Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 201 - Plant Genome, Genetics, and Genetic Mechanisms | 999 - Citrus, general/other | 1081 - Breeding | 100% |
This project is a continuation of the Grosser program citrus breeding effort that has been ongoing for the past 35 years. The program combines conventional breeding with all relevant emerging biotechnological tools to facilitate the citrus breeding and selection process. The program interacts very closely in a complementary fashion with program of Dr. Fred Gmitter. The goals of the project are to deliver new improved rootstocks and scions to the Florida Citrus Industry that will allow for sustainable and profitable citriculture in the now HLB-endemic world. The project is expected to deliver rootstocks that can be used to mitigate HLB in any commercial scion. The project is expected to generate improved sweet orange cultiars that cover the entire harvesting season, and will contribute substantially to the improved quality of NFC Florida orange juice as needed to increase juice consumption. The project will also generate new fresh market cultivars that will provide Florida growers with an opportunity to compete in the lucrative national and international fresh fruit markets, including higher quality seedless easy-peel tangerines, seedless fresh oranges, red-pigmented seedless and sweeter grapefruit, and unique acid fruits. The project is expected to expand opportunities for all phases of the Florida Citrus Industry.
Objective I. Rootstock Cultivars A. Hybridization1. Sexual: Crosses will be made with monoembryonic and polyembryonic selections derived from several Citrus species, hybrids, and related genera, as seed or pollen parents. Parents will be selected and combined in a complementary fashion, combining the desired traits. Emphasis will be placed on crosses maximizing HLB tolerance. Crosses will proceed annually in a progressive manner. Rootstock hybrids will be produced at both the diploid and tetraploid levels.2. Somatic hybridization: Intergeneric and interspecific allotetraploid somatic hybrids will be produced via protoplast fusion using our embryogenic culture + leaf protoplast model system. Selection of fusion parents will be based on feedback from field trials, performance of cultivars in our protoplast system, and performance in greenhouse/field seedling screens. Resulting somatic hybrids will be propagated for further testing by either in vitro, shoot multiplication and/or by rooted cuttings (Grosser and Gmitter, 1990; Grosser et al., 2000, 2005).B. Selection and EvaluationScreening: The Gauntlet High-Throughput Screening Program: Since HLB has become endemic in Florida, the ongoing UF program has screened more than 12,000 rootstock hybrids (diploid and tetraploid) in search of rootstocks that can mitigate or eliminate HLB in grafted commercial scions. Such rootstocks would be the ultimate solution, as they eliminate the need for psyllid control, antibiotics, thermotherapy, GMOs, etc. Seed from diploid and tetraploid rootstock crosses of superior parents are planted in flats of high pH, calcareous soil (brought to the CREC from the Indian River), and inoculated with both Phytophthora nicotianae and P. palmivora. Vigorous dark-green 'Gauntlet' rootstock hybrids that can handle the calcareous soil and Phytophthora, are grafted with HLB+ Valencia budsticks. HLB+ trees are grown out directly from the infected budwood to produce trees for field evaluation at the USDA Picos Farm in Fort Pierce. Gauntlet trees are evaluated annually for growth, tree health, and monitored for CLas titers using qPCR. Field performance: Replicated trials of advanced selections and standard rootstocks, all budded with common scion will be established at various representative citrus growing locations in Florida. Field design will target a minimum of six 4-tree replications planted in a randomized block design. Tree size and growth characteristics, stock-scion compatibility, field tolerance of stress and diseases (especially HLB) and influence on scion performance (fruit quality and yield) will be measured; also, advanced selections in field trials will be evaluated according to their financial performance. Superior selections will be patented and released according to IFAS/FFSP policy.Objective II. Processing Sweet Orange Cultivars A HybridizationSexual: Crosses will be made with monoembryonic seed parents and complementary pollen parents previously shown to produce progeny with sweet orange-like characteristics. Focus will be on using parents with good HLB tolerance, and most crosses will produce progeny containing 1/3 or 2/3 sweet orange. Potentially seedless triploid hybrids will be produced by interploid hybridizations, with recovery of triploid progeny facilitated by embryo rescue. Sweet orange-like triploids with superior fruit quality and adequate HLB tolerance already produced will be propagated and evaluated on a larger scale.Somatic hybridization and cybridization: Interspecific allotetraploid somatic hybrid breeding lines will be produced by the fusion of protoplasts derived from embryogenic callus cultures with leaf-derived