Root-mediated effects in carrot resistance to the carrot fly,Psila rosae.

Field experiments on two different soil types in Ireland assessed the extent and mechanisms of resistance toPsila rosae (F.), the carrot fly, with emphasis on the role of the carrot root. Ten carrot cultivars gave consistent results in terms of resistant and susceptible cultivars. Nonpreference oviposition was confirmed as a mechanism, and the use of egg traps, providing differential exposure of the main root, showed this was regulated by root factors, probably chemical constituents. Independent main root resistance to the larva was also confirmed, and this effect was established as consistent with a chemically mediated nonpreference. Antibiosis by the root was demonstrated. Such effects in three different modes indicate that main root properties are crucial in carrot resistance toPsila and suggest a pervasive influence of root chemicals on such resistance.