APS Abstracts of Presentations

A survey of pre- and post-harvest fungal diseases of carrot roots (Daucus carota L.) in Michigan
C. Saude (1), J. W. COUNTS (1), M. K. Hausbeck (1)
(1) Department of Plant Pathology, Michigan State University, East Lansing, MI
Phytopathology 96:S103

In fall 2005, a survey was conducted to assess the occurrence of pre- and post-harvest fungal pathogens of carrot roots grown for processing in Oceana, Mason and Newaygo Counties, MI. Approximately 30 carrot roots were randomly collected from each of the 13 fields surveyed and 10 roots were sampled from one storage facility in Newaygo County. Samples were collected based on various disease symptoms observed in fields and in storage. Diseased tissue was excised from the edge of developing lesions on carrot roots, crowns, petioles and leaves, then plated onto 4 different isolation media. Plates were maintained at 23–25°C and evaluated after 8 and 20 days. Field sampling of carrots resulted in the recovery of the following pathogens: Fusarium spp. (from 100% of the fields), Rhizoctonia spp. (85%), Pythium spp. (77%), Phytophthora spp. (46%), Alternaria radicina (38%), Geotrichum candidum (31%) and Chalara elegans (15%). Additionally, A. radicina (100% of sampled roots) and Geotrichum candidum (60%) were isolated from carrot roots sampled from the storage facility. This is the first report of the occurrence Phytophthora spp. in carrot fields and A. radicina in both carrot fields and storage in Michigan. The presence of both pathogens compounds the threat of crop losses to the carrot industry, which is already challenged by previously documented soilborne pathogens.

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