Enilson Luiz Saccol de Sá

Imobilização de nitrogênio em solo cultivado com milho em sucessão à aveia preta nos sistemas plantio direto e convencional

The present research aimed to evaluate the amount of nitrogen immobilized and its remineralization, in conventional and in no-till systems, during the corn cycle. A soil that was used for oats crop was seeded with corn and subjected to under conventional and no-till systems. Samples were collected from the top (0-5cm) soil layer on the day of the corn seeding and after 46, 62, 88 and 112 days. At the same time, the aerial parts of corn plants were collected and nitrogen accumulation was evaluated. Soil samples were assayed for mineral N, potentially mineralizable N and C, activity and immobilized N. Microbial nitrogen immobilization was higher in no-till system, reducing the soil mineral nitrogen concentration and resulting in a lower amount of nitrogen in the aerial parts of corn plants at the end of the growth cycle. Nitrogen remineralization was not observed, indicating that the microbial biomass acted more as an agent of organic N mineralization than as a source of potentially mineralizable N.

Genetic variability of soybean bradyrhizobia populations under different soil managements

Due to their ecologic and economic importance, bradyrhizobia have been extensively studied in recent years. Since 1992, Bradyrhizobium elkanii SEMIA 587 and SEMIA 5019 and Bradyrhizobium japonicum SEMIA 5079 and SEMIA 5080 have been widely used in most Brazilian soybean fields. The objective of this work was to estimate the genetic variability of bradyrhizobial isolates recovered from soils under rhizobial inoculation and different soil managements. Only 25% of the isolates demonstrated high similarities to the original strains, and a strong correlation was obtained between the bradyrhizobial genetic variability and soil management. A high level of genetic diversity was observed both within isolates (H = 5.46) as well as among the different soil practices. Soil under no-tillage presented a higher bradyrhizobia diversity compared with bradyrhizobia isolated from soil under conventional tillage. Serological characterization also indicated that B. elkanii strains SEMIA 587 and SEMIA 5019 were more competitive and presented a higher nodular occupancy capacity than strains belonging to B. japonicum species in Southern Brazilian soils.

Genetic diversity and symbiotic efficiency of population of rhizobia of Phaseolus vulgaris L. in Brazil

The genetic diversity and symbiotic efficiency among indigenous rhizobia isolates obtained from native field with or without organic fertilization and superficial mineral fertilization were investigated. Eighty-six indigenous rhizobia were isolated from these fields using four common bean varieties as trap-host. The common bean varieties Mexico 309 and Rio Tibagi selected the most efficient rhizobia strains because they showed the best yields and N contents results. The genetic characterization of 36 rhizobia isolates was evaluated by using electrophoretic profiles of amplification products using primers ERIC1-R and ERIC-2. Our results demonstrated that besides the large diversity in the indigenous rhizobial community, the genotype of the trap-host probably influences the selection of the most efficient strains.

Reinoculação de bactérias diazotróficas aumentando o crescimento de plantas de trigo

With this work, we aimed evaluate the supply of N from BNF and the ability of diazotrophic bacteria isolates, reinoculated in wheat plants, to enhancer root elongation. In this study, we access nitrogen fixation and root elongation of wheat plants by inoculation of diazotrophic bacteria under controlled conditions. Two tested isolates had been distinguished by enhanced 2.3 times root elongation than treatments without inoculation. All isolates can to supply nitrogen to the wheat plants until 21 days of development. By this study, we can to identify better isolates to inoculation in wheat plants.

Identificação de cultivares de milho eficientes na absorção de nitrogênio e na associação com bactérias diazotróficas

Cultivars adapted to environments poor in nitrogen and capable to associate with diazotrophic bacteria can represent an alternative for the producion of maize in agricultural systems which uses few amounts of fertilizers. Aiming at identifying efficient maize cultivars in nitrogen uptake and diazitrophic bacteria association an experiment was carried out with 32 maize cultivars under different doses of nitrogen. The highest detection of diazotrophic population, the smallest effect of N fetilization and the highest nitrogen content under no nitrogen fertlization can indicate that Santa Helena 8447 may be a promising cultivar to be used in further studies to select efficient cultivars for cultivation in soils of low fertility.

Alterações microbianas no solo durante o ciclo do milho nos sistemas plantio direto e convencional

The availability of black oat residues, with high C:N ratio, leads to microbial immobilization of soil nitrogen, demanding special strategies to supply nitrogen to subsequent crops. The objective of this work was to evaluate shifts in microbial community structure due to the availability of black oat residues and nitrogen applications during the corn growing season. Soil (Paleudult) samples were collected on the day of the corn seeding and after 46, 62, 88 and 112 days. Nitrogen fertilizer was applied 25 and 49 days after corn seeding. Changes in microbial community were assessed by microbial biomass carbon (C) and nitrogen (N), ninhydrin- reactive N (N-Nin) and carbohydrates (CHO) ratios, besides the analysis of the rDNA of bacteria and fungi. Changes in microbial community shown by rDNA analysis were more related to C:N and C:N-Nin ratios than to C:CHO ratio. The C:N and C:N-Nin ratios and the analysis of the rDNA showed that microbial community was predominantly fungal at the beginning of the evaluation period. After nitrogen application, the bacterial population became preponderant and, at the end of the evaluation period, microbial community turned back to a composition similar to the initial.

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.