protoplasts of the corresponding parents. Selection of parents will be based on feedback from previous and ongoing field evaluations, with focus on HLB tolerance and fruit quality. Fertile somatic hybrids will be used in interploid sexual crosses in efforts to generate seedless triploids mentioned above (Grosser and Gmitter, 1990; Grosser et al., 2000, 2005). Selection and EvaluationPrimary selection: Initial selection will be based on HLB tolerance, fruit/juice quality, and season of maturity. Brix, acidity, sugar/acid ratio, juice %, lbs. solids and juice color will be measured by running samples through the CREC Pilot Plant. Promising selections identified will also have sensory/organoleptic evaluations performed in collaboration with Dr. Yu Wang, and/or Florida orange juice companies such as Tropicana and Florida's Natural.Advanced testing: Primary selections will be propagated on superior HLB-tolerant rootstocks generated by our program, with commercial scion cultivars used for comparison, and planted in replicated trials at various representative citrus growing locations in Florida to assess performance on various stocks and consistency of yield and quality characteristics. Selections exhibiting superior performance will be patented and released according to IFAS/FFSP policy.Objective Ill. Fresh Fruit CultivarsHybridizationSexual: Interploid crosses will be made with monoembryonic seed parents and complementary pollen parents. Focus will be on using parents with good HLB tolerance, and that have the most potential for transmitting desired fresh fruit characteristics. Potentially seedless triploid hybrid production will be facilitated by embryo rescue when necessary. We have decades of experience showing us what traits are reliably transmitted from specific parents, and this information will be utilized in new annual crosses. For grapefruit improvement, we have several new high quality tetraploid pummelo hybrids that are now flowering. We ave also identified two grapefruit-like tetraploid somatic hybrids that are showing excellent HLB and canker tolerance. These will be utilized in interploid crosses with dark red grapefruit and selected diploid pummelos.Somatic hybridization and cybridization: Interspecific allotetraploid somatic hybrid breeding lines will be produced by the fusion of protoplasts derived from embryogenic callus cultures with leaf-derived protoplasts of the corresponding parents. Selection of parents will be based on feedback from previous and ongoing field evaluations, with focus on HLB tolerance and fruit quality. Fertile somatic hybrids will be used in interploid sexual crosses in efforts to generate seedless triploids.Selection and EvaluationPrimary selection: Initial selection will be based on HLB tolerance, fruit quality (flavor, size, external color, internal color, segment structure, peelability, etc.), and season of maturity. Promising candidates will be shown at our fruit displays for Industry Feedback; compiled information will be used to make decisions on which selections to move forward to advanced trials and entry into the DPI Parent Tree Program to generate a source of pathogen-free budwood. Pathogen-free legal budlines will also be maintained in the CREC repositories.Advanced testing: Superior selections will be propagated on superior HLB-tolerant rootstocks generated by our program, with commercial scion cultivars used for comparison, and planted in replicated trials at various representative citrus growing locations in Florida to assess performance on various stocks and consistency of yield and quality characteristics. Pollination requirements will be determined by controlled pollinations. Promising selections will be made available to growers for advanced field trials through the existing Fast Track program, and via MTAs. Selections exhibiting superior performance will be patented and released according to IFAS/FFSP policy. Note: in the event that a non-certified propagation greenhouse is made available by any funding agency, it will be fully utilized by accelerated advanced testing of promising clones prior to obtaining pathogen-free budwood from the Parent Tree Program.
Target Audience
Citrus growers, packers and processors affected by HLB.
Changes / Problems
Nothing Reported
Training & Professional Development
Brazilian intern student Maria Brenelli began her MS program, and working on development of new sweet orange clones.
Dissemination Streams
Publications in Scientific Journals and Trade Journals, presentations at Citrus Trade Shows, multiple fruit/juice displays showing new selections, multiple field tours with growers/nurserymen.
Next Reporting Steps
This research is a progressive continuum. We are planning multiple new scion/rootstock trials to determine which selections can be sustainable and profitable in the now HLB-endemic condition of Florida.
Target Audience
Target Audience: Citrus Growers, Packers & Processors.
Changes / Problems
Fruit/juice displays are now being done remotely by having participants pick up samples and sending in evaluations on line - as necessary due to covid restrictions. Will resume normal pathways when possible.
