RESUMO

Plant growth-promoting bacteria (PGPB) can be incorporated in biofertilizer formulations, which promote plant growth in different ways, such as fixing nitrogen and producing phytohormones and nitric oxide (NO). NO is a free radical involved in the growth and defense responses of plants and bacteria. NO detection is vital for further investigation in different agronomically important bacteria. NO production in the presence of KNO3 was evaluated over 1-3 days using eight bacterial strains, quantified by the usual Griess reaction, and monitored by 2,3-diaminonaphthalene (DAN), yielding 2,3-naphthotriazole (NAT), as analyzed by fluorescence spectroscopy, gas chromatography-mass spectrometry, and high-performance liquid chromatography. The Greiss and trapping reaction results showed that Azospirillum brasilense (HM053 and FP2), Rhizobium tropici (Br322), and Gluconacetobacter diazotrophicus (Pal 5) produced the highest NO levels 24 h after inoculation, whereas Nitrospirillum amazonense (Y2) and Herbaspirillum seropedicae (SmR1) showed no NO production. In contrast to the literature, in NFbHP-NH4Cl-lactate culture medium with KNO3, NO trapping led to the recovery of a product with a molecular mass ion of 182 Da, namely, 1,2,3,4-naphthotetrazole (NTT), which contained one more nitrogen atom than the usual NAT product with 169 Da. This strategy allows monitoring and tracking NO production in potential biofertilizing bacteria, providing future opportunities to better understand the mechanisms of bacteria-plant interaction and also to manipulate the amount of NO that will sustain the PGPB.

RESUMO

The aim of this work was to gain a more comprehensive and perspicacious view of the endophytic diazotrophic community (EDC) of tomato plant bacteria and assess the effects of chemical fertilization and the plant phenologic stage on the status of those microbes. When the EDC of stem and roots from tomato plants grown in a greenhouse with and without exogenous chemical fertilization was examined by pyrosequencing the nifH gene during the growth cycle, a high taxonomic and phylogenetic diversity was observed. The abundant taxa were related to ubiquitous endophytes such as Rhizobium or Burkholderia but also involved anaerobic members usually restricted to flooded plant tissues, such as Clostridium, Geobacter, and Desulfovibrio. The EDC composition appeared to be dynamic during the growth phase of the tomato, with the structure of the community at the early stages of growth displaying major differences from the late stages. Inorganic fertilization negatively affected the diversity and modified the profile of the predominant components of the EDC in the different growth stages. Populations such as Burkholderia and Geobacter plus the Cyanobacteria appeared particularly affected by fertilization.Our work demonstrates an extensive endophytic diazotrophic diversity, suggesting a high potential for nitrogen fixation. The effect of the phenologic stage and inorganic-chemical soil fertilization on the community structure indicated a dynamic community that responded to environmental changes. These findings contribute to a better understanding of endophytic associations that could be helpful in assisting to shape the endomicrobiome that provides essential benefits to crops.

Assuntos

RESUMO

Resumen Para los próximos 100 años se pronostica un incremento en la temperatura del planeta de casi 4 °C, lo cual pondrá en riesgo las especies que no logren adaptarse. En esta investigación se determinaron las respuestas morfofisiológicas de F. mexicana y los cambios en la población de bacterias fijadoras de nitrógeno atmosférico (BFN) asociadas a sus raíces, debido a dos condiciones ambientales con diferencias medias de temperatura de 5.1 oC: invernadero (temperatura alta, TA) y campo abierto (temperatura baja, TB); y con cuatro tratamientos: sin inocular (T), inoculadas con la cepa ocho (CP8), cepa cuatro (CP4) y con ambas cepas (CP8 + 4). Las BFN fueron aisladas de la rizosfera de F. mexicana y transformadas genéticamente con reporteros, para cuantificar la población al final del experimento. Se midió el peso seco de la parte aérea y la raíz, la tasa de asimilación de CO2 (A), el inicio de la floración, el número de flores y frutos; y la persistencia de las bacterias fijadoras de N atmosférico (BFN). Además, se evaluó la concentración de NO3, NH4, P y materia orgánica (MO) en el sustrato, al inicio y final del experimento. Las plantas sometidas a alta temperatura presentaron mayor peso seco de la parte aérea y fotosíntesis; con una disminución en el peso seco de la raíz, y en el número de flores y frutos. La MO en el sustrato disminuyó, mientras que la disponibilidad de NO3, NH4 y P aumentó. El incremento de temperatura y la mayor presencia de N en el substrato provocaron reducción en la población de BFN. Estos resultados sugieren que temperaturas altas estimulan el crecimiento de F. mexicana y tienen un impacto negativo sobre su reproducción y en las BFN asociadas a sus raíces.(AU)

