Sélectionner et cultiver Stevia rebaudiana Bertoni en milieu tempéré : exploration de la variabilité de la teneur et de la composition en glycosides de steviol

Stevia rebaudiana Bertoni, une herbe vivace de la famille des Asteraceae originaire du Paraguay, est d'un intérêt croissant en tant que source d’édulcorants naturels acoloriques, les glycosides de steviol (SVglys). Ces diterpénoïdes sont organisés autour d’un noyau de steviol et diffèrent par le nombre et la nature d’unités de sucre liées à ce noyau. Ils sont accumulés à des concentrations allant de 4 à 20% de la masse sèche des feuilles, selon le génotype, le stade phénologique et les conditions de croissance. S. rebaudiana apparaît comme une espèce alternative prometteuse en Europe, mais nécessite au préalable une évaluation de ses besoins en culture et un travail de sélection variétale afin d’optimiser la teneur et la composition en SVglys en milieu tempéré. L'objectif de ce travail était d'étudier les sources de variabilité génotypique et environnementale pour l’accumulation en SVglys et la production de biomasse foliaire. Une forte variabilité génotypique a été observée pour la composition en SVglys et, à un degré moindre, pour la teneur en SVglys ainsi que pour des critères morphologiques et de précocité. L’environnement (fertilisation, durée du jour, stade phénologique, âge de la plante) a également eu un effet sur l’élaboration de la biomasse foliaire et sur la teneur en SVglys, alors que la composition en SVglys a été moins affectée par ces facteurs. Ces résultats suggèrent des mécanismes biochimiques et génétiques complexes régissant la voie de biosynthèse des SVglys. Ils laissent également entrevoir des possibilités de sélection variétale et donnent des indications sur les exigences de S. rebaudiana pour sa culture sous nos climats. ABSTRACT : Stevia rebaudiana Bertoni, a perennial shrub of the Asteraceae family originating from Paraguay, is of increasing interest as a source of zero-calorie natural sweeteners: the steviol glycosides (SVglys). These diterpenoids differ in the number and the nature of sugar units bound to a steviol skeleton. They accumulate in leaves at concentrations ranging from 4 to 20%, according to genotype, phenological stage, and growth conditions. S. rebaudiana appears as a promising alternative culture in Europe, but requires investigations to assess its cultivation plant requirements and a breeding effort to optimize SVgly content and composition under temperate climate. The objective of this work was to explore the sources of genotypic and environmental variability for SVglys accumulation and leaf biomass production. High genotypic variability has been observed for SVgly composition and, to a lesser extent, for SVgly content as well as for morphological criteria and precocity. Leaf biomass and SVgly content varied also with the environment (fertilization, daylength, phenological stage) and over the years in perennial culture, while SVgly composition was less affected by these factors. These results suggested complex biochemical and genetic mechanisms regulating SVglys biosynthetic pathway. In parallel they revealed breeding potentialities and gave indications on S. rebaudiana requirements for its cultivation under temperate climate

Sélectionner et cultiver Stevia rebaudiana Bertoni en milieu tempéré : exploration de la variabilité de la teneur et de la composition en glycosides de steviol

Stevia rebaudiana Bertoni, une herbe vivace de la famille des Asteraceae originaire du Paraguay, est d'un intérêt croissant en tant que source d’édulcorants naturels acoloriques, les glycosides de steviol (SVglys). Ces diterpénoïdes sont organisés autour d’un noyau de steviol et diffèrent par le nombre et la nature d’unités de sucre liées à ce noyau. Ils sont accumulés à des concentrations allant de 4 à 20% de la masse sèche des feuilles, selon le génotype, le stade phénologique et les conditions de croissance. S. rebaudiana apparaît comme une espèce alternative prometteuse en Europe, mais nécessite au préalable une évaluation de ses besoins en culture et un travail de sélection variétale afin d’optimiser la teneur et la composition en SVglys en milieu tempéré. L'objectif de ce travail était d'étudier les sources de variabilité génotypique et environnementale pour l’accumulation en SVglys et la production de biomasse foliaire. Une forte variabilité génotypique a été observée pour la composition en SVglys et, à un degré moindre, pour la teneur en SVglys ainsi que pour des critères morphologiques et de précocité. L’environnement (fertilisation, durée du jour, stade phénologique, âge de la plante) a également eu un effet sur l’élaboration de la biomasse foliaire et sur la teneur en SVglys, alors que la composition en SVglys a été moins affectée par ces facteurs. Ces résultats suggèrent des mécanismes biochimiques et génétiques complexes régissant la voie de biosynthèse des SVglys. Ils laissent également entrevoir des possibilités de sélection variétale et donnent des indications sur les exigences de S. rebaudiana pour sa culture sous nos climats

Breeding and cultivation of Stevia rebaudiana Bertoni in temperate areas : exploration of steviol glycoside content and composition variability

