The main objectives are as follows:
* To develop quick and specific procedures to discriminate between mild and severe strains of citrus tristeza virus (CTV) and set up a simple protocol for detection of severe CTV strains in field trees or nursery plants.
* To use this technology for a)early screening of mild CTV isolates with protective capacity against severe isolates and b) monitoring cross protection in the field.
* To develop quick and reliable methods to diagnose and characterize psorosis-ringspot isolates from the Mediterranean area and South America.
* To search for the natural vector of psorosis-ringspot in the South American areas where this disease naturally spreads.
The results obtained in this project should provide technology to better control severe CTV isolates through eradication of new foci, sanitary control of nursery plants or cross protection. Measures a) and b) would be helpful in Mediterranean countries where severe isolates are uncommon, and measures b) and c) in South American areas where those isolates are widespread. Nucleic acid sequences from psorosis ringspot virus will give new insight on this new type of virus. Specific probes for quick detection of this virus and the possibility to control psorosis-ringspot vectors in South America will allow to control this disease.
The key activities envisaged are:
* Comparison of a panel of isolates of different biotype by SSCP analysis and sequencing those gene variants that might be associated to pathogenic characteristics. The diverging sequences will be used as targets for diagnosis of specific isolates by hybridisation or PCR. A simple protocol using tissue prints and nonisotopic probes will be assayed for field sampling.
* Mild isolates checked for the absence of minor pathogenic components will be assayed for cross protection in the greenhouse. The presence of the severe strain in co-inoculated plants will be monitored by SSCP, hybridisation and PCR and correlated with symptom expression. This technology will be validated with preimmunized field trees naturally exposed to severe CTV isolates in areas where these isolates are widespread.
* We will search for nucleic acid sequences associated with psorosis-ringspot virus and will use them to develop a hybridization or PCR protocol for diagnosis and to obtain additional virus sequences. New antibodies to the virus will be obtained. Biological characterisation, EM, serology and molecular probes will be used to compare psorosis-ringspot isolates from the Mediterranean region and South America.
* The most frequent insects (mainly aphids) found in citrus in South America will be tested for ability to transmit psorosisringspot.
Funding SchemeCSC - Cost-sharing contracts
13490 970 Cordeiropolis
1900 La Plata