Fort Pierce Field Test Site for Validating HLB and/or ACP Resistance

Fort Pierce Field Test Site for Validating HLB and/or ACP Resistance

Report Date: 10/15/2019
Project: 18-058C   Year: 2019
Category: Horticultural & Management
Author: Ed Stover
Sponsor: Citrus Research and Development Foundation

Update for this quarter:
No new plantings. Canker was assessed in a number of the transgenic trees from UF and USDA and in the trifoliate and trifoliate hybrid planting of UCRiverside. Growth and CLas titer data were collected on Stover lab transgenics. The Stover BRS permit was renewed and associated plantings were reported to be in compliance. The McNellis trees will be planted next quarter.

Previous quarter
A number of trials are underway at the Picos Test Site funded through the CRDF. A detailed current status is outlined below this paragraph. In the last quarter, the most significant advances have been: 1) Planting of USDA Mthionin transgenics with 108 transgenic Hamlin grafted on wild type Carrizo (7 events represented), 81 wild type Hamlin grafted on transgenic Carrizo (16 events represented) and 16 non-transgenic controls. 2) Planting was made of transgenics from Zhonglin Mou of UF under Stover permit, with 19 trees of Duncan, each expressing one of four resistance genes from Arabidopsis, and 30 Hamlin expressing one of the genes, along with ten non-transgenic controls of each scion type. 3) Renewal and approval for BRS permit effective 9/1/19 through 8/31/20. 4) Continuation of an experiment on pollen flow from transgenic trees. FF-5-51-2 trees are slightly more than 1000 ft from the US-802, and are self-incompatible and mono-embryonic. If pollen from transgenic trees is not detected from open-pollination, it should reduce isolation distances required by BRS. 5) Early-flowering transgenic Carrizo (flowered ex-vitro within five months of seed sowing, and used at 12 months) was used to pollinate some of the same FF-5-51-2 and some fruit appear to have set. 6) What should be the final samples from the C. Ramadugu-led Poncirus trial (#3 below) completed preparation and were shipped in ethanol to UC Riverside.

Previously established at the site:
1) The UF Grosser, Dutt and Gmitter transgenic effort has a substantial planting of diverse transgenics. These are on an independent permit, while all other transgenics on the site are under the Stover permit.

2) Under the Stover permit a replicated planting of 32 transgenic trees and controls produced by Dr. Jeff Jones at UF were planted. These trees include two very different constructs, each quite specific in attacking the citrus canker pathogen.

3) A broad cross-section of Poncirus derived material is being tested by USDA-ARS-Riverside and UCRiverside, and led by Chandrika Ramadugu. These are seedlings of 82 seed source trees from the Riverside genebank and include pure trifoliate accessions, hybrids of Poncirus with diverse parents, and more advanced accessions with Poncirus in the pedigree. Plants are replicated and each accession includes both graft-inoculated trees and trees uninfected at planting. Likely 2019 will be the last year for data collection.

4) More than 100 citranges, from a well-characterized mapping population, and other trifoliate hybrids (+ sweet orange standards) were planted in a replicated trial in collaboration with Fred Gmitter of UF and Mikeal Roose of UCRiverside. Plants were monitored for CLas titer 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. Manuscripts have been published reporting HLB tolerance associated QTLs and differences in ACP colonization. Trees continue to be useful for documenting tolerance in a new NIFA project.

5) A replicated Fairchild x Fortune mapping population was planted at the Picos Test Site in an effort led by Mike Roose to identify loci/genes associated with tolerance. This planting also includes a number of related hybrids (including our easy peeling remarkably HLB-tolerant 5-51-2) and released cultivars. Genotyping, HLB phenotyping and growth data have been collected and will continue to be conducted under a new NIFA grant.

6) Valencia on UF Grosser tertazyg rootstocks have been at the Picos Test Site for several years, having been CLas-inoculated before planting, and several continue to show excellent growth compared to standard controls (Grosser, personal comm.).

7) In a project led by Fred Gmitter there is a planting of 1132 hybrids of C. reticulata x C. latipes. C. latipes is among the few members of genus Citrus reported to have HLB resistance, and it is expected that there will be segregation for such resistance. The resulting plants may be used in further breeding and may permit mapping for resistance genes.

8) Seedlings with a range of pedigree contributions from Microcitrus are planted in a replicated trial, in a collaboration between Malcolm Smith (Queensland Dept. of Agriculture and Fisheries) and Ed Stover. Microcitrus is reported to have HLB resistance, and it is expected that there will be segregation for such resistance. The resulting plants may be used in further breeding and may permit mapping for resistance genes.

9) Conventional scions on Mthionin-producing transgenic Carrizo are planted from the Stover team and are displaying superior growth to trees on control Carrizo.

10) Numerous promising transgenics identified by the Stover lab in the last two years have been propagated and will be planted in the test site. New transgenics from Tim McNellis of PSU will be planted in the next quarter.

11) Availability of the test site for planting continues to be announced to researchers.

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