Chestnut

Abstract

AbstractCastanea sativa, European chestnut, the only native chestnut species in Europe, was derived from the Turkish Mediterranean gene pool.Castanea dentata, American chestnut, is the largest chestnut species native to North America. Although European and American chestnuts are both susceptible toCryphonectria parasitica, the causal agent of chestnut blight, the former is still a commercially viable species. The American chestnut, however, has been essentially eliminated as both a nut crop and a timber species. European and American chestnuts have been the focus of attention of professional and amateur plant breeders for more than a century. They have been selected for various traits, moved from numerous points of origin, hybridized, and redistributed across the landscape. This comes after centuries of domestication by native peoples of both continents. The American Chestnut Foundation is carrying out the largest and most active breeding program based on backcross breeding between the American chestnut and the blight‐resistant Chinese chestnut (Castanea mollissima). A comparison is made between backcross breeding and genetic engineering in terms of numbers of unknown genes introduced and speed of introducing additional genes. Research to develop transformation systems for American and European chestnut has followed similar paths. For both species, the preferred target tissue is somatic embryos derived from immature zygotic embryos. The selectable marker genebar, with the herbicide Finale® (active ingredient phosphinothricin), in combination with scorable markergfp, has proved to be effective in selecting for transformation events in American chestnut. ThenptIIselectable maker gene with kanamycin in combination with the scorable markerguswas used to transform European chestnut. Transgenic whole plants have been recovered for both species. The first two transgenic American chestnuts were planted in the field on June 7, 2006 in Syracuse, New York, USA. These trees contain the oxalate oxidase (OxO) gene originating from wheat, which has been shown to enhance pathogen resistance in several crop species including soybean, peanut, and sunflower.