Résumé
In Madagascar, plantations of Eucalyptus robusta are grown on more than 150,000 ha. Coppice-managed plantations of this species supply most of the charcoal to the capital, Antananarivo. A study of genetic variability and genotype x environment interactions for growth and wood volume production was undertaken. It involved five E. robusta trials (two provenance trials and three progeny trials) in two contrasting bioclimatic regions. The five trials were thinned to become seed orchards, and growth was monitored for more than 12 years in oldest trials. Growth results showed that the species is well adapted to the island. The results revealed the importance of the choice of provenances/progenies, especially with less suitable growing conditions. The best provenances mostly came from summer rainfall regions of Australia and the worst from marginal regions to the north and south of the natural range. Estimated provenance repeatability and family repeatability of the growth traits was high, and the estimated individual-tree heritability values were generally moderate. In the provenance trials, approximate gains from selecting provenances or progenies were higher than gains from selecting individual trees within provenances/progenies, and in the progeny trials, it was the opposite. Despite the thinning, individual selection would make it possible to achieve further significant genetic gains. Multisite analyses revealed high significant site effect; these sites differed by rainfall, temperature, and soil type. There were few provenance x site interactions, the best provenances at the two sites being largely the same. However, the progeny x site interactions were greater. Interest in this fast-growing species with high plasticity is increasing, especially in view of climate change, and our findings should help forestry decision-makers.