Efficiency of rhizobia selection in Rio Grande do Sul, Brazil using biological nitrogen fixation in Phaseolus lunatus

The aim of this research was to evaluate the capacity of symbiotic efficiency of native rhizobia from soils of the state of Rio Grande do Sul (RS), Brazil in Phaseolus lunatus L. plants. Soil and nodule samples from predominant legume plants such as Desmodium species were collected in seven locations of the state of RS. For the isolation of the rhizobia from the soil samples, lima bean “olho de cabra preto” variety and “leucena” (Leucena leucocephala) and plants were used as baits. Subsequently, the symbiotic characterization of the isolates was performed by inoculation on lima bean plants in vitro conditions. The selected bacterial isolates were evaluated for biological nitrogen fixation efficiency in a greenhouse experiment, being determined after: shoot dry mass, root dry mass, nodule dry mass, nitrogen (N) accumulated shoot and calculated the N fixation relative efficiency index. Among the 28 rhizobia isolates tested, 11 induced nodule formation in lima bean. The rhizobia Plu03 and Plu14 stimulated a greater increase of plant dry mass, nodule dry mass and nitrogen accumulation in the shoot, reflecting in a higher relative efficiency index. These results suggest that the isolates Plu03 and Plu14 are more efficient in promoting growth of lima bean, which could be recommended for future agronomic efficiency studies

Potential use of rhizobium for vegetable crops growth promotion

The system of vegetable crops production required large amounts of mineral fertilizers. One of the possible alternatives to assure the economic and environmental sustainability of this production system would be the use of promoting growth plant rhizobacteria (PGPR). However, care is needed to select a microorganism to be used in crops that are usually consumed raw, so human health is not at risk. It was important to search for PGPR, as rhizobium, that already were broadly used as inoculants for leguminous plants for several decades, without risks to human health. PGPR can promote growth and development of plants through direct and indirect mechanisms, by production and secretion of chemical substances in the rhizosphere. The direct mechanisms were involved with the uptake of nutrients by the plants (nitrogen, phosphorus and essential minerals) through phosphate solubilization, production of siderophores and growth regulators. The indirect mechanisms were involved with the decrease of inhibitory effects from various pathogenic agents related with biological pest control, thereby favoring plant growth. Nevertheless, due to its ability to promote beneficial effects to plants, effective bacterial colonization was extremely important. Some bacteria that colonized the rhizoplane may penetrate the plant roots and some strains may move to the aerial part, with decreased bacterial density, compared with colonizing populations in the rhizosphere or roots. It can be concluded that Rhizobia promotes plant growth using different mechanisms as biological nitrogen fixation and production of different plant growth regulators (e.g. auxins). Therefore, new studies with Rhizobia characterization and observation about its different mechanisms of promoting plant growth should be performed. Such information would be useful for the identification of plants with potential to increase agricultural production due to the benefits of using plant growth promoter’s rhizobia

Rizóbios autóctones eficientes na fixação de nitrogênio em Leucaena leucocephalano Rio Grande do Sul, Brasil

