MULTIPLE-POPULATION VERSUS HIERARCHICAL CONIFER BREEDING PROGRAMS - ACOMPARISON OF GENETIC DIVERSITY LEVELS

Advanced-generation domestication programs for forest-tree species has raised some concerns about the maintenance of genetic diversity in fo rest-tree breeding programs. Genetic diversity in natural stands was c ompared with two genetic conservation options for a third-generation e lite Pinus taeda breeding population. The breeding population was subd ivided either on the basis of geographic origin and selection goals (m ultiple-population or MPBS option) or stratified according to genetic value (hierarchical or HOPE option). Most allelic diversity in the nat ural stands of loblolly pine is present in the domesticated breeding p opulations. This was true at the aggregate level for both multiple-pop ulation (MPBS) and the hierarchical (HOPE) populations. Individual sub populations within each option had less genetic diversity but it did n ot decline as generations of improvement increased. Genetic differenti ation within the subdivided breeding populations ranged from 1 to 5%, genetic variability is within each subpopulation rather than among sub populations for both MPBS (>95%) and the HOPE approaches (>98%). Nei's G(st) estimates for among population differentiation were biased upwa rds relative to estimates of theta from Weir and Cockerham (1984).