Inbreeding depression in three generations of selfed families of silver birch (Betula pendula)

摘要

Inbreeding depression in terms of survival and growth vigour was investigated through 3 generations of selfing on the basis of a 13-year-old field progeny trial with silver birch (Betula pendula) in Finland. Survival exhibited significant decline from outcrossed (S0) to first-generation selfed trees (S1), and some recovery from second- (S2) to third-generation selfed trees (S3), indicating the rapid purging of lethal, sublethal or highly deleterious alleles by selfing. The continuous decline of growth vigour with increased inbreeding indicated a low efficiency in purging mildly deleterious alleles affecting quantitative traits and a low possibility of recovery in growth with further inbreeding. Linear effects of inbreeding on survival and growth vigour (taken as height, diameter at breast height and stem volume) explained the major variation caused by inbreeding and indicated that the additively combined dominant effects at different loci are the major source of inbreeding depression in this species. A weak and significant non-linear effect of inbreeding on height and stem volume was also observed, suggesting the existence of epistatic effects.