Detection of Alternaria dauci on Carrot Seed. J. O. Strandberg, Professor and Plant Pathologist, University of Florida, Institute of Food and Agricultural Sciences, Central Florida Research and Education Center, Sanford 32771. . Plant Dis. 72:531-534. Accepted for publication 4 January 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0531.

Alternaria dauci was detected within 7–10 days at 20 C when infested seeds were incubated on filter paper moistened with water or carrot leaf extract. The pathogen was identified by its characteristic conidia. 2,4-Dichlorophenoxyacetic acid (2,4-D) was used to inhibit seed germination. Carrot leaf extract did not improve the efficiency of detection. Concentrations of 2,4-D amine greater than 0.1% inhibited growth and sporulation of A. dauci, but concentrations of 2,4-D amine or reagent-grade 2,4-D between 0.0001 and 0.01% had no significant effects on the pathogen or efficiency of detection. Surface disinfestation of seeds with 0.1% Ca(OC1)₂ before testing eliminated many saprophytic fungi and improved the sensitivity of the test by twofold. Hot water treatment with or without 1% Ca(OC1)₂ reduced the proportion of infested seeds detected but greatly enhanced growth and sporulation of the pathogen on seeds where A. dauci survived this treatment. The test was demonstrated to be useful over the range of 0.001–14% infested seeds.

Keyword(s): Daucus carota L., seed testing, seedborne disease.