Abstract :

Faced with new environmental, economic and societal challenges in agriculture, plant breeding must rely on new selection strategies to maintain production while limiting the use of inputs. Targeted improvement of yield-related agronomic traits is made difficult by covariations with other undesired traits. In wild species, a comparative ecophysiology approach, based on the analysis of functional traits, i.e. traits related to the biological functions and performance of the plant (growth, survival and reproduction), has made it possible to highlight ecophysiological and biophysical constraints and trade-offs related to resource use. Identifying and quantifying these constraints in crop species, and their variability in the face of environmental factors, is essential for adapting targeted selection for traits of agronomic interest. This thesis focuses on the genetic variability of two phenotypic relationships particularly studied in functional ecology: the leaf economy spectrum and allometric relationships. Genotypes of five cereal species that are more or less domesticated and/or more or less selected were studied from this perspective. The comparative analysis of this intra- and interspecific variability was based on original data obtained during experiments in high-throughput phenotyping platforms and in the field. This work made it possible to i) highlight the selection of a strategy that favours resource acquisition functions during the domestication of durum wheat, ii) quantify the impact of light availability on the allometric response of 337 maize hybrids to edaphic water deficit, and iii) to illustrate the existence and genetic diversity of the leaf economy spectrum in 30 maize lines, 23 millet lines, 19 sorghum lines and 25 soft wheat lines under optimal and edaphic water deficit conditions. By means of multi-species and multi-genotype analyses, our comparative approach has made it possible to assess and discriminate the phenotypic variability of cereals in response to domestication and water stress. The study of constraints and trade-offs highlighted the non-existence of certain phenotypic combinations, a result that should be taken into account during varietal selection but also for cultivation practices.

Keywords: Comparative ecophysiology - Cereal - Leaf economy spectrum - Allometry - High-throughput phenotyping - Domestication - Agronomic selection - Environmental stress - Functional trait