Résumé
Biomass sorghum diversity offers the opportunity to develop multipurpose genotypes combining high grain and ligno-cellulosic biomass productions. It also provides a large spectrum of adaptive traits, particularly to drought. Sorghum breeding is thus of major interest for semi-arid, drought prone cropping environments as met in West Africa, to improve conjointly food and feed productions. This is the objective of the BIOSORG project that firstly aims to understand the elemental traits contributing to combine biomass and grain production and their stability under drought. Sorghum biomass accumulation depends both on C source (photosynthetic) and sink (organ development rate, number, size) processes. While sink strength related traits are commonly phenotyped and known to vary across sorghum genetic diversity, it is not the case regarding photosynthetic processes, much more difficult to measure to a large scale. Accordingly the impact of drought on C source-sink balance is in general not apprehended in the process of large population phenotyping. The present study aims to explore the relevance of modulated fluorescence for a large scale phenotyping, as a proxy of photosynthetic performance, of biomass sorghum genotypes under contrasted water situations. A field trial comparing two water treatments during stem elongation phase was carried out in 2013 and 2014 on 4 biomass sorghum hybrids in order to explore the relationship between leaf chlorophyll fluorescence (measured with a Walz PAM-2500) and photosynthetic level (measured with a Walz GFS-3000), their regulation by drought and their genotypic variability. 2014 trial was extended considering 12 more contrasted genotypes to confirm the relation on a larger diversity. The confirmation of the relationship between fluorescence and photosynthetic parameters, the genotypic variability of the Drought Factor Index (DFI) will be presented as well as a first appraisal of its relationship, across genotypes, with sink organ growth regulation by drought. (Résumé d'auteur)