1a. Objectives (from AD-416):
Develop and 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 at the USDA/ARS, Picos Road Farm and will be maintained for testing of transgenic citrus resistance to huanglongbing (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. This site will be available to University of Florida, Texam A&M University 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 was prepared at the U. S. Horticultural Research Lab’s Picos Farm in Ft. Pierce, to support Huanglongbing (HLB/Asian Citrus Psyllid)(ACP)/Citrus Bacterial Canker (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 three years, and were established under a different project number which is now terminated. University of Florida (UF) has provided more than 700 transgenic citrus plants expressing genes expected to provide Huanglongbing/Citrus Bacterial Canker (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, and 400 sweet oranges transformed with the antimicrobial peptide D4E1. Texas Agricultural & Mechanical trees expressing the snow-drop Lectin (to suppress Asian Citrus Psyllid) and ARS trees expressing garlic lectin 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 Candidatus (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 are being monitored for Liberibacter development and HLB symptoms. A USDA/ARS advanced selection which is 1/16th Poncirus, with commercial quality fruit, is performing extremely well. Data from this trial should provide information on markers and perhaps genes associated with huanglongbing (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 (CRDF) for an additional three years.