O presente estudo teve por objetivo avaliar o suprimento de N via FBN e a capacidade de isolados de bactérias diazotróficas, reinoculados em plantas de trigo, em promover o aumento do comprimento radicular. Foi feito um estudo sob condições controladas no qual avaliou a fixação biológica de nitrogênio e o aumento no comprimento radicular de plantas de trigo inoculadas com bactérias diazotróficas. Destacaram-se dois isolados testados pelo aumento de 2,3 vezes no comprimento radicular comparado aos tratamentos sem inoculação. Todos os isolados inoculados supriram a necessidade de N das plantas de trigo até os 21 dias de desenvolvimento. Por meio desta técnica foi possível identificar isolados promissores para inoculação em plantas de trigo.

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.

Cultivares adaptados a ambientes pobres em nitrogênio e capazes de se associar com bactérias diazotróficas podem representar uma alternativa para a produção do milho em sistemas agrícolas com baixa utilização de insumos. Visando identificar cultivares de milho eficientes na absorção de nitrogênio e na associação com bactérias diazotróficas foi conduzido um experimento em vasos avaliando-se 32 cultivares de milho em diferentes doses de N aplicado ao solo. A ocorrência de elevada população de bactérias diazotróficas e a baixa resposta à adubação nitrogenada juntamente com o maior acúmulo de N quando não foi aplicado nitrogênio no solo, indicaram que o cultivar Santa Helena 8447 pode ser promissor para futuros estudos de seleção de cultivares eficientes para cultivo em solos de baixa fertilidade.

ACKNOWLEDGEMENTS. We thank the Department of Biotechnology, New Delhi for financial support and the Department of Bioscience and Biotechnology, Banasthali University for providing the necessary facilities to carry out this work.

RESUMO Embora os rizóbios não apresentem a capacidade

In vitro rooting and the acclimatization of micropropagated rootstocks of apple trees is essential for plant development in the field. The aim of this work was to assess the use of rhizobia of Adesmia latifolia to promote rooting and acclimatization in micropropagated Marubakaido apple rootstock. An experiment involving in vitro rooting and acclimatization was performed with four strains of rhizobium and two controls, one with and the other without the addition of synthetic indoleacetic acid. The inoculated treatments involved the use of sterile inoculum and inoculum containing live rhizobia. The most significant effects on the rooting rate, primary-root length, number of roots, root length, fresh-shoot biomass, and fresh-root biomass were obtained by inoculation with strain EEL16010B and with synthetic indole acetic acid. However, there was no difference in the growth of apple explants in the acclimatization experiments. Strain EEL16010B can be used to induce in vitro rooting of the Marubakaido rootstock and can replace the use of synthetic indoleacetic acid in the rooting of this cultivar.

Serradella is a plant that belongs to the Fabaceae family, with recognized forage value and has the ability to associate symbiotically with rhizobia. The objective of this study was to isolate, authenticate and select effective rhizobia obtained from native serradella (Ornithopus micranthus) to reduce the need for mineral fertilizer. Nodules, roots of serradella and rhizosphere soil samples were collected in seven municipalities from Rio Grande do Sul and Santa Catarina states. Bacterial colonies were isolated and identified based on morphological characteristics. The authentification and initial selection of rhizobia were conducted in vitro. The most promising strains from the in vitro study were evaluated in a greenhouse experiment for 60 days. Among the 148 bacterial cultures characterized, 113 induced the formation of nodules in serradella while 32 isolate effectively increased fresh mass of plants under in vitro conditions. The strains UFRGS Om57, UFRGS Om59 and UFRGS Om148 formed nodules with greater dry mass and produced high dry mass of plants (shoots and roots) which allowed greater accumulation of N in the shoots.

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.