Chromosomes of the three diploid Brassica species, B. rapa (AA), B. nigra (BB) and B. oleracea (CC), were identified based on their morphological characteristics, especially on the condensation pattern appearing at the somatic pro-metaphase stage. The morphological features of the pro-metaphase chromosomes of the three Brassica spp. were quantified by imaging methods using chromosome image analyzing system II (CHIAS 2). As a result, quantitative chromosome maps or idiograms of the three diploid Brassica spp. were developed. The fluorescence in situ hybridization (FISH) method revealed the location of 45s rDNA (the 26s-5.8s-18s ribosomal RNA gene cluster) on the chromosomes involved. The number of 45s rDNA loci in the B. rapa, B. nigra and B. oleracea are five, three and two, respectively. The loci detected were systematically mapped on the idiograms of the three Brassica spp.

Quantitative karyotyping of three diploid Brassica species by imaging methods and localization of 45s rDNA loci on the identified chromosomes

A synthetic Brassica napus rapeseed with genome composition of ArArCcCc, made by combining Ar from B. rapa (ArAr) and Cc from B. carinata (BcBcCcCc), is valuable for making new genes available to breeders and gaining heterosis in crosses. An intergenomic hybrid AnArCnCc was made from a hybrid between natural Brassica napus (AnAnCnCn) and a synthetic rapeseed. To construct the synthetic Brassica napus, hexaploid plants (2n=54, ArArBcBcCcCc) were first obtained through chromosome doubling of trigenomic hybrids (2n=27, ArBcCc) between Brassica carinata (2n=34) and B. rapa (2n=20). Pentaploid hybrids (2n=46, ArAnBcCcCn) were then produced by crossing the hexaploid with the pollen of natural B. napus (2n=38). Chromosomes with dual and single Bc genomes were observed in somatic cells of hexaploid and pentaploid plants. About 80% of pollen mother cells of pentaploid hybrids had 19 or more bivalents, indicating that the bivalents from Ar/An and Cc/Cn chromosomes were normally formed. The occurrence of trivalents and quadrivalents at diakinesis suggested that Bc, An and Ar or Bc, Cn and Cc homologous pairing and exchange might happen. The variable number of laggards, 3 and 4 in most cases, were observed in the majority of PMCs at anaphase. Results from genomic in situ hybridization showed that the laggards belonged mainly to the Bc genome, suggesting that the Bc genome could be eliminated in the gametesof pentaploid hybrids. 16.15% of seeds derived from self-pollinated pentaploids have 38 chromosomes, and 90% of 38-chromosome seeds were completely excluded Bc genome. The cytological results of this experiment suggested that it is possible to obtain new materials with genome composition of ArArCcCc for rapeseed breeding.

Construction of novel Brassica napus genotypes through chromosomal substitution and elimination using interploid species hybridization.

Interspecific hybridization is a powerful tool for improvement of crop species, it has the potential to broaden the genetic base and create new plant forms for breeding programs. Synthetic allopolyploid is a widely-used model for the study of genetic recombination and fixed heterosis in Brassica. In Brassica napus breeding, identification and introgression of new sources of clubroot resistance trait from wild or related species into it by hybridization is a long-term crop management strategy for clubroot disease. Radish (Raphanus sativus L.) is a close relative of the Brassica and most radish accessions are immune to the clubroot disease. A synthesized allotetraploid Brassicoraphanus (RRCC, 2n = 36) between R. sativus cv. HQ-04 (2n = 18, RR) and Brassica oleracea var. alboglabra (L.H Bailey) (2n = 18, CC) proved resistant of multiple clubroot disease pathogen P. brassicae. To predict the possibility to transfer the clubroot resistance trait from the RR subgenome of allotetraploid Brassicoraphanus (RRCC, 2n = 36) into Brassica napus (AACC, 2n = 38), we analyzed the frequency of chromosome pairings in the F1 hybrids produced from a cross between B. napus cv. HS5 and the allotetraploid, characterize the genomic composition of some backcrossed progeny (BC1) using GISH, BAC-FISH and AFLP techniques. The level of intergenomic pairing between A and R genomes in the F1 hybrid was high, allosyndetic bivalents formed in 73.53% PMCs indicative of significant level of homeologous recombination between two genomes and high probability of incorporating chromosomal segments/genes from R-genome into A/C-genomes. The BC1 plants inherited variant extra R chromosomes or fragments from allotetraploid as revealed by GISH and AFLP analysis. 13.51% BC2 individuals were resistant to clubroot disease, and several resistance lines had high pollen fertility, Overall, the genetic material presented in this work represents a potential new genetic resource for practical use in breeding B. napus clubroot resistant cultivars.

