Abstract
Genomic selection patterns and hybrid performance influence the chance that crop (trans)genes can spread to wild relatives. We measured fitness(-related) traits in two different field environments employing two different crop–wild crosses of lettuce. We performed quantitative trait loci (QTL) analyses and estimated the fitness distribution of early- and late-generation hybrids. We detected consistent results across field sites and crosses for a fitness QTL at linkage group 7, where a selective advantage was conferred by the wild allele. Two fitness QTL were detected on linkage group 5 and 6, which were unique to one of the crop–wild crosses. Average hybrid fitness was lower than the fitness of the wild parent, but several hybrid lineages outperformed the wild parent, especially in a novel habitat for the wild type. In early-generation hybrids, this may partly be due to heterosis effects, whereas in late-generation hybrids transgressive segregation played a major role. The study of genomic selection patterns can identify crop genomic regions under negative selection across multiple environments and cultivar–wild crosses that might be applicable in transgene mitigation strategies. At the same time, results were cultivar-specific, so that a case-by-case environmental risk assessment is still necessary, decreasing its general applicability.
Highlights
The chance of crop alleles to introgress into their wild relatives is highly dependent on genetic and environmental selection patterns (Barton 2001; Stewart et al 2003)
This design allowed us to study similarities and differences in genomic selection patterns between different lettuce cultivar–wild crosses, hybrid performance in earlyand late-generation hybrids and environmental influence on hybrid fitness distributions. We address these specific questions: (i) Which crop genomic regions are under positive or negative selection and are these similar or different between the BC and Recombinant Inbred Lines (RILs) crossing populations? (ii) Do the crop–wild hybrid populations differ in their fitness distribution and do they include hybrid lineages that perform better than the wild parent? (iii) Are there environment specific effects on the fitness distributions? In particular, is there an indication that introgression is more likely to occur in a novel habitat compared to the original habitat of the wild relative? we discuss the likelihood of crop gene transfer to the wild relative and the implications for Environmental Risk Assessment (ERA) procedures
Fitness distributions were different among the two habitats used, indicating that introgression of crop alleles through hybridization might be more likely to occur in novel habitats, as opposed to the natural wild habitat of the wild parent
Summary
The chance of crop alleles to introgress into their wild relatives is highly dependent on genetic and environmental selection patterns (Barton 2001; Stewart et al 2003). Since the genetic background changes rapidly in the first phases of the introgression process, selection patterns may differ between early- and late-generation hybrids, as well as among individual plants within a certain category of hybrids (Barton 2001). Such patterns that affect the outcome of hybridization are interesting from a theoretical point of view (Rieseberg et al 2000; Burke and Arnold 2001) but are of high interest to Environmental Risk Assessment (ERA). To what extent genomic selection patterns can be generalized across different cultivars and whether the performance of hybrids differs between early- and late-generations and different environments (EFSA 2011)
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