La selección de rizobios nativos fijadores de nitrógeno (N) es importante para la producción de leucaena utilizada en la producción pecuaria. En el estado de Rio Grande do Sul (RS), Brasil es escasa la información de cepas nativas de rizobios con capacidad simbiótica con plantas de leucaena. El objetivo de este trabajo fue seleccionar rizobios nativos, eficientes en la fijación biológica de N en plantas de leucaena en RS. Se tomaron muestras de suelo y nódulos en diferentes localidades de RS, luego se utilizaron semillas de leucaena para obtener nódulos que fueron procesados en medios de cultivo para la obtención de los aislamientos. Se realizó un experimento en condiciones de invernade-ro para evaluar la eficiencia de los rizobios, mediante la determinación de la masa seca de la parte aérea (MSPA), masa seca de la raíz, número de nódulos y N acumulado de las plantas. Se seleccionaron los aislamientos de rizobios Leu01 y Leu02 como eficientes en la fijación de N por proporcionar aumento de la MSPA y acumulo de N en las plantas de leucaena similar al tratamiento control que recibió N mineral. Por tanto, estos aislamientos podrían ser promi-sores en futuros estudios en invernadero y campo de esta leguminosa.The selection of native rhizobia nitrogen (N)-fixing is important for the pro-duction of leucaena used in livestock production. In the state of Rio Grande do Sul (RS), Brazil there is little information of native isolates of rhizobia with symbiotic capacity with leucaena plants. The objective of this research was to select native rhizobia, efficient in the biological N fixation in leucaena plants in RS state. Soil and nodule samples were taken at different locations in RS, then leucaena seeds were used to obtain nodules that were processed in culture media to obtain the isolates. An experiment under greenhouse conditions was conducted to evaluate the efficiency of rhizobia isolates. The dry shoot dry mass (SDM), dry mass of the root, number of nodules and the N accumulated N of the plants were determined. The isolates of rhizobia Leu01 and Leu02 were selected as efficient in N fixation because they provide increase in MSPA and an accumulation of N in leucaena plants similar to the control treatment that received N mineral. These isolates could be promising in future greenhou-se and field studies of this legume.A seleção de rizóbios autóctones fixadores de nitrogênio (N) é importante para a produção de leucena utilizada para a produção pecuária. No estado do Rio Grande do Sul (RS), Brasil, existem poucas informações sobre isolados de rizóbios autócto-nes com capacidade simbiótica com plantas de leucena. O objetivo deste trabalho foi selecionar isolados de rizóbios autóctones, eficientes na fixação biológica de ni-trogênio em plantas de leucena no estado do RS. Foram coletadas amostras de solo e nódulos em diferentes locais do RS e, logo foram utilizadas sementes de leucena para obter os nódulos que em seguida foram processados em meios de cultura para obtenção dos isolados. Foi conduzido um experimento em casa de vegetação para avaliar a eficiência dos isolados de rizóbios, determinando-se a massa seca da parte aérea, massa seca da raiz, número de nódulos e nitrogênio acumulado nas plantas. Foram selecionados os isolados de rizóbios Leu01 e Leu02 como eficientes na fixação de N por proporcionarem o aumento da MSPA e acumulo de N nas plantas de leuce-na, semelhante ao tratamento controle não inoculado que recebeu fertilização nitrogenada, sendo estes isolados considerados como promissores que poderiam ser utilizados em outros estudos em casa de vegetação e campo desta leguminosa

Inoculante bacteriano incorporando bactérias fixadoras de nitrogênio na forma de fibras e/ou partículas em micro ou nanoescala produzidas através de electrospinning/electrospraying

Universidade Federal do Rio Grande do SulFundação de Amparo à Pesquisa do Estado do Rio Grande do SulTecnano Pesquisas e ServiçosAgronomiaFarmáciaDepositad

Rhizobial inoculation, alone or coinoculated with Azospirillum brasilense, promotes growth of wetland rice

Rhizobia and associative bacteria promote growth in rice plants (Oryza sativa L.) through a series of mechanisms, but most studies on inoculation have been performed based on inoculation with these bacteria in a separate or singular manner. The objective of this study was to assess the efficiency of single/isolated inoculation and inoculation combined with symbiotic rhizobia from forage legume and with Azospirillum brasilense on promoting growth and the root colonization process in wetland rice. Two rhizobia among four isolates from a greenhouse and a laboratory experiment were selected that efficiently promoted seed germination and rice plant growth in a sterilized substrate and in soil. The two most efficient isolates (UFRGS Vp16 and UFRGS Lc348) were inoculated alone or in combination with a commercial product containing A. brasilense in two field experiments using two wetland rice cultivars over two growing seasons. In the field experiments, these isolates coinoculated with A. brasilense promoted larger increases in the agronomic variables of wetland rice compared to the control without inoculation. Confocal laser microscopy confirmed the presence of inoculated bacteria tagged with gfp (UFRGS Vp16, UFRGS Lc348, and A. brasilense) colonizing the root surface of the rice seedlings, mainly in the root hairs and lateral roots

Genetic diversity and symbiotic compatibility among rhizobial strains and Desmodium incanum and Lotus spp. plants

