Résumé
Water shortage is one of the'main abiotic constraints affecting growth and yield in citrus. In this work, we investigated the tolerance to water stress of diploid and tetraploid seedlings of Rangpur lime (Citrus limonia) and also their behaviour as rootstocks of Valencia Delta orange (Citrus sinensis) variety. The tetraploid (4x1 line arose from chromosome doubling in nurrllar cells of diploid (2x1 Rangpur lime and has strictly the same allelic composition than the 2x one. At the beginning of the stress, leaf stomacal conductances of 4x seedlings and Valencia Delta orange grafted on 4x rootstocks were respectively lower than those of 2x seedlings and Valencia Delta orange grafted on 2x rootstocks. At the end of the experiment, 4x seedlings and Valencia Delta orange grafted on 4x showed the highest tolerances. This work suggests that greater tolerance is linked to a more efficient regulation of gas exchanges in 4x seedlings and varieties grown on 4x genotypes. Investigations of ABA root content in 2x and 4x suggest that constitutive biosynthesis of this hormone is higher in 4x. To have a better understanding of the impact of 2x and 4x rootstocks on scion, we have also investigated gene expression using 20 K cDNA microarrays and qRT-PCR in Valencia Delta leaves grafted on 2x and 4x rootstocks in control and water deficit conditions. Expression of candidate genes involved in water deficit tolerance was also monitored at the root level using qRT-PCR. In control condition, those different genes, including NCED1 which is involved in the last step of ABA biosynthesis, were all shown to be up regulated in 4x roots when compared to 2x. (Texte intégral)