also observed the presence of consistent and aqueous mucus in colonies from the three different areas. Only 7 bacterial phenotypic types and the commercial inoculant were efficient in the nodulation of V. unguiculata.

Co-inoculation and inoculation methods of plant growth-promoting bacteria in wheat yield performance

Several studies have reported the beneficial effects of inoculation of Azospirillum brasilense in wheat, but only a few of them have related the co-inoculation of A. brasilense and Rhizobium sp. and the evaluation of different inoculation methods. This study aimed i) to verify the efficiency of plant growth-promoting bacteria (PGPB) in subtropical environments, ii) to verify the efficiency of co-inoculation of A. brasilense and Rhizobium sp., and iii) to verify the efficiency of the management of different inoculation methods in the wheat crop. The experiments were carried out in Londrina and Apucarana, State of Paraná, Brazil, under a complete randomized block design, with four replications and nine treatments: T1) absence of nitrogen (N) topdressing, T2) 30 kg ha−1 of N topdressing, T3) 60 kg ha−1 of N topdressing, T4) A. brasilense Ab-V5 in the seeds, T5) A. brasilense Ab-V5 in post-emergence, T6) A. brasilense Ab-V5 + Rhizobium sp. 53GRM1 in the seeds, T7) A. brasilense Ab-V5 + Rhizobium sp. 53GRM1 in post-emergence, T8) commercial inoculant (A. brasilense Ab-V5 + Ab-V6) in the seeds, and T9) commercial inoculant (A. brasilense Ab-V5 + Ab-V6) in post-emergence. The number of ears per linear meter, number of spikelets, number of grains per spikelet, number of grains per ear, thousand-grain weight, number of spikelets to ears ratio, leaf nitrogen content, and grain yield were evaluated. Leaf N content and yield components showed no alterations due to the inoculation and co-inoculation performed both in the seed and in the post-emergence of seedlings. Treatments T3, T7, and T9 showed the highest means of grain yield (2077.50, 1743.12, and 1660.62 kg ha−1, respectively), demonstrating that co-inoculation with A. brasilense Ab-V5 + Rhizobium sp. 53GRM1 and inoculation with A. brasilense Ab-V5 + Ab-V6, both in post-emergence of seedlings, have the potential to replace the topdressing nitrogen fertilization in wheat.

Bacillus sp. RZ2MS9, a tropical PGPR, colonizes maize endophytically and alters the plant’s production of volatile organic compounds both independently and when co-inoculated with Azospirillum brasilense Ab-V5

ABSTRACTBacillus spp. are among the most efficient known plant growth-promoting rhizobacteria (PGPR). The PGPR Bacillus sp. strain RZ2MS9 is a multi-trait maize growth promoter previously isolated from guarana plants cultivated in the Amazon rainforest. However, there are several aspects of its interaction with the host that need further investigation. To achieve effective performance of microbial inoculants in crop production, it is necessary to monitor the plant’s colonization by a PGPR and to assess the potential synergy among beneficial strains. Here, we obtained a stable mutant of RZ2MS9 labelled with green fluorescent protein (RZ2MS9-GFP). We verified that the insertion of the plasmid did not affect either bacterial growth nor its ability to promote maize growth in vitro. Using fluorescent microscopy and qPCR, we demonstrated that RZ2MS9-GFP successfully colonizes maize’s roots and leaves endophytically. Subsequently, we evaluated whether RZ2MS9 has a synergistic effect on plant growth promotion when co-inoculated with Azospirillum brasilense Ab-V5, a commercial inoculant for maize. The two strains combined enhanced maize’s roots and shoots dry weight by 50.8% and 79.6%, respectively, when compared to the non-inoculated control. In addition, we used co-inoculation experiments in glass chambers to analyze the plant’s Volatile Organic Compounds (VOCs) production during the maize-RZ2MS9 and maize-RZ2MS9-Ab-V5 interaction. We found that the single and co-inoculation altered maize’s VOCs emission profile, with an increase in the production of indoles in the co-inoculation. Collectively, these results increase our knowledge about the interaction between the tropical PGPR Bacillus sp. RZ2MS9 and maize, and provide a new possibility of combined application with the commercial inoculant A. brasilense Ab-V5.ImportanceBacillus sp. RZ2MS9 is a PGPR, previously isolated from guarana plants cultivated in the Brazilian Amazon, which successfully promotes the growth of maize and soybean plants. To improve our knowledge about the interaction between this very promising PGPR and maize, we labelled RZ2MS9 with gfp and monitored it’s maize colonization. The transformation did not affect either RZ2MS9 growth nor its ability to promote maize growth in vitro. We demonstrated that RZ2MS9 colonizes endophytically maize’s roots and leaves. We also verified that the co-inoculation of RZ2MS9 and Azospirillum brasilense Ab-V5, a known commercial maize inoculant enhanced maize’s roots and shoots growth. Moreover, the co-inoculation altered the maize’s volatile organic compounds, increasing the production of indoles, that is related with decreased upon the reduction of fertilization. Certainly, our research contributed with better Bacillus sp. RZ2MS9 – maize interaction understanding and also provided new information concerning RZ2MS9 activity when applied with A. brasilense Ab-V5.