Persistencia de malezas gramíneas en cultivos de trigo del sudeste bonaerense

En la presente tesis se estudió la persistencia de especies poáceas en cultivos de trigo del sudeste de Buenos Aires. En dicha región, Avena fatua L. y Lolium multiflorum Lam. son las malezas poáceas más importantes, tanto por la dificultad de control como por sus efectos competitivos sobre el cultivo. A los efectos de cuantificar la persistencia de dichas especies, se estudió la composición de la comunidad de malezas en dos momentos del ciclo: preaplicación de herbicidas y precosecha. Individuos de ambas malezas fueron registrados en ambos momentos como consecuencia de “escapes” al control realizado con herbicidas, siendo A. fatua más constante que L. mutiflorum. Posteriormente, se estudiaron los procesos que definen la persistencia de ambas malezas. Los resultados obtenidos indican que el ajuste del momento de emergencia es jerárquicamente el factor más importante para explicar la persistencia de A. fatua. Se demostró que los modelos de germinación son diferentes según las semillas provengan de un lote agrícola o de una condición de no cultivo, siendo estas diferencias de naturaleza genética. Por otro lado, la variabilidad en la supervivencia a los herbicidas es el factor que mejor explica la persistencia de L. multiflorum, habiéndose documentado resistencia cruzada a los herbicidas inhibidores de la ALS, pyroxsulam, imazamox y flucarbazone, sin antecedentes previos en la región. Los índices de resistencia encontrados presentan variación con la temperatura ambiente en post-aplicación del herbicida, habiéndose registrado mayor resistencia con mayor temperatura. Además, se comprobó que los individuos resistentes presentan menor tiempo a floración que los susceptibles. Tal atributo puede significar una ventaja demográfica para dichas poblaciones. Queda así demostrada la persistencia de A. fatua y L. multiflorum durante el ciclo del cultivo más allá de las prácticas de control realizadas y la participación de dos procesos demográficos distintos (establecimiento y supervivencia) en dicha persistencia

Sequences of primers used in study.

<p>Sequences of primers used in study.</p

Distribution of sequences generated by degenerate and non-degenerate primers by genus.

<p>Percent mean abundances and standard deviations are shown. Genera are arranged in a gradient such that those predominant in the degenerate community are arranged on the left. There were no differences between the two communities in the relative abundance of any genus (p>0.05, 2-sample t-test on transformed variable).</p

Shannon diversity and equitability indices of pyrotag and Sanger communities.

<p>No differences were detected between any of the pyrotag communities; however, the Sanger community demonstrated significantly greater equitable than all the pyrotag communities (** p<0.01, ANOVA).</p

Distribution of sequences by taxa.

<p>Rare taxa are shown in Figure 2A and abundant taxa in Figure 2B. The Sanger community demonstrated significantly fewer species-level taxa than pyrosequencing (*** p<0.001, ANOVA). There were no differences between the pyrotag sequences.</p

Relative abundances of genera in Sanger and concatenated pyrotag datasets.

<p>Relative abundances of genera in Sanger and concatenated pyrotag datasets.</p

Relative abundances of genera in pyrotag sequences.

<p>Percent mean abundances (and standard deviations) of genera in the 3 pyrotag and Sanger sequence communities are shown, arranged in order of decreasing overall prevalence. Alphabets in parentheses indicate statistically significant differences between groups (p<0.05, 2-sample t-test on transformed variable). A- significant difference between V1–V3 & V4–V6, B- significant difference between V1–V3 & V7–V9, C- significant difference between V4–V6 & V7–V9 (2-sample t-test on transformed variable).</p

<i>Pglyrp</i>-Regulated Gut Microflora <i>Prevotella falsenii</i>, <i>Parabacteroides distasonis</i> and <i>Bacteroides eggerthii</i> Enhance and <i>Alistipes finegoldii</i> Attenuates Colitis in Mice

<div><p>Dysbiosis is a hallmark of inflammatory bowel disease (IBD), but it is unclear which specific intestinal bacteria predispose to and which protect from IBD and how they are regulated. Peptidoglycan recognition proteins (<i>Pglyrps</i>) are antibacterial, participate in maintaining intestinal microflora, and modulate inflammatory responses. Mice deficient in any one of the four <i>Pglyrp</i> genes are more sensitive to dextran sulfate sodium (DSS)-induced colitis, and stools from <i>Pglyrp</i>-deficient mice transferred to wild type (WT) germ-free mice predispose them to much more severe colitis than stools from WT mice. However, the identities of these <i>Pglyrp</i>-regulated bacteria that predispose <i>Pglyrp</i>-deficient mice to colitis or protect WT mice from colitis are not known. Here we identified significant changes in β-diversity of stool bacteria in <i>Pglyrp</i>-deficient mice compared with WT mice. The most consistent changes in microbiome in all <i>Pglyrp</i>-deficient mice were in <i>Bacteroidales</i>, from which we selected four species, two with increased abundance (<i>Prevotella falsenii</i> and <i>Parabacteroides distasonis</i>) and two with decreased abundance (<i>Bacteroides eggerthii</i> and <i>Alistipes finegoldii</i>). We then gavaged WT mice with stock type strains of these species to test the hypothesis that they predispose to or protect from DSS-induced colitis. <i>P</i>. <i>falsenii</i>, <i>P</i>. <i>distasonis</i>, and <i>B</i>. <i>eggerthii</i> all enhanced DSS-induced colitis in both WT mice with otherwise undisturbed intestinal microflora and in WT mice with antibiotic-depleted intestinal microflora. By contrast, <i>A</i>. <i>finegoldii</i> (which is the most abundant species in WT mice) attenuated DSS-induced colitis both in WT mice with otherwise undisturbed intestinal microflora and in WT mice with antibiotic-depleted intestinal microflora, similar to the colitis protective effect of the entire normal microflora. These results identify <i>P</i>. <i>falsenii</i>, <i>P</i>. <i>distasonis</i>, and <i>B</i>. <i>eggerthii</i> as colitis-promoting species and <i>A</i>. <i>finegoldii</i> as colitis-protective species.</p></div

