Sueli dos Santos Freitas

Microbial biomass and microcalorimetric methods in tropical soils

The type of organic matter (OM) plays an essential role in nutrient cycling in agricultural soil systems. Microbial activity in tropical soils was calorimetrically followed as a useful tool in this investigation. Tropical soil samples with different textures: Rhodic eutrudox (R), Typic eutrudox (V) and a Quartzipsamment (Q) from Brazil were amended with 25% cattle manure (E), municipal refuse compost (L), earthworm casts (H), the agrochemical trifluralin (T); (23 g, equivalent dose of 1.25 kg ha −1 ) were explored. The microbial activity was determined by calorimetry and simultaneously by fumigation–extraction (microbial biomass carbon, C) to compare both methods. The results for R, Q, and V soils were: (212.04 A , 195.99 B , 204.47 A ) for microbial biomass C and (0.692 B , 0.714 B , 0.784 A ) for thermal effect with P< 0.05, respectively, over a period of incubation of 91 days. The microbial activity of the modified soils decreases in the order: E, H, L and T. Both methods showed a coefficient of correlation r = 0.7443 and the statistical probability of occurrence of the event, P< 0.0001. From this correlation the utility of both methods for measuring the microbial activity in soils could be deduced.

Interação de bactérias fluorescentes do gênero Pseudomonas e de Bacillus spp. com a rizosfera de diferentes plantas

Despite numerous reports on plant growth-promoting rhizobacteria (PGPR), there are few of them explaining their mode of action. It is possible that some plants promote bacterial colonization in the rhizosphere to facilitate plant-bacterium interaction, as if there were a certain mutual specificity. The objective of this study was to verify if lettuce plants promote root colonization by fluorescent pseudomonads, in comparison with other plants and with Bacillus spp. Roots of lettuce and some other vegetables were sampled in different properties of small commercial producers in Campinas-SP, Brazil. Colony forming units (cfu) of fluorescent pseudomonads and Bacillus spp. were counted by serial dilution and plating. The numbers of fluorescent pseudomonads were significantly higher in lettuce rhizosphere than in other plants, unlike the numbers of Bacillus spp.Embora haja muitos trabalhos na literatura com rizobactérias promotoras do crescimento de plantas (RPCPs), existem poucos que expliquem seu mecanismo de ação. É possível que algumas rizosferas favoreçam a colonização radicular por RPCPs, facilitando o estabelecimento da interação planta-bactéria, como se houvesse certa especificidade entre ambas. O objetivo deste trabalho foi verificar se a rizosfera de alface, em comparação com a de outras espécies vegetais, favorece o estabelecimento de bactérias fluorescentes do gênero Pseudomonas, em comparação com as do gênero Bacillus. Coletaram-se amostras do sistema radicular de alface, rúcula, chicória, salsa e tiririca em oito propriedades de produtores comerciais de hortaliças, na região de Campinas, SP. Foi feita a contagem de Pseudomonas spp. fluorescentes e de Bacillus spp. por diluição em série e plaqueamento. De maneira geral, observou-se maior crescimento de Pseudomonas spp. fluorescentes na rizosfera de alface-crespa em relação à de outras plantas, mas isso não ocorreu com Bacillus spp.

Rizobactérias e alface: colonização rizosférica, promoção de crescimento e controle biológico

SUMMARY : RHIZOBACTERIA AND LETTUCE: ROOT COLONIZATION,PLANT GROWTH PROMOTION AND BIOLOGICAL CONTROL Plant growth-promoting rhizobacteria (PGPR) can increase the productivity of severalcrops, including lettuce. The main objective of this study was to compare the root and/orroot collar colonizing ability on the growth promotion ability. A method of evaluation ofroot colonization was tested with the main objective of speeding up screening trials forgrowth enhancement of lettuce. Additionally, the antagonism in vitro between rhizobacteriaand the pathogen Fusarium sp. was tested to verify if growth promotion ability wasdetermined by biological control. Sixty-four bacterial isolates of fluorescent pseudomonadsfrom the rhizosphere of different lettuce varieties were tested in vitro to verify their capabilityof colonizing lettuce roots. The presence of a turbid, milky and narrow fog around the rootzone indicated bacteria colonization. Only eight isolates colonized the root system, andthirty-eight did in the root collar region, as could be evaluated by visual means. A greenhousetrial was then carried out to verify the growth promotion capacity of the isolates in lettuce.The substrate was a mixture of soil and chicken manure, similar to the one used by producers.Twelve isolates promoted growth of plants. Among those, four increased root dry weight,nine enhanced the number of leaves and eleven colonized the root collar. The antagonismassay was performed in PDA medium and King’s B medium. Although twelve isolatesshowed antagonistic activity against

Promoção do crescimento de alface por rizobactérias

Rizobacterias promotoras do crescimento de plantas (RPCPs) podem ser uma alternativa para o aumento da produtividade de varias especies vegetais, inclusive alface. Conduziram-se quatro experimentos com isolados de rizobacterias de diversas origens para verificar sua capacidade de promocao de crescimento de plantas de alface. Ao todo, testaram-se 77 isolados de Pseudomonas do grupo fluorescente, 23 de Bacillus e 11 de outras bacterias rizosfericas em areia esterilizada, em solo esterilizado, em substrato formado por uma mistura de solo e esterco (1:1, em volume), de forma semelhante a usada pelos produtores, e em areia com a solucao nutritiva recomendada para cultivos hidroponicos, em duas concentracoes. Foi marcante o beneficio exercido pelas bacterias do genero Pseudomonas em contraposicao as dos outros generos, revelando algum favorecimento dessas bacterias na rizosfera de alface, de forma a promover melhor crescimento das plantas. Houve diferencas no comportamento dos isolados conforme a fertilidade do substrato.

