Effect of temperature on the relationship between Orobanche spp. and carrot (Daucus carota L.)

Orobanche crenata Forsk. and O. aegyptiaca Pers. parasitize carrot (Daucus carota L.) only in specific seasons in Israel. This study describes the relationship between temperature and the sensitivity of carrots to O. crenata and O. aegyptiaca. Field and controlled condition studies have shown that cool temperatures below 18°C are required for the two Orobanche species to parasitize carrot plants. In vitro studies demonstrated that carrots grown under an unfavorable regime (e.g., summer temperatures) have induced seed germination of both Orobanche species, and a substantial numbers of initial attachments were also observed. However, the development of the majority of the attached Orobanche organs ceased. We conclude that both Orobanche species require cool temperatures for effective parasitism on carrot to occur.