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A greenhouse experiment was performed to evaluate the effects of plant growth-promoting rhizobacteria (PGPR) on nodulation, biological nitrogen fixation (BNF) and growth of the common bean (Phaseolus vulgaris L. cv. Tenderlake). Single and dual inoculation treatments of bean with Rhizobium and/or PGPR were administered to detect possible changes in the levels of and interactions between the phytohormones IAA and cytokinin. Bean plants cv. Tenderlake were grown in pots containing Fluvic Neosol eutrophic (pH 6.5). Fourteen kilogram aliquots of soil contained in 15-l pots were autoclaved. Bean seeds were surface sterilized and inoculated with Rhizobium tropici (CIAT 899-standard strain) alone and in combination with one of the PGPR strains: Bacillus endophyticus (DSM 13796), B. pumilus (DSM 27), B. subtilis (DSM 704), Paenibacillus lautus (DSM 13411), P. macerans (DSM 24), P. polymyxa (DSM 36), P. polymyxa (Loutit L.) or Bacillus sp.(65E180). The experimental design was randomized block design with three replications. Beans co-inoculated with Rhizobium tropici (CIAT899) and Paenibacillus polymyxa (DSM 36) had higher leghemoglobin concentrations, nitrogenase activity and N 2 fixation efficiency and thereby formed associations of greater symbiotic efficiency. Inoculation with Rhizobium and P. polymyxa strain Loutit (L) stimulated nodulation as well as nitrogen fixation. PGPR also stimulated specific-nodulation (number of nodules per gram of root dry weight) increases that translated into higher levels of accumulated nitrogen. The activities of phytohormones depended on their content and interactions with Rhizobium tropici and Paenibacillus and/or Bacillus (PGPR) strains which affect the cytokinin in content in the common bean.

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In this study nodulated cowpea plants were exposed to a progressive drought-stress followed by rewatering in order to establish mechanisms related to the nodule sensitivity to N 2 fixation. Water stress caused a prominent decrease in the dry matter of leaf and nodule in contrast to the root growth that was stimulated. The drought-stressed plants showed a great decline in the ureide concentration of xylem sap whilst the concentration of the nodule leghaemoglobin decreased slightly. The stressed-nodules had significant accumulation of soluble carbohydrates in parallel to intense increase in the concentration of ureide, total amino acid and proline. After two days rewatering, the leaf growth showed a significant enhancement whereas in nodules a poor recovery was observed. In addition, the nodule N 2 fixation capacity did not improve after rehydration whereas the sap ureide experienced only a slight recovery and surprisingly the content of nodule soluble protein continued to drop. In contrast, a significant recovery in the nodule leghaemoglobin content was observed. Rewatering greatly induced depletion of both sucrose and total soluble sugar contents of nodules that were associated to a great decrease in the concentration of ureide, proline and amino acids, especially in leaves. Conversely the poor recovery of cowpea nodules after rehydration was apparently related to a carbohydrate shortage.Key words: leghaemoglobin, ureide, symbiose, water stress, Vigna unguiculata. Resumen Acumulación de componentes nitrogenados y reducción de carbohidratos en la fijación de nitrógeno de plantas de Vigna unguiculata (L.) Walp sometidas a estrés hídrico y rehidratadasA fin de establecer los mecanismos relacionados con la capacidad de los nódulos para fijar nitrógeno atmosférico, se expusieron plantas de Vigna unguiculata (L.) Walp noduladas a un estrés progresivo de sequía seguido de rehidratación. La sequía produjo una importante disminución en la materia seca de las hojas y de los nódulos, y en cambio estimuló el crecimiento de las raíces; por otro lado, hubo una gran disminución en la concentración de ureidos de la savia del xilema. Los nódulos sometidos a estrés presentaron una acumulación significativa de carbohidratos solubles, junto con un intenso aumento de la concentración de ureidos, aminoácidos totales y prolina, disminuyendo levemente la concentración de leghemoglobina. Tras dos días de rehidratación, el crecimiento de las hojas aumentó significativamente, pero tanto los ureidos de la savia como los nódulos sólo se recuperaron de forma leve, y no aumentó su capacidad de fijación de N 2 . Además, sorprendentemente, el contenido de proteínas solubles de los nódulos siguió disminuyendo, aunque el contenido de leghemoglobina se recuperó significativamente. Una rehidratación intensa indujo reducción tanto en el contenido de sacarosa como de azúcares solubles totales de los nódulos, junto con una gran disminución en la concentración de ureidos, prolina y aminoácidos, especialmente en las hojas. La pobre recuperación ...

Chemical fertilizers have been used in the cultivation of plants due to their high solubility and effect on crops yield. Biofertilizers with phosphate rock (PR) and potash rock (KR) plus sulfur inoculated with Acidithiobacillus may improve plant growth and contribute to addition of available P and K in soil. The effectiveness of biofertilizers from phosphate and potash rocks mixed with sulfur and Acidithiobacillus was studied in a Typic Fragiuldult soil of the Brazilian Northeast Tableland. Cowpea (cv. ''IPA 206'') was grown with and without rhizobia inoculation. Treatments were: (a) phosphate rock (1000 kg ha -1 ); (b) Biofertilizers-B P (250 and 500 kg ha -1 ); (c) triple superphosphate-TSP (250 kg ha -1 ); (d) potash rock (1000 kg ha -1 ); (e) biofertilizer-B K (250; 500 and 750 kg ha -1 ); (f) potassium chloride-KCl (250 kg K 2 0 ha -1 ); (g) control without P or K fertilization (P 0 K 0 ). The soil was maintained under water submersion covered with black plastic (solarization process) for a period of 30 days. Biofertilizers (B p and B K ) and soluble fertilizers increased plant growth and NPK uptake. Biofertilizers reduced soil pH, especially when applied in highest rates. Biofertilizers and TSP+KCl showed the best values of available P and K in soil. Rhizobial inoculation was effective on cowpea, but no nodules were formed by bacteria native from the soil, probably due to the effect of the solarization process. From obtained PK biofertilizers could be used as alternative for cowpea fertilization in Tableland soils.

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ABSTRACT. The sugarcane (Saccharum spp) presents economic importance, mainly for tropical regions, being an important Brazilian commodity. However, this crop is strongly dependent on fertilizers, mainly nitrogen (N). This study assessed the plant growth-promoting bacteria (PGPB) associated with sugarcane that could be used as a potential inoculant to the crop. We evaluated the genetic diversity of PGPB in the plant tissue of sugarcane varieties (RB 867515, RB 1011, and RB 92579). The primer BOX-A1R was used to differentiate the similar isolated and further sequencing 16S rRNA ribosomal gene. The 16S rRNA gene showed the presence of seven different genera distributed into four groups, the genus Bacillus, followed by Paenibacillus (20%), Burkholderia (14%), Herbaspirillum (6%), Pseudomonas (6%), Methylobacterium (6%), and Brevibacillus (3%). The molecular characterization of endophytic isolates from sugarcane revealed a diversity of bacteria colonizing this plant, with a possible biotechnological potential to be used as inoculant and biofertilizers.

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