High-throughput field phenotyping in cereals and implications in plant ecophysiology

[eng] Global climate change effects on agroecosystems together with increasing world population is already threatening food security and endangering ecosystem stability. Meet global food demand with crops production under climate change scenario is the core challenge in plant research nowadays. Thus, there is an urgent need to better understand the underpinning mechanisms of plant acclimation to stress conditions contributing to obtain resilient crops. Also, it is essential to develop new methods in plant research that permit to better characterize non-destructively plant traits of interest. In this sense, the advance in plant phenotyping research by high throughput systems is key to overcome these challenges, while its verification in the field may clear doubts on its feasibility. To this aim, this thesis focused on wheat and secondarily on maize as study species as they make up the major staple crops worldwide. A large panoply of phenotyping methods was employed in these works, ranging from RGB and hyperspectral sensing to metabolomic characterization, besides of other more conventional traits. All research was performed with trials grown in the field and diverse stressor conditions representative of major constrains for plant growth and production were studied: water stress, nitrogen deficiency and disease stress. Our results demonstrated the great potential of leave-to-canopy color traits captured by RGB sensors for in-field phenotyping, as they were accurate and robust indicators of grain yield in wheat and maize under disease and nitrogen deficiency conditions and of leaf nitrogen concentration in maize. On the other hand, the characterization of the metabolome of wheat tissues contributed to elucidate the metabolic mechanisms triggered by water stress and their relationship with high yielding performance, providing some potential biomarkers for higher yields and stress adaptation. Spectroscopic studies in wheat highlighted that leaf dorsoventrality may affect more than water stress on the reflected spectrum and consequently the performance of the multispectral/hyperspectral approaches to assess yield or any other relevant phenotypic trait. Anatomy, pigments and water changes were responsible of reflectance differences and the existence of leaf-side-specific responses were discussed. Finally, the use of spectroscopy for the estimation of the metabolite profiles of wheat organs showed promising for many metabolites which could pave the way for a new generation phenotyping. We concluded that future phenotyping may benefit from these findings in both the low-cost and straightforward methods and the more complex and frontier technologies.[cat] Els efectes del canvi climàtic sobre els agro-ecosistemes i l’increment de la població mundial posa en risc la seguretat alimentària i l’estabilitat dels ecosistemes. Actualment, satisfer les demandes de producció d’aliments sota l’escenari del canvi climàtic és el repte central a la Biologia Vegetal. Per això, és indispensable entendre els mecanismes subjacents de l’aclimatació a l’estrès que permeten obtenir cultius resilients. També és precís desenvolupar nou mètodes de recerca que permetin caracteritzar de manera no destructiva els trets d’interès. L’avenç del fenotipat vegetal amb sistemes d’alt rendiment és clau per abordar aquests reptes. La present tesi s’enfoca en el blat i secundàriament en el panís com a espècies d’estudi ja que constitueixen els cultius bàsics arreu del món. Un ampli ventall de mètodes de fenotipat s’han utilitzat, des sensors RGB a híper-espectrals fins a la caracterització metabolòmica. La recerca s’ha dut a terme en assajos de camp i s’han avaluat diversos tipus d’estrès representatius de les majors limitacions pel creixement i producció vegetal: estrès hídric i biòtic i deficiència de nitrogen. Els resultats demostraren el gran potencial dels trets del color RGB (des de la planta a la capçada) pel fenotipat de camp, ja que foren indicadors precisos del rendiment a blat i panís sota condicions de malaltia i deficiència de nitrogen i de la concentració de nitrogen foliar a panís. La caracterització metabolòmica de teixits de blat contribuí a esbrinar els processos metabòlics endegats per l’estrès hídric i la seva relació amb comportament genotípic, proporcionant bio-marcadors potencials per rendiments més alts i l’adaptació a l’estrès. Estudis espectroscòpics en blat van demostrar que la dorsoventralitat pot afectar més que l’estrès hídric sobre l’espectre de reflectància i consegüentment sobre el comportament de les aproximacions multi/híper-espectrals per avaluar el rendiment i d’altres trets fenotípics com anatòmics i contingut de pigments. Finalment, l’ús de l’espectroscòpia per l’estimació del contingut metabòlic als teixits de blat resulta prometedor per molts metabòlits, la qual cosa obre les portes per a un fenotipat de nova generació. El fenotipat pot beneficiar-se d’aquestes troballes, tant en els mètodes de baix cost com de les tecnologies més sofisticades i d’avantguarda

