|Yokomi, Raymond - Ray|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/20/2007
Publication Date: 10/17/2007
Citation: Mello,, A.F., Yokomi, R.K., Fletcher,, J. 2007. Assessment of Stubborn Disease Incidence in Citrus. In: Proceedings of the 17th International Organization of Citrus Virologists, October 22-26, 2007, Adana, Turkey. p. 173. Interpretive Summary:
Technical Abstract: Citrus stubborn disease, caused by Spiroplasma Citri, has occured in California for more than 90 years, however, detection methods for estimating disease incidence have not been well developed. Two 8 ha plots in Kern Co. CA were established and sampled in July and August, 2006. Different tissues of sweet orange were tested for spiroplasma cultivation and three sampling procedures for estimating disease incidence were compared using cultivation and PCR. Tissue at the fruit peduncle base and columella yielded cultivable spiroplasmas more consistently than did leaves, midribs, petioles, or bark. Stat sampling, in which every fifth tree row was sampled, resulted in estimated incidences of 46 and 1.3% by cultivation in groves 1 and 2, respectively. Hierarchical sampling, in which every fourth quadrat was sampled, resulted in incidences of 71.4 and 3.6% in groves 1 and 2 by culturing, and 85.7 and 3.6% in the same groves by PCR. In the third method, all trees contained within 6 separate blocks of 64 trees in each grove were sampled individually and yielded incidences of 49.7 and 1.6% by culturing and 53.4 and 1.6% by PCR. Thus, stubborn incidence in grove 1 was shown to be high while that of grove 2 was low. In these tests, PCR performed better than did culturing. Its advantage over culturing is that it permits a large number of samples to be analyzed since it is relatively inexpensive, sensitive, yet rapid. These data support the use of PCR for future epidemiology studies.