Apples

The overall objectives of modern apple breeding programs are to increase the marketability of fruit and reduce production costs. Developing well adapted cultivars with resistance to major pests is also a focus of all breeding programs. The apple is generally grown as a composite tree with a rootstock and a fruiting scion, making rootstock breeding as important as the development of scion cultivars. Genetic resistance has been found for a number of the major pests of apple. Engineering resistance to apple scab and fire blight has been the focus of many of laboratories. Most of the traits associated with adaptation and productivity have been shown to be quantitatively controlled, including chilling requirement, cold hardiness, plant vigor, season of flowering and duration of the juvenile period. Many of the traits associated with fruit quality are also quantitatively inherited including flavor, skin color, shape, size and texture. Several cDNA libraries have been developed to identify genes associated with pollination and apple fruit development. A number of apple linkage maps have been published using several different sets of parents and molecular markers have been linked to a number of monogenic traits. Mining of existing apple EST information promises to expand our knowledge of many genes important in the genetic improvement of apple.