2017 ASHS Annual Conference

Root knot nematodes (Meloidogyne spp.) are a major pest attacking carrots (Daucus carota) worldwide. Root knot nematodes cause galling and forking of the carrot root, rendering an infected carrot unfit for market. The current management practices of applying broad spectrum soil fumigants works well, but is coming under continuously restricted regulations, is costly for growers, and is considered damaging to the environment. Genetic resistance to nematodes would be an ideal solution to eliminate or strongly reduce the use of broad spectrum soil fumigants in carrot production. Resistance to M. javanica has already been discovered and mapped to the Mj-1 locus on chromosome 8 in a ‘Brasilia’ cultivar. Beyond M. javanica resistance, genetic resistance to M. incognita was discovered in three diverse sources of resistance, from Syria, Europe and South America, and resistance genes mapped. A consensus genetic map of the three populations revealed five non-overlapping QTLs for M. incognita resistance. Resistance was high in the original genetic backgrounds in which it was discovered and in mapping populations, but introgression of resistance genes into carrots with horticultural quality suitable for US commercial production has not yet been reported. In recent field trials new inbreds with M. incognita resistance genes from multiple genetic sources were observed to have been a high level of resistance combined with long, smooth root shape and excellent horticultural quality. Steps to deploy resistance will be discussed.