QTL analysis of water use efficiency in rice : [P114]

Water use efficiency is an important target for breeders in drought prone environments in order to save water resources. However direct evaluation of this trait is difficult. Carbon isotope discrimination (CID) has been proposed for several years as an index of water-use efficiency at the leaf level. The genetic dissection of this trait and other relevant parameters for water-use efficiency has been initiated in rice, within a NSF program; through a QTL analysis and fine mapping strategy. We report here QTL results on two segregating populations from the cross IR64xAzucena for carbon isotope discrimination, leaf morphological parameters, gas exchange data, stomatal conductance and leaf ABA concentrations, in greenhouse experiments. Globally, CID was correlated negatively with leaf width and plant height, and positively with leaf curling. Three significant QTLs have been identified for CID, two of them being antagonists on chromosome 4, and one other located on chromosome 5. The near-centromeric region of chromosome 4 presents a cluster of QTLs for CID, photosynthesis rate and stomatal conductance, supporting the involvement of carbon assimilation and stomatal conductance in the genetic variation of carbon isotope discrimination at this particular locus. However, the two other QTLs (on chromosome 4 long arm and on chromosome 5) may be rather related to structural variation in plants. Our data are compared with results obtained on other crosses and across cereals. Perspectives for a genomic analysis of water-use efficiency are presented. (Resume d'auteur)