Gene Introgression from Wild Relatives

Actinidia species are perennial, dioecious plants widely distributed in eastern and southeastern Asia. Their distributions often overlap, and hybridization among species is frequent in sympatric areas, where species, often descended from a common ancestor, share the same ecological niche. This condition leads to complex reticulate evolution and shapes multiple phenotypes which are potential parents for kiwifruit breeding. Hence, breeders have been introgressing traits of agronomic interest by crossing cultivated selections of A. chinensis var. chinensis and A. chinensis var. deliciosa to wild relatives and in some cases far more distantly related species, such as A. arguta. Among the new traits introgressed from undomesticated species are fruit size and shape, flesh color, high-nutritional value including high vitamin C content, edible skin, good storage life, disease resistance, and adaptation to different climates. In this chapter, we illustrate both the artificial and the natural hybridization of Actinidia species, and discuss introgression breeding, an important approach to kiwifruit breeding that exploits the genetic diversity of the natural interspecific hybrids found in the sympatric areas where different taxa overlap and cross.