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: 05/04/2021
Project: 18-039-C   Year: 2021
Category: Plant Improvement
Author: Jude Grosser
Sponsor: Citrus Research and Development Foundation

True sweet oranges: New OLL sweet orange candidates repeated for early-mid season maturity (consecutive years), including OLL-FB-4-13 (mentioned in previous report) and OLL-FB-9-33.  OLL-FB-4-13, OLL-FB-9-33, and OLL-FB-1-22 were selected for inclusion in the CRDF scion trial, and were entered into the Parent Tree Program (using special slots provided by Ben Rosson and Kristen Aslan).  A new selection OLL-FB-4-08 was identified with January 1 maturity (first time fruiting). Potential HLB resistance from ‘gauntlet’ rootstock candidates:  qPCR was run on leaves sampled from more than 625 gauntlet rootstock trees at the USDA Picos Farm, and 54% tested questionable or negative for active infection.  Among these, qPCR was run on roots on 60 of the best performing trees.  Among these, 13 trees had root ct values of 40, meaning no bacteria was detected in the roots. Two of these also had leaves that tested negative and 4 others questionable. We also identified 19 gauntlet rootstocks in this group that were negative for active root infections, and among these 4 had no active infections in the leaves, and 9 had questionable leaf infections.  Considering the severe fruit quality problems, especially from young trees the past 2 seasons in Florida, we also focused on identifying the best of these producing high brix fruit right off the bat.  3 potentially resistant rootstocks were identified producing high brix fruit: N+HBPxOrange19-12-3 (a backcross of UFR-4 onto it’s mom), B11-R5-T25-11-3 (a Flying Dragon hybrid with potential for high density plantings), and A+HBPxCH+50-7-12-11 (also tree-size controlling, with UFR-6 pollen parent).   Several gauntlet rootstocks are also showing an apparent tolerance mechanism, as they show consistently good tree health, but had higher CLas titers in the roots than the trees above; these include a few hybrids made with SugarBelle.  Identification of probable zygotic rootstocks at St. Helena showing good HLB tolerance:  5 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), two from HBPummelo x Shekwasha, and two from HBPummelo (open pollination).  One rootstock genotype has been recovered, and scaffold roots of the other selections have been cut in efforts to retreive the rootstock germplasm.   Fruit quality data was collected from the Trailer Park trial – two combinations of 3.75 year-old trees made 6.0 and 5.9 lbs solids per box: Valencia B9-65/UFR-4 and OLL-4/UFR-4, respectively. Yield data was collected from the St. Helena trial.  There was no issue with fruit drop, and lbs. solids across more than 50 rootstocks averaged around 6.0 lbs. solids per box.  Overall yield increased slightly.  These positive results were attributed to the continued year-round use of CRF containing an enhanced micronutrient package. Yield data was collected from the Peace River Valencia/rootstock trial, and the Duda trials.  Data analysis and entry onto the Rootstock Data Website: annual updates included: Duda Valencia APS rootstock trial, Duda Vernia rootstock trial, Smoak Valencia rootstock trial, Bryan Paul Doe Hill multi-scion rootstock trial, and the IMG navel/grapefruit rootstock trial. Data analyses for subsequent trial updates was performed for (in progress): Banack multi-scion rootstock trial, Hidden Golf Trailer Park trial, Wheeler Bros. scion/rootstock trial, Orie Lee OLL clone/rootstock demonstration trial, Teaching Block scion/rootstock trial, Bryan Paul Doe Hill Grove multi-scion/rootstock trial, Citra (PSREU) scion/rootstock trial, Hammond IR Minneola rootstock trial, IR Marsh grapefruit/rootstock trial, the St. Helena rootstock survey trial, and trial and the Peace River Valencia/rootstock trial.    

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