Marker Assisted Introgression: A Fast Approach to Assess the Value of Almond Genes and Integrate them in the Peach Genetic Background

Low levels of genetic variability in the commercial gene pool are a limitation for peach breeding. Introgression of new genes from wild or cultivated compatible Prunus species may provide novel variability for traits of crucial interest such as disease resistance, fruit quality or extended shelf life. Classical approaches to introgression are too slow due to the long intergeneration period of tree species like peach. Here we propose a three step method that would allow obtaining plants with a single introgressed fragment into an elite peach background in only two backcross generations with the help of molecular markers. The first step is to obtain a large BC1 progeny (N>1,000) and to select for individuals with a low number of introgressions (four or less). The second step consists of phenotyping a small collection of the selected individuals (N=15-20) for key traits and combine these data with the genotype information acquired in step one to identify major genes/QTLs and find their map positions. In the third step, only plants with desirable phenotypes (in some cases caused by genes of known chromosome positions) are advanced to a BC2 or BCS1 to obtain individuals with a single introgression in heterozygosis or homozygosis, respectively. Results from a case study involving the cross between ‘Texas’ almond and ‘Earlygold’ peach will be presented that show that the approach is feasible and anticipate possible drawbacks that may prolong the scheme proposed.