Efficacy of bioinoculants to control of bacterial and fungal diseases of rice (Oryza sativa L.) in northwestern Himalaya.

INTRODUCTION: Biological control holds great promise for environmentally friendly and sustainable management of the phytopathogens. The multi-function features of plant growth-promoting rhizobacteria (PGPR) enable to protect the plants from disease infections by replacing the chemical inputs. The interaction between the plant root exudates and the microbes stimulates the production of secondary metabolism and enzymes and induces systemic resistance in the plants. AIM: The aim was to identify the potential PGPR which would show an antagonistic effect against basmati rice fungal and bacterial diseases. METHODS: In the study, native originating microbes have been isolated, characterized using 16S rRNA sequencing, and used as potential antagonistic microbial isolates against diseases of rice plants. RESULTS: Rhizobacteria isolated from rhizosphere, endo-rhizosphere, and bulk soil samples of Basmati 370 exhibited promising inhibitory activity against rice pathogens. Molecular characterization of bacterial isolates based on 16S rRNA sequencing classified the bacterial isolates into different genera such as Bacillus, Pseudomonas, Streptomyces, Exiguobacterium, Aeromonas, Chryseobacterium, Enterobacter, and Stenotrophomonas. PGPRs exhibited biocontrol activities against various rice diseases like bacterial leaf blight, leaf blast, brown spot, and sheath blight and boost the plant growth traits. CONCLUSION: In the study, the potentially identified PGPRs isolates could be used as efficient bioinoculants as bio-fertilizers and biocontrol agents for sustainable rice crop production.

Identification of soybean Bradyrhizobium strains used in commercial inoculants in Brazil by MALDI-TOF mass spectrometry.

Biological nitrogen fixation (BNF) with the soybean crop probably represents the major sustainable technology worldwide, saving billions of dollars in N fertilizers and decreasing water pollution and the emission of greenhouse gases. Accordingly, the identification of strains occupying nodules under field conditions represents a critical step in studies that are aimed at guaranteeing increased BNF contribution. Current methods of identification are mostly based on serology, or on DNA profiles. However, the production of antibodies is restricted to few laboratories, and to obtain DNA profiles of hundreds of isolates is costly and time-consuming. Conversely, the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS technique might represent a golden opportunity for replacing serological and DNA-based methods. However, MALDI-TOF databases of environmental microorganisms are still limited, and, most importantly, there are concerns about the discrimination of protein profiles at the strain level. In this study, we investigated four soybean rhizobial strains carried in commercial inoculants used in over 35 million hectares in Brazil and also in other countries of South America and Africa. A supplementary MALDI-TOF database with the protein profiles of these rhizobial strains was built and allowed the identification of unique profiles statistically supported by multivariate analysis and neural networks. To test this new database, the nodule occupancy by Bradyrhizobium strains in symbiosis with soybean was characterized in a field experiment and the results were compared with serotyping of bacteria by immuno-agglutination. The results obtained by both techniques were highly correlated and confirmed the viability of using the MALDI-TOF MS technique to effectively distinguish bacteria at the strain level.

Components of rhizospheric bacterial communities of barley and their potential for plant growth promotion and biocontrol of Fusarium wilt of watermelon.

This work aimed to characterize antagonistic bacteria from the field-grown barley rhizosphere, and evaluate their potential for growth promotion and biocontrol of Fusarium wilt on watermelon caused by Fusarium oxysporum f. sp. Niveum (FON). Seven bacteria were isolated and screened for plant growth promoting and antagonistic traits. Based on the results of phenotypic characterization and 16S rRNA gene sequencing, the isolates were identified to be related to Bacillus methylotrophicus (DMK-1), Bacillus amyloliquefaciens subsp. plantarum (DMK-7-2), Bacillus cereus (DMK-12), Pseudomonas brassicacearum subsp. brassicacearum (DMK-2), Pseudomonas veronii (DMK-3), Paenibacillus polymyxa (DMK-8), and Ensifer adhaerens (DMK-17). All the isolates were positive for the production of indole-3-acetic acid (IAA) and ammonia (NH3), while negative for the production of hydrogen cyanide (HCN). Six bacteria strains (except DMK-17) were able to phosphate solubilization. All the bacteria strains, except DMK-8, were able to produce iron siderophore complexes, and possessed the proteolytic activity. Greenhouse experiment indicated six strains can decrease diseased percentage caused by FON. All the isolates enhanced plant biomass, six strains increased root volume, six strains increased root system activity in greenhouse test. Inoculation of mixtures of seven plant growth promoting rhizobacteria could be more effective in plant growth promotion and biocontrol of Fusarium wilt in watermelon.