Training & Professional Development
Continued hosting Brazilian student (Faculty of Agrarian and Veterinary Sciences of Jaboticabal City, São Paulo State) Mariá Brenelli de Paiva Vidotti, for an 18-month internship (2nd term, extended). Mariá is working on field trials evaluating OLL sweet orange clones and seedling-trees on new tetraploid rootstocks, and Vernia somaclone-derived seedling trees. She is now applying for an MS graduate program. 2. Continued hosting Egyptian PhD Student Lamiaa Mahmoud, from the Pomology Department, Faculty of Agriculture, Mansoura University. Lamiaa is conducting a sandwich dissertation research program (fully funded), studying biotechnology and genetics of citrus trees, with focus on salinity tolerance and HLB-tolerant rootstocks. Dr. Manjul Dutt is also involved with her supervision. 3. Hosted Moroccan visitor Anas Fadli on a 10-month internship as part of his MS program at the Mediterranean Agronomic Institute of Zaragoza, University of Lleida, Spain. Anas worked on rootstock screening for the NIFA-SCRI grant. Anas also completed a PhD from Morocco while at UF, and is now doing a post-Doc with Dr. Ute Albrecht at SWFREC. ?
Dissemination Streams
21. EXTENSION PROGRAM - 2020 Highlights · CREC Fresh Fruit Display at the Florida Citrus Showcase, Fort Pierce, FL. · State Capitol - UF/CREC Variety Improvement Program Orange Juice/Fruit Tasting at Gator Day in Tallahassee. This first-time effort was a huge success. · Two invited presentations 'UF-CREC Citrus Rootstock Evaluation for an HLB-Endemic Florida: The Way Forward' and 'Grapefruit Breeding for the now canker/HLB endemic Florida', Florida Citrus Showcase, Fort Pierce, FL. · 1 NVDMC sponsored Fruit/Juice Displays at the CREC, and 1 at Vero Beach (Fair Grounds), and 1 remote display with fruit sample pickup by participants. · 2 Field Tours of Lee Groves scion/rootstock trials (6 and 4 participants). · Field Tour of St. Helena and Tropicana trials (Rick Dantzler, CRDF) · Invited presentation for the on-line Florida Growers Citrus Institute entitled: 'Improved Genetics and Nutrition - The Way Forward' (narrated PP video). · Invited presentation for the on-line Citrus Expo entitled 'Varieties and Rootstocks for an HLB-Endemic Florida' (narrated PP video). · Mini-field Tours of CREC Trailer Park Block: 5 tours, 1-10 participants each. ?
Next Reporting Steps
Continue utilizing established pathways for product and information to clientele. <br><br>
<br>What was accomplished under these goals? 1. Solving HLB, Blight and Tristeza - Diploid Breeding: 5 crosses were conducted in 2020, in efforts to combine the HLB tolerance of SugarBelle with complementary parents that included Swingle, Kuharske, and 3 salt tolerant Shekwasha x HBPummelo hybrids showing good HLB tolerance (via stress tolerance genes). HLB Gauntlet Screening Program: Recovered seed from 2019 diploid and tetraploid crosses were planted in calcareous soil inoculated with both problematic species of Phytophthora (liquid inoculum supplied by Diane Bright in Dr. Johnson's lab was utilized). Replicate cuttings were produced from more than 50 new rootstock candidates. The first hybrids containing SugarBelle genetics have now been in the field for nearly one year, and several are showing exceptional health and tree growth.. Approximately 50 individual candidate rootstock hybrids (includes diploids and tetraploids) were selected following the calcareous soil/Phytophthora screen, and stick grafted with HLB+ Valencia. More than 50 HLB-Valencia grafted trees on candidate rootstock hybrids were wrapped and tagged for planting at the USDA Picos Farm. Zygotic seedlings derived from Orange 14 and showing promise were also prepared for inclusion at Picos Farm. Several 4+ year old gauntlet trees continued to show good tree growth, fruit production, and some repeated for high ct values (32 or above) 2-7 times during monthly winter tests. The best hybrid in the gauntlet S10 x S15-12-25 has been successfully propagated by cuttings and also introduced successfully into TC at Agromillora. Trees are being grafted for the Tri-State and other trials. A superior zygotic rootstock hybrid from 46x20-04-9 was recovered from the Wayne Jackson trial in LaBelle, and cuttings are being produced. This rootstock has also been entered into the alternating temperature chamber for rapid cleanup. Super-Root Mutants: Continued to work with Beth Lamb at Ruck's nursery to collect and evaluate 'super-root' mutants of UF rootstocks being propagated via tissue culture. UFR-6 clone #1 produced a few fruit of outstanding quality (several scions including Rio Red grapefruit) on just one-year old trees in the Tri-State planting. 