1994. Genetic diversity and population structure of red spruce (Picea rubens). Can. J. Bot. 72: [1778][1779][1780][1781][1782][1783][1784][1785][1786]. Allozyme variation at 36 loci was estimated for 19 populations of red spruce (Picea rubens Sarg.) from throughout its natural range. Average estimates of polymorphic loci (95% criterion), effective number of alleles per locus, and observed and expected heterozygosities are 23 %, 1.13, 7.47 % , and 7.89 %, respectively. Mean genetic distance among populations is 0.007, and 93% of the genetic diversity resides within red spruce populations. Comparisons with other species indicate that red spruce is less genetically variable than most other north-temperate woody plant species. Observed heterozygosity varied significantly among geographic regions, with northern cool-temperate populations having the highest mean observed heterozygosity, followed by central montane populations, then southern isolated populations with the lowest observed heterozygosity. Regional differences in genetic variability could be due to several factors, including migration from different glacial refugia, introgression of red spruce with more genetically variable black spruce in areas of sympatry in the north, and genetic drift followed by higher than expected levels of inbreeding in small isolated southern red spruce populations. Based on genetic distance, northern cool-temperate red spruce are more closely related to nonintrogressed red spruce than to nonintrogressed black spruce, suggesting that introgression is not a major factor contributing to greater genetic variability in the northern portion of the red spruce range. Relatively high genetic differentiation among populations, higher than expected levels of inbreeding, and evidence of reduced gene flow among populations suggest that low genetic variability evident in southern red spruce populations may be a result of genetic drift followed by inbreeding.Key words: Picea rubens, genetic diversity, isozymes, population genetic structure. HAWLEY, G.J., et DEHAYES, D.H. 1994. Genetic diversity and population structure of red spruce (Picea rubens). Can. J. Bot. 72 : 1778-1786. Les auteurs ont estimC la variation allozymique de 36 lieux dans 19 populations d'Cpinette rouge (Picea rubens Sarg.), provenant de l'ensemble de son aire de distribution. Les estimations moyennes pour les lieux polymorphiques (critkre de 95%), les nombres reels des allkles par lieu, et les hCtCrozygocitCs attendues et observkes sont respectivement de 23 %, 1,13, 7,47% et 7,89%. La distance gCnCtique moyenne entre les populations est de 0,007, et 93% de la diversit6 gCnCtique se retrouve i 1'intCrieur des populations d'kpinette rouge. Les comparaisons avec d'autres espkces indiquent que 1'Cpinette rougeposskde une variabilitC gknCtique moindre que la plupart des autres espkces ligneuses des regions tempCrCes du nord. L'hCtkrozygocitC observCe varie significativement entre les rCgions geographiques : les populations des regions froides nordiques montrent I'hCtCrozygocitC mo...