Soybean inoculants in Brazil: an overview of quality control.

The bacterial strains SEMIA 587 and 5019 (Bradyrhizobium elkanii), 5079 (Bradyrhizobium japonicum), and 5080 (Bradyrhizobium diazoefficiens) are recommended for soybean inoculants in Brazil. In several countries, the current regulations are insufficient to induce companies for improving the quality of their products, leading to low performance and subsequent abandonment of inoculant use. From 2010 to 2014, 1086 samples coming mainly from Argentina and the southern region of Brazil were analyzed for viable cells counting, strains identification, and purity analysis according to the SDA/MAPA no. 30/2010 Normative Instruction. Most products were imported and formulated in liquid carriers with 5.0 × 109 colony-forming units (CFU)/mL. The strains most frequently used were SEMIA 5079/5080. Only 2.21% of samples had contaminants. The guaranteed concentration of viable cells in inoculants mostly ranged from 4.1 × 109 to 5.0 × 109 CFU/mL or CFU/g. The most frequently found concentration was above 1.1 × 1010 CFU/mL or CFU/g, which was higher than the product guarantee. The inoculants used for soybean crop in Brazil have excellent quality, leading the country to the leadership in taking advantage of the biological nitrogen fixation benefits for a productive and sustainable agriculture.

Genomic identification and characterization of the elite strains Bradyrhizobium yuanmingense BR 3267 and Bradyrhizobium pachyrhizi BR 3262 recommended for cowpea inoculation in Brazil

ABSTRACT The leguminous inoculation with nodule-inducing bacteria that perform biological nitrogen fixation is a good example of an "eco-friendly agricultural practice". Bradyrhizobium strains BR 3267 and BR 3262 are recommended for cowpea (Vigna unguiculata) inoculation in Brazil and showed remarkable responses; nevertheless neither strain was characterized at species level, which is our goal in the present work using a polyphasic approach. The strains presented the typical phenotype of Bradyrhizobium with a slow growth and a white colony on yeast extract-mannitol medium. Strain BR 3267 was more versatile in its use of carbon sources compared to BR 3262. The fatty acid composition of BR 3267 was similar to the type strain of Bradyrhizobium yuanmingense; while BR 3262 was similar to Bradyrhizobium elkanii and Bradyrhizobium pachyrhizi. Phylogenetic analyses based on 16S rRNA and three housekeeping genes placed both strains within the genus Bradyrhizobium: strain BR 3267 was closest to B. yuanmingense and BR 3262 to B. pachyrhizi. Genome average nucleotide identity and DNA-DNA reassociation confirmed the genomic identification of B. yuanmingense BR 3267 and B. pachyrhizi BR 3262. The nodC and nifH gene analyses showed that strains BR 3267 and BR 3262 hold divergent symbiotic genes. In summary, the results indicate that cowpea can establish effective symbiosis with divergent bradyrhizobia isolated from Brazilian soils.

Genomic identification and characterization of the elite strains Bradyrhizobium yuanmingense BR 3267 and Bradyrhizobium pachyrhizi BR 3262 recommended for cowpea inoculation in Brazil.

The leguminous inoculation with nodule-inducing bacteria that perform biological nitrogen fixation is a good example of an "eco-friendly agricultural practice". Bradyrhizobium strains BR 3267 and BR 3262 are recommended for cowpea (Vigna unguiculata) inoculation in Brazil and showed remarkable responses; nevertheless neither strain was characterized at species level, which is our goal in the present work using a polyphasic approach. The strains presented the typical phenotype of Bradyrhizobium with a slow growth and a white colony on yeast extract-mannitol medium. Strain BR 3267 was more versatile in its use of carbon sources compared to BR 3262. The fatty acid composition of BR 3267 was similar to the type strain of Bradyrhizobium yuanmingense; while BR 3262 was similar to Bradyrhizobium elkanii and Bradyrhizobium pachyrhizi. Phylogenetic analyses based on 16S rRNA and three housekeeping genes placed both strains within the genus Bradyrhizobium: strain BR 3267 was closest to B. yuanmingense and BR 3262 to B. pachyrhizi. Genome average nucleotide identity and DNA-DNA reassociation confirmed the genomic identification of B. yuanmingense BR 3267 and B. pachyrhizi BR 3262. The nodC and nifH gene analyses showed that strains BR 3267 and BR 3262 hold divergent symbiotic genes. In summary, the results indicate that cowpea can establish effective symbiosis with divergent bradyrhizobia isolated from Brazilian soils.

