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: 08/07/2017
Project: 15-010   Year: 2017
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. Prepared 120 �gauntlet� trees (all HLB-affected Valencia on individual rootstock candidates) for planting at USDA Picos. Completed stick-grafting of approximately 150 new rootstock candidates selected from 2015 crosses, and selected and stepped up approximately 120 hybrid rootstock candidates from 2016 crosses from the high pH, calcareous/Phytophthora soil screen, including hybrids of Sugar Belle with disease resistant parent trifoliate orange 50-7 and others. Planted a small trial of EV-1 and EV-2 early Valencias on putatively HLB-tolerant rootstocks in efforts to identify rootstocks that can prevent fruit drop with these selections. Planted a new field trial with >2700 trees near Ft. Meade including some of the UFRs, releases from California and Spain, and several CREC hybrids also planted in other locations. Worked together with Dr. Ferrarezi at the IRREC, and a host of IR growers and the IRCL to plan a new rootstock trial for the IR region, based on scion cultivars of importance to the fresh fruit producers of the region. 2. Breeding of HLB tolerant/resistant processing sweet oranges and orange-like hybrids. Planted approximately 300 trees of promising new OLL sweet orange seedling selections including OLL-DC-3-36 and OLL-DC-3-40 (original trees showed no HLB symptoms after 4 years in the field under heavy pressure). Continued micro-grafting recovered hybrids from 2016 scion crosses, including several combinations that should produce seedless sweet orange-like fruit with improved HLB tolerance. 3. Screening of the UF-CREC germplasm collection to identify and validate HLB tolerant or resistant selections. We continue to monitor our germplasm collection and breeding families for performance against HLB. We have initiated a genomic selection effort based on phenotypic assessments and using a high density SNP chip for genotyping. This may lead to identification of genetic resources to facilitate HLB-tolerant scion and rootstock breeding. 4. Advanced field trials, release and commercialization of promising HLB tolerant/resistant scion and rootstock cultivars. Performed subjective HLB scoring on the 300+ �gauntlet� trees at the USDA Picos Farm; identified several new promising rootstock candidates. Rated trees in 5 different replicated rootstock trials throughout the state for HLB responses, and collected yield and juice quality information in 2 such locations. Other related activities: Worked with Dr. Ferrarezi to have IRREC land prepared for planting of propagated selected cybrid grapefruit clones (kumquat cytoplasm) of Flame, Ruby somaclone N11-11 and Marsh showing canker tolerance in greenhouse assays. The original N11-11 somaclone, derived from Ruby Red, has shown a strong recovery response from HLB, so these cybrids may be both canker and HLB tolerant. Planted a scion trial in the IR region with lemons from the CREC program, selected for high oil yields in the IR region; lemon�s HLB-tolerance has generated industry interest as an alternative citrus product. The Rootstock Selection Guide, has had over 515,000 hits in its first 23 months. Finally, an exhaustive review was prepared of the UF-CREC filed program for CRDF BOD, RMC, and any other interested entities, and presented.

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