Cytogenetic and Molecular Characterization of B-Genome Introgression Lines ofBrassica napusL.

Abstract

Brassica napus introgression lines (ILs), having B-genome segments from B. carinata, were assessed genetically for extent of introgression and phenotypically for siliqua shatter resistance. Introgression lines had 7–9% higher DNA content, were meiotically stable, and had almost normal pollen fertility/seed set. Segment introgressions were confirmed by fluorescent genomic in situ hybridization (fl-GISH), SSR analyses, and SNP studies. Genotyping with 48 B-genome specific SSRs detected substitutions from B3, B4, B6, and B7 chromosomes on 39 of the 69 ILs whereas SNP genotyping detected a total of 23 B-segments (≥3 Mb) from B4, B6, and B7 introgressed into 10 of the 19 (C1, C2, C3, C5, C6, C8, C9, A3, A9, A10) chromosomes in 17 ILs. The size of substitutions varied from 3.0 Mb on chromosome A9 (IL59) to 42.44 Mb on chromosome C2 (IL54), ranging from 7 to 83% of the recipient chromosome. Average siliqua strength in ILs was observed to be higher than that of B. napus parents (2.2–6.0 vs. 1.9–4.0 mJ) while siliqua strength in some of the lines was almost equal to that of the donor parent B. carinata (6.0 vs.7.2 mJ). These ILs, with large chunks of substituted B-genome, can prove to be a useful prebreeding resource for germplasm enhancement in B. napus, especially for siliqua shatter resistance.

Reconstituting the genome of a young allopolyploid crop, Brassica napus, with its related species

“…Generally, introducing genetic variation from the B genome of B. carinata to B. napus is very difficult. To date, only a few cases have successfully introgressed the B genome segments into B. napus, and it would be favourable to introduce the B genome segment to introduce resistance-related genes to B. napus (Dhaliwal et al, 2017;Navabi et al, 2010Navabi et al, , 2011Xiao et al, 2010). Based on the results described above, the inference is that homologous exchange events occurred between the B and A/C genomes.…”

“…These favourable variations may come from the founder parents, but they may also be caused by genomic changes, such as the chromosome rearrangement, homologous recombination, homoeologous shuffling, transposon activation and epigenetic modification. Desirable traits, such as the resistance to disease and pod shatter, that are harboured by the founder parents B. carinata and B. rapa, with high or low heritability, were introgressed to rapeseed easily or arduously through interspecific crossing (Dhaliwal et al, 2017;Diederichsen et al, 2009;Leflon et al, 2007;Raman et al, 2017). For example pod shatter resistance, which is a low heritability trait, was introduced to the B. napus along with the introgression of the B-genome segments from B. carinata, and these introgression lines showed higher pod strength than B. napus parents; some lines were almost equal to that of the B. carinata parents (Dhaliwal et al, 2017).…”

Molecular Diversity Analysis and Genetic Mapping of Pod Shatter Resistance Loci in Brassica carinata L.

“…Previous studies have reported that there is limited genetic variation for pod shatter resistance in the natural B. napus germplasm ( Bowman, 1984 ; Raman H. et al, 2014 ). Several research groups around the world are currently using B. carinata to expand the narrow genetic base of B. napus germplasm ( Cowling, 2007 ; Dhaliwal et al, 2017 ). In this study, only one QTL, Qpsr.wwai-C5 was identified on the C subgenome of B. carinata (chromosome C05), while other QTL were identified on the B subgenome (B1, B3, and B8).…”

“…In this study, only one QTL, Qpsr.wwai-C5 was identified on the C subgenome of B. carinata (chromosome C05), while other QTL were identified on the B subgenome (B1, B3, and B8). Previous studies have shown that fertile plants of B. napus carrying B genome introgressions can be generated ( Navabi et al, 2010 ; Dhaliwal et al, 2017 ). It remains to be established whether B and C genome derived lines exhibit pod shatter resistance expression or get silenced in the resynthesized B. napus ( Xu et al, 2009 ).…”

“…B. carinata is reported to be more resistant to seed shattering than B. napus, B. rapa , and, B. juncea ( Zhang et al, 2016 ). Interestingly, B. carinata is also known to hybridize with the A r ( B. rapa ) and A n C n ( B. napus ) genome species and produce viable ‘new type’ napus plants (A n A n C n/c C n/c ) with diverse C c genome ( Navabi et al, 2010 ; Tian et al, 2010 ; Banga et al, 2011 ; Dhaliwal et al, 2017 ). This knowledge prompted us to characterize genetic variation and identify genetic loci for pod shatter resistance in B. carinata to improve the level of shattering resistance in other Brassica crops, especially in canola.…”