A genetic analysis of the introgression process from crops to wild relatives : mapping quantitative trail loci for plant vigour under abiotic stress conditions

One of the discussed risks with regard to cultivation of genetically modified crops is the possibility of introgression of transgenes from crops to their wild relatives. After crop-wild hybridization, the persistence in later generations of the hybrids will depend on whether it confers a selective advantage. This will depend on the genetic make-up of the hybrid plant, consisting of a specific combination of wild and crop genomic blocks, on the environmental conditions, and the interaction between the environment and the genotypes. To understand the contribution of the crop genome and how the crop genome interacts with the wild genome to the performance of the hybrids, we have initiated a study in which we follow the process of introgression from crops to wild relatives using lettuce crop-wild hybrids growing under abiotic stress conditions as a model system. Improved yield under abiotic stress conditions is one of the major objectives of GM crop development at present. We created hybrid generations from Lactuca serriola L. (wild prickly lettuce) and L. sativa L. (cultivated lettuce). We studied the performance of the hybrids in F1S1 and BC1 hybrid populations under optimum conditions (no stress), drought, salinity and nutrient deficiency conditions. We genotyped the populations using Single Polymorphism (SNP) markers, constructed the genetic linkage maps of the two populations, then combined the phenotypic and genotypic data for Quantitative Trait Locus (QTL) analysis. In the F1S1 and BC1 populations we obtained QTLs associated with plant vigour under stress conditions as well as under control conditions. More than half of the stress-related QTLs were positively derived from the crop parent, indicating that lettuce crop-wild hybrids could receive traits from the crop that are advantageous for performance under abiotic stress conditions. Although many the QTL regions did not change from one treatment to another, QTL by treatment interaction was significant for biomass and plant height QTLs, suggesting that the mechanisms involved in tolerance to the different treatments were not the same. The QTLs were distributed across all lettuce linkage groups, but for some linkage groups, QTLs were concentrated in specific genomic regions. Such genomic regions are of interest for GM environmental risk assessment. Regions with beneficial QTLs could be avoided as a transgene inserted there would have more chance of persistence through genetic hitchhiking, while regions with non-beneficial or deleterious QTLs for the hybrids would be ideal for containment of a transgene.