Factores explicativos de la deserción de estudiantes de pedagogía

El objetivo del artículo es identificar los factores que influyen en la deserción de estudiantes de pedagogía, considerando sus características individuales y académicas. El estudio se realizó con 531 estudiantes de la cohorte 2009. La investigación es de tipo cuantitativo, con un diseño explicativo, longitudinal y no experimental. La información se recolectó a partir de datos secundarios, los cuales fueron analizados según el método de análisis de supervivencia, modelados a través de la regresión de riesgos proporcionales de Cox. Los resultados demostraron que las variables individuales que explican la deserción de los estudiantes corresponden al sexo y la procedencia de la región del Bio Bio. Por otro lado, las variables académicas que explican la deserción universitaria corresponden al promedio de notas de enseñanza media, el lugar en la lista de seleccionados, provenir de un establecimiento secundario científico-humanista, el total de asignaturas inscritas, el último promedio curricular y la suspensión de estudios. Se concluye que las capacidades asociadas al nivel de logro de los resultados académicos y la gestión de apoyo social para los estudiantes, se constituyen en aspectos significativos para mantener el compromiso por permanecer en el programa académico. En la medida que las capacidades y la gestión de apoyo sean positivas, los estudiantes contarán con interacciones favorables que apoyarán su participación a nivel institucional, lo cual favorecerá su desarrollo intelectual y académico. Finalmente, se concluye que a nivel de política institucional resulta relevante gestionar el apoyo de las capacidades y la adaptación de los estudiantes, ya que se contribuirá en la generación de un equilibrio positivo entre la integración académica y social, a partir de la configuración de elementos que apoyarán el desarrollo de un contexto de motivación que permitirá mantener el compromiso de los estudiantes por el logro de la meta de graduación

Phenotyping conservation agriculture management effects on ground and aerial remote sensing assessments of maize hybrids performance in Zimbabwe

n the coming decades, Sub-Saharan Africa (SSA) faces challenges to sustainably increasefood production while keeping pace with continued population growth. Conservation agriculture(CA) has been proposed to enhance soil health and productivity to respond to this situation.Maize is the main staple food in SSA. To increase maize yields, the selection of suitable genotypes andmanagement practices for CA conditions has been explored using remote sensing tools. They may playa fundamental role towards overcoming the traditional limitations of data collection and processing inlarge scale phenotyping studies. We present the result of a study in which Red-Green-Blue (RGB) andmultispectral indexes were evaluated for assessing maize performance under conventional ploughing(CP) and CA practices. Eight hybrids under different planting densities and tillage practices weretested. The measurements were conducted on seedlings at ground level (0.8 m) and from an unmannedaerial vehicle (UAV) platform (30 m), causing a platform proximity effect on the images resolution thatdid not have any negative impact on the performance of the indexes. Most of the calculated indexes(Green Area (GA) and Normalized Difference Vegetation Index (NDVI)) were significantly affectedby tillage conditions increasing their values from CP to CA. Indexes derived from the RGB-imagesrelated to canopy greenness performed better at assessing yield differences, potentially due to thegreater resolution of the RGB compared with the multispectral data, although this performance wasmore precise for CP than CA.The correlations of the multispectral indexes with yield were improvedby applying a soil-mask derived from a NDVI threshold with the aim of corresponding pixels withvegetation. The results of this study highlight the applicability of remote sensing approaches basedon RGB images to the assessment of crop performance and hybrid choice

Application of Trichoderma asperellum T34 on maize (Zea mays) seeds protects against drought stress

Abstract: Drought is currently one of the biggest threats to maize production. Trichoderma spp. is mainly used in agriculture as plant protection product with secondary beneficial effects on plants: improved growth, nutrient uptake and plant immunity. Here, we studied the physiological performance of maize plants under two different water regimes (fully irrigated and drought conditions) and three different seed treatments: application of Trichoderma asperellum strain T34, application of a chemical fungicide (CELEST XL) or the combination of both. Regardless of water regime, T34 treatment improved kernel P and C, kernel number and dry weight. Higher populations of T34 on the rhizosphere (T34 treatment) alleviated water stress better than lower T34 populations (T34+Q treatment). Under drought, T34 treatment improved leaf relative water content, water use efficiency, PSII maximum efficiency and photosynthesis. T34-treated maize seeds maintained sufficient T34 populations to alleviate drought throughout crop development suggesting an optimal dose of 104 and 105 colony forming units g−1 dry weight of rhizosphere under the studied conditions. This work helps to demonstrate the beneficial interaction between T. asperellum strain T34 and maize plants under drought

