Ear metabolism and genotype-by-environment interaction in field-grown durum wheat: identification of novel traits for crop improvement
- Autores: Raquel Martínez Peña
- Directores de la Tesis: Nieves Aparicio Gutiérrez (dir. tes.), Rubén Vicente Pérez (codir. tes.)
- Lectura: En la Universidad de Valladolid ( España ) en 2022
- Idioma: inglés
- Tribunal Calificador de la Tesis: Josefa Carmen Sillero Sánchez de la Puerta (presid.), Rut Sánchez Bragado (secret.), Luíza Lane de Barros (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia e Ingeniería Agroalimentaria y de Biosistemas por la Universidad de Valladolid
- Materias:
- Enlaces
- Tesis en acceso abierto en: UVADOC
- Resumen
Durum wheat (Triticum turgidum L. ssp. durum) represents one of the world's most essential and widely grown crops. However, to cope with the increasing demand of food for the future world's population in a context of climate change, more efforts are needed to understand the responses of durum wheat plants to existing and upcoming abiotic stresses. The knowledge of the environmental influences on grain yield and quality, as well as phenotype and metabolism, is essential to successfully select varieties better adapted to specific local agro-environments in terms of final products, through the identification of those parameters with interest to increase the efficiency of breeding programmes. This is especially relevant in the Mediterranean basin due to the high inter-annual variability of climatic conditions. In addition, preliminary studies have shown that a significant part of the carbon and nitrogen remobilised to the grains during the filling phase comes from the ears, especially under stress conditions, such as water scarcity or nutrient availability in the soil.
Therefore, in this PhD thesis we have evaluated the effects of genotype by environment interaction on the phenotype at different levels (plant canopy, whole plant and photosynthetic organs) by conducting field trials on a panel of commercial durum wheat varieties registered after the Green Revolution and cultivated in Spain in the last 40 years. To identify varieties with a consistently specific and broader adaptation to defined agro-environments, the present and future growing conditions associated with climate change that could take place in the Spanish region of Castile and León region were simulated, including optimal and stress conditions, such as water deficit, irrigation, high temperatures (late sowing), and low nutrient availability (different levels of fertilisation). A wide range of techniques and methodologies were used, from the evaluation of agronomic components and the industrial and nutritional quality of the grain to phenotyping and biochemical analyses. More specifically, in-depth physiological and biochemical analyses of the source and sink organs were carried out to understand the role of each organ, especially the ear, in the assimilation and translocation of carbon and nitrogen during grain filling in response to different abiotic stresses. All this under a holistic approach to identify new traits for the improvement of yield and grain quality in C3 cereals in Mediterranean climate conditions and to elucidate the role played by the different laminar and non-lamilar organs of the plant, mainly at the later stages of growth.
Different statistical analyses were used to elucidate the effect of the genotype, the environment and their interaction. They showed that the environment represents the main factor that strongly influences the canopy and plant growth, and the metabolism of photosynthetic organs, ultimately affecting the yield and the nutritional and industrial quality of the grain obtained at harvest. Nevertheless, the genetic influences were also notable for most of the evaluated agronomic and grain quality parameters. We identified the durum wheat varieties presented in our panel with high stability for the region of Castile and León under optimal and limiting growing conditions associated with climate change, also considering high yield and quality according to industrial standards. A retrospective study of the evolution of nutritional quality in the last forty years revealed that, despite the slight tendency of increased grain yield, the mineral concentration in the mature grains remain stagnant. Furthermore, we determined the varieties with the highest grain nutrient composition among our panel. Moreover, the correlations obtained between specific parameters such as grain yield and protein content with the concentrations of Ca, K, S and Fe could be of interest for crop improvement.
Next, source-sink dynamics were studied in durum wheat in response to contrasting nitrogen fertilisation levels to identify phenotypic and metabolic parameters at the whole plant level related to yield and grain quality in response to nitrogen. Low nutrient availability led to an imbalance in the carbon and nitrogen metabolism coordination at the whole plant level, associated with reduced grain yield and nutrient composition. The activities of key enzymes in carbon and nitrogen metabolism, as well as the levels of photoassimilates, showed not only the flag leaf but that each organ plays an essential role during grain filling, some with a higher photosynthetic capacity, others for the storage of nutrients that will be remobilised at later stages of grain filling, or that will play an essential role in the assimilation and recycling of nitrogen. Interestingly, the enzymatic activities of relevant enzymes such as Rubisco and sucrose content of the ear organs were positively associated with grain yield and quality, unlike leaves, suggesting, together with the regression models obtained with organ-specific isotopic signatures, the potential contribution of non-photosynthetic organs during grain filling.
Finally, concerning the previous study, the effect of water stress on the content of carbon and nitrogen metabolites with a role in grain filling was studied to study the tolerance of photosynthetic organs under water deprivation and to identify new breeding strategies involving the development of resilient varieties adapted to limiting conditions at the whole plant level. Water stress led to a significant decrease in yield, biomass, carbon and nitrogen assimilation, promoted water use efficiency and differentially modified grain quality traits in a subset of five durum wheat varieties. The results showed that the response to water stress is different according to the photosynthetic organ, with blades and peduncles being the most susceptible to water stress. In contrast, ear organs, mainly glumes and lemmas, showed tolerance at the most vulnerable stages of the plant, such as anthesis and grain filling. Quantitative calculations of metabolite content per organ showed surprisingly that the peduncle is the organ with the highest potential to provide nutrients to grain filling as a reservoir of carbon- and nitrogen-rich compounds, although it was susceptible to stress while the ears showed higher stability regardless of the water regime.
All these results highlighted the importance of combining plant agronomy, physiology and biochemistry to understand the mechanisms at the whole plant level controlling complex traits, such as grain yield and quality, especially in response to abiotic stresses to develop resilient crops adapted to future climate scenario.
