Mapping the mosaic of ancestral genotypes in a cultivar of oilseed rape (Brassica napus) selected via pedigree breeding

Abstract

Recent oilseed rape breeding has produced low glucosinolate cultivars that yield proteinaceous meal suitable for animal feed. The low glucosinolate character was introduced into modern cultivars from Brassica napus 'Bronowski', a cultivar that is agronomically inferior in most other respects. Residual segments of 'Bronowski' genotype in modern cultivars probably cause reduced yield, poorer winter hardiness, and lower oil content. The quantity and distribution of the 'Bronowski' genotype in the modern oilseed rape cultivar Brassica napus 'Tapidor' was investigated using a segregating population derived from a cross between 'Tapidor' and its high glucosinolate progenitor. This population was analyzed with 65 informative Brassica RFLP probes and a genetic linkage map, based on the segregation at 77 polymorphic loci, was constructed. The mapping identified 15 residual segments of donor genotype in 'Tapidor', which together occupy approximately 29% of the B. napus genome. Mapping the loci that control variation for the accumulation of total seed glucosinolates in the segregating population has identified three loci that together explain >90% of the variation for this character. All of these loci are in donor segments of the 'Tapidor' genome. This result shows the extent to which conventional breeding programmes have difficulty in eliminating residual segments of donor genotype from elite material.

Repeated Polyploidy Drove Different Levels of Crossover Suppression between Homoeologous Chromosomes inBrassica napusAllohaploids

“…Indeed, we observed that the high diversity of ptDNA found in the MU group (Figure 2) correlated with a high diversity of multilocus genotypes around PrBn (five out of seven accessions). These results are in close agreement with the findings of Sharpe and Lydiate (2003), who showed that the genome of oilseed rape cultivars is a mosaic of blocks from ancestral genotypes. We thus speculate that the MU and fu groups originated as genetically distinct lineages produced from at least two maternal diploid progenitors.…”

Identification of Quantitative Trait Loci for Rice Quality in a Population of Chromosome Segment Substitution Lines

“…Recently, to identify the QTLs, researchers have developed novel mapping populations such as chromosome segment substitution lines (CSSLs), introgression lines (ILs) or recombinant chromosome substitution lines (RCSLs) in rice (Doi et al 1997; Sobrizal et al 1999; Kubo et al 2002; Ebitani et al 2005; Li et al 2005; Hao et al 2006; Tian et al 2006; Xi et al 2006; Tan et al 2007), Brassica napus (Howell et al 1996; Burns et al 2003; Sharpe and Lydiate 2003), tomato (Eshed and Zamir 1995, 1996), Arabidopsis (Koumproglou et al 2002), wheat (Pestsova et al 2001), and barley (Matus et al 2003; Korff et al 2004).…”

Artificial introgression of a large chromosome fragment around the rice blast resistance gene Pi-ta in backcross progeny and several elite rice cultivars

“…In their study, the cultivar was developed by backcrossing breeding with selection for resistance to the tomato mosaic virus resistance gene TM-2. In soybean, although the sizes were undetermined, it was estimated that relatively large introgressed fragments in both linked and unlinked to the selected traits were identified in a cultivar that had been developed by pedigree breeding (Sharpe and Lydiate, 2003). In this study, unlinked segments from donor Katy in the backcross progeny were removed by the fifth backcross generation as expected.…”