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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Crop Diseases, Pests and Genetics Research » Research » Publications at this Location » Publication #235029
Title: Citrus Stubborn Severity is Associated with Spiroplasma Citri Titer but Not with Bacterial Genotype.

Author
item MELLO, ALEXANDRE - OKLAHOMA ST.UV-STILLWATER
item Yokomi, Raymond - Ray
item MELCHER, ULRICH - OKLAHOMA ST.UV-STILLWATER
item Chen, Jianchi
item FLETCHER, JACQUELINE - OKLAHOMA ST.UV-STILLWATER

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2009
Publication Date: 12/5/2009
Citation: Mello, A.F., Yokomi, R.K., Melcher, U., Chen, J., Fletcher, J. 2009. Citrus Stubborn Severity is Associated with Spiroplasma Citri Titer but Not with Bacterial Genotype. Plant Disease. 94:75-82.

Interpretive Summary: The impact of citrus stubborn disease (CSD), caused by Spiroplasma citri, on citrus production is associated with symptom severity. To assess whether symptom severity is associated with spiroplasma titer, 58 S. citri strains were obtained from trees showing severe or mild symptoms. DNA was extracted from each of these strains and subjected to molecular analysis. RAPD and SSR fingerprinting differentiated four S. citri populations, however, these were present in both mildly and severely symptomatic trees and suggested pathogenicity differences observed were not due to genetically distinct strains. Quantitative PCR (q-PCR), in contrast, demonstrated that spiroplasma titer is over 6000 fold greater in severely symptomatic trees compared to mildly symptomatic trees. In conclusion, the genotypic similarities among S. citri strains examined and the consistent evidence of higher bacterial titer in severely symptomatic trees compared to mildly infected trees, suggests that the latter, but not the former, is, at least in part, responsible for symptom severity in S. citri affected trees in the orchard evaluated.

Technical Abstract: The impact of citrus stubborn disease (CSD), caused by Spiroplasma citri, on citrus production is associated with symptom severity of infected citrus trees. To assess whether symptom severity was associated with spiroplasma titer in the plant, 58 S. citri strains were cultivated from severely and mildly affected trees. RAPD and SSR fingerprinting differentiated four S. citri populations. Each of the four types was present in both mildly and severely symptomatic trees, suggesting that pathogen strain differences do not account for differences in disease severity. PCR performed using primers specific for genes of the pathogenicity-related fructose operon yielded amplicons of expected size for strains from both severely and mildly symptomatic trees. Quantitative PCR (q-PCR), using as template DNA extracted from fruit columellas demonstrated that spiroplasma titer is over 6000 fold greater in severely symptomatic trees relative to mildly symptomatic trees. The genotypic similarities among S. citri strains obtained from severely and mildly symptomatic trees, and the consistent evidence of higher bacterial titer in severely symptomatic trees suggests that titer rather than genetic differences is, at least in part, responsible for symptom severity of S. citri affected trees.