The genus Prunus is a member of the Rosaceae, the third-most economicallyimportant plant family (Dirlewanger et al. 2002), and contains a large number of commercially valuable fruit and nut tree species, including almond, apricot, cherry, peach and plum, as well as a number of prized ornamental species. The genus is a member of the Spiraeoideae subfamily of Rosaceae, which contains other economically important genera including Malus (the apples) and Pyrus(the pears). The base chromosome number for the Spiraeoideae is x = 9, however there are many deviations from this, and Prunus forms part of the Amygdaleae tribe, which has a base chromosome number of x=8. The majority of the Prunus species are diploid, including peach (P. persica; 2n = 2x = 16) which, with a genome size of ~280 Mbp/C, has been adopted as the model organism for the genus (Shulaev et al. 2008), and has been the subject of a recent whole genome sequencing initiative (International Peach Genome Sequencing Initiative 2010; www.rosaceae. org/peach/genome).