Genetic Analyses On Brassica Rapa×Orychophragmus Violaceus Hybrids And Their Progenies

The wide hybridizations were extensively used in plant genetic researches and breeding programs. Up to now, the specific chromosome behaviors, such as chromosome doubling, formation of unreduced gametes, chromosome elimination and separation of parental genomes, have been reported in plant wide crosses. In this investigation, the intergeneric Hybrids between Brassica rapa ssp. chinesis L. (2n=20, AA), B. rapa L.(2n=20, AA) and Orychophragmus violaceus (L.) O. E. Schulz (2n=24, OO) were obtained through embryo rescue and their chromosomal/genomic compositions analyzed by the methods of genomic in situ hybridization (GISH) and amplified fragments length polymorphism (AFLP) to provide the molecular evidence for the complete and partial separation of the parental genomes proposed before. The results were described as follows.1. Among all seventy-two F1 plants, thirty-three ones from B. rapa var. chinesis cv. "Aijuehuang" × O. violaceus crosses and eight from nine B. rapa cultivars × O. violaceus crosses were obtained by embryo resuce, and the remainings were produced by harvested seeds, five from the crosses with "Aijuehuang" and twenty-six with the B. rapa cultivars.2. All F1 plants showed the similar morphology of their females and among them, three expressed the basal clustering branches and purple stems from O. violaceus, four had more than four petals and smaller petals, while eight had inflorescences developed from ovaries or siliques.3. The F1 plants were classified into five types according to the chromosome number in ovary cells and the chromosome behaviors in pollen mother cells (PMCs): type Ⅰ (2n=19-43), type Ⅱ(2n=19-22), type Ⅲ(2n=20), type Ⅳ(2n=18-20), type Ⅴ(2n=19-20). Except for those in typelll, all Fl plants had the cells with different chromosomes, but those with 2n=20 were most frequent in ovary cells. In all F1 plant, PMCs mainly had 10Ⅱ at diakinesis and showed the 10:10 segregations at anaphase Ⅰ (A Ⅰ). However, one plant of typeⅢ mainly produced PMCs with 10Ⅱ plus one chromosomal fragment and plants of type Ⅴ with 2n=19, 20 in ovary cells had diakinesis PMCs (2n≥40) with 2~7quadrivalents in few buds. Lagging chromosomes and chromosomal bridges appeared at high frequency in A I PMCs of types II ~ V.4^ GISH observations on PMCs of partial Fl plants showed that 1~2 O. violaceus chromosomes were detected in low frequency in some PMCs of seven plants, and 1~3 Brassica translocated chromosmes with the O. violceus fragments were observed in some PMCs of eleven plants, while all other cells contained only Brassica chromosomes.5 > Twenty pairs of AFLP primes were randomly selected and used for AFLP fingerprint analyses. Totally, 769 polymorphic bands were generated, including 113 ones specific for O. violaceus, 548 deleted in B. rapa ssp. chinesis IB. rapa and 108 novel for two parents. Moreover, most of the same deleted bands for Brassica females were exhibited in all Fl plants of the same combinations, indicating the deleted loci were selective. Clustering analysis using AFLP patterns showed that only one Fl plant from the cross with "Aijuehuang" had the similarity coefficient > 0.85 in comparison with "Aijuehuang" and the others were more distantly related with "Aijuehuang", but all B. rapa cultivars with the similarity coefficient > 0.75 were put in the same group and had the similarity coefficient < 0.67 with their Fl plants, indicating that the Fls were differentiated genetically from their Brassica parents after crossing with O. violaceus.6> F2 plants were morphologically similar to the Brassica parents and had good seed-sets. However six from the crosses with "Aijuehuang" and one with one B. rapa cultivar had yellow seeds.Finally the mechanisms behind the formation of these hybrids and their genetic constituents were discussed.