A Preview of Florida Citrus Breeding Projects

By Peter Chaires

The New Varieties Development & Management Corp. (NVDMC) board of directors has completed its 2023-24 budgeting process. Like other citrus industry organizations and private companies, the NVDMC board sought to address the need for immediate and short-term benefits, without abandoning a necessary focus on the future. Most of the funding will be directed to near-term benefit, with a principle focus on the orange juice stream, followed by development and evaluation of HLB-tolerant grapefruit, with very limited focus on specialty citrus. Below is a summary of NVDMC projects for 2023-24.

University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center (CREC) Plant Improvement Team

Principal Investigators: Fred Gmitter, Jude Grosser, John Chater and Yu Wang


1. Documentation of performance attributes of new and recently selected candidates: Evaluations of existing field trees will be made for appearance and juice quality (sweet oranges and similar hybrids); deep-red flesh and peel color, size and external appearance (grapefruit); and appearance, flavor, peelability and seed content (mandarins). Fruit from all categories will be selected for HLB tolerance. Identified selections will be presented at four Fruit Display Days.

Dozens of new, true sweet orange offspring have begun fruiting, and some have shown substantial HLB tolerance. The team will generate in-depth documentation of yield and quality (over time) for existing and new selections. The goal will be to identify the most consistently high performers, and to move these into more rigorous trials to demonstrate and document their superior performance, such that growers and others in the industry will have confidence in future planting decisions and investments.

The team has also identified several new grapefruit clones, as well as grapefruit hybrids, that have held up better against HLB than standard grapefruit. These also have improved canker tolerance. The goal in the coming season will be to sample these more frequently over the length of the production season, to document their productivity and fruit quality attributes over time.

2. Reassessment of previously released cultivars and other unreleased advanced selections under new regimen of oxytetracycline-injection technologies: The team recognizes that the industry is rapidly embracing oxytetracycline formulation injections as a tool to support improvements in tree health, with the goals of increasing yields and fruit quality.

The team will select cultivars from each variety category. The project will include un-injected control trees to be able to quantify and document differential performances (collected yield and fruit/juice quality data), if observed.

This research can have immediate impact for growers, in that the team may be able to demonstrate economic viability of varieties previously selected with input from industry for their excellent fruit and juice quality, and already released and therefore available now.

UF/IFAS Gainesville

Principal Investigator: Jose Chaparro


1. Continue the evaluation of the sweet orange-like populations generated by the breeding program: The freeze events of Dec. 24-25 caused significant cold damage to the young seedling populations. Data on progeny survival will be collected. The older progeny will be evaluated, and data collected on HLB infection. As in previous years, superior selections will be submitted to the Florida Department of Agriculture and Consumer Services Division of Plant Industry (DPI) for cleanup. Significant culling of the existing populations in the teaching grove was done in the fall of 2022 and will likely conclude in the fall of 2023.

Data on HLB tolerance and cropping of these selections will be collected.  Juice samples from the fruit harvested at the Indian River Research and Education Center (IRREC) and Gainesville test blocks will be analyzed for soluble solids content, titratable acidity, juice color and ‘off’ flavor development.

2. Seek grapefruit and grapefruit/pummelo hybrid plant improvement and enhanced tolerance to HLB and canker: The seedlings of crosses made in the spring of 2022 between the grapefruit-like selections with Flame and Hudson will be planted in the field.

A recently identified white-fleshed grapefruit-like selection, with apparent improved HLB tolerance, will be replicated and planted for additional evaluation.

3. Breed of specialty fruit with enhanced tolerance to HLB: Though no additional specialty fruit populations will be generated, there will be ongoing evaluation of existing populations to identify superior easy-peeling mandarin selections.

Fruit harvest and juice analysis data will be collected for any trees bearing fruit in the fall of 2023. Data on canker resistance, HLB tolerance and tree mortality will also be collected.

4. Accelerate introgression of HLB tolerance from Australian desert lime into commercial citrus germplasm: Evaluation will continue with existing BC1 populations for blotchy mottle, leaf retention, canopy health and tree height. Quantitative PCR will be used to determine the HLB bacterial titer within the hybrid seedlings twice per year. The fourth year of fruit quality data will be collected from one of the backcross populations during the fall of 2023.

UF/IFAS IRREC Post-Harvest Fruit Analysis

Principal Investigator: Mark Ritenour


1. Determine the ability of fruit from promising new fresh citrus selections, developed by the UF/IFAS and U.S. Department of Agriculture (USDA) breeding programs to produce excellent fruit quality and maintain quality after harvest and postharvest degreening treatments (when necessary).

2. Evaluate the effects of preharvest treatments (e.g., oxytetracycline trunk injections) of new citrus scion/rootstock selections on fruit quality and shelf life.

3. When greater fruit numbers are available, evaluate optimum decay control, storage temperature, and handling/treatments during harvest, packinghouse, and simulated transportation, and marketing conditions.

USDA Agricultural Research Service Citrus Breeding Project

Principal Investigator: Matt Mattia


1. USDA’s overall efforts are roughly directed 70% at producing sweet-
orange-like cultivars, 20% grapefruit-like and 10% specialty fruit.

2. Intensively screen newly fruiting breeding populations and variety collections for individuals that have HLB tolerance and commercial potential.

3. Continue progress on grafting a grower demo block at the A.H. Whitmore Farm as a place to showcase new varieties to citrus growers and processors in comparison to commercial standards.

4. Assess trees from irradiated buds of their most-grapefruit-like hybrid selections, showing some HLB-tolerance. Fruit will be assessed for low-seed count and lycopene pigmentation. Selections made last season need to be validated this season.

5. Select buds of priority selections, have them processed at DPI and establish material at the A.H. Whitmore Farm.

6. To expedite identification of short-term HLB solutions, cultivars will be identified in collaboration with industry for field evaluation of HLB-tolerance. In addition to fresh fruit types, the processing industry is working with USDA to identify potentially HLB-tolerant cultivars which may be combined to produce a satisfactory sweet-orange-like juice.

7. Repurpose an oxytetracycline field trial on a cross section of 12 scions with varying levels of HLB tolerance using an existing field trial for cold tolerance at the A.H. Whitmore Farm.


Principal investigator: Manjul Dutt


1. Several survivor Hamlin trees in Lake County have been observed to be tolerant to HLB and continue to produce fruit with high pounds solids even though they have high HLB bacterial titer. It is not known if the scions are tolerant, if there is a rootstock/scion interaction or if grower inputs coupled with improved genetics are responsible for the observations. A well replicated block will be planted using top performers to understand if this survivor trait is heritable. At the same time budwood will also be provided to the DPI parent tree program for cleanup.

2. A replicated block of Carney Orange 3 has been propagated and will be planted at CREC in early summer 2023. The trees will be divided into three groups, each under a unique nutrition program. The main goal of this study will be to evaluate the Carney Orange 3, propagated on the most popular Florida rootstock and to understand its growth, physiology and fruiting.

3. Several early-season sweet orange cultivars were acquired from the USDA at Riverside, California. Each of these seed-derived cultivars are being increased for propagation and replicated planting at a CREC grove. Additional genetic evaluation will be conducted on these trees to understand if any have potential HLB tolerance. 

FOOTNOTE: Peter Chaires is executive director of the New Varieties Development and Management Corp.