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: 03/17/2022
Project: 18-039-C   Year: 2022
Category: Plant Improvement
Author: Jude Grosser
Sponsor: Citrus Research and Development Foundation

True sweet oranges: This was a very exciting quarter for identifying true sweet orange candidates to replace Hamlin.  Multiple Vernia somaclone-derived seedling clones repeated for early maturity (first week of December) for the 3rd consecutive year.  The best of these was MB-R25-T7, which had a 16.17 ratio and the highest brix (11.16), and significantly higher soluble solids than the Hamlin control.  The Vernia somaclone-seedling population, planted in the Mathew Block at the Orie Lee Alligator Grove, has never had psyllid control.  We began supplementing trees with CRF about 2 years ago to prevent decline.  Trees were commercially harvested last week, and there was still no fruit drop observed.  At this time, the brix in the MB-R25-T7 was over 13.  This new Vernia clone was entered into the PTP in January. We also discovered a new early-maturing OLL clone in the somaclone-derived seedling block of OLLs (located in the Lee Family Home Grove in St. Cloud).  Clone FB-R7-T35 had a 14.12 ratio in mid-January with 12 brix, 5.7 lbs. solids/box (exceptionally high for a juvenile tree) with a 37.3 juice color score.  This clone had an extended juvenility and did not have fruit last year.  This new OLL clone will be entered into the PTP the first week of April, when new slots become available. Both of these clones are being propagated at the CREC to expedite further evaluation (with permission from DPI). Promising orange-like hybrid: Triploid hybrid C7-11-7 [Sugar Belle x (Murcott + Succari sweet orange)] produces fruit morphologically indistinguishable from a true sweet orange, but with better external color. The original tree is exceptionally productive and appears to have HLB tolerance slightly better than standard sweet oranges.  Juice from fruit of the original tree (with HLB for many years) had 13.87 brix, 15.1 ratio, 39.3 color score and 8.31 lbs. solids per box (double the state average for Hamlin!) in mid-January.  This selection will also be entered into the PTP in early April.  Potential HLB tolerance/resistance from ‘gauntlet’ rootstock candidates:  Rootstock sprouts recovered from 12 superior gauntlet trees that had the tops cut off to induce sprouting for rootstock recovery, all successfully grafted, were analyzed for CLas by PCR.  Most interestingly, multiple grafted trees from two of these rootstock candidates had ct values above 36, indicating no CLas bacteria replication; and both hybrids were from the same cross (A+HBPxOrange 3-12-12 and A+HBPxOrange 3-12-10). Both hybrids appear to be more vigorous than either parent. Orange 3 is UFR-1, and both tetraploid parents in this cross produce fruit with high soluble solids (good rootstock pedigree).  Further experiments are being designed to determine the value of strong rootstocks that do not support CLas replication in the root systems. Since recovered lines of these two rootstock candidates are pathogen free, TC propagation was initiated. A 3rd hybrid from this cross looks excpetional in the ‘gauntlet’ this spring, and it will also be cut to recover the rootstock.  CREC Trailer Park Trial:  A good candidate for juice blending was identified: 18A-10-11.  This selection is a low-seeded cybrid of ‘Furr’ that produces a large firm fruit, with exceptional quality juice (12.5 brix, 19.84 ratio and 46.1 color in mid-January). We used this selection in juice blends at both the CREC display and Gator Day at the State Capitol, and all were very well received.  The exceptional juice flavor holds up well to pasteurization.   Rootstock candidate identified from Strang/Gapway trial.  We were able to recover the x639 mutant (apparent deletion mutant) showing the exceptional HLB tolerance.  One successfully grafted tree and 12 rooted cuttings have been obtained.  PCR analysis showed a ct value of 40, indicating no CLas bacteria in the recovered rootstock.  Additional propagation is underway as needed for a more robust field trial.  (Also note that the GapWay property has been sold, so the trial has been lost; however, the rootstock tree was dug up and successfully moved back to the CREC).   Field Trial Data Collection, etc.:  various data (tree health, fruit quality, yield, etc.) was collected from the following trials: Tom Hammond, Greene River Citrus, IMG, Peace River Growers, Bryan Paul Citrus, Lee Family Groves, and Duda.  Data analysis and entry onto the Rootstock Data Website: new data posted on website included:  Jackson Citrus, Lykes, GFC Citrus, Lee Family Groves, Banack Citrus and Duda.  Trial data worked on, not yet added to website: Greene River Citrus, Peace River Growers, IMG, Bryan Paul Doe Hill, Citra trial, Cutrale, and the Serenoa trial. The Access Data Plan was also implemented on the website. 

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