Whole-genome characterization of embryonic stage inbreeding depression in a selfed loblolly pine family

Inbreeding depression is important in the evolution of plant populations an d mating systems. Previous studies have suggested that early-acting inbreed ing depression in plants is primarily due to lethal alleles and possibly ep istatic interactions. Recent advances in molecular markers now make genetic mapping a powerful tool to study the genetic architecture of inbreeding de pression. We describe a genome-wide evaluation of embryonic viability loci in a selfed family of loblolly pine (Pinus taeda L.), using data from AFLP markers from an essentially complete genome map. Locus positions and effect s were estimated from segregation ratios using a maximum-likelihood interva l mapping procedure. We identified 19 loci showing moderately deleterious t o lethal embryonic effects. These loci account for >13 lethal equivalents, greater than the average of 8.5 lethal equivalents reported for loblolly pi ne. Viability alleles shown predominantly recessive action, although potent ial overdominance occurs at 3 loci. We found no evidence for epistasis ill the distribution of pairwise marker correlations or in the regression of fi tness on the number of markers linked to deleterious alleles, The predomina nt role of semilethal alleles in embryonic inbreeding depression has implic ations for the evolution of isolated populations and for genetic conservati on and breeding programs in conifers.