Genetic diversity within a range of cultivars and landraces of flax (Linum usitatissimum L.) as revealed by RAPDs

Analysis of the extent and distribution of genetic diversity in crop plants is essential for optimizing sampling and breeding strategies. We used random amplified polymorphic DNA (RAPD) markers to assess genetic diversity and relationships in 22 Canadian cultivars, 29 selected world cultivars and 10 landraces of flax (Linum usitatissimum L.). RAPD variation was generally low and more variation was detected among, than within, the investigated flax accessions. Based on 53 variable RAPD loci observed for the 61 accessions, the landraces had a lower proportion of fixed recessive RAPD loci (0.427) (i.e., more genetic variation) than all of the flax cultivars examined (0.492). The linseed cultivars had a lower proportion of recessive loci (0.469) than the fiber flax cultivars (0.529). Canadian linseed cultivars had a lower proportion of recessive loci (0.465) than the selected world flax cultivars (0.512). A trend was also observed that the rate of loss in genetic variation in Canadian flax breeding programs over the last fifty years was approximately two variable loci per 100 loci per 10 years. Clustering analyses based on similarity estimates showed that the fiber cultivars were more related (or similar to each other) and were classified as a homogeneous group. All of the linseed cultivars were clustered in diverse groups with the nine landrace accessions. Implications of these findings for flax breeding and germplasm management are discussed.