Hybridization in nature: lessons for the introgression of transgenes into wild relatives.

Abstract

AbstractMany factors determine the chance of transfer of genes from crops to wild relatives: the distance and divergence between them, the extent of gene flow, and the fitness of hybrids. The spectrum of genes that can be transferred to a target species by genetic modification is much wider than that of traditional breeding, and the effects of gene exchange between GM crops and wild relatives may therefore be quite different. Important questions need to be answered: could the transgene escape and, if so, will it stay confined to the initial hybrids, for instance due to hybrid inviability or infertility? Or will it introgress into the wild relative, perhaps changing the genetic diversity of the wild species? What is the phenotypic effect of the transgene, and is it something entirely new to the recipient plant? Does it increase the fitness of F1 hybrids, backcrosses and later generations? Will the transgene stay intact and functional or will changes take place? The focus of this chapter is to see what we know of hybridization in nature, in order to identify what factors determine the exchange of genes between and within plant species and the success of hybrids. The goal is to identify the main processes involved, and see what this tells us about the study of the potential risks of escape of transgenes from GM crops to wild relatives. Although hybrids are present in many taxa, natural hybridization as a speciation mode is subject to discussion, except when it is coupled to polyploidization. It is also evident that a lot of baseline data on putative recipient wild relatives is still missing, hampering the evaluation of the risks of introgression of genes from GM crops to wild relatives.