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United States Department of Agriculture

Agricultural Research Service

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Location: Vegetable Crops Research

2013 Annual Report

1a. Objectives (from AD-416):
Develop carrot breeding stocks for production in organic agriculture systems with improved nutritional value, trial carrots in diverse growing locations, and release germplasm to the seed industry. Evaluate carrot foliage and selected root disease attack.

1b. Approach (from AD-416):
a) Note disease symptoms and evaluate pathogens in elite breeding stocks for organic systems. b) Evaluate leaf disease symptoms in four locations over the course of the project. c) Evaluate root diseases as needed. d) Determine identity of pathogens. e) Analyze differences found between organic and conventional production systems.

3. Progress Report:
This project was renumbered from 3655-21000-048-43A to 3655-21000-062-17A. In 2012 and 2013, we participated in monthly conference calls for this project to assist with planning field trials, carrying out the Washington State field trials, developing educational materials, assisting with disease evaluations for plant samples from field trials in the four participating states, and developing protocols for various plant ratings, particularly disease evaluations, including how to submit samples for verification of the causal agent(s) of foliar diseases. For the 2012 Washington organic and conventional carrot trials, we rated plant height twice early in the season, and the foliage of plants was rated in each plot for severity of foliar diseases at harvest. Cercospora leaf spot, caused by Cercospora carotae, was prevalent in the organic plots, but not in the conventional plots. Foliar dieback in the conventional trial appeared to be caused by herbicide injury, and no primary carrot pathogens were isolated from the leaves in the lab. In addition, leaf samples were sent to the lab from plots in the field trials at the University of Wisconsin (in September), at Purdue University, Indiana (in early October), from Hancock Research Station, Wisconsin (in late October), and from the University of California trials near Bakersfield, CA (in November). For the Wisconsin leaf samples, Cercospora leaf spot was detected on leaves from one conventional plot (Plot 19) and one organic plot (Plot 2); and the bacterial blight pathogen, Xanthomonas hortorum pv. carotae, was confirmed from leaf samples collected from organic Plot 7 and organic Plot 20. For the Indiana samples, Cercospora leaf spot was confirmed by microscopic examination and isolations onto agar media. The presence of the bacterial blight pathogen was verified by polymerase chain reaction (PCR assay) and, given this pathogen has not previously been documented in Indiana, by pathogenicity testing to complete Koch’s postulates. A manuscript for a Plant Disease Note is in preparation to document, for the first time, the presence of this pathogen in Indiana. It is possible the pathogen may have been introduced on seed planted in these plots, but this was not investigated because of the limited amount of seed available for planting each entry in duplicate field trials in each of four states. Leaf samples from 14 plots were received from Wisconsin in October 2012, from which Alternaria dauci, causal agent of Alternaria leaf blight, was detected from all 14 samples; Cercospora carotae was detected on one sample; and none of the samples tested positive for the X. hortorum pv. carotae. For the Bakersfield, CA trial, powdery mildew was present on all the entries in the organic trial, but bacterial blight was present in only one plot in the organic trial. In contrast, the plants in the conventional trial were very clean, with only a few plants showing powdery mildew and one plant with Alternaria leaf blight. The few leaf samples received confirmed these diagnoses. To date in 2013, we have assisted with planning the field trials, rating early plant height/vigor in the Washington trials, and modifying the various carrot assessment protocols as needed based on experience in 2012. We will assist with disease ratings at harvest in 2013. Assistance was also provided in 2012 and 2013 with editing the Carrot Improvement for Organic Agriculture (CIOA) poster and abstracts for presenting at the annual meetings of the International Society for Horticultural Science in 2012 and 2013 and the International Carrot Conference in August 2013. This research relates to objective 1 in evaluating carrot foliage and response to diseases by determining disease occurrence.

4. Accomplishments

Last Modified: 06/21/2017
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