Abstract The earth could experience a warming of 4 °C in the next one hundred years. This would put at risk the plants that can´t adapt. Fragaria mexicana is an endemic plant of temperate forest of Mexico. The response of this wild strawberry to temperature increasing has not been studied and could play an important role for event of global warming. This study determinate the morphological and physiological responses of F. mexicana and changes in the N2-fixing bacteria (BFN) population on its roots, due to two environmental conditions with differences of temperature 5.1 °C: greenhouse (high temperature, TA) and open land (low temperature, TB); and with four free-living nitrogen-fixing bacteria (BFN) treatments: non-inoculated (T), inoculated with strain eight (CP8), strain four (CP4), and strains eight and four mixed (CP8 + 4). BFN were isolated from the rhizosphere of F. mexicana and were genetically transformed with reporters to quantify the population at the end of the experiment. NO3, NH4 and P and organic matter (MO) in the substrate were determined at beginning and finish of the experiment. Shoot and root dry weight, photosynthetic rate, flowering and fructification starting, flowers and fruits number, were measured. Shoot dry weight and photosynthetic rate were lower in TB than TA, decreasing 3.1 g and 0.94 µmol m-2 s-1, respectively. Root dry weight was 3.0 g less in TA compared with TB. Number flowers decrease in 40.89 % and number fruits in 38.11 % on TA than TB. F. mexicana plants start flowering 14 days previously in TB than TA. MO in the substrate decrease in TA, while the concentration of NO3, NH4 and P, increased. Population of BFN was lower in TA. Results obtained indicated that higher temperature promotes the growth of F. mexicana and reduce its reproduction and BNF population associated with its roots.(AU)

Assuntos

RESUMO

Acidic ash derived volcanic soils (Andisols) support 50% of cereal production in Chile. Nitrogen (N) is essential for cereal crops and commonly added as urea with consequent environmental concerns due to leaching. Despite the relevance of N to plant growth, few studies have focused on understanding the application, management and ecological role of N2-fixing bacterial populations as tool for improve the N nutrition of cereal crops in Chile. It is known that N2-fixing bacteria commonly inhabits diverse plant compartments (e.g., rhizosphere and root endosphere) where they can supply N for plant growth. Here, we used culture-independent and dependent approaches to characterize and compare the putative N2-fixing bacteria associated with the rhizosphere and root endosphere of wheat plants grown in an Andisol from southern Chile. Our results showed significantly greater bacterial loads in the rhizosphere than the root endosphere. Quantitative PCR results indicated that the copy number of the 16S rRNA gene ranged from 1012~1013 and 107~108 g-1 sample in rhizosphere and root endosphere, respectively. The nifH gene copy number ranged from 105~106 and 105 g-1 sample in rhizosphere and root endosphere, respectively. The total culturable bacteria number ranged from 109~1010 and 107~108 CFU g-1 sample in rhizosphere and 104~105 and 104 CFU g-1 sample in root endosphere using LB and NM-1 media, respectively. Indirect counts of putative N2-fixing bacteria were 103 and 102~103 CFU g-1 sample in rhizosphere and root endosphere using NFb medium, respectively. Sequencing of 16S rRNA genes from randomly selected putative N2-fixing bacteria revealed the presence of members of Proteobacteria (Bosea and Roseomonas), Actinobacteria (Georgenia, Mycobacterium, Microbacterium, Leifsonia, and Arthrobacter), Bacteroidetes (Chitinophaga) and Firmicutes (Bacillus and Psychrobacillus) taxa. Differences in 16S rRNA and putative nifH-containing bacterial communities between rhizosphere and root endosphere were shown by denaturing gradient gel electrophoresis (DGGE). This study shows a compartmentalization between rhizosphere and root endosphere for both the abundance and diversity of total (16S rRNA) and putative N2-fixing bacterial communities on wheat plants grown in Chilean Andisols. This information can be relevant for the design and application of agronomic strategies to enhance sustainable N-utilization in cereal crops in Chile.

