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: 05/10/2017
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: A set of approximately 70 new rootstock candidates, stick-grafted with HLB-infected Valencia, were rotated into the �hot psyllid� house in cooperation with Dr. Nian Wang. The previous set of 50 rootstock candidates were removed from the �hot psyllid� house and prepared for field planting at the USDA Picos Farm in Fort Pierce. Twenty five new crosses were made using parents that have demonstrated HLB tolerance or have yielded offspring exhibiting high levels of tolerance. 2. Breeding of HLB tolerant/resistant processing sweet orange-like hybrids: At least 35 crosses were made this spring, to develop HLB-tolerant scion cultivars, using tolerant breeding lines with complementary characteristics. Fruit samples of some HLB-tolerant candidate selections were processed and pasteurized; several were found that produced good juice with no bitterness or off-flavors as typically found in mandarin hybrids. Three Valencia clones identified previously as rather tolerant in germplasm collection screening were observed still to be performing well; new anatomical and molecular studies have been initiated to determine underlying mechanisms of their tolerance; further, they have been entered into the DPI PTP for cleanup, and trees have been propagated directly for further field testing. Additionally, cybrid grapefruit clones (kumquat cytoplasm) of Flame, Ruby somaclone N11-11 and White Marsh showing significantly improved canker tolerance in greenhouse assays, were propagated for anticipated field planting at IRREC (~200 trees). Collected leaf samples from approximately 1000 transgenic trees and 300 �gauntlet� trees for qPCR to determine HLB infection status. Trees in both categories with good appearance were identified for further close observations. 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. We reorganized our field data collection team, to focus on collecting data from our most critical trials. A new planting was made of seedless and easy to peel fresh mandarins, some exhibiting HLB-tolerance, in Pasco County. A large rootstock trial was planned and organized in the Peace River region. Completed yield and fruit quality data collection from the St. Helena Project. Preliminary analysis of the data shows an overall slight increase in lbs. solids over last year, with some rootstocks increasing in yield, and some decreasing. Trees on Swingle have shown a remarkable recovery. Collected yield and fruit quality data from 3 year old trees in the OLL sweet orange clone/rootstock trial near St. Cloud. Completed young tree assessments in the large new Camp Mack and Basinger rootstock trials with Lykes; Hamlin and Valencia trees on ~60 rootstock candidates were assessed for size, fruiting, overall health, and HLB disease symptoms. Other related activities: Minor revisions were made to the Rootstock Selection Guide, which has incidentally had over 389,000 hits in its first 17 months.

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