/pdf/cytological-and-morphological-analysis-of-hybrids-between-51l6gr3u4l.pdf

Cytological and morphological analysis of hybrids between Brassicoraphanus, and Brassica napus for introgression of clubroot resistant trait into Brassica napus L.

The present study is concerned with a Brassica campestris-alboglabra monosomic addition line (AA + 1 chromosome from C, 2n = 21) which harbours a B. alboglabra (a form of B. oleracea, CC, 2n = 18) chromosome with a gene controlling seed colour. Random amplified polymorphic DNA marker analysis revealed 19 markers specific to the alien C-genome chromosome of the addition line. One of these markers was inferred to be close to the seed colour gene. The location of the seed colour gene in a terminal region of the alien chromosome was deduced from what could have been homoeologous recombination or chromosomal deletion. Studies on mitotic prometaphase chromosomes of the addition line indicated that the alien chromosome was apparently chromosome 1 of B. alboglabra. The use of the present addition line is discussed in the context of breeding for yellow-seeded B. alboglabra and B. napus (AACC, 2n = 38).

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1997.00133.x

Identification and Chromosomal Assignment of RAPD Markers Linked with a Gene for Seed Colour in a Brassica Campestris‐Alboglabra Addition Line

Breeding programs aiming at transferring desirable genes from one species to another through interspecific hybridization and backcrossings often produce monosomic and disomic additions as intermediate crossing products. Such aneuploids contain alien chromosomes added to the complements of the recipient parent and can be used for further introgression programs, but lack of homoeologous recombination and inevitable segregation of the alien chromosome at meiosis make them often less ideal for producing stable introgression lines. Monosomic and disomic additions can have specific morphological characteristics, but more often they need additional confirmation of molecular marker analyses and assessment by fluorescence in situ hybridization with genomic and chromosome-specific DNA as probes. Their specific genetic and cytogenetic properties make them powerful tools for fundamental research elucidating regulation of homoeologous recombination, distribution of chromosome-specific markers and repetitive DNA sequences, and regulation of heterologous gene expression. In this overview we present the major characteristics of such interspecific aneuploids highlighting their advantages and drawbacks for breeding and fundamental research.

Production of alien chromosome additions and their utility in plant genetics.

The alien C-genome chromosome in aBrassica campestris-alboglabra monosomic addition line was characterized by random amplified polymorphic DNA (RAPD) analysis. The alien chromosome carried three loci, Ec, Wc and Lap-1C, controlling synthesis of erucic acid, white flower colour and a fast-migrating band of leucine aminopeptidase (Lap-1Cc) respectively. The RAPD analysis revealed 17 markers specific to the alien chromosome. Among 45 offspring plants from the selfed addition line the alien C-chromosome was transmitted to 15 plants, four plants had only parts of this chromosome and the remaining 26 plants did not carry the chromosome.

Random amplified polymorphic DNA markers of the Brassica alboglabra chromosome of a B. campestris-alboglabra addition line.

Meiosis was studied in pollen mother cells of two Brassica campestris (AA) and one B. alboglabra (CC) accessions, their resynthesized B. napus amphidiploids (AACC), and digenomic hybrids produced (AAC). The two parental species exhibited different chromatin condensation patterns at diakinesis, which enabled the differentiation between genomes and the detection of auto- and allosyndesis in the amphidiploids and digenomic hybrids. Corresponding chromatin condensation differences were manifested at mitotic prometaphase. The diploid accessions were characterized as to glucosinolate composition, restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD), and isozyme patterns. All 20 RFLP probes and 9 RAPD primers tested gave discriminatory bands for the A and C genomes. For isozymes, 14 out of 17 analysed loci had alleles that discriminated between these genomes. In addition to the already established locations of flower colour, erucic acid content, and leucine aminopeptidase enzyme genes in the C genome, other genome-specific isozyme and DNA-based markers amounted to 89 and 112 in the two B. campestris accessions and 135 in the B. alboglabra accession. Sinigrin synthesis is an additional character controlled by the C genome, The combination of different marker systems and cytological techniques for the characterization of the A and C genomes and their constituent chromosomes has obvious implications for plant breeding, assessment of gene introgression in nature, and evolutionary studies.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1995.00251.x

Characterization of the A and C Genomes of Brassica Campestrisand B. Alboglabra

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Random amplified polymorphic DNA markers of the Brassica alboglabra chromosome of a B. campestris-alboglabra addition line.

Characterization of the A and C Genomes of Brassica Campestrisand B. Alboglabra