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: 04/02/2020
Project: 18-039-C   Year: 2020
Category: Plant Improvement
Author: Jude Grosser
Sponsor: Citrus Research and Development Foundation

Potential breakthrough: The Florida NFC industry would love to have high quality sweet orange cultivars that mature in the December/early January window to replace Hamlin. The EV’s (that mature in November) appear to be too early for this slot. During this quarter, we evaluated fruit quality from 80 new Vernia clones (somaclone-derived seedlings and a few cybrids), that were mostly grown in St. Cloud (Orie Lee Mathew Block) without psyllid control on their own roots. From fruit harvested the first week of December, 7 clones were identified that had ratios higher than 15, indicating full maturity at this time (they are: R24T2; R25T2; R25T12; R25T7; R25T5; R26T10; and R26T4. Two clones with much higher soluble solids were also identified: N40W-V7-9 (also 14.51 ratio) and 18A-V8. These clones are being propagated for further evaluation. These clones have clear potential to fill this slot, and Vernia has shown much better tolerance to HLB than Hamlin.

Rooted cuttings were obtained from approximately 30 new gauntlet rootstock candidates. A population of 60+ vigorous rooted cuttings of the best Picos gauntlet rootstock selection S10xS15-12-25 were moved up to 4×4 citripots to be budded for an advanced field trial; a 2nd set of 80+ cuttings of this selection were successfully rooted, This hybrid is a sour orange-type produced from a cross of HBPummeloxShekwasha mandarin X HBPummeloxCleo mandarin (with both parents previously selected for salinity tolerance). The original gauntlet tree was vigorous yet a precocious heavy bearer.

Potential gauntlet rootstock resistance: Monthly PCR testing was initiated on the top 50 gauntlet rootstock candidates at the USDA Picos Farm. 10 selections were identified that repeated for ct values of 32 or above, indicating no active CLas infection; and their roots were also negative; they were: A+HBPxWhite 1-12-13; A+HBPxWhite 1-12-20; A+HBPxSORP-13-79; A+HBPxSORP-13-60; Orange 15 mutants 25 & 34; A+HBPxCH+50-7-12-8l A+HBJL2xOrange19-09-7; and S10xUS-812-11-2. Several others were negative/questionable both samplings, including A+VolkxOrange 19-11-8 that is producing abundant polyembryonic seed. These results show promise for development of a rootstock that can completely mitigate the disease.

The first gauntlet SugarBelle rootstock (S13xLB8-9-15-16) continues to show no HLB symptoms although the ct value indicated a high CLas titer (but no titer was detected in the roots). The high titer was attributed to heavy psyllid pressure on the tree. Limited cuttings of this selection were put on the mistbed for further evaluation of this promising rootstock.

Seasonal Field Trial Data Collection (tree health status, yield and fruit quality where possible) during the quarter was collected from the following trials: Duda, Smoak, Wheeler Bros., IMG, Bryan Paul, Post Office Block, Peace River Growers, Hidden Golf Course trial, Banack, Hammond, Teaching Block, OrangeCo., CPI and Serenoa. Two new trials were added to the website and four trials were updated.

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