PROMOÇÃO DE CRESCIMENTO DE LOTUS CORNICULATUS L. E AVENA STRIGOSA SCHREB PELA INOCULAÇÃO CONJUNTA DE TRICHODERMA HARZIANUM E RIZÓBIO

Alem da fixacao de nitrogenio (N) em simbiose com leguminosas, os rizobios tambem podem promover o crescimento vegetal em gramineas pela producao de acido indol-acetico (AIA), hormonio pertencente ao grupo das auxinas. Outro grupo de microrganismos associados a promocao de crescimento vegetal sao as especies do genero Trichoderma. Alem disso, existem evidencias que especies de Trichoderma podem favorecer a nodulacao de leguminosas por rizobios. O presente trabalho teve como objetivo avaliar a promocao de crescimento em plantas de duas especies forrageiras, Lotus corniculatus L. (cornichao) e Avena strigosa Schreb (aveia preta), pela inoculacao com isolados de rizobio e Trichoderma harzianum (produto inoculante comercial) em experimento realizado em vasos com mistura esterilizada de areia e vermiculita, em casa de vegetacao. Testou-se a inoculacao de cinco bacterias fixadoras de nitrogenio (UFRGS Lc322; UFRGS Lc434; UFRGS Lc524; SEMIA816 e U510) em sementes pre-germinadas de aveia preta e cornichao, tanto isoladamente quanto em conjunto com o fungo T. harzianum. Os tratamentos inoculados foram comparados a controles, os quais receberam diferentes niveis de adubacao nitrogenada: 0 e 80 Kg N ha-1 para o cornichao; e 40 e 80 Kg N ha-1 para a aveia preta. A inoculacao com os rizobios, isoladamente e em mistura com T. harzianum, promoveu o aumento do nitrogenio mineral absorvido e da massa vegetal da parte aerea das plantas de aveia preta, em comparacao ao tratamento controle sem inoculacao (Controle +N/2), nao havendo diferencas quanto ao teor de N da parte aerea, entre os tratamentos inoculados e o tratamento controle sem inoculacao que recebeu o dobro de nitrogenio (Controle +N). A excecao foi o tratamento UFRGS Lc434 +T. harzianum, o qual nao diferiu do Controle +N/2. Nas condicoes de conducao do experimento, em casa de vegetacao, houve maior estimulo a producao de massa seca da parte aerea das plantas de aveia preta inoculadas com os rizobios SEMIA816, UFRGS Lc434 e UFRGS Lc524, isoladamente. Nos testes com L. corniculatus, a producao de massa seca e o teor de nitrogenio total acumulado na parte aerea do tratamento Controle +N nao diferiram das plantas dos tratamentos inoculados com os rizobios SEMIA816 e UFRGS Lc524, isoladamente, e dos tratamentos inoculados com os rizobios em conjunto com o T. harzianum (U510 +T. harzianum, SEMIA816 +T. harzianum, UFRGS Lc322 +T. harzianum, e UFRGS Lc524 +T. harzianum), o que evidencia que os rizobios inoculados foram eficientes na fixacao de nitrogenio atmosferico em simbiose com plantas de L. corniculatus.

UNIVERSITY EDUCATION AND TRAINING OF MICROBIOLOGISTS IN BRAZIL: 1990-2000

This paper aims to contribute to the discussion and concern on the future of microbiology in Brazil. This work presents a survey carried out in 2001 that shows a picture of Microbiology status in Brazil. Most of the conclusions are based on the data collected from the university courses and from the data supplied by the Brazilian National Research Council (CNPq) and the Coordination for the Improvement of Higher Level Personnel (CAPES). However, some of the affirmatives are more based on the experiences with postgraduate teaching in microbiology than on the data provided by official institutions. Such affirmatives were made in order to improve the development of the microbiology in Brazil. Also, a plan that proposes higher number of scholarships awarded to microbiology, to increase the possibility to form a critical mass necessary for further development of the Brazilian microbiology, is presented in order to produce discussion and more debate on the future of the Microbiology in Brazil.

Caracterização e influência de rizóbios isolados de alfafa na germinação e desenvolvimento inicial de plântulas de arroz

The inoculation of leguminous plants with rhizobia is one of the main methods of biotechnological use of microorganisms in order to obtain biological nitrogen fixation in agriculture. However, in recent years it has been attributed to these microorganisms the ability to produce phytohormones, mainly indole acetic acid (IAA), and to promote the growth in grasses. Thus, the objectives of this study were to quantify the indole acetic acid produced by rhizobia from alfalfa and to evaluate the effect of inoculation of these microorganisms on the germination of rice seed and to perform the genetic characterization of these isolates. Nine rhizobia, from nodules of alfalfa, were evaluated for their ability to produce IAA equivalents and for their influence in inoculating these microorganisms on germination and seedling development of rice. Moreover, these rhizobia producers of IAA were identified by the 16S region of DNAr. The equivalent production of indole acetic acid was observed in all tested isolates, with values ranging from 43.04 to 101.26µg mL-1 in culture medium. Regarding the germination of rice seeds, the inoculation with rhizobia accelerated this germination and its growth. Microorganisms UFRGS Ms58, UFRGS Ms515, UFRGS Ms195, UFRGS Ms205, UFRGS Ms2010 and UFRGS 2012 were identified as belonging to the species of Sinorhizobium meliloti. Microorganisms Ms55 UFRGS, UFRGS Ms75 and UFRG Ms72 were identified as belonging to the species of Rhizobium sp.