|Boiteux, L - EMBRAPA, BRASIL|
Submitted to: Compendium
Publication Type: Review Article
Publication Acceptance Date: March 11, 2002
Publication Date: N/A
Technical Abstract: Breeding for disease and pest resistance is complicated by carrot's predominantly outcrossing mating behavior and associated sensitivity to inbreeding depression, making the fixation of genetic resistance difficult. Recurrent selection has been the predominant breeding strategy, with some major resistance genes being incorporated via simple backcrossing programs. Sources of resistance have been identified for many pathogens and tests of carrot, but selection and incorporation into commercial cultigens has only been exercised for those with important and widespread economic impact. Major breeding efforts have been devoted to control of aster yellows phytoplasm; leaf blight powdery mildew cavity spot caused by Pythium species; carrot fly and root-knot induced by nematodes of the genus Meloidogyne. Sources of varying levels of resistance have been identified for motley dwarf virus comples and black crown rot but inheritance studies and breeding for resistance have not been initiated. The rapid development of improved carrot populations via recurrent selection is dependent upon the fixation of favorable alleles. In this scenario, the employment of closely linked molecular markers has been a useful tool to increase frequency of resistance alleles during recurrent selection cycles. Molecular markers are also important tools in backcrossing programs to minimize 'linkage drag' in elite lines employed for development of resistant F1 hybrids. Employment of molecular markers in carrot breeding for disease resistance has been limited to a locus controlling M. hapla resistance and to the Mj-1 locus. These markers are the basis for efficiency of marker-assisted selection systems that are now being employed by seed companies.