|Folimonova, S. y.|
|Robertson, C. j.|
|Garnsey, S. m.|
|Dawson, W. o.|
Submitted to: International Positive Strand RNA Virus Symposium
Publication Type: Abstract only
Publication Acceptance Date: 5/26/2007
Publication Date: 6/1/2007
Citation: Folimonov, A., Folimonova, S., Robertson, C., Garnsey, S., Hilf, M.E., Dawson, W. 2007. Cross-protection by Citrus Tristeza Virus: prevention of superinfection occurs only when plants are protected by isolates of the same strain.. International Positive Strand RNA Virus Symposium. Interpretive Summary: Cross-protection is a phenomenon seen with plant viruses where a mild isolate of the virus can protect a plant against disease development caused by a severe isolate of the virus. Citrus tristeza virus is a virus which infects citrus. There are mild isolates of CTV which cause no disease and severe isolates which can cause disease which leads to economic losses. In some parts of the world, cross-protection is used to produce citrus commercially where severe strains of CTV predominate. This study determined that cross-protection occurs between isolates if they are nearly identical genetically. This information can aid in the selection of mild isolates which can effectively protect trees against severe isolates.
Technical Abstract: Citrus tristeza virus (CTV) is the most important virus of citrus worldwide. CTV has a 19.3 kb RNA genome, is transmitted by aphids, and accumulates in trees predominantly in phloem-associated cells. Inoculation of trees with mild strains of CTV has been used to allow citrus production in areas where severe isolates are endemic. However, there has been no understanding why some mild isolates cross-protected and others failed. Major CTV isolates fall into at least five sequence groups, which we refer to as strains. Yet there is considerable variation in symptom phenotype within each strain. To examine the cross-protection potential of CTV strains, citrus trees were infected individually with 13 isolates derived from these five groups, and challenge-inoculated with a GFP-tagged T36 CTV construct. The ability of this construct to superinfect infected trees was determined by visual observation of GFP expression after three months. Only isolates of the T36 strain were able to prevent superinfection by the T36-based CTV construct. Isolates of the VT, T3, T68, or T30 strains did not cross-protect against T36. These results also provide an explanation of the fact that many CTV isolates are composed of populations of more than one CTV sequence.