Genome-wide approach to dissecting the genetic basis of heterosis

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Heterosis is the phenomenon whereby the progeny of a cross between two inbred lines have enhanced fitness or performance relative to one or both parents. It has been successfully exploited in plant breeding and evolutionary biology. However, its genetic basis remains largely unknown despite the proposal of multiple models to explain heterosis over the past decades. The failure of these models to explain heterosis is due to lack of knowledge on genome-wide heterozygosity and the distribution of genetic effects at heterotic loci across the hybrid genome. Here I propose a novel approach to assessing genome-wide heterozygosity and the distribution of genetic effects contributing to heterosis. I will use canola (Brassica napus L.) for such assessment. B. napus (2n=38, AACC genome) originated from hybridization between diploid progenitor species B. rapa (2n=20, AA genome) and B. oleracea (2n=18, CC genome), but its genetic diversity is reduced due to domestication and intensive breeding. I will make three types of crosses: spring canola × spring canola (narrow cross), spring canola × winter canola (intermediate cross) and spring canola × resynthesized B. napus lines (wide cross). The resynthesized lines are derived from interspecific cross, B. rapa × B. oleracea. The parents and hybrid progeny from the three crosses will be genotyped using a SNP (single nucleotide polymorphism) array and phenotyped for the total biomass and other traits. Genome-wide heterozygosity will be estimated. I will conduct genome-wide prediction of SNP effects under different gene action models. The expected results are: no relationship between heterosis and heterozygosity in narrow cross; (ii) a linear relationship in intermediate cross; and (iii) nonlinear relationship in wide cross. The proposed research will significantly improve our current understanding of the genetic basis of heterosis and inbreeding depression in canola and other plant species. It will also be of practical value to genomic selection of parental lines for maximizing the amount of heterosis in hybrid canola, a major crop that is rapidly expanding in Canada and elsewhere due to its superiority of yield and other traits over traditional open-pollinated cultivars.