The Identification and Exploitation of Resistance in Carrots and Wild Umbelliferae to the Carrot Fly, Psila rosae (F.)

Partial plant resistance to the carrot fly, Psila rosae, has been identified in several Nantes varieties of carrot, Daucus carota, which reduces larval damage to the roots and the number of pupae remaining in the soil after cropping by 50%. The resistance of the Nantes variety 'Sytan' was found to be consistent at 12 sites in 5 European countries over two seasons. The resistance has been shown to be based on antibiosis and correlated with concentrations of chlorogenic acid in the roots. The resistance complements cultural and chemical methods for controlling P. rosae. Thus, in field experiments over two seasons it was shown that carrots could be left in the ground for a longer period providing a greater sowing/harvesting interval with a resistant variety than a susceptible one because of the reduction in damage and the delayed development of insects on the resistant variety. In two seasons at two sites a partially-resistant variety required only one-third of the dose of insecticide to provide a marketable crop compared with a susceptible carrot variety. In a breeding programme involving the variety 'Sytan', male sterile lines, inbreds and selections with improved levels of resistance were developed. Much higher levels of resistance were identified in certain wild Daucus species and 15 years of crossing and selection produced lines with significantly higher levels of resistance than exists in the variety 'Sytan'. A range of resistant carrot material bred at Horticulture Research International has been released to seed companies for use in the production of improved carrot varieties. The partially-resistant variety 'Flyaway' was made available to amateur gardeners in 1993 and to commercial growers in 1995 as a result of this research.