Development and evaluation of tools to analyze the response of tomato (Solanum lycopersicum L.) rootstocks under nitrogen deficiency in a breeding context

Root system architecture contributes to crop performance under biotic and abiotic stresses but is, at the same time, considerably affected by adverse conditions. It is therefore receiving increasing attention from the scientific community, which is developing root system ideotypes for given environmental constraints and evaluation tools for breeders. The challenge is fraught with many practical difficulties, however, which comprise the observation and the quantification of root system architecture. This thesis was conducted in the frame of the RootOPower EU project that aims to develop a suite of tools to enhance agronomic stability and sustainability of crops under combined abiotic stresses. We used a novel high throughput phenotyping platform in aeroponics to investigate the genetic determinism of root growth and development in tomato (Solanum lycopersicon) under nitrogen deficiency, in relation with biomass production. A segregating population of 144 recombinant inbred lines generated from an interspecific cross between S. lycopersicum and S. pimpinellifolium has been used for the QTL analysis of root system architecture and biomass production under control and nitrogen deficient conditions. To achieve the required throughput, we evaluated different optical methods to assess plant nitrogen content and we validated near-infrared microscopy to estimate the nitrogen content of small leaf samples. We also deployed a model-based formalism of root system architecture to perform in-depth analysis of genetic correlations between traits. The RIL population, used as rootstock, revealed interesting shoot responses to the root genotype. QTLs were observed for three major processes which shape root system architecture, viz. root growth rate, root branching and root tropism.(SC - Sciences) -- UCL, 201

Determination by near infrared microscopy (NIRM) of nitrogen and carbon content of tomato (Solanum lycopersicum L.) leaf powder

Near infrared microscopy (NIRM) has been developed as a rapid technique to predict the chemical composition of foods, reduce analytical costs and time and ease sample preparation. In this study, NIRM has been evaluated as an alternative to classical chemical analysis to determine the nitrogen and carbon content of small samples of tomato (Solanum lycopersicum L.) leaf powder. Near infrared spectra were obtained by NIRM for independent leaf samples collected on 216 plants grown under six different levels of nitrogen. From these, 30 calibration and 30 validation samples covering the spectral range of the whole set were selected and their nitrogen and carbon contents were determined by a reference method. The calibration model obtained for nitrogen content proved to be excellent, with a coefficient of determination in calibration (R(2)c) higher than 0.9 and a ratio of performance to deviation (RPDc) higher than 3. Statistical indicators of prediction using the validation set were also very high (R(2)p values > 0.90). However, the calibration model obtained for carbon content was much less satisfactory (R(2)c < 0.50). NIRM appears as a promising and suitable tool for a rapid, non-destructive and reliable determination of nitrogen content of tiny samples of tomato leaf powder

Determination by near infrared microscopy of the nitrogen and carbon content of tomato (Solanum lycopersicum L.) leaf powder

Near infrared microscopy (NIRM) has been developed as a rapid technique to predict the chemical composition of foods, reduce analytical costs and time and ease sample preparation. In this study, NIRM has been evaluated as an alternative to classical chemical analysis to determine the nitrogen and carbon content of small samples of tomato (Solanum lycopersicum L.) leaf powder. Near infrared spectra were obtained by NIRM for independent leaf samples collected on 216 plants grown under six different levels of nitrogen. From these, 30 calibration and 30 validation samples covering the spectral range of the whole set were selected and their nitrogen and carbon contents were determined by a reference method. The calibration model obtained for nitrogen content proved to be excellent, with a coefficient of determination in calibration (R²c) higher than 0.9 and a ratio of performance to deviation (RPDc) higher than 3. Statistical indicators of prediction using the validation set were also very high (R²p values > 0.90). However, the calibration model obtained for carbon content was much less satisfactory (R²c < 0.50). NIRM appears as a promising and suitable tool for a rapid, non-destructive and reliable determination of nitrogen content of tiny samples of tomato leaf powder

Increasing fluctuations of soil salinity affect seedling growth performances and physiology in three Neotropical mangrove species

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity. Aims and methods The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl). Results Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production. Conclusions This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings’ morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage

Determination by near infrared microscopy (NIRM) of nitrogen content in tomato(Solanum lycopersicum L.) leaf powder

