Characterization of the Meloidogyne javanica resistance locus employing molecular markers and isolation of candidate disease resistance loci in the carrot (Daucus carota L.) genome

Resistance to pathogens and insects are major genetic attributes necessary for economic production of carrot (Daucus carota L.) in several regions of the world. Sources of resistance have been identified to virtually all major carrot pests and diseases. The breeding efforts, however, have been concentrated on diseases and pests with major economic impact. The main fungal diseases are leaf blight caused by Alternaria dauci; black root rot caused by A. radicina; leaf spot/early blight (Cercospora carotae); powdery mildew (Erysiphe heraclei); and cavity spot caused mainly by Pythium violae. The bacterial diseases of importance in carrots are: leaf spot caused by Xanthomonas campestris pv. carotae, and soft root rot caused by Erwinia species. The root-knot disease induced by the nematodes of the genus Meloidogyne is another serious problem worldwide. The aphid Cavariella aegopodii (as the vector of the carrot motley dwarf viral complex), the leafhopper Macrosteles fascifrons (as the vector of the aster yellow phytoplasm), and the carrot fly, Psila rosae, are the major pests. This chapter provides an overview of achievements towards the genetic control of these diseases and pests in carrot. A review is also presented dealing with of the current map efforts to localize disease loci in carrot including the M. hapla resistance locus (derived from the wild subspecies D. carota subssp. azoricus) and the M. javanica resistance locus (Mj-1, derived from the Brazilian cultivar ‘Brasília’).