Using sequence data from the ITS region (internal transcribed spacers ITS-1 and ITS-2 of nuclear DNA and the 5.8 rRNA gene), chloroplast DNA (cpDNA) sequence data from the trnL intron, and cpDNA re...

Phylogeny of tribe brassiceae (Brassicaceae) based on chloroplast restriction site polymorphisms and nuclear ribosomal internal transcribed spacer and chloroplast trnL intron sequences

Intergeneric hybrids between Brassica juncea (2n=36), B. carinata (2n=34) and Orychophragmus violaceus (2n=24) were produced when B. juncea and B. carinata cultivars were used as female parents. The hybrids between B. juncea and O. violaceus had an intermediate morphology except for petal colour and were partially fertile. The hybrids between B. carinata and O. violaceus had a matroclinous morphology and were nearly fertile. Cytological analysis of the hybrids and their progenies gave the following results. (1) In the hybrids between B. juncea and O. violaceus, the somatic tissues of the roots, leaves and styles were mixoploid (2n=12–42), and cells with 24, 30 or 36 chromosomes were the most frequent. Based on the recorded numbers and behaviour of the mitotic and meiotic chromosomes, complete and partial separation of the parental genomes was proposed to have occurred during mitosis. This resulted in the occurrence of cells with possibly complete and incomplete complements of the parental species and cells with parental complements and some additional chromosomes from the other parent. (2)  Pollen mother cells (PMCs) possibly with both parental chromosome complements, only B. juncea chromosomes or a complete B. juncea complement with additional O. violaceus chromosomes were more competitive in entering meiosis. The majority of fertile gametes were deduced to have been produced by PMCs with a B. juncea complement with or without additional O. violaceus chromosomes. (3) The progeny plants from selfed hybrids between B. juncea and O. violaceus were morphologically either of a B. juncea, hybrid or variable type. Cytologically they were grouped into six types according to the frequencies of cells with various chromosome numbers. All of the plants except 2 which constituted two types, were mixoploids, composed of cells with various chromosome numbers, mainly in a certain serial range. (4) The hybrid plants between B. carinata and O. violaceus were mixoploids with chromosome numbers in the range of 12–34, and cells with 2n=34 were the most frequent. The main categories of PMCs with 17 bivalents at metaphase I and 17 : 17 segregations at anaphase I contributed to the high fertility of the hybrids and the fact that their progeny after selfing were mainly plants with 2n=34. Somatic and meiotic separation of the parental genomes was proposed to have occurred in the hybrids between B. carinata and O. violaceus. (5) Mitotic and meiotic elimination of what could be O. violaceus chromosomes might also have contributed to the observed mitotic and meiotic cell types in the two kinds of hybrids studied. Finally, the possible mechanisms behind these cytological observations and their potential in the production of Brassica aneuploids were discussed.

Production and cytogenetics of the intergeneric hybrids Brassica juncea×Orychophragmus violaceus and B. carinata×O. violaceus

To further utilize the valuable germplasm Orychophrugmus violaceus for Brassica genetics and breeding, a B. napus x O. violaceus cross was repeated with embryo rescue. All F 1 plants except one B. napus haploid were mixoploids (2n = 17-39 in ovaries) with 2n = 31, 37, 38 and 39 as the maximal chromosome numbers in individuals, but the higher numbers mostly appeared in pollen mother cells (PMCs) with a preponderance of 2n = 30, 37 and 38. Only one chromosome and one chromosome segment of O. violaceus were detected at a low frequency in some ovary cells and PMCs with 2n = 37, 38 and 39 as determined by genomic in situ hybridization analysis. The fatty acid profiles of seeds from the majority of the F 1 and F 2 plants were similar to those of female B. napus cv. 'Oro', but some were obviously different in the percentages of oleic, linoleic and erucic acids, and some F 2 plants (2n = 38) with good seed set had high percentages of oleic (>70.0%) or linoleic (to 38.3%) acids and low erucic acid ( <1%). Subsequently, many kinds of B. napus aneuploids (2n = 28, 30, 34, 36, 37, 39 and 42), without O. violaceus chromosomes, were derived from F 2 progeny and microspores of partial F 1 plants. Finally, the cytological mechanisms behind the variations in chromosome numbers were discussed together with the implications of these aneuploids for Brassica genome research and of the plants with altered fatty acid profiles for improving the oil quality of B. napus.

Genomic in situ hybridization analysis of Brassica napus x Orychophragmus violaceus hybrids and production of B. napus aneuploids

A pentaploid hybrid plant (2n = 50, AACCO) between Brassica napus (AACC) and Orychophragmus violaceus (OO) showed matroclinous morphology and some patroclinous characters. Cloned progenies were mixoploid, consisting of various cells with 38-53 chromosomes, half of the cells with 50 chromosomes. The 50 chromosomes were mainly paired as 25 bivalents and segregated as 25:25 or 22:28; many other segregations were observed in some cells. Progenies produced by selfing had 38-47 chromosomes. Plants with 38 chromosomes were cytologically stable; in all other plants the chromosome number of individual cells varied between the genotype-specific maximum number and 38, indicating loss of chromosomes during mitosis. The mixoploid plants with 44 chromosomes mainly produced two kinds of mixoploid progenies with 44 and 41 chromosomes, respectively. All plants with 2n = 38 had the same morphology as the parental B. napus and were normal in fertility. These chromosome pairings and segregations in the pentaploid and its progeny support the hypothesis that O. violaceus is a natural polyploid species with a basic chromosome number of 3.

