Establishment And Cytogenetics Of Brassica Napus-Orychophragmus Violaceus Alien Additions And Substitutions

Due to the fact that the artificially synthesized allopolyploids from wide crosses are rarely used for production, the cytogenetic techniques including chromosome addition, substitution, elimination and translocation are ultilized to introduce the individual chromosomes or chromosome fragments from the wide sepecies into the targeted species or crops to change their genetic composition and genetic characteristics, which results in the production of alien chromosome lines. The crucifer Orychophragmus violaceus (L.) O. E. Schulz (2n=24) with large purple flowers is cultivated as an ornamental plant in China and shows some distinct morphological and cytological features, which can be used as good germplasm for genetic improvement of Brassica crops. Previously intergeneric somatic hybrids between Brassica napus L.(2n=38, AACC) and O. violaceus were produced and backcrossing progenies developed. In this study, by further selection and identification of the backcrossing progenies in successive generations, nine out of potential twelve mono-/disomic alien addition lines carrying one or two copies of individual O. violaceus chromosomes were established. One disomic substitution line was selected by crossing the addition line with the serrated leaves of O. violaceus with one B. napus nullisomics. Morphological and cytological characterizations of these B. napus-O. violaceus alien addition and substitution lines are made and described as follows:1. These mono-/disomic alien addition lines (MA1-MA9)(2n=39, AACC+1IO;2n=40, AACC+1IIO) were distinguishable from each other by their distinct phenotypes, for some expressed the traits specific for O. violaceus (serrated leaves, basal clustering stems, purple flowers, respectively), and the others showed the new traits for two parents (female sterility, the petals with white margins, the up-curled leaves on young plants, early flowering). The disomic substitution line derived from the addition line with the serrated leaves of O. violaceus and one B. napus nullisomics still gave the serration formation.2. The rDNA loci on three O. violaceus chromosomes were active and gave differential amounts of rRNA transcripts in the B. napus background, showing the variable degrees of nucleolar dominance.3. The O. violaceus chromosomes added to or substituted into the B. napus background were stably maintained in somatic cells without variations in chromosome numbers. The two O. violaceus chromosomes in additions and substitutions mainly showed the normal pairing and segregation during meiotic divisions of pollen mother cells (PMCs), but were segregated precociously and lagged in some PMCs. They often appeared at the periphery of daughter cells. In the addition and substitution, no bivalents formed by the chromosomes from two species were observed, indicating the lack of their homoeologous relationship. In addition, some chromosomes from B. napus were lagged and lost during meiotic divisions, likely resulting from the induction of alien O. violaceus chromosomes. These alien chromosomes could be transmitted to the progeny through male and female gametes.4. The behavior of parental genomes in intergeneric somatic hybrids between B. napus and O. violaceus were analyzed by using genomic in situ hybridization (GISH). In mitotic and meiotic cells, the chromosomes from O. violaceus were distinguished from those from B. napus by their larger size and staining patterns. In interphase nuclei of the hybrid, O. violaceus-origin chromatin appeared as large heterochromatic blocks and at prophase was non-randomly distributed, typically towards one side of the nucleus. In PMCs at prophase I of meiosis, O. violaceus chromosomes appeared as one or two deeply stained chromatin blocks that resolved into bivalents late, after bivalents from B. napus were visible. Then bivalents of O. violaceus congressed to the equatorial plate and segregated at anaphase I after those from B. napus. The different behaviour of O. violaceus chromosomes in the hybrids indicates that they have differential condensation states at interphase and progress later through the cell cycle and meiosis than B. napus chromosomes. This difference in behaviour may restrict or prevent the formation of bivalents of mixed genome origin. However, two O. violaceus chromosomes in the addition and substitution condensed prior to those of B. napus and showed earlier segregation, which suggested that their cytological behavior changed in the background of B. napus.5. The fatty acid profiles of these additions had no obvious difference from those of B. napus parent, and only one line presented much higher content of the erucic acid.