|Yokomi, Raymond - Ray|
Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/10/2008
Publication Date: 7/26/2008
Citation: Mello,, A.F., Yokomi, R.K., Payton,, M., Fletcher,, J. 2008. Citrus stubborn symptom severity and Spiroplasma citri location within the tress canopy. American Phytopathological Society Annual Meeting. 98:S104.
Technical Abstract: The severity of symptoms of citrus stubborn disease (CSD) within an orchard can range from mild to severe, but whether factors other than pathogen titer or duration of infection impact severity is not known. We tested the hypothesis that the canopy distribution of the pathogen, Spiroplasma citri, is related to symptom severity. When fruits were harvested randomly from the canopies of trees from a commercial orchard and S. citri presence assessed by culturing from fruit receptacles, a greater percentage of samples from severely symptomatic trees yielded cultures, and bacteria grew to log phase more quickly, than from mildly symptomatic trees. In a second experiment, both fruits and leaves from two canopy aspects (east and west) and three canopy tiers (top, middle, and base) were subjected to q-PCR, using P58 gene-based primers, on DNA from fruit columellas and leaf petioles. The percentage of samples testing PCR-positive was significantly greater from severely symptomatic than from mildly symptomatic trees, and columellas yielded more q-PCR positives than did petioles. However, neither canopy aspect (east vs west) nor tier (upper, middle or lower) correlated significantly with percentage S. citri detection. The data suggest that, within this orchard, CSD severity is unrelated to the overall within-tree pathogen distribution, but is correlated with the percentage of samples containing the pathogen.