Part B – The UF/CREC-Citrus Improvement Program’s Field Trial Evaluations (Complementary to Part A- the UF/CREC Core Citrus Improvement Program)

Part B - The UF/CREC-Citrus Improvement Program's Field Trial Evaluations (Complementary to Part A- the UF/CREC Core Citrus Improvement Program)

Report Date: 11/19/2021
Project: 18-039-C   Year: 2021
Category: Plant Improvement
Author: Jude Grosser
Sponsor: Citrus Research and Development Foundation

True sweet oranges: With the passing of Louise Lee, the trial block containing the OLL somaclone seedling population is in jeopardy of being sold for development.  Efforts to rescue the most promising clones from these trial blocks continued.  Multiple selected OLL and Vernia clones have been propagated under permit from DPI, and will be planted at St. Helena.  Potential HLB tolerance/resistance from ‘gauntlet’ rootstock candidates:  Rootstock sprouts were recovered from 12 superior gauntlet trees that had the tops cut off to induce sprouting for rootstock recovery.  All have been successfully grafted to recover the 12 diverse rootstock genotypes (seed trees of these selection were not available).  Following clean-up, these rootstocks will be propagated by cuttings and TC micropropagation for avanced trials.  10 more promising rootstock selections were provided to Agromillora for TC micropropagation initiation.  These include 3 more promising gauntlet SugarBelle hybrids (one SugarBelle x trifoliate orange 50-7 hybrid), and hybrids of [salt tolerant HBPummelo x Shekwasha] with trifoliate orange 50-7 and x639.  Agromillora has already generated 3500 shoots from the promising S10xS15-12-25 gauntlet rootstock hybrid previously introduced.  This collaboration with Agromillora will greatly accelarate the planting of important stage 2 rootstock trials.  CREC Trailer Park Trial:  10 trees each of 65 promising new scions available in the Parent Tree Program (selected based on feedback from Fruit Displays and breeder intuition), all on UFR-5 rootstock, were wrapped, planted and mapped. Trees were grown at Southern Citrus Nursery.  Overage trees will be planted at 3 other diverse locations.  This will provide a valuable resource to our new hire Dr. John Chater regarding advanced trials and commercialization of the best selections.Rootstock candidate identified from Strang/Gapway trial.  In November of 2019, we planted approximately 100 HLB+ Valencia trees on selected rootstocks (good trees left over from a CRDF-funded greenhouse nutrition/rootstock study) in the Gapway grove near the CREC, under permit from DPI.  Most of the trees were successfully established.  This summer we identified one superior tree, that even with a 24 ct value before planting, grew off twice as fast as any of the other trees, and already set a good crop of fruit, and showed no HLB symptoms.  We cut this tree to induce rootstock sprouts, and the rootstock genotype has been recovered.  SSR marker analysis shows that the rootstock is from x639, but flow cytometry analysis suggests that there has been a deletion, as the tree repeatedly shows less than the typical diploid amount of DNA.  Further investigation is underway.      St. Helena: Following removal of all under-performing trees, the irrigation system was repaired and the grove prepared for the major resetting operation.  Approximately 600 reset trees are ready to plant, including a new population of Vernia somaclone-derived seedlings, rescued promising selected OLL and Vernia somaclone seedling-derived clones from the Orie Lee trials in St. Cloud (mentioned above, permission granted from DPI to plant rescued sweet orange genotypes at this location), new sweet orange/rootstock combinations, and some new early and mid-season orange-like hybrid scion candidates. Planting is expected to begin this quarter.   CREC Block 16:  a new population of 175 protoclones of EV-1 and EV-2 were planted in efforts to identify a more robust clone of Early Valencia, and possibly a seedless clone.  At present, the available EV clones are showing an HLB response similar to Hamlin regarding fruit drop.   Field Trial Data Collection, etc.:  Tree height data was collected from the Duda, Peace River and CREC Teaching Block trials. Seed fruit from UFR and a few other promising rootstock selections was harvested for seed extraction (seed to be extracted by Southern Citrus Nursery).  Fruit was sampled from all scion trial blocks, and promising early-maturing selections were identified and included in the October Fruit Display – data forthcoming.   Data analysis and entry onto the Rootstock Data Website: annual updates included: Premier Indian River grapefruit trial, Greene Citrus lemon trial, IMG navel & grapefruit/rootstock trial, Duda Vernia/rootstock trial, St. Helena rootstock Survey trial, and CREC scion/rootstock trial.  Trial data from 20 additional trials is being prepared for website updates, including 8 new trials not yet posted.  Initiated creation of a database using Microsoft Access with information from all field trials. 

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