Ecological interactions affect the bioactivity of medicinal plants.

Essential oils produced by medicinal plants possess important bioactive properties (antibacterial, antioxidant) of high value for human society. Pollination and herbivory can modify the chemical defences of plants and therefore they may influence the bioactivity of essential oils. However, the effect of ecological interactions on plant bioactivity has not yet been evaluated. We tested the hypothesis that cross-pollination and simulated herbivory modify the chemical composition of essential oils, improving the bioactive properties of the medicinal plant Lepechinia floribunda (Lamiaceae). Through controlled experiments, we showed that essential oils from the outcrossed plant progeny had a higher relative abundance of oxygenated terpenes and it almost doubled the bacteriostatic effect on Staphylococcus aureus, compared to inbred progeny (i.e., progeny produced in absence of pollinators). Herbivory affected negatively and positively the production of rare compounds in inbred and outcrossed plants, respectively, but its effects on bioactivity still remain unknown. We show for the first time that by mediating cross-pollination (indirect ecosystem service), pollinators can improve ecosystem services linked to the biological activity of plant's essential oils. We stress the importance of the qualitative component of pollination (self, cross); an aspect usually neglected in studies of pollination services.

Population Genomics Provide Insights into the Global Genetic Structure of Colletotrichum graminicola, the Causal Agent of Maize Anthracnose.

Understanding the genetic diversity and mechanisms underlying genetic variation in pathogen populations is crucial to the development of effective control strategies. We investigated the genetic diversity and reproductive biology of Colletotrichum graminicola isolates which infect maize by sequencing the genomes of 108 isolates collected from 14 countries using restriction site-associated DNA sequencing (RAD-seq) and whole-genome sequencing (WGS). Clustering analyses based on single-nucleotide polymorphisms revealed three genetic groups delimited by continental origin, compatible with short-dispersal of the pathogen and geographic subdivision. Intra- and intercontinental migration was observed between Europe and South America, likely associated with the movement of contaminated germplasm. Low clonality, evidence of genetic recombination, and high phenotypic diversity were detected. We show evidence that, although it is rare (possibly due to losses of sexual reproduction- and meiosis-associated genes) C. graminicola can undergo sexual recombination. Our results support the hypotheses that intra- and intercontinental pathogen migration and genetic recombination have great impacts on the C. graminicola population structure. IMPORTANCE Plant pathogens cause significant reductions in yield and crop quality and cause enormous economic losses worldwide. Reducing these losses provides an obvious strategy to increase food production without further degrading natural ecosystems; however, this requires knowledge of the biology and evolution of the pathogens in agroecosystems. We employed a population genomics approach to investigate the genetic diversity and reproductive biology of the maize anthracnose pathogen (Colletotrichum graminicola) in 14 countries. We found that the populations are correlated with their geographical origin and that migration between countries is ongoing, possibly caused by the movement of infected plant material. This result has direct implications for disease management because migration can cause the movement of more virulent and/or fungicide-resistant genotypes. We conclude that genetic recombination is frequent (in contrast to the traditional view of C. graminicola being mainly asexual), which strongly impacts control measures and breeding programs aimed at controlling this disease.

Can Essential Oils Be a Natural Alternative for the Control of Spodoptera frugiperda? A Review of Toxicity Methods and Their Modes of Action

Spodoptera frugiperda is a major pest of maize crops. The application of synthetic insecticides and the use of Bt maize varieties are the principal strategies used for its control. However, due to the development of pesticide resistance and the negative impact of insecticides on the environment, natural alternatives are constantly being searched for. Accordingly, the objective of this review was to evaluate the use of essential oils (EOs) as natural alternatives for controlling S. frugiperda. This review article covers the composition of EOs, methods used for the evaluation of EO toxicity, EO effects, and their mode of action. Although the EOs of Ocimum basilicum, Piper marginatum, and Lippia alba are the most frequently used, Ageratum conyzoides, P. septuplinervium. O. gratissimum and Siparuna guianensis were shown to be the most effective. As the principal components of these EOs vary, then their mode of action on the pest could be different. The results of our analysis allowed us to evaluate and compare the potential of certain EOs for the control of this insect. In order to obtain comparable results when evaluating the toxicity of EOs on S. frugiperda, it is important that methodological issues are taken into account.

Effect of Selected Volatiles on Two Stored Pests: The Fungus Fusarium verticillioides and the Maize Weevil Sithophilus zeamais.

New agronomic practices and technology enabled Argentina a larger production of cereal grains, reaching a harvest yield of 26.5 million metric tons of maize, of which, about 40% was exported. However, much of the maize production is lost annually by the attack of fungi and insects (2.6 million tons). In this study, the antifungal effect of selected volatiles on Fusarium verticillioides, its mycotoxin production, and the repellent and insecticidal activities against the weevill Sithophilus zeamais, an insect vector of F. verticillioides, were evaluated. The compounds tested were (2E)-2-hexenal, (2E)-2-nonenal, (2E,6Z)-2,6-nonadienal, 1-pentanol, 1-hexanol, 1-butanol, 3-methyl-1-butanol, pentanal, 2-decanone, and 3-decanone, which occur in the blend of volatile compounds emitted by various cereal grains. The most active antifungals were the aldehydes (2E)-2-nonenal, (2E)-2-hexenal, and (2E,6Z)-2,6-nonadienal (minimum inhibitory concentration values of <0.03, 0.06, and 0.06 mM, respectively). The occurrence of fumonisin B1 also was prevented because these compounds completely inhibited fungal growth. The best insecticidal fumigant activities against the maize weevil were shown by 2-decanone and 3-decanone (lethal concentration ≤ 54.6 µL/L (<0.28 mM)). Although, all tested compounds showed repellent activity against S. zeamais at a concentration of 4 µL/L, (2E,6Z)-2,6-nonadienal was the most active repellent compound. These results demonstrate the potential of (2E,6Z)-2,6-nonadienal to be used as a natural alternative to synthetic pesticides on F. verticillioides and S. zeamais.

