2017 ASHS Annual Conference

Cavity spot of carrot is an important disease of carrots in many regions of the world. The disease is caused by several Pythium species, especially Pythium violae and P. sulcatum. Field trials were conducted from 2013 to 2016 to identify carrot lines with low susceptibility to cavity spot, to contribute to the USDA carrot breeding program. Several cultivars were included as commercial checks. The lines were also assessed for incidence of Pythium forking (carrot root dieback) in 2016 and for the severity of carrot leaf blights caused by Cercospora carotae and Alternaria dauci, in 2015 and 2016. Leaf blights were rated from 0 (healthy leaves) to 5 (dead leaves). Carrots were seeded into ‘muck’ soil (pH 5.7- 6.5, organic matter 65- 78%), in an area where the diseases occur naturally. Harvested carrots were washed and rated for cavity spot incidence and disease severity (DSI). Orange and purple pigmented carrot lines were identified with low cavity spot incidence and severity that were consistent over the four years. There was no correlation between cavity spot incidence and severity and either Pythium forking or leaf blight severity. However, three orange lines and two purples lines had low forking (0-9%) and low cavity spot (0-7%), as did cv. Uppercut (5% forking and 10% cavity spot). One orange breeding line had low cavity spot (7%), low forking (8%) and low leaf blight ratings (1.7 and 1.0). It may be possible to select carrots with resistance to more than one disease.