Contaminación por metales pesados: Implicaciones en salud, ambiente y seguridad alimentaria

Contamination by heavy metals in water resources, soil and air poses one of the most severe problems that compromise food safety and public health at global and local level. In this review, the specific problem of contamination by mercury (Hg), arsenic (As), cadmium (Cd) and lead (Pb) in the environment and food is presented. A description of the sources of contamination, exposure in living beings, accumulation and retention in food and consumer products is carried out. Study cases and results in some countries included Colombia are discussed.La contaminación por metales pesados y metaloides en recursos hídricos, suelos y aire plantea una de las más severas problemáticas que comprometen la seguridad alimentaria y salud pública a nivel global y local. En esta revisión, se aborda el problema específico de contaminación por mercurio (Hg), Arsénico (As), Cadmio (Cd) y Plomo (Pb) en ambiente y alimentos. Se presenta una descripción sobre las fuentes de contaminación y exposición en seres vivos así como la incorporación y retención en alimentos y productos de consumo humano. Se abordan casos de estudio y resultados obtenidos en algunos países del mundo incluido Colombia

UAV and Ground Image-Based Phenotyping: A Proof of Concept with Durum Wheat

Climate change is one of the primary culprits behind the restraint in the increase of cereal crop yields. In order to address its effects, effort has been focused on understanding the interaction between genotypic performance and the environment. Recent advances in unmanned aerial vehicles (UAV) have enabled the assembly of imaging sensors into precision aerial phenotyping platforms, so that a large number of plots can be screened effectively and rapidly. However, ground evaluations may still be an alternative in terms of cost and resolution. We compared the performance of red-green-blue (RGB), multispectral, and thermal data of individual plots captured from the ground and taken from a UAV, to assess genotypic differences in yield. Our results showed that crop vigor, together with the quantity and duration of green biomass that contributed to grain filling, were critical phenotypic traits for the selection of germplasm that is better adapted to present and future Mediterranean conditions. In this sense, the use of RGB images is presented as a powerful and low-cost approach for assessing crop performance. For example, broad sense heritability for some RGB indices was clearly higher than that of grain yield in the support irrigation (four times), rainfed (by 50%), and late planting (10%). Moreover, there wasn't any significant effect from platform proximity (distance between the sensor and crop canopy) on the vegetation indexes, and both ground and aerial measurements performed similarly in assessing yield

El informe de arbitraje según la recomendación de publicación y la productividad de los evaluadores

El informe de arbitraje de artículos de investigación es un género en el que se cristaliza una parte del proceso colectivo de construcción del conocimiento. Debido a su carácter confidencial, existen muy pocos trabajos que aborden empíricamente este género. A su vez, esos pocos estudios tienen una serie de limitantes, como la falta de definición de la unidad de análisis y la falta de integración de los datos discursivos con los datos sociales de quienes los producen. En este trabajo, presentamos un modelo que busca superar limitantes. Aplicamos este modelo para describir cómo varía el informe de arbitraje según dos atributos extralingüísticos, la recomendación de publicación (aceptar, condicionar o rechazar) y el número de artículos publicados por los evaluadores. Los resultados muestran que ambos atributos extralingüísticos se asocian a cambios específicos del discurso de este género, siendo la recomendación de publicación más determinante que la productividad de los evaluadores.The referee report of research articles is a discursive genre in which a part of the collective process of building knowledge is crystalized. Given its confidentiality, there is little empirical work on this genre. Among these few contributions, a series of limitations can be identified, such as the lack of definition of the unit of analysis or the lack of integration between discursive and sociometric data. In this article, we present a model that contributes to overcoming these limitations. The model was applied with the purpose of analyzing the variation of referee reports according to two extralinguistic variables, i.e., publication recommendation (accepted, conditioned, rejected) and referee's number of published articles. The results showed that both extralinguistic attributes were associated with specific discourse variations, of which publication recommendation was more decisive than referee's academic productivity

Evaluating Maize Genotype Performance under Low Nitrogen Conditions Using RGB UAV Phenotyping Techniques

