|Yokomi, Raymond - Ray|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 10/22/2010
Publication Date: 11/7/2010
Citation: Saponari, M., Doddapaneni, H., Loconsole, G., Giampetruzzi, A., Saldarelli, P., Yokomi, R.K. 2010. Studies of Seedling Yellows Amelioration of Citrus tristeza virus Strain Mixtures to Elucidate Mechanisms of Cross Protection [abstract]. International Organization of Citrus Virologists Proceedings. 31:s93. Interpretive Summary:
Technical Abstract: Citrus tristeza virus (CTV) cross-protection involves a mild strain of CTV preventing or interfering with infection or symptom expression by a severe strain. It is used to protect citrus when virulent stem pitting strains of CTV and efficient aphid vectors are endemic. However, the mode of action of cross protection is unknown and its durability is questionable. To this end, molecular interactions were studied in tests with sour orange (SO) and Duncan grapefruit (DGF) inoculated with a presumptive protective field strain containing a mixture of three CTV genotypes and each of these genotypes alone separated by aphid transmission. All SO and DGF infected with the field source or a genotype defined as non-standard (NS) did not show severe symptoms; whereas plants infected with CTV strains with VT or T3 genotypes showed strong seedling yellows symptoms. Replication of each genotype strain and their combinations were assessed over time by immunocapture real time reverse transcription polymerase chain reaction assay using specific probes designed from sequences from the P20 gene for each genotype strain. The virus isolates were further differentiated by single strand conformational polymorphism analysis of the P25 coat protein amplicon. After 12 months, cross protection was observed in all SO and DGF inoculated with the field strain even though the host plant supported the replication of all genotype strains at the same level. When SO and DGF where inoculated at the same time with each separate genotype strain to re-create the field source, SO expressed mild stunting and mild seedling yellows but DGF was showed strong seedling yellows. SO and DGF inoculated with the NS genotype and challenged one month later with VT or T3 genotype strains, no cross protection was observed and all plants contained similar titers of each genotype as those observed showing cross protection. Thus, cross protection was not induced by the NS genotype alone or other variant acquired by aphid transmission and left open the question of interactions of the CTV quasispecies population in the field source isolate. High throughput sequencing approach has been undertaken to further investigate this hypothesis of the quasispecies complex.