Abstract The objective of this research was to evaluate the inoculation and co-inoculation of bacteria with biotechnological potential, isolated from Brachiaria decumbens Stapf. and Brachiaria humidicola (Rendle) Schweickerdt, under germination and seedling growth of B. decumbens cv. Basilisk, as well as, to verify the influence of the co-inoculum in the soil indigenous bacterial community. For this, two assays in a completely randomized design were set up. The experimental period was 21 days. In a germination chamber, 25 treatments were evaluated (24 bacterial inoculants and a control – without inoculation). In greenhouse assay, were used five co-inoculations (bacterial consortium). The bacterial consortium was obtained based on the bacterial strain performance in the germination test. In addition, the control and one treatment with mineral fertilizer (NPK) were tested. In germination test, the seed inoculation promoted increases of 61, 40, 144, 82, 6, 96, 91 and 52% in germination vigor, speed germination index, number of absorbent hairs, number of plumules, primary root length, hypocotyl length, total length, and dry matter of seedlings, respectively, when compared to control. The co-inoculation also increased the growth parameters of B. decumbens plants when compared to the control treatment. In addition, promoted changes in the soil bacterial community structure. Becoming an important strategy to increase the germination rate and germination speed of B. decumbens plants.

Abstract Plant growth-promoting bacteria (PGPB) have received great interest in recent decades. However, PGPB mechanisms remain poorly understood in forage species. We aimed to evaluate roots endophytic and rhizospheric bacteria strains from Brachiaria humidicola and Brachiaria decumbens. The strains were evaluated for biological nitrogen-fixing in saline stress (0 to 10.0 g L-1 of NaCl), N-acyl homoserine lactones and indole-like compounds (ILC) production, the activity of hydrolytic enzymes, and inorganic phosphate solubilization (IPS) under different C sources. The diversity of strains was assessed by BOX-PCR. About 58% of strains were positive for BNF. High salinity levels reduced the growth and BNF. About 58% produced N-acyl homoserine lactones. The ILC was present in 39% of strains. Cellulase, polygalacturonase, pectate lyase, and amylase production were observed in 77, 14, 22, and 25% of strains, respectively. The IPS was observed in 44, 81, and 87% of isolates when glucose, mannitol and sucrose were used, respectively. Comparing two plant species and niches, the strains associated with B. humidicola and root endophytic presented more PGPB mechanisms than others. We found high strain diversity, of which 64% showed similarity lower than 70%. These results can be supporting the bioproducts development to increase forage grasses production in tropical soils.

Abstract Grass from the genus Brachiaria spp. predominates in pastures with low fertile soils. This scenario highlights the importance of the association with microorganisms to foster plant growth, which becomes essential to the successful establishment of this forage in such environments. This study aimed to evaluate the genetic variability and identify the mechanisms of plant growth promotion, in vitro, of bacteria associated with Brachiaria decumbens Stapf. and Brachiaria humidicola (Rendle.) Schweickerdt in Pernambuco, Brazil. We evaluated 20 isolates of diazotrophic bacteria obtained from the endophyte or rhizosphere communities. The genetic characteristics were determined via sequencing the 16S rRNA region, which allowed us to identify ten different bacterial genera: Bacillus sp., Burkholderia sp., Enterobacter sp., Klebsiella sp., Microbacterium sp., Pantoea sp., Ralstonia sp., Rhizobium sp., Sinomonas sp., and Sphingomonas sp., with a specificity of the genus Rhizobium sp. to Brachiaria decumbens Stapf.. The phenotypic and functional characteristics revealed that 100% of the bacterial strains produced indol-3-acetic acid (IAA) with the addition of L-tryptophan, and 60% presented IAA production independent of the L-tryptophan pathway. We also detected that 70% of the isolated bacteria possessed the capacity to solubilize phosphorus. The analysis of the enzymatic output revealed that 30% of the bacterial isolates produced cellulase, 60% produced pectate lyase, 15% produced polygalacturonase, and 30% produced amylase. We also detected the production of N-acyl homoserine lactones in 65% of bacterial strains. In summary, our results showed that plants of B. decumbens Stapf. and B. humidicola (Rendle.) Schweickerdt interacted with different bacterial genera capable of promoting plant growth.