Plant-associated fluorescent Pseudomonas from red lateritic soil: Beneficial characteristics and their impact on lettuce growth.

Fluorescent Pseudomonas are ubiquitous soil bacteria that usually establish mutualistic associations with plants, promoting their growth and health by several mechanisms. This makes them interesting candidates for the development of crop bio-inoculants. In this work, we isolated phosphate-solubilizing fluorescent Pseudomonas from the rhizosphere and inner tissues of different plant species growing in red soil from Misiones, Argentina. Seven isolates displaying strong phosphate solubilization were selected for further studies. Molecular identification by rpoD genotyping indicated that they belong to different species within the P. fluorescens and P. putida phylogenetic groups. Screening for in vitro traits such as phosphate solubilization, growth regulators synthesis or degradation, motility and antagonism against phytopathogens or other bacteria, revealed a unique profile of characteristics for each strain. Their plant growth-promoting potential was assayed using lettuce as a model for inoculation under controlled and greenhouse conditions. Five of the strains increased the growth of lettuce plants. Overall, the strongest lettuce growth promoter under both conditions was strain ZME4, isolated from inner tissues of maize. No clear association between lettuce growth promotion and in vitro beneficial traits was detected. In conclusion, several phosphate solubilizing pseudomonads from red soil were isolated that display a rich array of plant growth promotion traits, thus showing a potential for the development of new inoculants.

Systematics of the Trichoderma harzianum species complex and the re-identification of commercial biocontrol strains.

Trichoderma harzianum is known as a cosmopolitan, ubiquitous species associated with a wide variety of substrates. It is possibly the most commonly used name in agricultural applications involving Trichoderma, including biological control of plant diseases. While various studies have suggested that T. harzianum is a species complex, only a few cryptic species are named. In the present study the taxonomy of the T. harzianum species complex is revised to include at least 14 species. Previously named species included in the complex are T. guizhouense, T. harzianum, and T. inhamatum. Two new combinations are proposed, T. lentiforme and T. lixii. Nine species are described as new, T. afarasin, T. afroharzianum, T. atrobrunneum, T. camerunense, T. endophyticum, T. neotropicale, T. pyramidale, T. rifaii and T. simmonsii. We isolated Trichoderma cultures from four commercial biocontrol products reported to contain T. harzianum. None of the biocontrol strains were identified as T. harzianum s. str. In addition, the widely applied culture 'T. harzianum T22' was determined to be T. afroharzianum. Some species in the T. harzianum complex appear to be exclusively endophytic, while others were only isolated from soil. Sexual states are rare. Descriptions and illustrations are provided. A secondary barcode, nuc translation elongation factor 1-α (TEF1) is needed to identify species in this complex.

A new PGPR co-inoculated with Bradyrhizobium japonicum enhances soybean nodulation.

A new PGPR (plant growth promoting rhizobacteria) strain was isolated from soybean seeds and the bacterial mechanisms related to plant growth promotion were evaluated and characterized. Isolates were genotypically compared and identified by amplification of partial sequences of 16S DNAr as Bacillus amyloliquefaciens strain LL2012. Isolates were grown until exponential growth phase to evaluate the atmospheric nitrogen fixation, enzymatic activities, phosphate solubilization, siderophores and phytohormones production. LL2012 strain was able to grow and to produce high levels of auxin, gibberellins and salicylic acid in chemically defined medium. Co-inoculation of soybean plants with LL2012 strain and the natural symbiont (Bradyrhizobium japonicum) altered plant growth parameters and significantly improved nodulation. Our results show that the association of LL2012 with B. japonicum, enhanced the capacity of the latter to colonize plant roots and increase the number of nodules, which make the co-inoculation technique attractive for use in commercial inoculant formulations following proper field evaluation.