Genetic architecture of carbon isotope composition and growth in E ucalyptus across multiple environments

Summary In the context of climate change, the water‐use efficiency ( WUE ) of highly productive tree varieties, such as eucalypts, has become a major issue for breeding programmes. This study set out to dissect the genetic architecture of carbon isotope composition (δ 13 C ), a proxy of WUE , across several environments. A family of E ucalyptus urophylla  ×  E . grandis was planted in three trials and phenotyped for δ 13 C and growth traits. High‐resolution genetic maps enabled us to target genomic regions underlying δ 13 C quantitative trait loci ( QTL s) on the E . grandis genome. Of the 15 QTL s identified for δ 13 C , nine were stable across the environments and three displayed significant QTL ‐by‐environment interaction, suggesting medium to high genetic determinism for this trait. Only one colocalization was found between growth and δ 13 C . Gene ontology ( GO ) term enrichment analysis suggested candidate genes related to foliar δ 13 C , including two involved in the regulation of stomatal movements. This study provides the first report of the genetic architecture of δ 13 C and its relation to growth in E ucalyptus . The low correlations found between the two traits at phenotypic and genetic levels suggest the possibility of improving the WUE of E ucalyptus varieties without having an impact on breeding for growth.