This work aimed to evaluate the symbiotic compatibility and nodulation efficiency of rhizobia isolated from Desmodium incanum, Lotus corniculatus, L. subbiflorus, L. uliginosus and L. glaber plants by cross-inoculation. Twelve reference strains and 21 native isolates of rhizobia were genetically analyzed by the BOX-PCR technique, which showed a high genetic diversity among the rhizobia studied. The isolates were also characterized based on their production of indolic compounds and siderophores, as well as on their tolerance to salinity. Fifteen of the 33 rhizobia analyzed were able to produce indolic compounds, whereas 13 produced siderophores. All the tested rhizobia were sensitive to high salinity, although some were able to grow in solutions of up to 2% NaCl. Most of the native rhizobia isolated from L. uliginosus were able to induce nodulation in all plant species studied. In a greenhouse experiment using both D. incanum and L. corniculatus plants, the rhizobia isolate UFRGS Lu2 promoted the greatest plant growth. The results demonstrate that there are native rhizobia in the soils of southern Brazil that have low host specificity and are able to induce nodulation and form active nodules in several plant species

Growth promotion of rice by rhizobia at different levels of nitrogen fertilization

Embora os rizóbios não apresentem a capacidade de fixar nitrogênio em plantas de arroz, estes podem estimular o crescimento da parte aérea e da raiz, aumentando a absorção de nutrientes, como o nitrogênio, e a produtividade. Com o trabalho, avaliou-se o efeito de rizóbios em promover o crescimento de plantas de arroz em função de doses de nitrogênio (N). Efetuouse um experimento com vasos contendo solo e plantas da cultivar IRGA 424. As plantas foram inoculadas com oito isolados de rizóbios e adubadas com doses equivalentes a 0, 40, 80 e 160kg N ha-1. Avaliou-se a matéria seca e a quantidade de N acumulada na parte aérea e o perfilhamento das plantas. O efeito do N no crescimento de arroz aumentou com a inoculação de rizóbios. A matéria seca da parte aérea das plantas inoculadas e que receberam, aproximadamente, metade da maior dose de N foi equivalente às que receberam a maior dose desse nutriente e sem inoculação. Além disso, a inoculação com rizóbios aumentou o perfilhamento e a absorção de N. A inoculação de rizóbios em arroz, embora não dispense a adubação nitrogenada, tem potencial para aumentar a produção e a eficiência do uso do N.Although rhizobia do not show the ability to fix nitrogen in rice plants, they can stimulate shoot and root growth and even increase productivity and also can increase the plant efficiency in the absorption of nutrients such as nitrogen. This study evaluated the effect of rhizobia in promoting the growth of rice plants fertilized with nitrogen (N). An experiment was developed in pots containing soil and rice of the cultivar IRGA 424. The plants were inoculated with eight isolates of rhizobia and fertilized with 0, 40, 80 and 160kg N ha-1. We evaluated the dry matter of shoots, tillering and amounts of N absorbed by the shoots. The effect of N on rice growth increased by inoculation of rhizobia. Inoculated plants and fertilized with approximately half of the higher N dose, produced shoot equivalent of the plants that received the highest dose of this nutrient and without inoculation. Moreover, inoculation with rhizobia increased tillering and absorption of N. The practice of rhizobia inoculation in rice, although not replace the nitrogen fertilization, have great potential for rice farmers, allowing greater production and efficiency of N use

Metal-resistant rhizobacteria change soluble-exchangeable fraction in multi-metal-contaminated soil samples

There is a complex interaction between various components of the soil ecosystem, including microbial biomass and soil chemical contaminants such as heavy metals and radionuclides, which may greatly affect the efficiency of bioremediation techniques. The aim of this study was to investigate microbial capacity to change pH, changes in the metal soluble-exchangeable fraction, and effects of initial heavy metal contents on soil samples in microbial solubilization/immobilization capacity. The soil samples used in this study were collected at a known metal-contaminated site. Three highly metal-resistant bacteria were isolated from rhizosphere soil samples collected on weed species identified as Senecio brasiliensis, Senecio leptolobus, and Baccharis trimera. A completely randomized experimental design in a factorial arrangement was used, with three replicates. In general, with an acid pH, the isolates neutralized the contaminated growth media. In a neutral or basic initial pH, increases in pH were observed in the media, so these bacteria have an alkalizing effect on the growth media. Soluble metal contents were quite different and depend on the microbial species and heavy metal contents in the soil samples. The soluble-exchangeable fraction of metal such as Cu, Zn, Ni, Cr, Cd, Pb, and Ba may be unavailable after inoculation with heavy metalresistant rhizobacteria. A promising approach seems to be the application of inoculants with metal-resistant bacteria in bioremediation of multi-metal-polluted environments to improve the efficiency of this environmentally friendly technology

