Hybrids between Brassica napus and B. nigra show frequent pairing between the B and A/C genomes and resistance to blackleg
High frequencies of homoeologous and even non-homologous chromosome recombination in Brassica hybrids can transfer useful traits between genomes, but also destabilise synthetic allopolyploids. We produced triploid hybrids (2n = 3x = ABC) from the cross B. napus (rapeseed, 2n = 4x = AACC) × B. nigra (black mustard, 2n = 2x = BB) by embryo rescue and allohexaploid hybrids (2n = 6x = AABBCC = 54) by chromosome doubling of the triploids. These hybrids demonstrated resistance to blackleg disease (causal agent: Leptosphaeria maculans) inherited from their B. nigra parent. In order to assess the possibility of transfer of this resistance between the B genome and the A and C subgenomes of B. napus, as well as to assess the genomic stability of allohexaploids from the cross B. napus × B. nigra, frequencies of non-homologous chromosome pairing in these hybrids were assessed using classical cytogenetics and genomic in-situ hybridization. Meiosis was highly irregular, and non-homologous chromosome pairing between the B genome and the A/C genomes was common in both triploid hybrids (observed in 38% of pollen mother cells) and allohexaploid hybrids (observed in 15% of pollen mother cells). Our results suggest that introgression of blackleg resistance from the B genome into the A or C genomes should be possible, but that allohexaploids from this genome combination are likely unstable.
KeywordsBrassica Interspecific hybridization Cytogenetics Meiotic stability Leptosphaeria maculans Introgression breeding
Analysis of variance
Bacterial artificial chromosome fluorescent in-situ hybridization
Cytoplasmic male sterility
False discovery rate
Genomic in-situ hybridization
Pollen mother cell
Volume of diseased tissue in scoring blackleg disease infection of rapeseed
The radius of healthy tissue in the cross section of the stem in scoring blackleg disease infection of rapeseed
Girdling of the stem according to a 0–9 point scale for scoring blackleg disease infection of rapeseed
Lesion length according to a 0–9 point scale for scoring blackleg disease infection of rapeseed
Profundity of necrosis according to a 0–9 point scale for scoring blackleg disease infection of rapeseed
Advice on FISH/GISH chromosome staining and embryo rescue by Ghader Mirzhagaderi, Olivier Coriton and Anne-Marie Chèvre is gratefully acknowledged, as is the assistance and support in plant cultivation and cross pollination by Ingrid Schneider-Hüther and Petra Degen. Furthermore, we would like to thank Volker Wissemann for providing the infrastructure for flow cytometry.
RG provided the experimental design advised by ASM, produced the hybrids, collected and analysed the meiotic and phenotypic data and wrote the manuscript. DA performed L. maculans resistance tests of parental cultivars by cotyledon inoculation and adult plant resistance tests of hybrids and parental cultivars, with input into experimental design, analysis and supervision from BK. ASM supervised RG and assisted in interpretation and analysis of results. All authors contributed to critical revision of the manuscript.
This work was supported by Deutsche Forschungsgemeinschaft (DFG) Emmy Noether grant MA6473/1-1.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Human and animal studies
This article does not contain any studies with human or animal subjects performed by any of the authors.
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