Genomic selection (GS) is a modern breeding approach where genome-wide single-nucleotide polymorphism (SNP) marker profiles are simultaneously used to estimate performance of untested genotypes. In this study, the potential of genomic selection methods to predict testcross performance for hybrid canola breeding was applied for various agronomic traits based on genome-wide marker profiles. A total of 475 genetically diverse spring-type canola pollinator lines were genotyped at 24,403 single-copy, genome-wide SNP loci. In parallel, the 950 F1 testcross combinations between the pollinators and two representative testers were evaluated for a number of important agronomic traits including seedling emergence, days to flowering, lodging, oil yield and seed yield along with essential seed quality characters including seed oil content and seed glucosinolate content. A ridge-regression best linear unbiased prediction (RR-BLUP) model was applied in combination with 500 cross-validations for each trait to predict testcross performance, both across the whole population as well as within individual subpopulations or clusters, based solely on SNP profiles. Subpopulations were determined using multidimensional scaling and K-means clustering. Genomic prediction accuracy across the whole population was highest for seed oil content (0.81) followed by oil yield (0.75) and lowest for seedling emergence (0.29). For seed yieId, seed glucosinolate, lodging resistance and days to onset of flowering (DTF), prediction accuracies were 0.45, 0.61, 0.39 and 0.56, respectively. Prediction accuracies could be increased for some traits by treating subpopulations separately; a strategy which only led to moderate improvements for some traits with low heritability, like seedling emergence. No useful or consistent increase in accuracy was obtained by inclusion of a population substructure covariate in the model. Testcross performance prediction using genome-wide SNP markers shows considerable potential for pre-selection of promising hybrid combinations prior to resource-intensive field testing over multiple locations and years.

During the final step of oogenesis, the oocyte nucleus is subject to large-scale modifications that correlate with transcriptional silencing. While oocytes with dense chromatin around the nucleolus are silent (SN, surrounded nucleolus), oocytes with uncondensed chromatin (NSN, non-surrounded nucleolus) are transcriptionally active. It is believed that epigenetic mechanisms that participate in gene expression regulation could play a role in this event. In this context, we examined the behaviour of heterochromatin and related histone modifications during the NSN to SN transition by immunostaining. Using fluorescent in situ hybridization on three dimensionalpreserved nuclei (3D-FISH), we also studied the distribution of centromeric, pericentromeric and ribosomal (rDNA) sequences in relation to the nucleolus (also called the nucleolus-like body, NLB). We observed that in NSN-type oocytes, pericentromeric heterochromatin is aggregated within chromocenters. In SN-type oocytes, pericentromeric heterochromatin and centromeres form a discontinuous ring around the NLB. rDNA sequences, which initially present a pearl necklace structure, gather together in seven highly condensed foci at the NLB periphery. H3K9me3 and H4K20me3 heterochromatin marks clearly label chromocenters, whereas H3K4me3 and H4K5ac are totally excluded from heterochromatin regions, even in the very compact SN-nuclei. Remarkably, H3K27me3 displays an intermediate behavior. It appears that GV oocyte nuclei exhibit a specific epigenetic landscape. Histone modifications, related to both active and repressive chromatin structures, seem to follow the large-scale chromatin movements that occur during the NSN to SN transition. We also demonstrate that, while heterochromatin regions re-localize around the NLB, rDNA sequences adopt a highly compact structure in SN-type oocytes.

Chlorophyll levels provide important information about plant growth and physiological plasticity in response to changing environments. The stay-green gene NON-YELLOWING 1 (NYE1) is believed to regulate chlorophyll degradation during senescence, concomitantly affecting the disassembly of the light-harvesting complex and hence indirectly influencing photosynthesis. We identified Brassica napus accessions carrying an NYE1 deletion associated with increased chlorophyll content, and with upregulated expression of light-harvesting complex and photosynthetic reaction center (PSI and PSII) genes. Comparative analysis of the seed oil content of accessions with related genetic backgrounds revealed that the B. napus NYE1 gene deletion (bnnye1) affected oil accumulation, and linkage disequilibrium signatures suggested that the locus has been subject to artificial selection by breeding in oilseed B. napus forms. Comparative analysis of haplotype diversity groups (haplogroups) between three different ecotypes of the allopolyploid B. napus and its A-subgenome diploid progenitor, Brassica rapa, indicated that introgression of the bnnye1 deletion from Asian B. rapa into winter-type B. napus may have simultaneously improved its adaptation to cooler environments experienced by autumn-sown rapeseed.

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