Location: Vegetable Crops ResearchTitle: Incidence and severity of cavity spot of carrot as affected by pigmentation, temperature, and rainfall Author
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2014
Publication Date: 7/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58902
Citation: Saude, C., Simon, P.W., McDonald, M.R. 2014. Incidence and severity of cavity spot of carrot as affected by pigmentation, temperature, and rainfall. Plant Disease. 98(7):929-936. Interpretive Summary: Cavity spot is a fungal disease of carrot that results in brown pits on the surface of the root. It is one of the most significant carrot diseases world-wide in reducing marketability, especially after even short post-harvest storage. Breeding for resistance to this disease has been minimal since disease attack is uneven across infested fields. Well-established field testing has been developed in Canada and this manuscript reports reliable evaluations of genetic resistance for a broad genetic sampling of carrots. Included among samples were not only familiar orange carrots, but also red and purple. Interestingly purple carrots were very resistant to cavity spot, while orange carrots varied in resistance, while red carrots were generally quite susceptible. Temperature and rainfall also influenced the severity of cavity spot infection. This information is of interest to vegetable growers, breeders, and plant pathologists interested in predicting and limiting cavity spot attack in carrots.
Technical Abstract: Field trials to determine the effect of carrot pigmentation and weather parameters on cavity spot of carrot (CS) were conducted in the Holland/Bradford Marsh region of Ontario between 2002 and 2009. Twenty three colored carrots from the USDA-ARS breeding program at the University of Wisconsin (5) and commercial seed companies (18) were seeded in organic soil (pH 6.4 – 7.2, 39- 60% organic matter) in late May to early June and harvested in late October or early November. Carrots were assessed for CS severity mid-season and post harvest. Evaluations post harvest indicated that the purple pigmented carrot from breeding line ‘USDA 106-3’ and cultivars Purple Rain and Purple Haze consistently had low CS severity. The orange pigmented ‘USDA 101-23’, ‘Cellobunch’, ‘YaYa’ and ‘Envy’ had moderate CS and the red pigmented carrot breeding line ‘USDA 104-3’ and cultivars Atomic Red, Proline Red, Dragon and an unnamed line from India had high CS. Differences in CS severity in carrot cultivars between evaluations at mid-season and post harvest suggest that some carrots are more susceptible to Pythium spp. inoculum in soil (alloinfection) and others to secondary infection (autoinfection) that can be attributed to the Pythium sp. involved in CS. Cavity spot severity was positively correlated with total rainfall two and three months after seeding, and was negatively correlated with number of days with air temperature = 30ºC three and four months after seeding. Soil temperature and total rainfall were the best predictors of CS incidence and severity. These results could allow a forecast of disease incidence and severity at harvest.