RESUMO

Arbuscular mycorrhizal fungi play an important role on nutrient supply to plants, specially P. However, the availability of inoculants for large-scale usage in agriculture is still limited because these organisms are obligatory symbionts. The use of symbiosis stimulants such as flavonoids can be an alternative to improve the beneficial effects of mycorrhiza for plant nutrition. The aim of this study was to evaluate the effect of the isoflavonoid biostimulant formononetin (7-hydroxy, 4'-methoxy isoflavone) in combination with three levels of phosphorus fertilization on mycorrhizal colonization, nodulation, and productivity of soybean, under field conditions. A 3 x 4 factorial scheme (levels of P: 0, 60 and 120 kg ha-1 P2O5 and doses of formononetin: 0, 25, 50 and 100 g ha-1) was used with five replicates. The following parameters were quantified at full bloom: plant height, shoot dry weight, nodule number, nodule dry weight, mycorrhizal colonization, and shoot N and P concentrations. Productivity was also evaluated at the end of the crop cycle. Formononetin stimulated mycorrhizal colonization at lower levels of P (0 and 60 kg ha-1), with colonization increasing from 56 to 64%. When applied with 60 kg ha-1 P2O5, formononetin increased soybean productivity to values similar to those observed when 120 kg ha-1 de P2O5, was applied. At doses above 50 g ha-1, formononetin applied to the seeds can reduce the need of P fertilization by 50%.

Os Fungos micorrízicos arbusculares desempenham papel importante no fornecimento de nutrientes para as plantas, especialmente P. No entanto, a disponibilidade de inoculantes com esses fungos, para o uso em larga escala na agricultura é ainda limitada, porque estes organismos são simbiontes obrigatórios. O uso de estimulantes simbióticos, como os flavonóides, podem ser uma alternativa para melhorar os efeitos benéficos da micorrrização na nutrição das plantas. O objetivo neste estudo foi avaliar o efeito do isoflavonóide bioestimulante formononetina (7-hidroxi, 4'-metoxi isoflavona) em combinação com três níveis de adubação fosfatada sobre a colonização micorrízica, a nodulação e a produtividade da soja, em condições de campo. Um esquema fatorial 3 x 4 (níveis de P: 0, 60 e 120 kg ha-1 de P2O5 e doses de formononetina: 0, 25, 50 e 100 g ha-1) foi utilizado, com cinco repetições. Os seguintes parâmetros foram quantificados em plena floração: altura da planta, matéria seca da parte aérea, número e matéria seca de nódulos, colonização micorrízica, e concentrações de N e P na parte aérea das plantas. A produtividade também foi avaliada no final do ciclo da cultura. A Formononetina estimulou a colonização micorrízica em níveis mais baixos de P (0 e 60 kg ha- 1), com aumentos de 56-64%. Quando aplicado com 60 kg ha-1 de P2O5, a formononetina aumentou a produtividade da soja, alcançando valores semelhantes aos observados quando foi aplicado 120 kg ha-1 de P2O5. Em doses acima de 50 g ha- 1, a formononetina aplicada na semente pode reduzir a necessidade de fertilização fosfatada em 50%.

Assuntos