I. E. Marriel

Genetic diversity of Paenibacillus polymyxa populations isolated from the rhizosphere of four cultivars of maize (Zea mays) planted in Cerrado soil

Abstract A tropical Brazilian soil (Cerrado) was planted with four cultivars of maize (CMS04, CMS11, CMS22 and CMS36) and the genetic diversity of the Paenibacillus polymyxa populations present in their rhizospheres was determined after 90 days of sowing. For that, a total of 67 isolates were identified as P. polymyxa by classical biochemical tests and were analyzed for DNA polymorphism with the randomly amplified polymorphic DNA (RAPD) and amplification of repetitive DNA sequences (rep) methods. The amplification patterns obtained using three arbitrary primers and the primer BOXA1R were used separately to construct dendrograms based on the unweighted pair groups method with arithmetic means (UPGMA). Fifty-four genotypic groups were formed when data from different PCR amplifications were combined, showing a high level of genetic polymorphism among P. polymyxa strains. A dendrogram based also on combined PCR data, followed by cluster analysis with minimum-variance criteria (Ward) and Euclidean distance, showed that P. polymyxa strains could be divided into two main clusters. One cluster was formed predominantly by strains from maize cultivars CMS04 and CMS36, while the other cluster was formed predominantly by strains of maize cultivars CMS11 and CMS22. Multivariate analysis of variance (MANOVA) allowed the correlation between the genetic structure of P. polymyxa populations and the different cultivars of maize to be studied. The results showed that the strains isolated from the rhizospheres of the different maize cultivars were significantly different.

Localization of Pantoea ananatis inside lesions of maize white spot disease using transmission electron microscopy and molecular techniques

The etiological agent of maize white spot (MWS) disease has been a subject of controversy and discussion. Initially the disease was described as Phaeosphaeria leaf spot caused by Phaeosphaeria maydis. Other authors have suggested the existence of different fungal species causing similar symptoms. Recently, a bacterium, Pantoea ananatis, was described as the causal agent of this disease. The purpose of this study was to offer additional information on the correct etiology of this disease by providing visual evidence of the presence of the bacterium in the interior of the MWS lesions by using transmission electron microscopy (TEM) and molecular techniques. The TEM allowed visualization of a large amount of bacteria in the intercellular spaces of lesions collected from both artificially and naturally infected plants. Fungal structures were not visualized in young lesions. Bacterial primers for the 16S rRNA and rpoB genes were used in PCR reactions to amplify DNA extracted from water-soaked (young) and necrotic lesions. The universal fungal oligonucleotide ITS4 was also included to identify the possible presence of fungal structures inside lesions. Positive PCR products from water-soaked lesions, both from naturally and artificially inoculated plants, were produced with bacterial primers, whereas no amplification was observed when ITS4 oligonucleotide was used. On the other hand, DNA amplification with ITS4 primer was observed when DNA was isolated from necrotic (old) lesions. These results reinforced previous report of P. ananatis as the primary pathogen and the hypothesis that fungal species may colonize lesions pre-established by P. ananatis.

Different effects of transgenic maize and nontransgenic maize on nitrogen-transforming archaea and bacteria in tropical soils.

ABSTRACT The composition of the rhizosphere microbiome is a result of interactions between plant roots, soil, and environmental conditions. The impact of genetic variation in plant species on the composition of the root-associated microbiota remains poorly understood. This study assessed the abundances and structures of nitrogen-transforming (ammonia-oxidizing) archaea and bacteria as well as nitrogen-fixing bacteria driven by genetic modification of their maize host plants. The data show that significant changes in the abundances (revealed by quantitative PCR) of ammonia-oxidizing bacterial and archaeal communities occurred as a result of the maize host being genetically modified. In contrast, the structures of the total communities (determined by PCR-denaturing gradient gel electrophoresis) were mainly driven by factors such as soil type and season and not by plant genotype. Thus, the abundances of ammonia-oxidizing bacterial and archaeal communities but not structures of those communities were revealed to be responsive to changes in maize genotype, allowing the suggestion that community abundances should be explored as candidate bioindicators for monitoring the possible impacts of cultivation of genetically modified plants.

