Photo By Frank Giles
By Peter Chaires
The New Varieties Development and Management Corp. (NVDMC) has awarded funding to citrus projects for the 2024–25 season. Exciting things are happening in crop transformation, but significant progress is also being made in conventional breeding. The NVDMC board continues to support conventional breeding projects, each with a focus on near-term results, while still setting a foundation for the future. Below are summaries of 2024–25 project objectives.
UF/IFAS CREC
The NVDMC board has communicated the belief that oxytetracycline (OTC) is the HLB treatment holding the greatest promise to restore fruit production and quality in the near term and has shared its desire to know how new citrus scion cultivars may perform following injection treatments. To provide such information, the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center (CREC) team will begin a second season of injections using currently available technologies and materials to determine the benefits and risks in doing so.
The second season will use the same individual trees that were treated previously. These selections are currently growing in field trials at multiple locations. Some previously released mandarin hybrid and grapefruit cultivars will be selected for inclusion in the comparative injection experiments. Some varieties, such as LB8-9 Sugar Belle® and Marathon, already demonstrate substantial field tolerance to HLB, but injection treatments may result in substantial improvements in yield and fruit quality. By comparing outcomes with and without injection, the team may be able to draw conclusions on the return on investment in injections, even among more tolerant varieties.
Performance data collection of advanced candidates is another research objective. Evaluations of existing field trees of advanced selections will be made for fruit appearance and juice quality (sweet oranges and similar hybrids); deep red flesh, peel color, size and external appearance (grapefruit); and appearance, flavor, peelability and seed content (mandarins). Superimposed across all categories is selection for tree health as a measure of HLB tolerance. The primary focus will be directed to sweet oranges and sweet orange-like hybrids, with the greatest potential to impact and support the juice stream.
Selections from populations currently in the field will be made. The CREC team has various families from hybridizations and other approaches to creating phenotypic diversity. They plan to continue to screen these populations in the coming season. As new selections are identified, they will present them through Fruit Display Days, to be held at least four times in the coming season.
UF/IFAS GAINESVILLE
Jose Chaparro, UF/IFAS associate professor, will evaluate mandarin and orange-like selections for HLB tolerance and juice quality as part of his UF/IFAS breeding program in Gainesville. Research plots will be established of citrus selections for evaluation of HLB tolerance and potential for processing. The experiment will consist of 28 selections, including 19 sweet orange-like selections, six mandarins and three grapefruit-like selections. Industry standards will serve as controls.
Another project in Gainesville will be accelerated introgression of HLB tolerance from Australian desert lime (Eremocitrus glauca) into commercial citrus germplasm, including first-generation grapefruit, mandarin and orange hybrids. These populations are now being used to create a diverse pool of second-generation hybrids for breeding and selection. The first backcrossed generation will be planted in the field to monitor for blotchy mottle, leaf retention, canopy health and tree height. Quantitative PCR will be used determine the CLas bacterial titer within the hybrid seedlings twice per year.
UF/IFAS POST-HARVEST
Post-harvest projects led by Mark Ritenour, UF/IFAS professor, will:
- Determine the ability of fruit from promising new fresh citrus selections, developed by the UF/IFAS and U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) breeding program, to produce excellent fruit quality and maintain quality after harvest and post-harvest degreening treatments.
- Evaluate the effects of pre-harvest treatments (e.g., OTC trunk injections) of new citrus scion/rootstock selections on fruit quality and shelf life.
- Evaluate optimum decay control, storage temperature and handling/treatments during harvest, packinghouse, and simulated transportation and marketing conditions, when greater fruit numbers are available.
USDA-ARS CITRUS BREEDING
USDA-ARS researcher Matt Mattia estimates thatUSDA’s overall efforts are directed 70% at producing sweet orange-like cultivars, 20% grapefruit-like selections and 10% specialty fruit. USDA-ARS projects for the upcoming season will:
- Screen newly fruiting breeding populations and variety collections for individuals that have HLB tolerance and commercial potential.
- Continue progress on grafting a grower demo block at the Whitmore Foundation Farm as a place to showcase new varieties to citrus growers and processors in comparison to commercial standards.
- Assess trees from irradiated buds of the most grapefruit-like hybrid selections showing some HLB tolerance. These are in field plantings, and fruit will be assessed for low seed count and lycopene pigmentation. Selections made last season will be validated this season.
- Select buds of priority selections (irradiated and conventional hybrids), pass through the Division of Plant Industry’s shoot-tip grafting program and establish material at the Whitmore Farm as well as coordinating second tests in collaboration with NVDMC, Florida Citrus Processors Association and the Citrus Research and Development Foundation.
- Expedite identification of short-term HLB solutions. Cultivars will be identified in collaboration with industry for field evaluation of HLB tolerance.
- Identify potentially HLB-tolerant cultivars which may be combined to produce a satisfactory sweet orange-like juice.
- Repurpose an OTC 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 Whitmore Farm.
- Screen material for cold and stress tolerance associated with HLB and utilize the screening as an early selection tool.
EVALUATION OF EARLY-SEASON SWEET ORANGES
Manjul Dutt, UF/IFAS assistant professor, will be working on three early-season orange projects at CREC.
Project 1: Several Hamlin trees have been observed to be tolerant to HLB and continue to produce fruit with high pounds solids even though they have high CLas titer.It is not known if the scion is tolerant, if there is a rootstock-scion interaction or if grower inputs coupled with improved genetics are responsible for the observations. Dutt will thoroughly evaluate all the trees in this block, select top performers and propagate additional trees to understand if this survivor trait is heritable.
Project 2: A block of 600 irradiated Carney Orange 3 (a Parson Brown clone with better color) trees budded onto US-942 was planted at CREC in December 2023. Trees are being maintained as per standard industry procedures and will be routinely evaluated for HLB. The main goal of this study is to identify superior HLB-tolerant selections with lower peel oil and seed content.
Project 3: Dutt obtained several early-season sweet orange cultivars from the USDA at Riverside. Each of these seed-derived cultivars are being propagated for replicated planting at a CREC grove. Additional genetic evaluation will be conducted on these trees to understand if any have potential HLB tolerance.
Peter Chaires is the executive director of NVDMC.
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