Plants on contaminated mining soils often show a reduced growth due to nutrient depletion as well as trace elements (TEs) toxicity. Since those conditions threat plant's survival, plant growth-promoting rhizobacteria (PGPRs), such as rhizobia, might be of crucial importance for plant colonization on TE-contaminated soils. Native rhizobia from mining soils are promising candidates for bioaugmented phytoremediation of those soils as they are adapted to the specific conditions. In this work, rhizobia from Zn- and Cd-contaminated mining soils were in vitro screened for their PGP features [organic acids, indole-3-acetic acid (IAA), and siderophore (SID) production; 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity; and Ca(PO) solubilization] and Zn and Cd tolerance. In addition, some type and reference rhizobia strains were included in the study as well. The in vitro screening indicated that rhizobia and other native genera have great potential for phytoremediation purposes, by exerting, besides biological N fixation, other plant growth-promoting traits. Leucaena leucocephala-Mesorhizobium sp. (UFLA 01-765) showed multielement tolerance and an efficient symbiosis on contaminated soil, decreasing the activities of antioxidative enzymes in shoots. This symbiosis is a promising combination for phytostabilization.

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High yields obtained from soybean [Glycine max (L.) Merrill], and consequent profits, are related to efficient symbiosis of soybean with nitrogen fixing bacteria of the Bradyrhizobium genus. Inoculation with strains belonging to the Bradyrhizobium japonicum, B. elkanii, and B. diazofficiens species, approved by the Brazilian Ministry of Agriculture (MAPA), is a common practice for this crop. However, variations in the composition of inoculants can change the quality of the product. The aim of this study was to genetically identify and to evaluate the symbiotic efficiency of isolates with cultural characteristics different from those of strains approved by MAPA and which are present in two commercial inoculants for soybean. Isolates obtained from inoculants and the strains SEMIA 5079 (CPAC 15), SEMIA 5080 (CPAC 7), SEMIA 587 (BR 96), and SEMIA 5019 (BR 29), indicated in the formulation of these inoculants, were tested for symbiotic efficiency in soybeans (cultivar: COODETEC 5G 830 RR) in a greenhouse. Identification by partial sequencing of the 16S rRNA gene, together with BOX-PCR analysis, showed that variant isolates were not similar to the inoculant strains indicated in the commercial products, despite belonging to the same genus and/or species. No loss was observed in the nodulation ability of the isolates; however, significant differences were reported in the symbiotic efficiency of the isolates compared to the inoculant strains approved by MAPA. Nevertheless, the presence of morphological variants did not influence the efficiency of inoculant products.

were characterized for their nodulation capacity on M. pudica and common bean, and their tolerance to Ni in culture medium. Bacteria were also partially identified by their 16S rRNA gene sequences. In addition, recA, gyrB, nodC and nifH genes from five representative isolates were sequenced for phylogenetic studies. Results In situ detection indicated the exclusive presence of Paraburkholderia sp. within the nodules. This identification was confirmed for most of the isolates by the analysis of their 16S rRNA gene sequences. All isolates identified as Paraburkholderia sp. were able to effectively nodulate M. pudica, but those tested in common bean produced ineffective

The formononetin biostimulant may be an option for reducing P fertilization once it stimulates mycelial growth of arbuscular mycorrhizal fungi and increases plant ability to take up nutrients through the roots, especially phosphorus. The objective of this study was to evaluate the effect of formononetin associated with phosphorus fertilization in maize. Field experiments were conducted in a randomized block design with a 3 × 4 factorial arrangement (0, 50 or 70, and 140 kg ha -1 P 2 O 5 ; and formononetin application rates: 0, 25, 50, and 100 g ha -1 ), with four replications. Formononetin (100 g ha -1 ) increased the mycorrhizal colonization rate up to 30% in maize in the fi rst four weeks after emergence when no P fertilizer was applied, and to 17% when 50 or 70 kg ha -1 of P 2 O 5 were applied. The application of 50 and 100 g ha -1 of formononetin signifi cantly increased plant height, ear height, and grain yield (22% -76%) when no P fertilizer was applied. The use of formononetin in the fi eld stimulates mycorrhizal colonization, has a positive effect on maize yield, and reduces the need for P fertilizer application in maize.However, this effect was evident only at low P soil contents.