JANUARY 2006 BUDWOOD DISTRIBUTION SUSPENDED

Citrus Clonal Protection Program Bulletin -January 9, 2006

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The CCPP has confirmed that one tristeza positive tree has been identified in the Lindcove Foundation and Evaluation Block. The tree was identified in January as positive in the annual Mexican lime test and was confirmed as positive by the laboratory test ELISA. The tree, VI 105 – CRC 1452 Citrumelo, was immediately removed from the planting and surrounding trees were retested and were found to be free of tristeza. This is the first tree to be found positive for tristeza in the Foundation Block in more than 10 years.

The causal agent of tristeza is a virus named Citrus tristeza closterovirus (CTV). Different types of CTV cause a variety of potentially harmful diseases of citrus namely quick decline, stem pitting, and seedling yellows. CTV is spread naturally by some aphid species and can also be spread by using infected budwood to make new propagations. This particular infection was likely through natural spread of the virus by aphids that first fed on an infected tree elsewhere and then moved to this citrumelo tree in the CCPP collection at Lindcove. This particular tree of VI 105 was first planted in 1989 and has tested negative for tristeza up to six times annually over the ensuing years. Tristeza has not been found to be spread through seed even from infected trees.

Trees in the CCPP Foundation collection are tested several times annually for tristeza by both index to Mexican lime and by ELISA. This citrumelo tree was tested negative in June of 2005 when 2 buds were distributed and no buds were cut from this tree at the January or September 2005 distributions.

The Mexican lime test in which this positive was identified was started on October 14, 2005. In mid-October tissue was harvested from all registered trees in the CCPP collection for routine annual indexing by graft inoculation to Mexican lime, the indicator variety for tristeza. Tissue is harvested from the four quadrants (N-S-E-W) of each tree and is then graft inoculated into two Mexican limes each which are then grown in a quarantine greenhouse at specific temperatures that are optimum for tristeza symptom expression. Only one of the two limes that were inoculated using tissue from this citrumelo tree was positive indicating that the infection was in its very early stages before it had spread throughout the entire tree.

As a precaution and until the entire collection can be retested the budwood distribution scheduled for the week of January 16 th, 2006 has been suspended. As of the first evaluation of the Fall bio-indexing test no other Foundation Block trees have yet indicated the presence of tristeza. The Fall index will be completed in March 2006. All trees will be retested by ELISA during the Spring of 2006 starting April 3rd and routine annual indexing to Mexican lime will continue on schedule. We at CCPP feel that is best to take these precautions now and if the collection remains otherwise free of tristeza to resume normal budwood distribution.

Currently we are considering alternative options to fill January orders before the normal June 2006 cutting. We will keep you posted as to the final approach and will do all that we can to see that orders are filled in the safest way while keeping the citrus industry protected. Please keep visiting our web site for updates on the situation.

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