Development and Commercialization of Improved New Disease Resistant Scions and Rootstocks – the Key For a Sustainable and Profitable Florida Citrus Industry

Development and Commercialization of Improved New Disease Resistant Scions and Rootstocks - the Key For a Sustainable and Profitable Florida Citrus Industry

Report Date: 11/17/2018
Project: 15-010   Year: 2018
Category: Plant Improvement
Author: Fred Gmitter
Sponsor: Citrus Research and Development Foundation

Activities are reported by project objectives below. 1. Development of rootstocks that can impart HLB tolerance/resistance to grafted scions. Seedlings are being grown of over one dozen unreleased rootstocks already shown to control tree size support good fruit loads and to have minimal HLB symptom expression. These will be propagated with sweet orange scions for field planting at the St. Helena site next season. As part of the �gauntlet� screening, we stick-grafted approximately 75 new candidate rootstock hybrids produced from HLB-tolerant parents in 2017 with HLB+ Valencia sweet orange for HLB screening. We produced rooted cuttings of approximately 100 gauntlet candidate rootstock hybrids including 47 hybrids combining HLB-tolerant �LB8-9� Sugar Belle� with complementary rootstock germplasm (including salt tolerant pummelo/mandarin hybrids and trifoliate orange 50-7). Replicated cuttings will be used for further HLB-tolerance assessment. �Super Root Mutants� of 10 selections of UFR and other rootstocks discovered by Beth Lamb at the Phillip Rucks Nursery Tissue Culture Lab were potted up; this group includes 3 mutants of UFR-1, 3 of UFR-3, one of UFR-4, one of UFR-17 and one of SO+50-7. These lines are producing feeder roots at a much higher density than the standard clones, and we will screen these selections for potentially enhanced HLB tolerance. 2. Breeding of HLB tolerant/resistant processing sweet oranges and orange-like hybrids. New hybrids produced have been potted up to grow until field planting next season. 3. Screening of the UF-CREC germplasm collection to identify and validate HLB tolerant or resistant selections. The data from this continued effort are being analyzed cumulatively across multiple seasons to more accurately identify and characterize tolerant individuals. 4. Advanced field trials, release and commercialization of promising HLB tolerant/resistant scion and rootstock cultivars. We continued focused effort on field trial data management, analysis and interpretation. Files from more than 80 sites have been opened, conditions of the trials have been noted, and plans for 2018-19 field data collection have been developed and prioritized, based on this information. Efforts to review and summarize data have continued, and information is being organized for inclusion in our soon-to-be available website. We completed data analysis from evaluation of young resets of new sweet orange selections on multiple rootstocks in LaBelle/Immokalee trials, for tree size, health and yield: UFR-17, UFR-15 and 46×20-04-42 (pummelo x Cleo) were outstanding performers here. UFR-4 also did well. The best combinations for tree health and early fruit production were Valencia B9-65/UFR-17 and OLL-20/UFR-17. Our field team visited 10 field trial sites this summer, assessed trees for condition, and contacted grove management personnel, to make them aware of our continued interest in the trials. We planted one new rootstock trial, an additional 400+ trees in a fresh fruit scion trial, and 250 grapefruit hybrids at the IRREC.We collected detailed botanical and morphological information to support IP protection for release of 2 new rootstocks, one sweet orange and a deep red grapefruit.Finally, a very substantial effort was undertaken this year to rescue promising individual trees of diverse scion and rootstock germplasm from our 50-acre research block at the GCREC in Balm. These blocks have not been irrigated since early fall of 2017, and we were forced to leave the site. All trees in this block were subjectively assessed for potential HLB tolerance, as well as general overall health and appearance, using a 0-4 scale (0=dead; 4=completely heathy appearing tree). We harvested budwood from ~2300 individuals with scores = 3 and propagations for field planting in another location. Between June and end of September 2018, we had to revisit the block and collect additional budwood from trees that were not successfully propagated. We are growing off these trees for planting in 2019 at a new location.

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