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: 08/10/2021
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 this trial are underway, and permission was obtained from DPI (Ben Rosson) to propagate the rescued trees at the CREC.  Clones being rescued include those showing earlier maturity, higher soluble solids, and better HLB tolerance.  Potential HLB resistance from ‘gauntlet’ rootstock candidates:  qPCR was completed on root samples from 45 additional promising gauntlet rootstock candidates.  18 rootstock candidates had ct values above 30, including 6 that had ct values of 40 (no bacterial detected).  Among these, 5 rootstock candidates showed suppression of CLas in the Valencia scion; including 3 vigorous pummelo x latipes hybrids (13-76, 13-53 and 13-43), and two [Amblycarpa+HBPummelo] x [sour orange + rangpur] hybrids (13-15 and 13-12). Note that C. latipes and the sour orange+rangpur are highly HLB tolerant parents.  Pathogen-free material of top gauntlet rootstocks sent to TC labs for micropropagation include potentially HLB resistant S10xS15-12-25, S11x50-7-16-12, S11x50-7-16-6, and A+HBPxCH+50-7-12-11; and potentially HLB tolerant LB8-9(SugarBelle)xS13-15-16, LB8-9(SugarBelle)xS10-15-9, S10xS15-12-34, and A+HBPxCH+50-7-12-39. Note that S10, S11, S13 & S15 are all salt tolerant pummelo/mandarin parents.  Molecular marker analysis of the promising super-root mutant UFR-1 clone#28 (Fast 28, discovered by Beth Lamb at the Rucks TC lab) showed that it is a deletion mutant of UFR-1; this vigorous rootstock continues to look promising in the field with sweet orange and grapefruit scions.  Additional liners are being propagated at the Rucks TC lab for advanced trials. Identification of probable zygotic rootstocks at St. Helena showing good HLB tolerance (mentioned in previous report):  6 trees on apparent zygotic rootstocks were identified producing 3 – 3-5 boxes of Vernia/Valquarius fruit per tree with 12 – 12.5 brix.  One is a tetraploid from Orange 12 (Nova+HBP-derived), one from Purple 2 (Nova+HBPxCleo+SO), two from HBPummelo x Shekwasha, and two from HBPummelo (open pollination).  Since the staked-up scaffold roots did not sprout, we cut the tops (scion) off the trees as necessary to recover the rootstock genotypes.  Two of the trunks have begun to sprout. We plan to generate pathogen-free material of these selections, followed byTC micropropagation to generate material for advanced trials. We also identified a truly stellar Valquarius tree on rough lemon; we are conducting a molecular marker test on the roots to see if the rootstock is a unique zygotic. If so, it will be treated as the above rootstocks.   St. Helena: The entire trial was assessed tree by tree, and all under-performing trees were pink-flagged for removal.  This has created approximately 2000 rotational spaces, and new rootstock candidates along with new early-mid season sweet orange candidates will be planted.  Tree removal and replanting are expected to get underway this quarter. Field Trial Data Collection:  Tree size data was collected from the following trials: Bryan Paul, Smoak, Greene  River Citrus(lemon), Tom Hammond, Post Office and Peace River.  Tree health assessment data was collected from the Mislevy trial. Data analysis and entry onto the Rootstock Data Website: annual updates included: Heller Bros., Peace River, Bryan Paul Doe Hill, Smoak, Post Office, and Tom Hammond.  Trial data being uploaded and analyzed included data from the follwoing trials: St. Helena, Premier Citrus, Greene River, Lee Family Groves, IMG, Banack, Cutrale and Wayne Simmons. 

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