Genetics of isozyme loci in Brassica campestris L. and in the progeny of a trigenomic hybrid between B. napus L. and B. campestris L.

Abstract

F2 progeny of Brassica campestris crosses were analyzed for single-locus inheritance of glucosephosphate isomerase, leucine aminopeptidase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, and shikimate dehyrogenase enzymes. In most of the F2 families, the observed inheritance data for six polymorphic isozyme loci coincided well with the ratios expected under Mendelian segregation of either codominant alleles or dominant-recessive alleles when a null allele was involved. Complete linkage was observed for one locus pair (Lap-2A/6Pgd-2Ac), with the recombination frequency estimated to be r .apprxeq. 0.000. From isozyme analyses made on resynthesized Brassica napus (AACC) and the actual parents B. campestris (AA) and B. alboglabra (CC) and on a trigenomic hybrid (AAC) between B. napus and B. campestris, it was possible to recognize A and C genome specific isozyme loci through the nonoverlapping electrophoretic mobilities of alleles characteristic of each genome. The trigenomic hybrid was selfed and genetic analyses of the offspring indicated that the A genome specific isozyme loci displayed a normal disomic inheritance. The C genome specific isozyme loci, on the other hand, showed nonrandom loss in the aneuploid offspring, thereby indicating the nonrandom loss of C genome chromosomes. At least 4 of the 8 C genome specific isozyme loci studied were located on separate chromosomes. The apparent occurrence of multiplicates of certain isozyme loci supports the concept that duplication of structural nuclear genes prevails in the diploid Brassica genomes.