ABSTRACT Studies have shown the synergism of co-inoculation with symbiotic and non-symbiotic N2-fixing bacteria, efficiently contribute to plant development. However, for crops such as forage legumes, data on the use of co-inoculation are still incipient, requiring studies to identify the contribution of this technique for application in pasture areas, thus ensuring greater sustainability. The objective of this study was to evaluate the effects of co-inoculation of Azospirillum brasilense (Ab-V5) and native rhizobia isolated from two forage legumes, Crotalaria spectabilis and Lupinus albus. Two experiments were installed in pots with 8dm3. Both were conducted in a randomized block design (DBC) with four replications and an 8 x 2 factorial scheme with six bacterial strains and two control treatments without inoculation (with presence or absence of mineral nitrogen), co-inoculated or not with the Ab-V5 strain. Plants were cultivated until the time of flowering when shoot (SDM) and root dry matter (RDM), number (NN) and nodule dry matter (NDM), and relative symbiotic efficiency (RSE) were evaluated. Isolates 05-21 and 06-03, for C. spectabilis and L. albus, respectively, indicated higher potential to promote plant growth when co-inoculated with Ab-V5, showing potential to act as substitutes for nitrogenous chemical fertilizers, reducing costs and increasing the sustainability of production.

ABSTRACT Currently, one of the most used practices in national coffee production is skeletal pruning, to preserve productive capacity, correct plant architecture, minimize the occurrence of diseases, among others. Also, it reduces the plants diameter, exposing the soil to climatic conditions, erosion, loss of moisture and nutrients, negatively affecting the development of coffee. The use of cover plants intercropped with coffee is presented as a technique to avoid and minimize these problems. Therefore, the objective of this research was to evaluate the effect of cover crops on the chemical and physical characteristics of the soil and the skeleton coffee tree. The experiment took place at Fazenda Boa Esperança, city of Serrania, South of Minas Gerais, from October/2017 to December/2018, in randomized blocks, composed of 8 treatments with and without cover crops. Three replicates per treatment were used, totaling 24 experimental plots, each with 14 plants, being the 10 central considered useful for evaluation. The cover crops contributed to the improvement of nutrient contents in the soil, maintained a better level of humidity and milder temperatures providing a greater development to the skeletonized coffee. They also positively influence weed control, but none could suppress all plants present in the research.

RESUMO O objetivo do estudo foi analisar a capacidade das bactérias diazotróficas, isoladas da rizosfera de Brachiaria brizantha, crescer em meios com diferentes valores de pH e concentrações salinas, de produzir ácido 3-indol acético (AIA) e solubilizar fosfato. Os testes de acidez e salinidade foram realizados em meio FAM sólido. Para acidez foram usados os valores de 4.0, 5.0, 6.0 e 7.0. Para salinidade foram utilizadas as seguintes concentrações: 0.01; 5.02; 9.99; 14.96; 19.98; 24.95; 29.98; 34.94; 39.97; 44.94 and 49.96 gꞏL-1. No teste de produção de AIA, as estirpes foram cultivadas em meio DYGS líquido, na ausência e presença de triptofano (Trp). A solubilização de fósforo, foi realizada em meio GL líquido. Todas as estirpes foram capazes de crescer em todos os valores de pH analisados. Já em relação aos testes de diferentes concentrações salinas, produção de AIA e solubilização de fosfato, foi verificada alta diversidade, havendo estirpes que se destacaram. As estirpes UNIFENAS 100-51; UNIFENAS 100-52; UNIFENAS 100-60; UNIFENAS 100-63 e UNIFENAS 100-65, foram as que apresentaram maior crescimento nas três maiores concentrações salinas. Na presença de triptofano, as estirpes UNIFENAS 100-63 e UNIFENAS 100-69 foram as que apresentaram maior produção de AIA. Já em solubilização de Fosfato in vitro, a estirpe UNIFENAS 100-52 foi a que obteve melhor resposta. Baseado nesses resultados, observa-se a importância de estudos relacionados às características fisiológicas e metabólicas de bactérias diazotróficas, de modo a garantir maior sucesso no campo.

ABSTRACT The objective of this study was to evaluate the ability of diazotrophic bacteria isolated from Brachiaria brizantha rhizosphere to grow at different pH values and salt concentrations, to produce indoleacetic acid (IAA), and to solubilize phosphate. Both acidity and salinity tolerance tests were performed on modified solid FAM medium. Acidity resistance tests were performed at pH values of 4.0, 5.0, 6.0, and 7.0, while, salt resistance was evaluated at concentrations of 0.01, 5.02, 9.99, 14.96, 19.98, 24.95, 29.98, 34.94, 39.97, 44.94, and 49.96 gL-1 NaCl. For the IAA production assay, bacterial strains were cultivated in liquid DYGS medium both in the absence and presence of tryptophan (Trp). In addition, phosphorus solubilization assay was performed in GL liquid medium. All strains grew at every pH value tested, and a high diversity was observed after salt resistance, IAA production, and phosphate solubilization testing. Strains UNIFENAS 100-51, UNIFENAS 100-52, UNIFENAS 100-60, UNIFENAS 100-63, and UNIFENAS 100-65 were those with the best growth at the highest salt concentrations. Furthermore, in the presence of Trp, strains UNIFENAS 100-63 and UNIFENAS 100-69 were the ones with the highest IAA production. Strain UNIFENAS 100-52 showed the best response to the in vitro phosphate solubilization assay. Based on these results, it can be seen that studies related to the physiological and metabolic characteristics of diazotrophic bacterial strains are important to ensure greater success in the field.