UPDATE-JANUARY 2006 BUDWOOD DISTRIBUTION SUSPENDED

Citrus Clonal Protection Program Bulletin -January 25, 2006

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We at the CCPP would like to thank all of you for the valuable input that we received following the announcement of the tristeza (CTV) finding in the Foundation and Evaluation Block at Lindcove. During the past few days we have carefully considered all of the different options in an attempt to find a safe alternative to fill the January budwood orders. Our approach is based on careful consideration of industry input and only after consulting with other scientists and industry experts. We at CCPP have to carefully balance our dual mission of servicing and protecting the California citrus industry.

We would like to share with you the different scenarios entertained as well as the reasoning behind our final approach to the issue.

Why don’t we use the screenhouse resource for the January budwood cut? Because CTV findings in the Foundation and Evaluation Block have been rare (the current one was the first in over a decade) the screenhouse trees have been carefully maintained as varieties backups. As a result of this only a very small number of screenhouse trees, primarily early release varieties, have been registered for budwood distribution. The Foundation Block currently holds 286 registered trees and has been the primary source of budwood for almost 50 years.
The Foundation Block trees produce large amounts of good budwood year after year at a very low cost for maintenance after being established compared to screenhouse trees. With field grown budwood trees CCPP is able to evaluate tree health and trueness-to-type of fruit allowing us to fulfill two of the basics that the program established upon, production of disease tested as well as true-to-type budwood. Additionally, CCPP is able to supply thousands of buds from a single field tree each year and be able to expect more again the next year.
On the other hand the potted screenhouse trees typically have a productive life-span of about 4 years and, if pruned for budwood, that span is cut to about 2 years of good budwood production. Field trials would also need to be established to evaluate the type of fruit that these trees might produce. The maintenance of registration of trees is a large part of the program in both cost and labor. Maintaining registered trees in both the screenhouse and the Foundation Block would simply duplicate the disease testing, record keeping, labor and cost with minimum return to the industry. We do not know yet how the screenhouse ground plantings will behave as budwood sources but we can not expect from them the full range of benefits of the field trees.
Based on the above facts we at CCPP believe that we should carefully continue cutting field grown budwood for as long as possible. However, if it is the desire of the industry in the future the CCPP can start allocating resources for the preparation of the screenhouse trees to play a more significant role in the regular budwood distribution.

Why don’t we cut the budwood in January store it and release after the CTV testing is concluded? The appropriate time for CTV sampling and testing is after the 1st of April when the virus titter is at detectible levels with the available diagnostic techniques. It will take about 2 weeks to conclude the testing of the approximately 100 trees that CCPP received budwood orders for the January budwood cut. Therefore, nurseries will not have the budwood before the mid of April. That brings us very close to the regular June cut which can be performed with a high degree of confidence for the absence of tristeza since the spring testing will have been performed and concluded under optimum conditions. If harvested in January the budwood could not exit the Lindcove Research and Experiment Station and therefore would need to be stored on the premises. We contacted the personnel of the station and they have offered to assist in the maintenance of the budwood for the period of the 3 months however, the quality and viability of the stored budwood can not be guaranteed by the CCPP or by the Lindcove station. In the same communication with the Lindcove station we were informed that many trees are already starting to flush which reduces even more the chances of successful budwood storing. The question of waiting until the mid of April for budwood of questionable quality probably has a different answer for each one of you but, the feedback we had from some nurseries indicated that the middle of April would be too late anyway.

Why don’t we use the tristeza indexing in Mexican lime to determine which trees are free of CTV and cut budwood only from those varieties? The October test in which we identified the positive tristeza tree included 50% of the registered trees of our collection and it is not yet completed. There are several more months of bio-indexing time left. The positive tree was identified in the first reading of symptoms meaning that more tristeza positives may arise in the coming months. This is quite possible since only one of the two limes inoculated with tissue from the positive Foundation tree expressed symptoms. This would indicate that this infection was relatively new with low CTV titers which may result to slow lime reactions or that the infection had not yet spread throughout the entire tree. It would certainly follow that there may have been more natural spread of the virus in the days and weeks following the October harvest of test materials. The most recent completed lime index that we can refer to is the one of March ’05, which included the other 50% of the registered trees. However, between March and today there were at least two aphid flights therefore we simply can not base any decisions on these data. In summary, for half of the trees the data are old and under the pressure of aphid flights and for the other half the data collection is not completed.

Based on the above we have decided to take the following actions:

1. Monday January the 30th of 2006 travel to Lindcove to collect budwood from the registered screenhouse trees of Early Release varieties ordered in the January cut.

2. Test the entire Block for tristeza using ELISA beginning Monday April 3rd of 2006.

3. Continue with the scheduled Mexican lime bioindexing of the Foundation Block.

4. Resume the normal budwood cutting on the week of the 12th of June 2006.

We understand that the above actions do little to relieve the immediate needs of nurseries for budwood but we strongly believe that in the long run this approach have much more advantages than disadvantages.
The current situation presents an excellent opportunity for all of us serving the California citrus industry to reorganize, prioritize and be proactive for our future needs. The CCPP has served the industry successfully for many decades and it is going to be a vital part of any changes that the industry will plan for the future in regard not only to the current issue but to several others standing on our doorstep.

Once more our thanks for your input and support.

click here for original announcement