Bioactivities of Ketones Terpenes: Antifungal Effect on F. verticillioides and Repellents to Control Insect Fungal Vector, S. zeamais.

Maize is one the most important staple foods in the world. However, numerous pests, such as fungal pathogens, e.g., Fusarium verticillioides, and insects, such as Sitophlilus zeamais, attack maize grains during storage. Many F. verticillioides strains produce fumonisins, one of the most important mycotoxin that causes toxic effects on human and animal health. This situation is aggravated by the insect fungal vector, Sitophlilus zeamais, which contributes to the dispersal of fungal spores, and through feeding damage, provide entry points for fungal infections. The aim of this study was to evaluate in vitro bioassays, the antifungal activity on F. verticillioides M3125 and repellent effects against S. zeamais of ketone terpenes. In addition, we performed Quantitative structure-activity relationship (Q-SAR) studies between physico-chemical properties of ketone terpenes and the antifungal effect. Thymoquinone was the most active compound against F. verticillioides (Minimum Inhibitory Concentration, MIC: 0.87) affecting the lag phase and the growth rate showing a total inhibition of growth at concentration higher than 2 mM (p < 0.05). The Q-SAR model revealed that the antifungal activity of ketone compounds is related to the electronic descriptor, Pi energy. Thymoquinone showed a strong repellent effect (-77.8 ± 8.5, p < 0.001) against S. zeamais. These findings make an important contribution to the search for new compounds to control two stored pests of maize.

Actividad antifúngica del aceite esencial de cinco especies de Juniperus de Argentina / Antifungal activities of the essential oil of five species of Juniperus from Argentina

The chemical composition of the leaf oils of five Juniperus species (Juniperus sabina L., Juniperus communis Lam., Juniperus scopulorum Sarg., Juniperus virginiana L., Juniperus chinensis L., Cupressaceae) was determined by co-chromatography with authentic samples, GC-MS and Kováts retention indices. Sabinene was the most abundant component in the oils of Juniperus from western Patagonia Argentina. However, limonene and germacrene B constituted 25.1 percent and 11.5 percent of the oil of J. sabina. J. virginiana showed high concentration of alpha-humulene and limonene (31.4 and 15.9 percent respectively), while isobornyl acetate and germacrene B were also the main compounds of J. chinensis. Essential oils extracted of Juniperus were evaluated in vitro for their efficacy against Fusarium verticillioides, Aspergillus flavus, Aspergillus parasiticus, Candida albicans and Rhodotorula infection. Candida albicans was not inhibited for the essential oils of Juniperus. However, F. verticillioides, A. flavus, A. parasiticus and Rhodotorula were inhibited for these oils.

La composición de los aceites esenciales de la hoja de cinco especies de Juniperus (Juniperus sabina L., Juniperus communis Lam., Juniperus scopulorum Sarg., Juniperus virginiana L., Juniperus chinensis L., Cupressaceae), se determinó mediante una co-cromatografía con muestras auténticas de dos columnas de diferente polaridad, CG-EM y los índices de retención de Kovats. El sabineno fue el componente más abundante en los aceites de Juniperus del oeste de la Patagonia Argentina. Sin embargo, el limoneno y el germacreno B son otros componentes importantes del aceite esencial de J. sabina con el 25,1 por ciento y 11,5 por ciento respectivamente. En J. virginiana el alfa-humuleno y el limoneno (con el 31,4 por ciento y 15.9 por ciento respectivamente) mostraron ser también importantes, mientras que el acetato de isobornilo y el germacreno B fueron también los principales componentes de la J. chinensis. Los aceites esenciales extraídos de Juniperus se evaluaron in vitro para determinar su eficacia contra Fusarium verticillioides, Aspergillus flavus, Aspergillus parasiticus, Candida albicans y Rhodotorula. Candida albicans no se inhibió por la acción de los aceites esenciales de Juniperus. Sin embargo, F. verticillioides, A. flavus, A. parasiticus y Rhodotorula fueron inhibidos.

Antifumonisin activity of natural phenolic compounds A structure-property-activity relationship study.

Fumonisin B(1) (FB(1)) is a Fusarium mycotoxin that has received considerable attention from food regulatory agencies, since it shows immunotoxic, neurotoxic, hepatotoxic, nephrotoxic and carcinogenic properties in animals. Although several publications have reported that some natural phenolic compounds can cause a reduction in mycotoxin production, little is known about the molecular properties related to their antitoxigenic activities. The objective of this work was to evaluate which of these molecular properties are important in antifumonisin activity, with this being the first structure-activity relationship study concerning the antimyctoxigenic activity of natural phenolic compounds. The results of the experimental determination of the FB(1) inhibition capacity for ten natural phenolic compounds revealed thymol, carvacrol, and isoeugenol followed by eugenol to be the most active antifumonisin compounds. Lipophilicity, molar refractivity and saturated area were demonstrated to be the molecular properties or descriptors which best explained the antifumonisin activity of these phenolic compounds. A mathematical expression, obtained by QSAR analysis, was able to predict the antifumonisin activity of other structurally related molecules. These findings could provide an important contribution in the search for new compounds with antifumonisin activity.

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.