Maize is the most cultivated cereal in Africa in terms of land area and production, but low soil nitrogen availability often constrains yields. Developing new maize varieties with high and reliable yields using traditional crop breeding techniques in field conditions can be slow and costly. Remote sensing has become an important tool in the modernization of field-based high-throughput plant phenotyping (HTPP), providing faster gains towards the improvement of yield potential and adaptation to abiotic and biotic limiting conditions. We evaluated the performance of a set of remote sensing indices derived from red-green-blue (RGB) images along with field-based multispectral normalized difference vegetation index (NDVI) and leaf chlorophyll content (SPAD values) as phenotypic traits for assessing maize performance under managed low-nitrogen conditions. HTPP measurements were conducted from the ground and from an unmanned aerial vehicle (UAV). For the ground-level RGB indices, the strongest correlations to yield were observed with hue, greener green area (GGA), and a newly developed RGB HTPP index, NDLab (normalized difference Commission Internationale de I´Edairage (CIE)Lab index), while GGA and crop senescence index (CSI) correlated better with grain yield from the UAV. Regarding ground sensors, SPAD exhibited the closest correlation with grain yield, notably increasing in its correlation when measured in the vegetative stage. Additionally, we evaluated how different HTPP indices contributed to the explanation of yield in combination with agronomic data, such as anthesis silking interval (ASI), anthesis date (AD), and plant height (PH). Multivariate regression models, including RGB indices (R2 > 0.60), outperformed other models using only agronomic parameters or field sensors (R2 > 0.50), reinforcing RGB HTPP's potential to improve yield assessments. Finally, we compared the low-N results to the same panel of 64 maize genotypes grown under optimal conditions, noting that only 11% of the total genotypes appeared in the highest yield producing quartile for both trials. Furthermore, we calculated the grain yield loss index (GYLI) for each genotype, which showed a large range of variability, suggesting that low-N performance is not necessarily exclusive of high productivity in optimal conditions

Leaf versus whole-canopy remote sensing methodologies for crop monitoring under conservation agriculture: a case of study with maize in Zimbabwe

Enhancing nitrogen fertilization efficiency for improving yield is a major challenge for smallholder farming systems. Rapid and cost-effective methodologies with the capability to assess the effects of fertilization are required to facilitate smallholder farm management. This study compares maize leaf and canopy-based approaches for assessing N fertilization performance under different tillage, residue coverage and top-dressing conditions in Zimbabwe. Among the measurements made on individual leaves, chlorophyll readings were the best indicators for both N content in leaves (R < 0.700) and grain yield (GY) (R < 0.800). Canopy indices reported even higher correlation coefficients when assessing GY, especially those based on the measurements of the vegetation density as the green area indices (R < 0.850). Canopy measurements from both ground and aerial platforms performed very similar, but indices assessed from the UAV performed best in capturing the most relevant information from the whole plot and correlations with GY and leaf N content were slightly higher. Leaf-based measurements demonstrated utility in monitoring N leaf content, though canopy measurements outperformed the leaf readings in assessing GY parameters, while providing the additional value derived from the affordability and easiness of using a pheno-pole system or the high-throughput capacities of the UAVs

Metabolome profiling supports the key role of the spike in wheat yield performance

Although the relevance of spike bracts in stress acclimation and contribution to wheat yield was recently revealed, the metabolome of this organ and its response to water stress is still unknown. The metabolite profiles of flag leaves, glumes and lemmas were characterized under contrasting field water regimes in five durum wheat cultivars. Water conditions during growth were characterized through spectral vegetation indices, canopy temperature and isotope composition. Spike bracts exhibited better coordination of carbon and nitrogen metabolisms than the flag leaves in terms of photorespiration, nitrogen assimilation and respiration paths. This coordination facilitated an accumulation of organic and amino acids in spike bracts, especially under water stress. The metabolomic response to water stress also involved an accumulation of antioxidant and drought tolerance related sugars, particularly in the spikes. Furthermore, certain cell wall, respiratory and protective metabolites were associated with genotypic outperformance and yield stability. In addition, grain yield was strongly predicted by leaf and spike bracts metabolomes independently. This study supports the role of the spike as a key organ during wheat grain filling, particularly under stress conditions and provides relevant information to explore new ways to improve wheat productivity including potential biomarkers for yield prediction