Cytogenetics and morphology of the pentaploid hybrid between Brassica napus and Orychophragmus violaceus and its progeny

Introgression of Genes from Wild Crucifers

Meiosis was studied in pollen mother cells (PMCs) with 2n = 31 in the intergeneric hybrid between Brassica nupus L. (2n = 38) and Orychophrugmus violoceus (L.) O.E. Schulz (2n = 24). Three patterns of chromosome behaviour were observed. (I) All 31 chromosomes proceeded directly to the second division, giving rise to unreduced gametes. (II) Two groups of 12 and 19 chromosomes moved to opposite poles during the first division and produced, after the second division, four daughter chromosomal groups: two with 12 chromosomes and two with 19 chromosomes. Accordingly, these two types of gametes have the same number of chromosomes as found in the gametes produced by the two parental species. They probably contain complete chromosome complements of O. violaceus and B. napus respectively. (III) At anaphase 1, 19 univalents possibly of B. nupus origin, moved to the poles in different numbers but most frequently in a 9:10 distribution. Twelve chromosomes, possibly of O. violuceus origin, appeared as six bivalents that lagged behind and were not included in the telophase I nuclei. The presumable O. violaceus chromosomes were thus not synchronous with those of B. napus. PMCs with more than 6 bivalents and with univalents at the equatorial plate were the most frequent category observed. There were indications that even in these cells, six bivalents often lagged behind at a later stage. The apparent separation of parental genomes and subsequent formation of pollen with either of the parental genomes (type II above) explains the production of plants with 2n = 38 of B. napus morphology among the progenies of these hybrids.

Meiotic Behaviour in Intergeneric Hybrids between Brassica Napus and Orychophragmus Violaceus

Plant morphology and cytogenetics of progenies from intergeneric hybrids between Brassica juncea and Orychophragmus violaceus were studied. The progenies comprised three F3 populations derived from three mixoploid F2 plants with different morphology and chromosome numbers. The following results were obtained. (1) The differences in plant morphology were maintained among the three F3 populations. (2) All F3 plants were mixoploids, mainly composed of cells with serial chromosome numbers in certain ranges. In plants with similar serial numbers, the cells with the highest three chromosome numbers accounted for 66–89% of the total cells. (3) In mitotic metaphase spreads, it was possible to differentiate some large and more darkly stained chromosomes which showed a later chromatid separation than the others. Lagging chromosomes and micronuclei were often observed in anther-wall cells. (4) In pollen mother cells (PMCs) at diakinesis and metaphase I, some large and more darkly stained bivalents and univalents were easily distinguished, and the chromosomes composing these bivalents segregated later than the others. Various segregation patterns were observed at anaphase I. At both anaphase/telophase I and II, some large and darkly stained chromosomes lagged between or were included in polar groups or daughter nuclei. (5) The differentiable large and darkly stained chromosomes in mitotic and meiotic cells were conceived as of O. violaceus origin. Differences in timing between the parental chromosomes during mitotic and meiotic divisions very likely contribute to the complete and partial separation of parental genomes proposed to occur in the B. juncea×O. violaceus hybrids.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1998.00143.x

Morphology and Cytogenetics of F3 Progenies from Intergeneric Hybrids Between Brassica Juncea and Ovychophragmus Violaceus

The wide hybridization and polyploidization play a significant role in the evolution of higher plants On the contrary, the artificially synthesized allopolyploids are genetically unstable and fail to be used as crops One reason for this situation may be that the allopolyploids in nature are the products of natural selection and evolution and it is difficult for human to repeat and perform the process in short periods Another reason is that we know little about the interaction mechanisms between the genomes of different origins So the genetics and epigenetics after allopolyploidizations are now studied by multidisciplinary approaches The spatial separation of parental genomes in hybrid cells have been observed in some sexual and somatic hybrids, but the biological meanings remain to clarify The abnormal chromosome behaviors in plant wide crosses, such as pseudogamy, semigamy, chromosome elimination and the mitotic and meiotic separation of parental genomes, may indicate the incompatibility of two parental species at gametic and chromosomal levels The systematic studies at different levels on chromosomal behavior and genetics in plant hybridizations are needed to undermine the mechanisms responsible for the formation and evolution of new species

Chromosomal behaviors in plant wide hybridizations and their genetic and evolutionary implications

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Meiotic Behaviour in Intergeneric Hybrids between Brassica Napus and Orychophragmus Violaceus

Morphology and Cytogenetics of F3 Progenies from Intergeneric Hybrids Between Brassica Juncea and Ovychophragmus Violaceus

Chromosomal behaviors in plant wide hybridizations and their genetic and evolutionary implications