Erika Banchio

Total Phenolic Content, Radical Scavenging Properties, and Essential Oil Composition of Origanum Species from Different Populations

The aim of this work was to compare the antiradical activity, total phenol content (TPC), and essential oil composition of Origanum vulgare spp. virens, Origanum x applii, Origanum x majoricum, and O. vulgare spp. vulgare cultivated in Argentina in different localities. The experiment was conducted in the research station of La Consulta (INTA-Mendoza), the research station of Santa Lucia (INTA-San Juan), and Agronomy Faculty of National University of La Pampa, from 2007 to 2008. The composition of the essential oils of oregano populations was independent of cultivation conditions. In total, 39 compounds were identified in essential oils of oregano from Argentina by means of GC-MS. Thymol and trans-sabinene hydrate were the most prominent compounds, followed by gamma-terpinene, terpinen-4-ol, and alpha-terpinene. O. vulgare vulgare is the only Origanum studied which is rich in gamma-terpinene. Among tested oregano, O. x majoricum showed the highest essential oil content, 3.9 mg g(-1) dry matter. The plant extract of O. x majoricum had greater total phenol content values, 19.36 mg/g dry weight, than the rest of oregano studied. To find relationships among TPC, free radical scavenging activity (FRSA), and climate variables, canonical correlations were calculated. The results obtained allow us to conclude that 70% of the TPC and FRSA variability can be explained by the climate variables (R(2) = 0.70; p = 8.3 x 10(-6)), the temperature being the most important climatic variable.

Competitiveness of a Bradyrhizobium sp. Strain in Soils Containing Indigenous Rhizobia

The success of rhizobial inoculation on plant roots is often limited by several factors, including environmental conditions, the number of infective cells applied, the presence of competing indigenous (native) rhizobia, and the inoculation method. Many approaches have been taken to solve the problem of inoculant competition by naturalized populations of compatible rhizobia present in soil, but so far without a satisfactory solution. We used antibiotic resistance and molecular profiles as tools to find a reliable and accurate method for competitiveness assay between introduced Bradyrhizobium sp. strains and indigenous rhizobia strains that nodulate peanut in Argentina. The positional advantage of rhizobia soil population for nodulation was assessed using a laboratory model in which a rhizobial population is established in sterile vermiculite. We observed an increase in nodule number per plant and nodule occupancy for strains established in vermiculite. In field experiments, only 9% of total nodules were formed by bacteria inoculated by direct coating of seed, whereas 78% of nodules were formed by bacteria inoculated in the furrow at seeding. In each case, the other nodules were formed by indigenous strains or by both strains (inoculated and indigenous). These findings indicate a positional advantage of native rhizobia or in-furrow inoculated rhizobia for nodulation in peanut.

Systemic Induction of Monoterpene Biosynthesis in Origanum × majoricum by Soil Bacteria

Italian oregano (Origanumxmajoricum) was subjected to root system inoculation with three species of plant growth-promoting rhizobacteria (PGPRs) (Pseudomonas fluorescens, Bacillus subtilis, Azospirillum brasilense), and essential oil (EO) content and plant growth were measured. Composition of monoterpenes, a major EO component, was analyzed qualitative and quantitatively by gas chromatography. Total EO yield for plants inoculated with P. fluorescens or A. brasilense was 3.57 and 3.41 microg/mg fresh weight, respectively, approximately 2.5-fold higher than controls, without change of quantitative oil composition. The major EO compounds, cis- and trans-sabinene hydrate, gamma-terpinene, carvacrol, and thymol, showed increased biosynthesis. Carvacrol was the only terpene showing significant increase of R% in plants inoculated with A. brasilense. Plant growth parameters (shoot and root fresh and dry weights, numbers of leaves and nodes) were evaluated. Shoot fresh weight was significantly increased by all three PGPR species, but only P. fluorescens and A. brasilense increased root dry weight. These two species have clear commercial potential for economic cultivation of O.xmajoricum. Knowledge of the factors affecting yield and accumulation of monoterpenes is essential for improving production of these economically important plant compounds.

Phytochemical Induction by Herbivores Could Affect Quality of Essential Oils from Aromatic Plants

Plant tissues may show chemical changes following herbivory. In aromatic plants such changes could affect the specific compounds on which commercial exploitation is based. This possibility was analyzed for Mintosthachys mollis, a member of the Lamiaceae native to Central Argentina with medicinal and aromatic uses in the region, and two types of insect herbivores: a leaf miner and a gall insect. Analysis of the essential oils of mined/undamaged leaves, as well as leaves from stems with and without galls, revealed changes in concentrations of the two main monoterpenes. A decrease in pulegone concentration was associated with both types of insect damage, whereas menthone increased significantly only in mined leaves. Inducible chemical changes in aromatic and medicinal plants may be common and widespread; their economic implications deserve investigation.

Molecular diversity of peanut-nodulating rhizobia in soils of Argentina.

