The genetic base of Brassica napus canola need to be broadened for exploitation of heterosis at a greater level in the breeding of F 1 hybrid canola cultivars. In this study, we evaluated 228 inbred B. napus canola lines derived from six B. napus × B. oleracea interspecific crosses and following two breeding methods (F 2-and BC 1-derived lines) to understand the effect of the B. oleracea alleles on heterosis for different agronomic and seed quality traits. Test hybrids of the inbreds derived from crosses involving vars. botrytis (cauliflower), alboglabra (Chinese kale) and capitata (cabbage) cv. Badger Shipper, on an average, gave about 10% mid-parent heterosis (MPH), and about 67% of the test hybrids gave higher seed yield than the common B. napus parent indicating that B. oleracea alleles can contribute to heterosis for seed yield in spring B. napus canola hybrids. This was also evident from a positive correlation of the genetic distance of the inbred lines from the common B. napus parent with MPH for seed yield (r = 0.31) as well as with hybrid yield (r = 0.26). Almost no correlation was found between genetic distance and MPH for seed oil and protein content as well as with the performance of the test hybrids for these two traits. The occurrence of positive correlation between seed yield of the inbred lines and test hybrids suggested the importance of the genes exerting additive effect for high seed yield in the hybrids. Very little or almost no heterosis was found for the other agronomic traits as well as for seed oil and protein content. While comparing the two breeding methods, no significant difference was found for seed yield of the test hybrids or the level of MPH; however, the BC 1-derived inbred and test hybrid populations flowered and matured earlier and had longer grain-filling period than the F 2-derived population. Thus, the results suggested that the B. oleracea gene pool can be used in the breeding of spring B. napus canola to improve seed yield in hybrid cultivars.

The narrow genetic base of Brassica napus L. canola, especially of its C genome, is an impediment for continued improvement of this crop. We investigated the gene pools of different variants of B. oleracea L. to improve agronomic and seed quality traits of B. napus canola. For this, B. napus canola inbred populations were developed from six interspecific crosses, involving a single B. napus canola line and six accessions of B. oleracea belonging to four variants of this species, following two breeding techniques (F2– and BC1–derived lines). Among these, the population derived from crossing with var. italica gave the greatest seed yield and also had shorter duration of flowering than most of the other populations. The population developed using var. botrytis had the highest seed oil content, and seed yield was comparable with the population developed using var. italica. Populations based on var. capitata had the lowest oil but greater protein content than most of the populations. Several lines from these interspecific crosses exceeded seed yield of the B. napus parent and also had acceptable agronomic and seed quality traits. Comparing the two breeding techniques, the F2–derived population gave greater yield than the BC1–derived population, whereas the BC1–derived population flowered and matured earlier than the F2–derived population. Genetic distance of the inbred lines from the B. napus parent showed positive correlation of r ≥ 0.4 with days to flowering and seed protein content and negative correlation with seed oil content, whereas correlation with seed yield was negative and weak (r = −0.18). Thus, the results showed that the B. oleracea gene pool, especially var. italica and botrytis, can be used to improve spring B. napus canola, as well as to broaden the genetic base of this crop.

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A genome-wide association study (GWAS) was carried out by using a Brassica napus population of 175 lines, developed from six B. napus × B. oleracea interspecific crosses, and 5,743 single nucleotide polymorphism (SNP) markers to identify quantitative trait loci (QTL) for agronomic and seed quality traits and to understand the effect of B. oleracea alleles on these traits. Heritability of these traits varied from 52.9 to 84.1%. About 79% of the SNPs were positioned to the nine C genome chromosomes, while only 21% to the 10 A genome chromosomes; this was largely due to little genetic variation in the A genome of this population, as expected. However, the SNPs were distributed throughout the entire length of the chromosomes suggesting their usefulness in GWAS. The C genome SNPs detected nine genomic regions affecting these traits. This included the genomic regions of C2 and C5 affecting days to flowering, C1 affecting the duration of grain-filling period, C1, C5, and C8 affecting oil content, and C1, C2, and C6 affecting glucosinolate content; among these, some of the loci has not been reported previously. The QTL alleles of B. oleracea which can be beneficial in oilseed B. napus, such as the C5 QTL allele for the earliness of flowering, were also identified. Several putative candidate genes were identified in the QTL regions. Thus, the results provided evidence of the utility of the B. oleracea gene pool for use in unveiling the unidentified QTL in B. napus as well as its use in breeding. INTRODUCTIONBrassica napus canola (AACC, 2n = 38) is the second largest oilseed crop in the world after soybean [Glycine max (L.) Merr.]. The current annual production of Brassica oilseeds in the world is about 71 million metric tonnes (Statista, 2019

Broadening the genetic base of the C genome of Brassica napus canola is needed for continued improvement of this crop. For this, we developed few hundred canola lines from B. napus × B. oleracea interspecific crosses involving a B. napus canola line and six B. oleracea accessions belonging to four varieties, viz. vars. alboglabra, botrytis, capitata and italica, and following two breeding methods (F2- and BC1 (F1 × B. napus)-derived lines). The objective of this study was to understand the genetic structure of this population regarding the alleles introgressed from B. oleracea by using SSR markers, and to investigate the inheritance of B. oleracea alleles in these re-constituted canola lines. Marker analysis showed that the four B. oleracea varieties were genetically quite distinct. Several canola lines derived from these six crosses tended to group together with their B. oleracea parent demonstrating that the wide diversity of the B. oleracea gene pool can be exploited for broadening the genetic base of the C genome of B. napus canola. Loss of several B. oleracea alleles occurred during the development of these inbred lines. While comparing the two breeding methods for introgression of B. oleracea alleles, significantly greater loss of alleles occurred in the F2-derived population as compared to the BC1-derived population. Thus, the knowledge from this study can be used for efficient introgression of exotic alleles from B. oleracea into B. napus for broadening the genetic base of this crop.