Submitted to: Journal of Plant Pathology
Publication Type: Abstract only
Publication Acceptance Date: 10/20/2007
Publication Date: 8/24/2008
Citation: Mello,, A.F., Yokomi, R.K., Chen, J., Wayadande,, A., Fletcher,, J. 2008. Transmission of Spiroplasma citri to Carrots by Circulifer tenellus. Journal of Plant Pathology 90(2, Suppl.), S2.463. Interpretive Summary:
Technical Abstract: Spiroplasma citri is a wall-less bacterium that causes citrus stubborn disease (CSD) and brittle root in horseradish. Recently, carrot purple disease was reported in Washington State, and attributed to S. citri, but the mechanisms of transmission and fulfillment of Koch’s postulates were not completed. The objectives of this work were to confirm S. citri as the causal agent of carrot purple leaf and evaluate its transmission by the leafhopper Circulifer tenellus. C. tenellus was exposed for 24 hours to feeding sachets containing S. citri isolated from carrots. After a 30-day latent period, 5 to 10 insects were transferred to 20-day-old carrot seedlings for one or two days. Plants exposed to insects fed on buffer only served as negative controls while periwinkle plants exposed to infected insects was used as the positive control. S. citri infection was based on symptoms, bacterial cultivation and PCR. Purple leaves in carrots and yellow and small leaves in periwinkle became evident 10 to 15 days after plant exposure to infected insects. Plants exposed to buffer only-fed insects had no symptoms, and S. citri was not detected by PCR or culturing. Only symptomatic carrot and periwinkle plants yielded cultures of spiroplasma and amplicons of expected size by PCR. The rate of transmission of S. citri to carrots was 15 % which was almost 5 times lower than that to periwinkle (~70%), showing that the transmission of the pathogen to carrot is possible but is less efficient than to periwinkle.