Interação entre fungos micorrízicos arbusculares e bactérias diazotróficas em trigo

The aim of this work was to evaluate the inoculation effect of two new endophytic diazotrophic bacteria and the interaction between arbuscular mycorrhizal fungi (AMF) and these bacteria on wheat plants. The experiment was carried out in a greenhouse with the two strains of diazotrophic bacteria, IAC11HT (Achromobacter insolitus) and IAC12HT (Zoogloea ramigera), and two AMF (Glomus sp. and Acaulospora sp.). There was synergistic effect of the co-inoculation on root colonization by diazotrophic bacteria with the AMF of the genus Acaulospora. The plants colonized by Glomus associated to bacterial strains showed higher growth, accumulation and exploitation of the nutrients than plants colonized by Acaulospora sp., however, this effect did not surpass the treatments in which bacteria and fungi were inoculated separately. Although there were non-beneficial effects of the AMF-diazotrophic bacteria co-inoculation, for the most parameters assessed, these news bacteria strains promoted doubled shoot dry matter, shoot N and P concentration and accumulation in wheat plants.

Enzymatic activity measured by microcalorimetry in soil amended with organic residues

Enzymatic activity is an important property for soil quality evaluation. Two sequences of experiments were carried out in order to evaluate the enzymatic activity in a soil (Rhodic Eutrudox) amended with cattle manure, earthworm casts, or sewage sludges from the municipalities of Barueri and Franca. The activity of commercial enzymes was measured by microcalorimetry in the same soil samples after sterilization. In the first experiment, the enzyme activities of cellulase, protease, and urease were determined in the soil samples during a three month period. In the second sequence of experiments, the thermal effect of the commercial enzymes cellulase, protease, and urease on sterilized soil samples under the same tretaments was monitored for a period of 46 days. The experimental design was randomized and arranged as factorial scheme in five treatments x seven samplings with five replications. The treatment effects were statistically evaluated by one-way analysis of variance. Tukey´s test was used to compare means at p < 0.05. The presence of different sources of organic residues increased the enzymatic activity in the sampling period. Cattle manure induced the highest enzymatic activity, followed by municipal sewage sludge, whereas earthworm casts induced the lowest activity, but differed from control treatment. The thermal effect on the enzyme activity of commercial cellulase, protease, and urease showed a variety of time peaks. These values probably oscillated due to soil physical-chemical factors affecting the enzyme activity on the residues.

Microbial enzymatic activity and thermal effect in a tropical soil treated with organic materials

Bacteria and fungi are the most active decomposers of organic materials in soil. They directly affect plant nutrient availability, and chemical and physical properties of soils. This investigation aimed at quantifying the effect of several organic materials on microbial activity of a Rhodic Eutrudox. Soil samples were incubated over a period of 91 days with the following organic materials: cattle manure (CM), earthworm humus (HM), and city sewage sludge from Barueri (BA) and Franca (FR). The activities of cellulase, protease and urease enzymes, the soil microbial carbon content (by fumigation-extraction method) and the exothermal effect were evaluated. Experimental design was randomized and arranged as factorial scheme five treatments × seven samplings with five replications. Organic materials promoted oscillations in m icrobial carbon (mg C g -1 soil), and enzyme activities - cellulase (μg glucose g -1 soil 24 h -1 ), protease (mg Tyr g -1 soil 2 h -1 ), urease (mg NH 4 + -N g -1 soil 2 h -1 ) - and the total thermal effect (J g -1 soil),

Potencial de rizobactérias na promoção de crescimento e controle da podridãoradicular em alface hidropônica

ABSTRACT Alface e a hortalica folhosa mais produzida em sistemashidroponicos no Brasil devido a boa qualidade desses sistemas e doproduto obtido. Alem disso, ha diminuicao dos danos causados porpatogenos veiculados pelo solo (23, 24). No entanto, o cultivohidroponico favorece o desenvolvimento de Pythium spp. pela baixadiversidade de microrganismos, liberacao de exsudatos radiculares ricosem carbono, temperaturas adequadas, fornecimento de oxigenio,mecanismos rapidos, eficientes e uniformes de disseminacao dezoosporos no ambiente (22, 26). Mesmo sem sintomas visiveis,como escurecimento e podridao radicular, Pythium spp. podem causarperdas em plantas entao denominadas assintomaticas (25). Alemde ser dificil o controle de doencas causadas pelo patogeno nocultivo hidroponico, a falta de produtos registrados limita o cultivode alface nesse sistema (22). Uma alternativa interessante paracombater especies de Pythium e o controle biologico, que podeocorrer por diversos mecanismos de atuacao, entre os quais inducaode resistencia, antibiose, competicao, hiperparasitismo, predacao ehipovirulencia (6).