Redução na adubação nitrogenada em Triticum sp. inoculado e coinoculado

Using techniques of inoculation and co-inoculation of plant growth-promoting rhizobacteria (PGPR) could be an alternative with great potential for the wheat agricultural market, aiming towards a higher fertilizer efficiency and a subsequent reduction in environmental impacts. The objective of this study was to evaluate the efficiency of rhizobia symbiont inoculants isolated from legumes, individually and combined with Azospirillum brasilense, in promoting the growth of the wheat crop. The experiments were performed with the cultivars BRS Parrudo and TBIO Sossego, both inoculated and co-inoculated with the rhizobia UFRGS Vp16 and UFRGS Lc348, and A. brasilense, and under nitrogen dosage levels recommended for wheat plants. Inoculation of rhizobia, isolated or combined with A. brasilense, promotes increases in the production of wheat grains with half of the nitrogen dose recommended in the two evaluated cultivars, standing as an economically viable and ecologically sustainable alternative for the agricultural market.A utilização das técnicas de inoculação e coinoculação de rizobactérias promotoras do crescimento de plantas (RPCPs) pode ser uma alternativa com grande potencial para o mercado agrícola do trigo, visando uma maior eficiência no uso de fertilizantes e consequentemente redução do impacto ambiental. O objetivo deste trabalho foi avaliar a eficiência da inoculação de rizóbios simbiontes em leguminosas, isoladamente e em conjunto com Azospirillum brasilense, na promoção de crescimento da cultura do trigo. Os experimentos foram realizados com as cultivares BRS Parrudo e a TBIO Sossego, inoculadas e coinoculadas com os rizóbios UFRGS Vp16 e UFRGS Lc348, e A. brasilense, e sob níveis de doses de nitrogênio recomendadas para plantas de trigo. A inoculação de rizóbios, isoladamente ou em coinoculação com A. brasilense promove aumentos de produção de grãos de trigo com metade da dose de nitrogênio recomendada nas duas cultivares avaliadas, sendo uma alternativa economicamente viável e ecologicamente sustentável para o mercado agrícola

Inoculação e coinoculação de rizobactérias promotoras de crescimento em plantas de arroz irrigado

Aiming at obtaining high productivity and reduction of production costs, new techniques have been studied in rice crops, such as the use of plant growth promoting rhizobacteria (PGPR). The objective of this study was to evaluate the efficiency of inoculation and co-inoculation of rhizobia and Azospirillum brasilense in promoting the growth of irrigated rice plants cultivated in the field. Two experiments were conducted in the field, in the 2014/15 and 2015/16 crops, at the Rio Grande do Sul Rice Experiment Station. The experiment was composed of seven treatments, with two control treatments, without inoculation (81 kg ha-1 N and 135 kg ha-1 N, equivalent to 60% and 100%, respectively, of the recommended nitrogen dose). The other five treatments received only 60% of the N dose and were inoculated with the UFRGS Vp16 (Burkholderia sp.) and UFRGS Lc348 (Mesorhizobium sp.) Rhizobia, and with the commercial product containing the A. brasilense AbV5 and AbV6 strains. Inoculation and co-inoculation with PGPR may represent a viable alternative to reduce the amount of nitrogen fertilizers in rice crops.Visando a obtenção de altas produtividades e redução dos custos de produção, novas técnicas vêm sendo estudadas nas lavouras de arroz, como a utilização de rizobactérias promotoras de crescimento de plantas (RPCPs). O objetivo do trabalho foi avaliar a eficiência da inoculação e coinoculação de rizóbios e Azospirillum brasilense na promoção de crescimento de plantas de arroz irrigado cultivadas a campo. Foram conduzidos dois experimentos a campo, nas safras 2014/15 e 2015/16, na Estação Experimental do Instituto Rio Grandense do Arroz. O experimento foi composto por sete tratamentos, sendo dois tratamentos controle, sem inoculação (81 kg ha-1 de N e 135 kg ha-1 N, equivalente a 60% e 100%, respectivamente, da dose de nitrogênio recomendada). Os outros cinco tratamentos receberam apenas 60% da dose de N e foram inoculados com os rizóbios UFRGS Vp16 (Burkholderia sp.) e UFRGS Lc348 (Mesorhizobium sp.), e com o produto comercial contendo as estirpes de A. brasilense AbV5 e AbV6. A inoculação e coinoculação com RPCPs podem representar uma alternativa viável para reduzir a quantidade de adubos nitrogenados nas lavouras de arroz