Amélioration variétale de l'arachide (Arachis hypogaea L.) pour l'adaptation à la sécheresse. Proposition d'une approche intégrée pour la sélection

Drought is a multiform constraint which is expressed at different plant organisation levels. The present project was aimed at integrating knowledge generated by experiments carried out in Senegal within the framework of a breeding programme geared towards improving groundnut yield under drought conditions. The first chapter analyses a half-diallel cross performed on an original population under recurrent selection for drought adaptation. The selection indices, calculated using the DIOGENE software, were used to estimate genetic gains relative to the main agronomic characters according to selection pressure. In the second chapter, the genetic variability of phenological, agronomic and physiological characters was studied on five new early varieties. The measurement periods during which varietal differences are best detected were established for these characters. The yield-based drought response indices and the dry matter pardoning coefficients were higher for the new varieties compared to the check. The third chapter covers this variability analysis in greater depth by focusing on new genetic material consisting in two series of quasi-isogenic lines. Genetic variability was revealed in these lines as well as correlations between yield and physiological parameters, i.e. mainly fluorescence parameters, despite the closeness between lines. However, these correlations were not stable across lines and environments, showing that groundnut has different drought adaptation strategies. The fourth study was conducted with four varieties to physiologically analyse drought adaptation strategies observad in the field. The first strategy was characterised by late stomatal closure and high protoplasmic tolerance during drought, the second maintained a water status but seemed less efficient than the first with respect to groundnut field productivity under all conditions. This work was pursued with the same cultivars at the molecular level. The gene transcript kinetics under drought, obtained using RTPCR, showed that Phospolipase D and Cysteine protease gene expressions were stimulated by stress in the most susceptible cultivars, whereas their was higher LEA gene expression in the resistant one. These interconnected experiments conducted at different plant organisation levels led to the development of a general methodological model and of new improved genotypes to meet the social demand. (Résumé d'auteur