Temporal dynamics of microbial communities in the rhizosphere of two genetically modified (GM) maize hybrids in tropical agrosystems

The use of genetically modified (GM) plants still raises concerns about their environmental impact. The present study aimed to evaluate the possible effects of GM maize, in comparison to the parental line, on the structure and abundance of microbial communities in the rhizosphere. Moreover, the effect of soil type was addressed. For this purpose, the bacterial and fungal communities associated with the rhizosphere of GM plants were compared by culture-independent methodologies to the near-isogenic parental line. Two different soils and three stages of plant development in two different periods of the year were included. As evidenced by principal components analysis (PCA) of the PCR-DGGE profiles of evaluated community, clear differences occurred in these rhizosphere communities between soils and the periods of the year that maize was cultivated. However, there were no discernible effects of the GM lines as compared to the parental line. For all microbial communities evaluated, soil type and the period of the year that the maize was cultivated were the main factors that influenced their structures. No differences were observed in the abundances of total bacteria between the rhizospheres of GM and parental plant lines.

Endophytic microbial community in two transgenic maize genotypes and in their near-isogenic non-transgenic maize genotype

BackgroundDespite all the benefits assigned to the genetically modified plants, there are still no sufficient data available in literature concerning the possible effects on the microbial communities associated with these plants. Therefore, this study was aimed at examining the effects of the genetic modifications of two transgenic maize genotypes (MON810 – expressing the insecticidal Bt-toxin and TC1507 – expressing the insecticidal Bt-toxin and the herbicide resistance PAT [phosphinothricin-N-acetyltransferase]) on their endophytic microbial communities, in comparison to the microbial community found in the near-isogenic non-transgenic maize (control).ResultsThe structure of the endophytic communities (Bacteria, Archaea and fungi) and their composition (Bacteria) were evaluated by denaturing gradient gel electrophoresis (DGGE) and the construction of clone libraries, respectively. DGGE analysis and the clone libraries of the bacterial community showed that genotype TC1507 slightly differed from the other two genotypes. Genotype TC1507 showed a higher diversity within its endophytic bacterial community when compared to the other genotypes. Although some bacterial genera were found in all genotypes, such as the genera Burkholderia, Achromobacer and Stenotrophomonas, some were unique to genotype TC1507. Moreover, OTUs associated with Enterobacter predominated only in TC1507 clone libraries.ConclusionThe endophytic bacterial community of the maize genotype TC1507 differed from the communities of the maize genotype MON810 and of their near-isogenic parental genotypes (non-Bt or control). The differences observed among the maize genotypes studied may be associated with insertion of the gene coding for the protein PAT present only in the transgenic genotype TC1507.

Molecular detection of nifH gene‐containing Paenibacillus in the rhizosphere of sorghum (Sorghum bicolor) sown in Cerrado soil

Aims:  To develop a polymerase chain reaction (PCR)‐based approach for the detection of nifH gene‐containing Paenibacillus in environmental samples.

Decomposition of Arachis pintoi and Hyparrhenia rufa litters in monoculture and intercropped systems under lowland soil

Tropical grasslands under lowland soils are generally underutilized and the litter of forage legumes may be used to recover these degraded pastures. The objective of this work was to study the dynamics of litter decomposition of Arachis pintoi (pinto peanut), Hyparrhenia rufa (thatching grass) and a mixture of both species in a lowland soil. These treatments were analyzed in three areas: grass monoculture, legume monoculture and legume intercropped with the grass during the dry and wet seasons. Litter bags containing the legume, grass or a mixture of both species were incubated to estimate the decomposition rate and microorganism colonization. Decomposition constants (K) and litter half-lives (T1/2) were estimated by an exponential model whereas number of microorganisms in specific media were determined by plate dilution. The decomposition rate, release of nutrients and microorganisms number, especially bacteria, increased when pinto peanut was added to thatching grass, influenced by favorable lignin/N and C/N ratios in legume litter. When pinto peanut litter was incubated in the grass plots, 50% N and P was released within about 135 days in the dry season and in the wet season, the equivalent release occurred within 20 days. These results indicate that A. pintoi has a great potential for nutrient recycling via litter and can be used to recover degraded areas.

