|Yokomi, Raymond - Ray|
Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Abstract Only
Publication Acceptance Date: 10/22/2010
Publication Date: 11/7/2010
Citation: Yokomi, R.K., Metheney, P., Grafton-Cardwell, E., Stewart-Leslie, J. 2010. Current status of Citrus tristeza virus in Central California [abstract]. Conference of International Organization of Citrus Virologists. 31:s23. Interpretive Summary:
Technical Abstract: The Lindcove Research and Extension Center (LREC), Exeter, CA has 51 ha of citrus and is the field site and screenhouses for the University of California Citrus Clonal Protection Program (CCPP). LREC maintains a zero tolerance of Citrus tristeza virus (CTV) infected trees to protect the CCPP and research projects. Regional management of CTV in central California is conducted by the Citrus Pest Detection Program (CPDP) operated by the Central California Tristeza Eradication Agency, Tulare, CA. However, LREC lies in a district in which growers voted to stop removing CTV-infected trees in 1996. From 1990 to 2006, an average of 3 newly infected trees per year were removed from the research and CCPP orchards at LREC. In 2007, the Center had 52 infected trees, triggering a 0.8 km survey for CTV in commercial citrus around the Center and resulting in an estimate of 1.2% incidence. In 2008, 83 new infections were found at the LREC and an aphid control program was initiated at the LREC and in commercial and dooryard citrus and pomegranate in a 3 to 5 km area around the station. As part of this program, citrus was treated with foliar acetamiprid in the spring and systemic imidacloprid was applied to citrus and pomegranate in the fall. Pomegranate is an overwintering host of the primary vector of CTV in the San Joaquin Valley, the cotton or melon aphid, Aphis gossypii. This aggressive aphid control program was applied to 92% of the citrus acreage in the area and reduced new infections at the LREC to 52 and 20 in 2009 and 2010, respectively. In addition, the CPDP continued to survey citrus 1.6 km around the LREC and the 2010 survey resulted in an estimated CTV incidence of 3.55%. This is in contrast to an estimate of 0.362% infection (with 90% of the 2010 survey completed) from in all 5 Pest Control Districts representing over 78,000 ha of citrus in central California. The CPDP has begun recently to assess CTV strains with the monoclonal antibody MCA13. Only 4 suspect MCA13 positive trees were found so far outside the LREC area; whereas 15 trees were confirmed positive for MCA13 in the 1.6 km area around the LREC. Extracts from these MCA13 positive samples were assessed by multiplex TaqMan® real-time- RT-PCR assay: 11 reacted with T36NS probe vs. 4 with the VT3 probe. Biocharacterization show that VT3 strains from this area induce strong seedling yellows reaction. MCA13 positive trees are being removed in an effort to mitigate spread of potential severe strains of CTV.