THE MATING SYSTEM AND POPULATION STRUCTURE OF BLACK SPRUCE IN CENTRAL NEW BRUNSWICK AND ITS INFLUENCE ON TREE IMPROVEMENT STRATEGY

The mating system and population structure of six stands of black spruce (Picea mariana Mill. B.S.P.) in central New Brunswick were investigated by means of isozyme analysis. Eleven enzyme systems, coding for 14 loci, were assayed. Regular Mendelian inheritance could not be demonstrated at two loci (MDH-1 and SDH), whilst linkage relationships and linkage disequilibria among several of the remaining loci left only six independent, polymorphic loci for several analyses.;Differences in various measures of genetic diversity among the stands were not significant and only one per cent of the total genetic variation was due to differences among stands. There was no correlation between geographic and genetic distances, suggesting that isolation by distance is not important in producing differentiation.;Results from several analyses of intra-population structure demonstrated very little development of family clustering, possibly due to the early-successionist reproductive strategy of the species. Effective population sizes were large, but due to inadequacies in the data, the effect of natural selection on maintenance of polymorphisms could not be determined.;These results suggest that improvement effort should be concentrated on intra-population sampling and that the comparison-tree method of selection is relatively efficient. Estimates of genetic variances and heritabilities from open-pollinated progeny tests making standard assumptions are likely to be acceptably accurate.;Mating system parameters were estimated by both single locus and multilocus methods. Differences between estimates by the two methods were not great, implying that forms of non-random mating other than selfing were not significant. For the six stands, multilocus estimates of outcrossing rates ranged from 0.891 to 0.976. Frequencies of homozygotes in four of the six stands were lower than expected after allowance for the mating system. The most likely explanation for this is some form of negative assortative mating.