Parental Genome Separation and Elimination of Cells and Chromosomes Revealed by AFLP and GISH analyses in a Brassica carinata × Orychophragmus violaceus Cross

Abstract

The phenomenon of parental genome separation during the mitotic divisions of hybrid cells was proposed to occur under genetic control in intergeneric hybrids between cultivated Brassica species and Orychophragmus violaceus (2n = 24). To elucidate further the cytological and molecular mechanisms behind parental genome separation, Brassica carinata (2n = 34) x O. violaceus hybrids were resynthesized and their chromosome/genomic complements analysed. F(1) hybrids of the cross were obtained following embryo rescue, and were investigated for their cytological behaviour and subjected to genomic in situ hybridization (GISH) and amplified fragment length polymorphism (AFLP) to determine the contribution of parental genomes. All the F(1) plants with high fertility closely resembled B. carinata in morphological attributes. These were mixoploids with 2n chromosome numbers ranging from 17 to 35; however, 34, the same number as in B. carinata, was the most frequent number of chromosomes in ovary and pollen mother cells (PMCs). GISH clearly identified 16 chromosomes of B. nigra in ovary cells and PMCs with 2n = 34 and 35. However, no O. violaceus chromosome was detected, indicating the presence of the intact B. carinata genome and elimination of the entire O. violaceus genome. However, some AFLP bands specific for O. violaceus and novel for the two parents were detected in the leaves. Cells with fewer than 34 chromosomes had lost some B. oleracea chromosomes. F(2) plants were predominantly like B. carinata, but some contained O. violaceus characters. The cytological mechanism for the results involves complete and partial genome separation at mitosis in embryos of F(1) plants followed by chromosome doubling, elimination of cells with O. violaceus chromosomes and some introgression of O. violaceus genetic information.