Effect of regeneration procedures on genetic diversity in Brassica napus and B-rapa as estimated by isozyme analysis

This investigation was conducted to assess changes in the genetic structure of two varieties of two species of annual Brassica. Seeds of B. napus cv. ''Topas'' and B. rapa ''Broccoletto'' were sent to nine research institutes in different geographical areas of Europe for regeneration. The multiplied material was sent back after one year of regeneration and analysed electrophoretically. The original populations of each species and their multiplied samples were stained for 12 different enzymes, of which 4 were found to be polymorphic (DIA, SKD, GPI and PER). It was possible to detect considerable differences in isozyme patterns in B. napus and allelic frequencies in B. rapa, both within and between populations. When the original population was compared with the regenerated samples, the Chi-square homogeneity test for all pairwise comparisons revealed distinctness with a 99% probability for B. napus and 95% probability for B. rapa with one or more of the enzyme systems examined. Furthermore, the average of gene diversity analysis (Nei, 1973) revealed that some regenerated populations have less while others have increased genetic variation compared with the original population. These observations indicated that the frequencies were non-random and considerable shifts in genetic diversity have occurred during multiplication. In addition, different regeneration procedures have caused the fixation of certain alleles.