RSα sequencing is a valuable tool for identification of bacterial strains, and for evaluating the genetic structure of indigenous rhizobial populations. The purpose of this study was to evaluate, qualitatively, the presence or absence of RSα fragment in peanut‐nodulating strains isolated from plants grown at four sites in central Argentina. RSα fragment was found in only three of 26 indigenous strains, and in one of three inoculant strains analyzed. In contrast to results from studies of other symbiotic nitrogen‐fixing bacteria, such as soybean‐nodulating strains, no correlation was found between generation time and presence of RSα sequence. Phylogenetic analysis of the 16S rRNA gene sequence grouped peanut‐nodulating strains into two clusters, Bradyrhizobium japonicum vs. B. elkanii, and showed divergence among strains positive for RSα sequence. Our results confirm the genetic diversity previously reported for various peanut‐nodulating rhizobial strains, and indicate that the RSα fragment is not applicable as a marker or tool for competition assays at the field or ecological level. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of Plant Growth-Promoting Effects of Fluorescent Pseudomonas Strains Isolated from Mentha piperita Rhizosphere and Effects of Their Volatile Organic Compounds on Essential Oil Composition

Many species or strains of the genus Pseudomonas have been characterized as plant growth promoting rhizobacteria (PGPR). We used a combination of phenotypic and genotypic techniques to analyze the community of fluorescent Pseudomonas strains in the rhizosphere of commercially grown Mentha piperita (peppermint). Biochemical techniques, Amplified rDNA Restriction Analysis (ARDRA), and 16S rRNA gene sequence analysis revealed that the majority of the isolated native fluorescent strains were P. putida. Use of two Repetitive Sequence-based PCR (rep-PCR) techniques, BOX-PCR and ERIC-PCR, allowed us to evaluate diversity among the native strains and to more effectively distinguish among them. PGPR activity was tested for the native strains and reference strain P. fluorescens WCS417r. Micropropagated M. piperita plantlets were exposed to microbial volatile organic compounds (mVOCs) emitted by the bacterial strains, and plant biomass parameters and production of essential oils (EOs) were measured. mVOCs from 11 of the native strains caused an increase in shoot fresh weight. mVOCs from three native strains (SJ04, SJ25, SJ48) induced changes in M. pierita EO composition. The mVOCs caused a reduction of metabolites in the monoterpene pathway, for example menthofuran, and an increase in menthol production. Menthol production is the primary indicator of EO quality. The mVOCs produced by native strains SJ04, SJ25, SJ48, and strain WCS417r were analyzed. The obtained mVOC chromatographic profiles were unique for each of the three native strains analyzed, containing varying hydrocarbon, aromatic, and alogenic compounds. The differential effects of the strains were most likely due to the specific mixtures of mVOCs emitted by each strain, suggesting a synergistic effect occurs among the compounds present.

Anatomical, Morphological, and Phytochemical Effects of Inoculation with Plant Growth- Promoting Rhizobacteria on Peppermint (Mentha piperita)

Plant growth-promoting rhizobacteria (PGPR) generally exert their effects through enhancement of plant nutrient status and/or phytohormone production. The effects of PGPR on aromatic plant species are poorly known. We measured plant growth parameters, chlorophyll content, trichome density, stomatal density, and levels of secondary metabolites in peppermint (Mentha piperita) seedlings inoculated with PGPR strains Bacillus subtilis GB03, Pseudomonas fluorescens WCS417r, P. putida SJ04, or a combination of WCS417r + SJ04. The treated plants, in comparison with controls, showed increases in shoot biomass, root biomass, leaf area, node number, trichome density, and stomatal density, and marked qualitative and quantitative changes in monoterpene content. Improved knowledge of the factors that control or affect biosynthesis of secondary metabolites and monoterpene accumulation will lead to strategies for improved cultivation and productivity of aromatic plants and other agricultural crops without the use of chemical fertilizers or pesticides.

Aromatic Plants of Yungas Part I: Chemical Composition of the Essential Oil of Hyptis floribunda Briq. Ex. Micheli

Abstract The essential oil of Hyptis floribunda Briq. ex. Micheli collected from Oran, Argentina (Yungas area) was analyzed by GC and GC/MS. In the oil, 17 compounds were identified. The oil was found to be rich in sesquiterpene hydrocarbons (74.6%), the most abundant being bicyclogennacrene (37.8%), γ-cadinene (17.9%) and δ-cadinene (10.7%). Elemol (11.4%) was the major oxygenated sesquiterpene.

Systemic Induction of Secondary Metabolite Biosynthesis in Medicinal Aromatic Plants Mediated by Rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) are increasingly accepted and important in agricultural production worldwide. There is rising demand for food produced without synthetic chemical products, for sustainable agricultural methods, and for a holistic vision of development associated with environmental protection. In this study, we found that the effects of PGPR inoculation and volatile organic compound (VOC) emission on various aromatic plant species (Origanum majorana [sweet marjoram], Origanum x majoricum [Italian oregano], Ocimum basilicum [sweet basil], Tagetes minuta [wild marigold], Mentha x piperita [peppermint]) varied depending on the inoculated strain (Pseudomonas fluorescens WCS417r, Azospirillum brasilense Sp7, Bacillus subtilis GB03, or their combination). PGPR-inoculated plant species display host response specificity. The responses we observed were diverse. In most cases, the growth parameters evaluated (leaf number, shoot fresh weight, root dry weight) were significantly increased by P. fluorescens inoculation. Essential oil (EO) yield was increased to varying degrees in O. majorana, O. x majoricum, and T. minuta inoculated with P. fluorescens. Monoterpene accumulation was increased ~2-fold in most cases and 24-fold in O. majorana.

Production of Volatile Organic Compounds in PGPR

Bacteria affect plant growth through several mechanisms. A recently described mechanism involves the production of microbial volatile organic compounds (mVOCs), which are gaseous molecules capable of interacting with plants in the soil environment. mVOCs may promote plant growth directly, through induced resistance systemic (ISR), or indirectly through suppression of phytopathogens (biocontrol). In this chapter, we describe several experimental designs for evaluation of mVOCs effects on plant growth, ISR or biocontrol mechanisms; potential problems with the methodologies and possible solutions. To date, relatively few mVOCs have been identified and their effects on plant growth characterized. Generally, the effect observed on a particular plant–bacterium interaction was attributed to the pool of mVOCs produced, like an evidence of synergism among chemical compounds.