Mating system and population structure in a black spruce (Picea mariana (Mill.) B.S.P.) clonal seed orchard in Northwestern Ontario

Abstract

Multi-locus enzyme systems were studied in a black spruce {Picea maniana (Mill.) B.S.P.) clonal seed orchard in northwestern Ontario. The embryonic and megagametophytic tissues of each clone were sampled and electrophoretically analysed to examine the inheritance pattern of 8 polymorphic loci. With the exception of leucine aminopeptidase (Lap) and aconitase (Aco), allozyme segregation followed expected 1:1 ratios. The mating system is characterized by a moderate level of selfing (s=0.15) and a small effective population size. The ratio of genetically effective males to receptive females was calculated to be 0.31. Although the parental population was in Hardy-Weinberg equilibrium, the majority of the enzyme systems examined revealed a deviation from the Hardy-Weinberg equilibrium in the filial generation. Several loci exhibited heterogeneous pollen pools and there was an observed excess of heterozygotes. Indications of non-random mating and small effective population size invalidate two basic seed orchard assumptions, namely, random mating and large population size.