Oral Technical Session: Disease Diagnosis and Detection

9-O

Estimation of ‘Candidatus Liberibacter asiaticus’ populations in Texas citrus trees.
M. KUNTA (1), C. de la Garza (1), J. V. da Graça (1), C. C. Parra (1), M. Sétamou (1), E. S. Louzada (1)
(1) Texas A&M University-Kingsville, Weslaco, TX, U.S.A.

To determine which citrus tissues have relatively high ‘Ca. Liberibacter asiatus’ (CLas) populations for reliable, early detection of Huanglongbing, we determined cell populations in various tissues collected from infected field trees in Texas using the previously described grand universal regression equation Y=13.82-0.2866X, where Y is the log of the target copy number and X is the Ct values of the assay. Overall, significantly higher CLas populations were recorded in grapefruit compared to sweet orange. They also varied with plant tissue, with pedicil, columella, and midribs having significantly higher titers compared to other tissues. Lowest bacterial titers were consistently recorded in young shoots, young leaves, flower buds, and leaf blades, especially leaf margins. Analysis of variance (ANOVA) showed that there is no significant difference (p>0.05) in bacterial concentrations in symptomatic leaf and root samples nor was there any significant difference in test results among different distances from the trunk or quadrants where the root samples were collected. Thin roots and root intersections, specifically fibrous feeder roots, consistently showed higher bacterial concentrations compared to thicker roots and thicker intersections.