Genetic characterization of exotic germplasm in spring-type Brassica napus L.: Validation, confirmation, tester complementation and prediction of hybrid seed yield quantitative trait loci

Quantitative trait loci (QTL) for hybrid seed yield in the oilseed B. napus L. were previously identified using biparental mapping populations in which the exotic parental alleles increase hybrid seed yield of spring-type germplasm. The utility of these QTL in breeding programs was evaluated by further characterization of their effects in the same (validation) and different (confirmation) genetic backgrounds and tester combinations. Results from the validation test of six hybrid seed yield QTLs show that most of the exotic QTL alleles do increase hybrid seed yield, although the additive effects were substantially overestimated in the original QTL study. Thus, marker assisted selection for hybrid seed yield QTLs in the original hybrid combination was successful and may be useful for providing increased yield stability across environments. Results from the confirmation test of seven hybrid seed yield QTL show that most QTL affected hybrid seed yield; however, in new hybrid combinations the exotic QTL alleles often decreased yield as compared to the spring-type allele. It was also apparent that QTL expression was dependent on tester complementation and genetic background effects, along with environment interactions. Thus, further characterization is required for successful utilization of the hybrid seed yield QTLs in B. napus breeding programs.;One previously confirmed hybrid seed yield QTL on linkage group N3 from the winter-type B. napus cultivar 'Ceres' was further characterized in the original spring-type ('Mamoo') genetic background in hybrid combination with 27 diverse testers. Seven tester combinations showed significant hybrid seed yield differences between the 'Ceres' and 'Marnoo' QTL allele. Marker saturation of the QTL region, through the use of synteny with Arabidopsis thaliana, and subsequent genotyping of the testers provided a survey of tester QTL genetic/allelic diversity, haplotype decay and trait localization. Genetic distance within the QTL was not useful in predicting hybrid performance and only marginal significance for one molecular marker was found with the association analysis. However, there is also evidence that the 'Ceres' N3 hybrid seed yield QTL is influenced by tester (allelic or inter-locus epistatic) interactions.