2. Other Sweet Orange Research: Processing: Produced a population of protoclones of EV-1 and EV-2 in efforts to identify a more robust early Valencia clone - trees will be planted in spring of 202 (Ahmad Omar). We also evaluated two blocks of 1-2 year old EV trees on leftover gauntlet rootstock cuttings (Frielander Block in Lake Wales, and Mislevy Block in Bowling Green); identified a rootstock showing potential to prevent fruit drop and produce fruit of very high quality (C2-4-1 x WGFT+50-7-12-3). Continued data collection on early 'Valencia' and Vernia and 'OLL series' somaclones/somaclone-derived seedlings. OLL Sweet Orange Projects: We continued our cooperation with Tropicana/PepsiCo (Allison Drown) via our collaborative Demonstration Block with Jason Griffin in Haines City, and providing Gio Ljpkemeule with fruit samples for sensory analysis. Orange-like hybrids: We identified another sweet orange-like seedless triploid hybrid C4-8-25 that was fully colored and mature in October (SugarBelle x [Succari + Murcott]. This selection has processing and fresh fruit potential, as it can be peeled. It was entered into the PTP. Several other orange-like hybrids with processing potential were identified. We also identified new triploid hybrids that have good juice blending potential (at the current 10% limit), for improving the color and flavor of Florida NFC, including KE-6-4 (Ambersweet zyg. x 4X Succari) that has a 40 color score in November. This clone was sensory-evaluated by Tropicana and they liked the flavor. This selection was also entered into the PTP. 3. Fresh Fruit Improvement: Seedless Triploids: Mandarin/Sweet orange: 2020 interploid crosses continued to focus on obtaining triploids with zipperskins, early and late maturity, and HLB tolerance; this includes production of sweet orange-like hybrids (especially early maturing) with potential for improved HLB tolerance. Interploid crosses were conducted from 18 different parental combinations, including 6 that were designed to produce sweet orange-like fruit. Pollen parents included 4x Valencia, Murcott+Ortanique, 4x 304 and Page+(Clementine x Satsuma). LB8-8 and LB8-9, Temple, Clementine, and G-96 were the predominant seed parents used. Embryo rescue was completed, now ploidy analysis and micrografting are underway. Micrografting of triploid hybrids produced during 2019 continued. Approximately 50 new triploid hybrids were planted as resets as spaces became available in CREC blocks. Grapefruit/Pummelo: 55 new triploid hybrids were planted as resets in various blocks at the CREC as spaces became available. 10 interploid crosses were conducted primarily using HLB tolerant, high quality red pummelos x 4x Hudson red grapefruit. Embryo rescue was completed, and ploidy analysis and micrografting are underway. Two large trials of new CREC red grapefruit and pummelo clones on new candidate rootstocks were planted with Bryan Paul and English Bros. Citrus. Trees were propagated at Briteleaf nursery and the CREC. A large trial of grapefruit-like hybrids was also partially planted with Richard Davis (Groveland), with the remainder to be planted in 2021. Irradiation: Pummelette: we continued evaluating fruit from irradiated canker-tolerant pummelette trees (Kinsey Block) for seed content and fruit quality. KW-3-7 was identified to have a higher juice content, and much less granulation, although it does have a few seeds per fruit. Somatic Hybridization/Cybridization: Because of the previously reported compromised trees at the IRREC trial (in cooperation with Johnny Ferrarezi), and the new unreasonable U-Farm charge rates, we decided to move the cybrid trial to another non-UF site. Trees are being propagated to accommodate this. Dr. Omar is still producing new cybrids of red grapefruit and sweet oranges with kumquat cytoplasm, in an effort to improve canker and HLB tolerance (See Dr. Omar's report for more details). Dr. Omar is also continuing efforts to generate new tetraploid breeding parents, focusing on using Tango and W. Murcott as the embryogenic parent, and various high quality diploid mandarins from the CREC breeding program as leaf parents. <br><br><b>Publications</b><br>