2019-11_18-016 – Testing grapefruit trees expressing an anti-NodT antibody for resistance to HLB

Testing grapefruit trees expressing an anti-NodT antibody for resistance to HLB

Report Date: 01/13/2020
Project: 18-016   Year: 2019
Category: Plant Improvement
Author: Timothy McNellis
Sponsor: Citrus Research and Development Foundation, Inc.

The present reporting period runs from September 15 – December 15, 2019. Mr. Chad Vosburg is the M.S. degree student in the Penn State Department of Plant Pathology graduate program who is working on the project. Chad took a trip to Fort Pierce, FL, November 15 – 25, 2019. During this trip, he set up additional plant propagations for 1-2 runs of an HLB resistance test for all the FT-scFv grapefruit lines. Existing propagated plants that had been cut back to induce a new flush of growth were not yet growing out in order to allow for the setup of an HLB infection test. Personnel at the USHRL are monitoring the plants to determine when they have reached the optimal stage of re-growth to start an HLB resistance test using psyllid-mediated transmission. Chad also learned how to propagate citrus by grafting. In particular, he grafted the highest expressing line of FT-scFv to rough lemon rootstocks, since this line propagates very poorly by rooted cuttings. This will provide sufficient plants to test for HLB resistance of this highest expressing line, which would be the most likely to have a strong resistance phenotype. In addition, Chad grafted the next two highest expressing lines to rough lemon rootstocks known to be HLB infected. Rough lemon supports a relatively low CLas titer and this will form an additional test for HLB resistance, as we wait for psyllid-mediated tests to commence. A field test of two of the FT-scFv lines is now set up at the Pecos Farm at the USHRL, with 10 plants per transgenic line, plus non-transgenic controls, having been planted in the field. Chad has sampled these plants for time zero measurements of CLas titers. We anticipate that the first run of an HLB resistance test will be initiated during the next reporting period. Mr. Jeremy Held, a Ph.D. student in the Intercollege Graduate Program in Plant Biology at Penn State, continued his analysis of graft-transmissibility of the FT-scFv protein in the grapefruit lines. Initial tests for FT-scFv transmissibilty to non-transgenic scions did not yield any FT-scFv protein detection signal. However, we are now optimizing the protein isolation procedure to enrich the protein samples for for phloem tissue content. The FT-scFv protein is expected to be limited to the phloem in the non-transgenic scion, making it more difficult to detect than in the transgenic FT-scFV rootstock plants.

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