The chemical analysis of plant samples is time consuming and expensive. Near infrared spectroscopy techniques were developed, inter alia, as a rapid technique to predict the chemical composition of foods. In this study near infrared microscopy (NIRM) was used for the first time to determine the nitrogen content in reduced quantity of tomato leaf powder. A total of 72 tomatoes sample corresponding to 6 groups of 12 plants under 6 levels of nitrogen concentration. This experiment was performed with 3 simultaneous repetitions (216 samples submitted to analysis in total). For the model constructed, 30 samples were used in the calibration stage and 30 samples were used in the independent validation stage. The calibration and validation sets analyzed were chosen to cover the full range of spectra variation obtained from the NIRM analysis. The nitrogen content was determined by combustion according to the Dumas method. Standard error of calibration (SEC), coefficient of determination at the calibration stage (R²c) and ratio of performance to deviation (RPDc) were excellent (R²c values higher than 0.90 and RPDc values higher than 3). The coefficient of determination at the validation stage (R²p) and standard error of prediction were excellent (R²p values higher than 0.90). A model using all the information from the samples of the calibration and validation sets was constructed to improve the accuracy of the future prediction. The study indicated that NIRM is a promising and suitable tool for a rapid, non-destructive and reliable determination of the chemical composition in tomato leaf powder

impact of cadmium and zinc on root system of Lolium perenne and Trifolium repens

Urbanization, industrialization and agricultural practices have resulted in soil contamination with heavy metals in many world areas. Phytostabilisation is an emerging solution to limit pollutant dispersion out of the contaminated area without expensive costs. However, because of the heavy metal phytotoxicity, the implementation of a plant cover could be jeopardized. Therefore, we assessed the impact of Cd and Zn, 2 common metal pollutants, on the setting up of root system of 2 plant models, Lolium perenne and Trifolium repens. After 1 month of metal application, we measured the root mass, length and diameter according to the depth thanks to scanner and image analysis. These results were linked to root metal concentrations. We focused also on ultrastructural modifications by means of histochemical analyses and on quantification of structural polysaccharides and lignin through Van Soest global method and lignin staining. Drastic alterations of root system were highlighted, especially for Lolium perenne

Comparative analysis of Cd and Zn impacts on root distribution and morphology of Lolium perenne and Trifolium repens: implications for phytostabilization

Backgrounds and aims The phytostabilization potential of plants is a direct function of their root systems. An experimental design was developed to investigate the impact of Cd and Zn on the root distribution and morphology of Lolium perenne and Trifolium repens. Methods Seedlings were transplanted into columns filled with washed quartz and irrigated daily with Cdor Zn-containing nutrient solutions during 1 month. Root biomass, root length density (RLD) and diameter were subsequently quantified as a function of depth. Pot experiments were also performed to quantify metal, lignin and structural polysaccharides concentrations as well as cell viability. Results Lolium perenne accumulated Cd and Zn in the roots whereas T. repens was unable to restrict heavy metal translocation. Cadmium and Zn reduced rooting depth and RLDbut induced thick shoot-borne roots in L. perenne. Cd-induced root swelling was related to lignification occurring in the exodermis and parenchyma of central cylinder. Hemicelluloses and lignin did not play a key role in root metal retention. Cadmium slightly reduced mean root cell viability whereas Zn increased this parameter in comparison to Cd. Conclusions Even though plant species like Lolium perenne and Trifolium repens may appear suitable for a phytostabilization scheme based on their shoot metal tolerance, exposure to toxic heavy metals drastically impairs their root distribution. This could jeopardize the setting up of phytostabilization trials. The metal-induced alterations of root system properties are clearly metal- and speciesspecific. At sites polluted with multiple metals, it is therefore recommended to first test their impact on the root system of multiple plant species so as to select the most appropriate species for each site

Relationships between root system morphology and biomass production under nitrogen deficiency in grafted tomato

This project aims to improve our understanding of the architectural response of the tomato (S. lycopersicon) root system to low nitrogen input and to assess the quantitative genetic variability of this response in order to develop rootstocks that enhance the agronomic stability and sustainability of tomato under low nitrogen

Effets des variations saisonnières sur les performances de croissance et la physiologie des palétuviers des Antilles

Les Mangroves des Antilles sont soumises aux variations saisonnières du climat. Les différences de précipitations entre la saison des pluies et la saison sèche induisent de fortes variations édaphiques (inondation, salinité). Les projections du changement climatique prévoient une augmentation de la saisonnalité dans les Antilles. Les saisons sèches deviendraient encore plus sèches et les variations édaphiques plus importantes. Ces nouvelles conditions pourraient être des contraintes physiologiques potentielles pour les palétuviers