Genetic Analyses On Progenies Of Intergeneric Hybrids Between Brassica Napus And Orychophragmus Violaceus

Wide hybridization can be used to study the evolution of plants and establish alien chromosome lines.Alien addition lines are widely utilized for plant genetics and breeding. Cytogenetics of intergeneric hybrids between Brassica napus L.(2n=38) and Orychophragmus violaceus(L.) O.E.Schulz(2n=24) and their progenies have been extensively investigated.The separation of parental genomes during the mitotic and meiotic divisions of the hybrid cells is proposed,following pseudogamy,semigamy and chromosome elimination in plant wide crosses.However,no stable B.napus-O,violaceus addition lines have been obtained in the progenies of sexual hybrids.In this study,inbred lines(F₈-F₁₀) derived from one hybrid of these two species are characterized for morphology,cytology and genomic compositions.In addition,backcross progenies of two generations derived from the somatic hybrids between B.napus and O.violaceus after pollinated by B.napus parent are produced and characterized at morphological, cytogenetical and molecular levels,and several B.napus - O.violaceus monosomic addition lines with obvious phenotypic traits are established.The results are described as follows:1.One F₅ plant(2n=31) of one B.napus cv.Oro×O.violaceus hybrid with slightly yellow petals and the 12:19 and 15:16 segregations in its pollen mother cells(PMCs) produced 18 F₆ plants with distinct morphological characters and wide variations in fertility and chromosome numbers(2n=25-38).Three plants(Nos.1-3) out of the 18 F₆ plants were morphologically B.rapa-like by having oval and less waxy but greener leaves and two of them(No.1 and 3) were totally sterile.Two most B.rapa-like F₇ plants from the plant No.2 were chosen through morphology for successive selfcrossing to F₁₀ generation and two populationsâ… ,â…¡were produced.1.1.A few morphological variations were observed within or between the two populations.They were more similar to B.rapa on leaves shape and flowering time etc, but more similar to B.napus on some botanical characters such as length of siliques and 1000 seed weight.1.2.Two populations both displayed self-incompatibility at some degrees withâ…¡being more evident.1.3.With progression of generations,chromosomes number of plants from two populations gradually increased and centred at the number of B.napus(2n=38). Chromosome pairins at meiotic diakinesis of hybrids between B.rapa-like plants and B. rapa revealed that chromosomes lost in B.rapa-like plants possibly belonged to C genome of B.oleracea.No intact O.violaceus chromosomes or chromosome fragments were founded by genomic in situ hybridization(GISH) observations in these B. rapa-like progenies.1,4.AFLP analysis showed that B.rapa-like progenies(F₁₀) had more DNA bands novel for two parents and deleted from B.napus parent than specific bands for O. violaceus.The AFLP clustering analysis distinguished populationsâ… andâ…¡at 0.92 correlation coefficient,showing that they had very similar genomic compositions with a degree of genetic diversity.In addition,they had more distant genetic distances from B. rapa and B.oleracea.Genetic distance between the two populations and B.rapa seemed to be wider than that with B.oleracea.2 Genetic analysis of intergeneric somatic hybrids between B.napus cv. Huashuang 3 and O.violaceus and progenies2.1.Three hybrids(Nos.98,100,101) derived from three different calli were sterile for male and partially fertile for female in individual.Hybrids Nos.98,101 both showed the similar morphology intermediate between two parents,displaying serrated leaves,many basic branches from O.violaceus and yellow petals with red stripes. Hybrids No.100 resembled B.napus mainly in morphology with pale yellow petals with slightly purple stripes.The cpDNA of all somatic hybrids was of B.napus type.AFLP analysis indicated that these hybrids had closer genetic relationship with O.violaceus than with B.napus,and the young and flowering plants of hybrid No.101 had some difference in AFLP profiles,and the same for the plants from cultured buds of the plant in field and from subcultured buds on medium.These hybrids were mixoploids (2n=51-67) with 19-28 O.violaceus chromosomes.Chromosomes in pollen mothe rcells (PMCs) at meiotic diakinesis mainly formd bivalents and showed bi-/multipolar segregations at anaphaseâ… .2.2.After pollinated by B.napus parent and with embryo rescue,hybrid 101 gave rise to 20 BC₁ plants,in which 9 plants shown the typical serrated leaves of O.violaceus, the others had B.napus-type leaves.All BC₁ plants were partially fertile for male but totally sterile for female by showing the abnormal structure of ovules.They were mixoploids(2n=41-54) with 9-16 chromosomes from O.violaceus.About one half of O. violaceus chromosome in PMCs at meiotic diakinesis underwent homoeologous pairings in BC₁ plants.Multipolar segregations occurred with a lower frequency in Aâ… PMCs of BC₁ plants than in hybrids.2.3.After polinated with the pollen grains of several BC₁ plants,Huashuang 3 produced plentiful BC₂ seeds which generally had low germination rate and speed.BC₂ plants showed segregations for female fertility,leaves shape and flowering time in some BC₂ combinations.Eight BC₂ plants examined by GISH had still some chromosome variations(2n=39-43) with 2-5 chromosomes from O.violaceus.Still nearly one half of O.violaceus chromosomes underwent homoeologous pairings in BC₂ plants.O. violaceus chromosomes were frequently lagged in Aâ… PMCs,but many daughter groups at Aâ…¡or nuclei at Tâ…¡contained O.violaceus chromosomes.During mitotic divisions of majority of anther-wall cells,the sister ehromatids of O.violaceus chromosomes were equally distributed into daughter cells but unequally for some.2.4.In BC₂ and several BC₂F₁ populations,five B.napus - O.violaceus monosomie addition lines with one O.violaceus chromosome were obtained,which showed specific phenotypic traits,such as serrated leaves of O.violaceus(O₁),B.napusphenotype (O₂),pale petals(O₃),basal clustering branches(O₄) and female sterility(O₅). The first four lines showed high seed-sets by selfing or open- pollination.2.5.In these hybrids and progenies,the chromosomes of O.violaceus were easily distinguished from those of B.napus by their large size and dark staining.