Inbreeding in black spruce (Piceamariana (Mill.) B.S.P.): self-fertility, genetic load, and performance

Abstract

Effects of inbreeding in a natural population of black spruce (Piceamariana (Mill.) B.S.P.) were studied using progenies from self-, open-bag, open, and pollen-mix pollinations. Self-pollination resulted in significant reductions in seed set and early height. The numbers of embryonic lethals were estimated comparatively by using two different models. Based on full seed data, the population carried an average genetic load of five to seven embryonic lethal equivalents per zygote. The total number of lethal equivalents, acting from the time of pollination through age 6 years, ranged from about six to eight. The role of polyembryony in maintaining heterozygosity is discussed. Significant differences among female parents with respect to seed weight, percent germination, and 2- and 6-year heights indicated substantial variation owing to additive genetic and maternal effects. Relative self-fertility in the species, although generally high, varied widely among parents.