Resumen Pastos del género Brachiaria spp. predomina en pasturas con suelos poco fértiles. Este escenario resalta la importancia de la asociación con microorganismos para fomentar el cultivo de plantas. Este estudio tuvo como objetivo evaluar la variabilidad genética e identificar los mecanismos de promoción del crecimiento de las plantas, in vitro, de bacterias asociadas con Brachiaria decumbens Stapf. y Brachiaria humidicola (Rendle.) Schweickerdt en Pernambuco, Brasil. Evaluamos 20 aislamientos de bacterias diazotróficas obtenidas de la comunidad de endofitas o rizosfera. Las características genéticas se determinaron mediante la secuenciación de la región 16S rRNA, lo que permitió identificar diez géneros bacterianos diferentes: Bacillus sp., Burkholderia sp., Enterobacter sp., Klebsiella sp., Microbacterium sp., Pantoea sp., Ralstonia sp., Rhizobium sp., Sinomonas sp., y Sphingomonas sp., con una especificidad del género Rhizobium sp. a Brachiaria decumbens Stapf.. Las características fenotípicas y funcionales revelaron que el 100% de las cepas bacterianas producían ácido indol-3-acético (AIA) con la adición de L-triptófano y el 60% presentaban producción de AIA independientemente de la vía de L-triptófano. También detectamos que el 70% de las bacterias aisladas poseían la capacidad de solubilizar el fósforo. El análisis de la producción enzimática reveló que el 30% de los aislados producían celulasa, 60% pectato liasa, 15% poligalacturonasa y el 30% producía amilasa. También detectamos la producción de N-acyl homoserine lactones en el 65% de las cepas bacterianas. En resumen, las plantas de B. decumbens Stapf. y B. humidicola (Rendle.) Schweickerdt interactuó con diferentes géneros de bacterias capaces de promover el crecimiento de la planta.

RESUMO A seleção de bactérias tolerantes a salinidade poderá propiciar maior promoção de crescimento vegetal em solos com estresse salino. Objetivou-se isolar e selecionar isolados bacterianos de cana-de-açúcar, tolerantes à salinidade e promotores de crescimento vegetal, e avaliar a diversidade genética. Para tanto, bactérias endofíticas de raiz e rizosfera, de cana-de-açúcar, foram isoladas, em meio de cultura com e sem NaCl. Avaliou-se a densidade populacional bacteriana, o potencial para a fixação biológica de nitrogênio (FBN), produção de ácido indol acético (AIA), solubilização de fosfato inorgânico e produção da molécula quorum sensing. Além disso, a diversidade genética foi avaliada pela técnica da Eletroforese em Gradiente de Gel Desnaturante (DGGE) do NifH. Testes de tolerância à salinidade também foram realizados. Não houve diferença estatística na densidade populacional. Quanto a FBN, produção de AIA, solubilização de fosfato e produção da molécula quorum sensing, houve alto percentual de isolados positivos. Na técnica do DGGE do gene nifH, o dendrograma indicou alta variabilidade genética. Portanto, houve a seleção de bactérias que possam contribuir para o melhor desenvolvimento da cana-de-açúcar em solos salinos.

ABSTRACT The selection of salinity tolerant bacteria may provide greater promotion of plant growth in soils with salt stress. This study aimed to isolate and select bacterial isolates of sugarcane, tolerant to salinity and plant growth promoters, and assess genetic diversity. To do so, endophytic root and rhizosphere of sugarcane, were isolated in culture medium with and without NaCl. The bacterial population density, the potential for biological nitrogen fixation (BNF), production of indole acetic acid (IAA), inorganic phosphate solubilization and quorum sensing molecule production were evaluated. Furthermore, the genetic diversity was assessed by Denaturing Gradient Gel Electrophoresis (DGGE) of nifH. Salinity tolerance tests were also conducted. There was no statistical difference in population density. As for the potential for BNF, IAA production, phosphate solubilization and quorum sensing molecule production, there was a high percentage of positive isolates. In the technique of DGGE nifH, the dendrogram showed high genetic variability. So there was the selection of bacteria that can contribute to the better development of sugarcane in saline soils.