Distinct Soil Bacterial Communities Revealed under a Diversely Managed Agroecosystem

<div><p>Land-use change and management practices are normally enacted to manipulate environments to improve conditions that relate to production, remediation, and accommodation. However, their effect on the soil microbial community and their subsequent influence on soil function is still difficult to quantify. Recent applications of molecular techniques to soil biology, especially the use of 16S rRNA, are helping to bridge this gap. In this study, the influence of three land-use systems within a demonstration farm were evaluated with a view to further understand how these practices may impact observed soil bacterial communities. Replicate soil samples collected from the three land-use systems (grazed pine forest, cultivated crop, and grazed pasture) on a single soil type. High throughput 16S rRNA gene pyrosequencing was used to generate sequence datasets. The different land use systems showed distinction in the structure of their bacterial communities with respect to the differences detected in cluster analysis as well as diversity indices. Specific taxa, particularly Actinobacteria, Acidobacteria, and classes of Proteobacteria, showed significant shifts across the land-use strata. Families belonging to these taxa broke with notions of copio- and oligotrphy at the class level, as many of the less abundant groups of families of Actinobacteria showed a propensity for soil environments with reduced carbon/nutrient availability. Orders Actinomycetales and Solirubrobacterales showed their highest abundance in the heavily disturbed cultivated system despite the lowest soil organic carbon (SOC) values across the site. Selected soil properties ([SOC], total nitrogen [TN], soil texture, phosphodiesterase [PD], alkaline phosphatase [APA], acid phosphatase [ACP] activity, and pH) also differed significantly across land-use regimes, with SOM, PD, and pH showing variation consistent with shifts in community structure and composition. These results suggest that use of pyrosequencing along with traditional analysis of soil physiochemical properties may provide insight into the ecology of descending taxonomic groups in bacterial communities.</p> </div

<i>P</i>. <i>falsenii</i>, <i>P</i>. <i>distasonis</i>, and <i>B</i>. <i>eggerthii</i>, but not <i>A</i>. <i>finegoldii</i>, predispose mice depleted of intestinal microflora to colitis.

<p>(<b>A</b>) WT mice were depleted of intestinal microflora by treatment with antibiotics and then gavaged every other day with <i>P</i>. <i>falsenii</i>, or <i>P</i>. <i>distasonis</i>, or <i>B</i>. <i>eggerthii</i>, or <i>A</i>. <i>finegoldii</i>, or stools from WT mice as a control, and also treated with DSS. (<b>B</b>) Mice were monitored over time for survival, change in body weight, and stool scores and rectal bleeding. (<b>C</b>) Gross rectal bleeding on day 10 in mice gavaged with <i>P</i>. <i>falsenii</i>, or <i>P</i>. <i>distasonis</i>, or <i>B</i>. <i>eggerthii</i>, but not in mice gavaged with <i>A</i>. <i>finegoldii</i> or stools from WT mice. (<b>D</b>) Representative hematoxylin-eosin stained sections from day 9 of the colons from mice gavaged with bacteria or WT stools or from untreated mice as indicated; BL, blood; EP, epithelial cells; LP, lamina propria; G, goblet cells; MM, muscularis mucosa; SM, submucosa; and IN, inflammatory cell infiltrations are indicated; size bar = 100 μm. (<b>E</b>) Severity of histopathological changes in the colon of mice gavaged with <i>P</i>. <i>falsenii</i> (Pf), or <i>P</i>. <i>distasonis</i> (Pd), or <i>B</i>. <i>eggerthii</i> (Be), or <i>A</i>. <i>finegoldii</i> (Af), or stools from WT mice and treated with DSS. The results are means ± SEM of 6 (in B) or 4 (in E) mice/group; significance of differences: *, <i>P</i><0.05; **, <i>P</i><0.001; as indicated (in B) or <i>versus</i> WT (in E); #, <i>P</i><0.05 Af <i>versus</i> Pf, Pd, and Be (all <i>P</i><0.001 for Af <i>versus</i> Pf and Be, except for hyperplasia).</p