Urease Inhibitors of Agricultural Interest Inspired by Structures of Plant Phenolic Aldehydes

The plant phenolic natural products (PNPs) protocatechuic aldehyde, syringaldehyde and vanillin were used as platforms for obtaining four urease inhibitors. Urea (urease substrate) or thiourea (urease inhibitor) core was added to the structure of newly synthesized compounds to provide inhibitors up to 230-fold more active than the PNPs they originated from. The PNP derivatives are mixed inhibitors with higher affinity to urease active site. Two compounds were as efficient as N-(butyl)thiophosphoric triamide (NBPT) toward soil. Overall, PNPs derivatives are promising urease inhibitors for use as additive in urea-based fertilizers formulations.

Resíduos de sorgo e a mineralização do nitrogênio em LATOSSOLO VERMELHO fase cerrado

Management alterations induce significant modifications on organic matter quality and quantity, on N quantity and forms and on the mineralization process. The aim of this work was to study the influence of straw on the N mineralization rates of the N-NH4+ and N-NO3 forms during the decomposition of residues of two sorghum genotypes. The experimental design consisted of a 3x2x3 complete block outline, including two soil managements, three cultural residues and two nitrogen levels, with three replications. Percolation tubes were prepared with 20 g of soil mixed with 20 g of sand. Each tube with soil and sand received 0.1g residual straw from the two sorghum genotypes, with and without 50 mg N kg-1 in the form of ammonium nitrate. A control treatment was maintained without straw in the presence and absence of N. After an initial seven day incubation period, N was extracted weekly, over 49 days, using 100 mL of 0.01 mol L-1 CaCl2. The forms N-NH4+ and N-NO3- were determined spectroscoptically (UV/VIS) in the percolated extracts. N mineralization dependent on sorghum genotype and applied N. Sorghum straw influenced time and amount of N mineralized. The N-NH4+/ N-NO3- ratio showed variability during the incubation time as influenced by the incorporated residue. That ratio increased up to fifteen days of incubation time and decreased in subsequent periods. Without residues the mineralization potential was higher in the N-NO3 form.

Matéria seca e acúmulo de nutrientes em genótipos de milho contrastantes quanto a aquisição de fósforo

Com o intuito de avaliar o efeito do estresse de P sobre atributos morfologicos do sistema radicular de genotipos de milho contrastantes quanto a eficiencia na aquisicao de fosforo, conduziu-se um experimento em casa-de-vegetacao da Embrapa Milho e Sorgo, Sete Lagoas, MG, onde foram testados oito genotipos de milho, provenientes do programa de melhoramento da Empresa. O delineamento experimental utilizado foi o inteiramente casualizado, em esquema fatorial 8 x 2, com tres repeticoes, correspondendo a oito genotipos (tres linhagens: L1 = ineficiente, L2 e L3 = eficientes; e cinco hibridos: H1, H2 e H3 = eficientes, H4 e H5 = ineficientes) e dois niveis de P (baixo e alto). As plantas foram crescidas em solucao nutritiva com duas concentracoes de P equivalentes a 2,3 µM e 129 µM. A composicao da solucao nutritiva foi a seguinte, em mg L-1: N-NO3 152; N-NH4 18,2; Ca 141,1; K 90,1; Mg 20,8; S 18,8; Fe 4,3; Mn 0,5; B 0,27; Cu 0,04; Zn 0,15; Mo 0,08; Na 0,04 e HEDTA 20,06. Aos 18 dias do transplantio, verificou-se que, sob condicoes de estresse de P em solucao nutritiva, os hibridos H5, H1 e H2 apresentaram os maiores valores de massa seca total e da parte aerea, em relacao aos demais. De modo geral, tanto os hibridos como as linhagens, quando foram crescidos em solucao com baixo nivel de P, apresentaram maior relacao raiz/parte aerea, do que os materiais que cresceram em solucao com alto nivel do nutriente. A concentracao de N na parte aerea das plantas foi significativamente superior no tratamento com baixo nivel de P na solucao nutritiva. Os hibridos H1 e H2 e a linhagens L3 acumularam as maiores quantidades de P na parte aerea, independentemente do nivel de P na solucao. Esses resultados foram influenciados pelas maiores producoes de producao de materia seca apresentadas pelos referidos materiais. Independente do nivel de P houve variacao no conteudo do nutriente na parte aerea dos hibridos, nao sendo observado o mesmo comportamento para as linhagens.