A exploração e o conhecimento dos mecanismos de interação bactéria-planta podem ser utilizados para a produção sustentável de diversas culturas, como a cana-de-açúcar. O objetivo deste trabalho foi isolar e prospectar bactérias associadas à cultura da cana-de-açúcar com capacidade de fixar nitrogênio e solubilizar fosfato inorgânico em áreas com e sem aplicação de cupinicida. Bactérias endofíticas, de folha e raiz, e do rizoplano foram isoladas de três variedades comerciais (RB 92579, RB 867515 e RB 863129) de cana-de-açúcar, cultivadas no Nordeste brasileiro, em áreas com e sem aplicação de cupinicida, aos quatro meses após o plantio. Foram obtidos 272 isolados, selecionados quanto à sua capacidade de solubilizar fosfato inorgânico e fixar nitrogênio. O uso do cupinicida não provocou alterações nas comunidades microbianas endofíticas de folha e raiz e epifíticas do rizoplano. As variedades estudadas apresentam uma comunidade bacteriana associada com potencial aplicação para a promoção de crescimento vegetal, pois possuem a capacidade de fixar N2 e solubilizar fosfato inorgânico.

The exploration and knowledge of bacteria-plant interaction mechanisms may be used for a more sustainable production of several crops, e.g., of sugarcane. The objective of this paper was to isolate bacteria associated with sugarcane with the ability to fix nitrogen and solubilize inorganic phosphate in areas with and without the application of termiticide. Endophytic bacteria were isolated from leaves and roots and from the rhizoplane, four months after planting of three commercial sugarcane varieties (RB 92579, RB 867515 and RB 863129), in the Northeast of Brazil. Altogether, 272 isolates were obtained and selected for their capacity to solubilize inorganic phosphate and fix nitrogen. Termiticide application induced no changes in the endophytic microbial communities of leaf and root and the epiphytic bacteria of the rhizoplane. A bacterial community associated with the studied sugarcane varieties was identified, which could be applied for plant growth promotion, since it can fix N2 and solubilize inorganic phosphate.

A formação e regeneração de protoplastos foram avaliadas em duas linhagens selvagens e duas linhagens mutantes para coloração de conídios em Metarhizium flavoviride. O cultivo em meio líquido seguido do tratamento do micélio com Novozym 234 na presença de KCl 0,7 M como estabilizador osmótico, resultou na produção de 5,05´10(6) a 1,15´10(7) protoplastos´mL-1. A porcentagem de regeneração das diferentes linhagens variou de 6,65 a 27,92%. Após a regeneração, uma das linhagens selvagens produziu espontaneamente variantes estáveis, com morfologia alterada. Embora variantes morfológicos já tenham sido observados após regeneração de protoplastos em bactérias, esta parece ser a primeira vez que tal ocorrência é descrita em fungos filamentosos. Um desses variantes, além da linhagem selvagem da qual ele foi originado, foi testado para sensibilidade aos fungicidas benomil e captano.

Protoplast isolation and regeneration were evaluated in two wild-type and two colour mutant strains of Metarhizium flavoviride. Cultivation in liquid medium, followed by mycelium treatment with Novozym 234 in the presence of KCl 0.7M as osmotic stabilizer, produced 5.05 x 10(6) to 1.15 x 10(7)x mL-1 protoplasts. The percentage of regeneration ranged from 6.65 to 27.92%. Following protoplast regeneration, one strain produced spontaneously stable morphological variant colonies. Although colonies with altered morphology have been reported in bacteria following protoplast regeneration, this is the first time that the same is described in a filamentous fungus. The original strain and one derived variant were tested for sensitivity to the fungicides benomyl and captan.