Positive assortative mating with selection restrictions on group coancestry enhances gain while conserving genetic diversity in long-term forest tree breeding

Abstract

Selection and mating principles in a closed breeding population (BP) were studied by computer simulation. The BP was advanced, either by random assortment of mates (RAM), or by positive assortative mating (PAM). Selection was done with high precision using clonal testing. Selection considered both genetic gain and gene diversity by "group-merit selection", i.e. selection for breeding value weighted by group coancestry of the selected individuals. A range of weights on group coancestry was applied during selection to vary parent contributions and thereby adjust the balance between gain and diversity. This resulted in a series of scenarios with low to high effective population sizes measured by status effective number. Production populations (PP) were selected only for gain, as a subset of the BP. PAM improved gain in the PP substantially, by increasing the additive variance (i.e. the gain potential) of the BP. This effect was more pronounced under restricted selection when parent contributions to the next generation were more balanced with within-family selection as the extreme, i.e. when a higher status effective number was maintained in the BP. In that case, the additional gain over the BP mean for the clone PP and seed PPs was 32 and 84% higher, respectively, for PAM than for RAM in generation 5. PAM did not reduce gene diversity of the BP but increased inbreeding, and in that way caused a departure from Hardy-Weinberg equilibrium. The effect of inbreeding was eliminated by recombination during the production of seed orchard progeny. Also, for a given level of inbreeding in the seed orchard progeny or in a mixture of genotypes selected for clonal deployment, gain was higher for PAM than for RAM. After including inbreeding depression in the simulation, inbreeding was counteracted by selection, and the enhancement of PAM on production population gain was slightly reduced. In the presence of inbreeding depression the greatest PP gain was achieved at still higher levels of status effective number, i.e. when more gene diversity was conserved in the BP. Thus, the combination of precise selection and PAM resulted in close to maximal short-term PP gain, while conserving maximal gene diversity in the BP.

Assortative mating and gene flow generate clinal phenological variation in trees

“…During this period, assortative mating will generate phenotypes with extreme genetic values in each population. Hence the genetic variance within populations increases as predicted by previous analytical models [24,34] and numerical simulations [28,32,44]. Gene flow during the early generations preferentially imports alleles from neighboring populations (Figure 8), owing to the fact that populations at this stage are genetically undifferentiated over the whole grid and parents exhibiting similar phenotypes are more likely to be in neighboring populations.…”

Using Norway spruce clones in Swedish forestry: Swedish forest conditions, tree breeding program and experiences with clones in field trials

“…The focus here is to demonstrate the ability of a breeding population to support propagation populations like seed orchards and clone mixtures. The simulation uses the same genetic parameters based on Swedish experience as was used to evaluate and develop the Swedish breeding strategy (Rosvall et al 1998;Rosvall and Mullin 2003). The only change in settings is that the current simulation starts with a selected breeding population, rather than randomly selected founders as was used in previous simulations.…”

Improving floral initiation in potted <i>Picea abies</i> by supplemental light treatment

“…Among the 27 clones with female flowers there were on average 27 female flowers ramet -1 , enough to complete the desired crosses to produce the next generation in the breeding population. A treatment effect of this magnitude increases the effectiveness of a breeding programme, as the breeder can do the crosses according to the concept of positive assortative mating (Rosvall and Mullin 2003).…”