Stevia rebaudiana Bertoni, une herbe vivace de la famille des Asteraceae originaire du Paraguay, est d'un intérêt croissant en tant que source d’édulcorants naturels acoloriques, les glycosides de steviol (SVglys). Ces diterpénoïdes sont organisés autour d’un noyau de steviol et diffèrent par le nombre et la nature d’unités de sucre liées à ce noyau. Ils sont accumulés à des concentrations allant de 4 à 20% de la masse sèche des feuilles, selon le génotype, le stade phénologique et les conditions de croissance. S. rebaudiana apparaît comme une espèce alternative prometteuse en Europe, mais nécessite au préalable une évaluation de ses besoins en culture et un travail de sélection variétale afin d’optimiser la teneur et la composition en SVglys en milieu tempéré. L'objectif de ce travail était d'étudier les sources de variabilité génotypique et environnementale pour l’accumulation en SVglys et la production de biomasse foliaire. Une forte variabilité génotypique a été observée pour la composition en SVglys et, à un degré moindre, pour la teneur en SVglys ainsi que pour des critères morphologiques et de précocité. L’environnement (fertilisation, durée du jour, stade phénologique, âge de la plante) a également eu un effet sur l’élaboration de la biomasse foliaire et sur la teneur en SVglys, alors que la composition en SVglys a été moins affectée par ces facteurs. Ces résultats suggèrent des mécanismes biochimiques et génétiques complexes régissant la voie de biosynthèse des SVglys. Ils laissent également entrevoir des possibilités de sélection variétale et donnent des indications sur les exigences de S. rebaudiana pour sa culture sous nos climats.Stevia rebaudiana Bertoni, a perennial shrub of the Asteraceae family originating from Paraguay, is of increasing interest as a source of zero-calorie natural sweeteners: the steviol glycosides (SVglys). These diterpenoids differ in the number and the nature of sugar units bound to a steviol skeleton. They accumulate in leaves at concentrations ranging from 4 to 20%, according to genotype, phenological stage, and growth conditions. S. rebaudiana appears as a promising alternative culture in Europe, but requires investigations to assess its cultivation plant requirements and a breeding effort to optimize SVgly content and composition under temperate climate. The objective of this work was to explore the sources of genotypic and environmental variability for SVglys accumulation and leaf biomass production. High genotypic variability has been observed for SVgly composition and, to a lesser extent, for SVgly content as well as for morphological criteria and precocity. Leaf biomass and SVgly content varied also with the environment (fertilization, daylength, phenological stage) and over the years in perennial culture, while SVgly composition was less affected by these factors. These results suggested complex biochemical and genetic mechanisms regulating SVglys biosynthetic pathway. In parallel they revealed breeding potentialities and gave indications on S. rebaudiana requirements for its cultivation under temperate climate

Nitrogen Limitation Alters Biomass Production but Enhances Steviol Glycoside Concentration in Stevia rebaudiana Bertoni

The need for medicinal and aromatic plants for industrial uses creates an opportunity for farmers to produce alternative crops. Stevia rebaudiana Bertoni, a perennial shrub originat- ing from Paraguay, is of increasing interest as a source of zero-calorie natural sweeteners: the steviol glycosides (SVglys). The aim of this study was to investigate the relevance of nitrogen (N) supply for leaf yield and for SVgly concentrations in leaves, which are the two major components of S . rebaudiana productivity. In this regard, the relationship between leaf N concentration, CO 2 assimilation, leaf production and SVgly accumulation was investi- gated. The experiments were conducted consecutively in growth-chamber (CC: controlled conditions), in greenhouse (SCC: semi-controlled conditions) and in field conditions (FC) on two genotypes. In CC and SCC, three levels of N fertilization were applied. Plants were grown on four locations in the FC experiment. Both N supply (CC and SCC) and location (FC) had a significant effect on N content in leaves. When light was not limiting (SCC and FC) N content in leaves was positively correlated with CO 2 assimilation rate and biomass accumulation. Irrespective of the growth conditions, N content in leaves was negatively correlated with SVgly content. However, increased SVgly content was correlated with a decreased ratio of rebaudioside A over stevioside. The evidence that the increased SVgly accumulation compensates for the negative effect on biomass production suggests that adequate SVgly productivity per plant may be achieved with relatively low fertilization

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Can species distribution models really predict the expansion of invasive species?

