GENETIC VARIATION IN CANADIAN AND EUROPEAN POPULATIONS OF THE COLONIZING WEED SPECIES APERA SPICA-VENTI.

Apera spica-venti L., a widely distributed weed in Europe, has recently become established as a weed of winter cereals in Canada. Levels of genetic variation were compared between and within nine Canadian and six native European populations grown under uniform conditions. Both the Canadian and European populations showed high levels of variation among populations with respect to 31 life history and morphological traits. As one would have predicted, greater differences were recorded among the European populations, although only one population in each group was clearly distinct from the other populations. High levels of genetic variability in allozyme characters were also evident in both the Canadian and European populations (percentage of polymorphic loci = 57 to 62 %, number of alleles per locus = 2.53 and levels of heterozygosity = 0.23). There was, however, little or no divergence in allozyme characters among populations, with all populations having very high genetic identity values (0.948 to 0.998) and only 1.0 to 2.4 % of the total gene diversity allocated to the among-population component. The extent of within-population variation in the 31 life-history and morphological characters were similar in both introduced and native populations. Studies of population structure in three Canadian populations indicated that most of the variation in nine morphological characters occurred among progeny within families rather than among families. Estimates of outcrossing rate (t) using allozyme markers at two loci equalled 1.0, indicating random mating. Selfing experiments indicated that the plants were predominantly self-incompatible. The amounts and patterns of genetic variation are consistent with what one would expect in an outcrossing species and do not support the hypothesis of genetically depauperate introductions. [ABSTRACT FROM AUTHOR]