Abstract
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.
Highlights
Interspecific hybridization is a powerful tool for improvement of crop species, it has the potential to broaden genetic base and create new plant forms for breeding programs [1]
Synthetic allopolyploids are widely used to exploit related species for valuable agronomic trait through interspecific hybridization [3, 4]. They are mainly utilized as genetic bridge materials for introgression of target genes/regions that are absent in natural genetic background of cultivated crop species [5, 6], e.g. the Ogu-INRA cytoplasmic male sterility (CMS) system [6, 7] and clubroot disease resistance of Raphanobrassica [8]
We noticed the hybrids had dark green leaves with similar serrated margins to Huashuang 5 (HS5), but without long petioles observed in Brassicoraphanus (Fig 2J)
Summary
Interspecific hybridization is a powerful tool for improvement of crop species, it has the potential to broaden genetic base and create new plant forms for breeding programs [1]. Synthetic allopolyploids are widely used to exploit related species for valuable agronomic trait through interspecific hybridization [3, 4] They are mainly utilized as genetic bridge materials for introgression of target genes/regions that are absent in natural genetic background of cultivated crop species [5, 6], e.g. the Ogu-INRA cytoplasmic male sterility (CMS) system [6, 7] and clubroot disease resistance of Raphanobrassica [8]. In Rapeseed (Brassica napus) breeding, identification and introgression of new, stable and durable clubroot resistant traits from wild or closely related species into it, either through interspecific or intraspecific hybridization has been an important research objective for the improvement of this oilseed crop [9]. Interspecific and introgressive hybridization hold such potential [19], and pyramiding of different sources of clubroot resistance genes into a single line might provide alternative durable resistance to a broad spectrum of P. brassicae
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