<div><p>Predictive studies are of paramount importance for biological invasions, one of the biggest threats for biodiversity. To help and better prioritize management strategies, species distribution models (SDMs) are often used to predict the potential invasive range of introduced species. Yet, SDMs have been regularly criticized, due to several strong limitations, such as violating the equilibrium assumption during the invasion process. Unfortunately, validation studies–with independent data–are too scarce to assess the predictive accuracy of SDMs in invasion biology. Yet, biological invasions allow to test SDMs usefulness, by retrospectively assessing whether they would have accurately predicted the latest ranges of invasion. Here, we assess the predictive accuracy of SDMs in predicting the expansion of invasive species. We used temporal occurrence data for the Asian hornet <i>Vespa velutina nigrithorax</i>, a species native to China that is invading Europe with a very fast rate. Specifically, we compared occurrence data from the last stage of invasion (independent validation points) to the climate suitability distribution predicted from models calibrated with data from the early stage of invasion. Despite the invasive species not being at equilibrium yet, the predicted climate suitability of validation points was high. SDMs can thus adequately predict the spread of <i>V</i>. <i>v</i>. <i>nigrithorax</i>, which appears to be—at least partially–climatically driven. In the case of <i>V</i>. <i>v</i>. <i>nigrithorax</i>, SDMs predictive accuracy was slightly but significantly better when models were calibrated with invasive data only, excluding native data. Although more validation studies for other invasion cases are needed to generalize our results, our findings are an important step towards validating the use of SDMs in invasion biology.</p></div

Is <i>V</i>. <i>v</i>. <i>nigrithorax</i> niche at equilibrium in its invaded range?

<p>Climatic niche occupied by <i>V</i>. <i>v</i>. <i>nigrithorax</i> in its European invasion range during 2004–2010 (a) and 2011–2015 (b) along the first two axes of the PCA (see (c) for details), showing an evolution during the two periods. Grey shading depicts the occurrence density of the species. The solid and dashed contour lines represent 100% and 50% respectively of the available (background) climate in Europe. (c) Contribution of the climate variables to the first two axes of the PCA (bio1: annual mean temperature, bio4: temperature seasonality, bio5: mean temperature of the warmest month, bio6: mean temperature of the coldest month, bio12: annual precipitation, bio13: precipitation of the wettest month, bio14: precipitation of the driest month, and bio15: precipitation seasonality). (d) Histograms showing the observed niche overlap D (D = 0.45) (bars with a diamond) and simulated niche overlaps (grey bars) on which tests of niche equivalency and niche similarity were calculated from 1000 iterations [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193085#pone.0193085.ref054" target="_blank">54</a>]: niches are similar but not equivalent.</p

SDMs predictions and predictive accuracy.

<p>(a) Climate suitability gradient map, from 0 to 1, predicted by the model (current ensemble consensus) using invasive data from 2004 to 2010 (blue points). Red points represent invasive data recorded after 2010 (2011–2015) that are used to evaluate the model. The dotted circle around the first invasion data (blue triangle) delimits all points that are within 150km of the first invasion data. (b) Climate suitability of all possible points (between 150 and 850 km of the first invasion data) according to their distance to the first invasion (grey points). The full line represents the median climate suitability according to the distance, whereas the dotted lines represent the 10%, 30%, 70% and 90% quantiles (blue and red points as above). Evaluation (red) points above the median have a higher predicted suitability than expected given their distance to the first invasion occurrence. (c) Boxplots representing the range of climate suitability values for all possible points (grey) and invasive data (calibration data in blue and evaluation data in red) depending on their distance to the first invasion data. In all three cases, the predicted suitability of evaluation points is lower than the predicted suitability of calibration points, but is higher than expected given their distance to the first invasion occurrence (all possible points, in grey).</p

Comparing SDMs predictive accuracy when trained with or without native data.

<p>Percentiles of validation points (further than 150km from the first invasion record) depending on whether or not native data was accounted for to calibrate the models and on the cut-off year that was used to split the invasive data into calibration and evaluation data. Percentiles are obtained by comparing the predicted climate suitability of a given validation point to the distribution of climate suitability values of all points being at the same distance from the first invasion record than the validation point (i.e., grey points in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193085#pone.0193085.g002" target="_blank">Fig 2B</a>). Percentiles higher than 50^th thus mean that the predicted climate suitability of the validation point is higher than expected given its distance to the first invasion record. For all cut-off years, paired t-test were computed to assess the difference between models with and without native data: a red star indicates significantly higher values (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193085#pone.0193085.s001" target="_blank">S1 Table</a>).</p

Predicting the invasion risk by the alien bee-hawking Yellow-legged hornet Vespa velutina nigrithorax across Europe and other continents with niche models

a b s t r a c t Vespa velutina nigrithorax, an Asian bee-hawking hornet, has been unintentionally introduced in southwestern France before 2004 and is currently widely spreading across the country. Its arrival in northern Spain was reported in 2010. The potential invasion risk of the species is assessed using climatic suitability models. We used eight different modelling techniques within an ensemble forecast framework to show that the invasion success in south-western France could have been predicted using data from the native Asian range of the species, while we further used data from both the native and invaded ranges (including a recently established population in Korea) to better predict its potential invasion range across all continents. Results are discussed in terms of the interest of ecological niche modelling for invasion biology, realised niche of the invasive wasp, potential threats to native entomofauna and economic impacts of this new predator. A particular attention is paid to beekeeping activities that are nowadays already threatened by a wide panel of adversary factors