1a. Objectives (from AD-416):
Maintain a test site for evaluation of transgenic citrus scion and rootstock genotypes and expression vector strategies for resistance to Huanglongbing and the vector, Asian citrus psyllid.
1b. Approach (from AD-416):
A citrus production site will be maintained at the USDA/ARS Picos Rd. Farm for testing of transgenic citrus resistance to HLB and psyllid. Ongoing strategies to identify resistance to HLB and/or its psyllid vector include many transgenic approaches. All of these research projects ultimately require testing in the field where HLB and psyllid are endemic. The Picos Farm of the U.S. Horticultural Research Laboratory in Ft. Pierce, FL is ideal for this use. It is decided that the best use of this site is to test for HLB/psyllid resistance and control and therefore HLB infected trees are not removed and many citrus blocks are not receiving psyllid control sprays. This site will be available to UF, TAMU and ARS researchers. In addition to transgenic trees, some non-transgenic citrus with reasonable probability of resistance, will be tested.
3. Progress Report:
This project is related to Objective 1: Create new genetic combinations of citrus, Objective 2: Screen germplasm for important traits and select superior individuals, Sub objective 1 D: Create new scions and rootstocks with potential resistance to huanglongbing (HLB) and citrus bacterial canker (CBC) by genetic transformation. A transgenic test site has been prepared at the U. S. Horticultural Research Lab's Picos Farm in Ft. Pierce, to support HLB/Asian Citrus Psyllid (ACP)/CBC resistance screening for the citrus research community. There are numerous experiments in place at this site where HLB, ACP, and citrus canker are widespread. The first trees have been in place for more than two years. University of Florida (UF) has provided 550 transgenic citrus plants expressing genes expected to provide HLB/CBC resistance, which have been planted in the test site. University of Florida planted an additional 89 trees including preinoculated trees of sweet orange on a complex tetraploid rootstock that appeared to confer HLB resistance in an earlier test. U.S. Horticultural Research Lab has a permit approved from Animal Plant and Health Inspection Service (APHIS) to conduct field trials of their transgenic plants at this site, with several hundred transgenic rootstocks in place: ARS scientist has planted several hundred rootstock genotypes transformed with the antimicrobial peptide D4E1. A material transfer agreement is in place to permit planting of Texas A&M defensin transgenics and Texas A&M trees expressing the snow-drop Lectin (to suppress Asian Citrus Psyllid) are now on the ARS permit. More than 100 transgenic trees from ARS and Texas A&M have been planted for assessment of effects of lectins on ACP. Information has been provided to complete the permit application by Texas A&M to plant transgenics which have altered Ca metabolism to target CBC, HLB and other diseases. More than 120 citranges, from a well-characterized mapping population, and other trifoliate hybrids (+ sweet orange standards) have been planted in a replicated trial in collaboration with University of Florida and University of California/Riverside. Plants will be monitored for Liberibacter development and HLB symptoms. Data from this trial should provide information on markers and perhaps genes associated with HLB resistance, for use in transgenic and conventional breeding. Additional plantings are welcome from the research community. This project has been renewed by Citrus Research Development Foundation for an additional three years.