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: 09/14/2016
Project: 15-010   Year: 2016
Category: Plant Improvement
Author: Fred Gmitter
Sponsor: Citrus Research and Development Foundation

Our project is focused on the following objectives: 1. Development of rootstocks that can impart HLB tolerance/resistance to grafted scions. 2. Breeding of HLB tolerant/resistant processing sweet orange-like hybrids. 3. Screening of the UF-CREC germplasm collection to identify and validate HLB tolerant or resistant selections. 4. Advanced field trials, release and commercialization of promising HLB tolerant/resistant scion and rootstock cultivars. The project began on 1 November 2015. Annual data collection from several ongoing field trials of rootstocks for the 2015-16 season was completed. Trees were assessed for HLB incidence and severity through all plantings, and yields and fruit quality was determined in selected replicated trials. Mutant selections of Valencia orange, produced and planted 10 years ago were found to be exhibiting few or no HLB symptoms. Fruit from the best of these were tested for juice quality and a few were also analyzed for volatile components and compared with standard sweet orange. The CREC plant breeding team�s collective field evaluation records have been reviewed, consolidated and organized for more efficient record keeping, and new files have been added. Newly released early Valencia cultivars EV-1 and EV-2 ( were propagated at the CREC as potential legal budwood increase or foundation trees and distributed to 20 licensed nurseries to expedite introduction to our industry. These have the potential to replace Hamlin and help improve the quality of Florida juice products. Approximately 1000 liners of gauntlet candidate rootstocks produced from rooted cuttings were grafted with either EV-1 or potentially HLB tolerant OLL seedling lines (four lines being tested) for subsequent field evaluation. Gauntlet HLB Screening: HLB-infected Valencia budstick grafting of new candidate rootstocks continued, approximately 150 new hybrids were grafted during this quarter. Two more sets of gauntlet rootstocks,were rotated into a �hot psyllid� house and approximately 100 trees were prepared for field planting. Gauntlet rootstock and transgenic trees at Picos Farm were sampled and PCR tested. The large majority of the best gauntlet trees remain PCR+, but Ct values were generally higher than commercial trees, indicating lower bacterial titer in the best performing trees. One healthy tree remains PCR-negative. Several transgenic trees remain PCR-negative or have very high Ct values after 5 years, mostly trees containing NPR-1 or SABP-2, and 11 trees containing Xa21. Two-year old transgenic trees containing the Valencia beta-glucanase gene look quite good. Six super-root ‘sports’ of UFR rootstocks (from UFR 1,3 and 6) being tissue propagated at Ruck’s nursery were identified by Beth Lamb. She provided us the cultures and we grew out liners from these cultures and they were budded with a potentially HLB-tolerant OLL seedling line for field testing. These ‘sports’ grow feeder roots much more quickly than the original clones – which could enhance their performance against HLB. We produced approximately 300 cuttings of rootstock SG-6-50 – recovered from cut-off field trees planted near Clewiston in 1997. This rootstock candidate is a hybrid of Smooth Flat Seville and Swingle, and is showing good HLB tolerance. Original seed trees produced seedy, polyembryonic fruit, but were destroyed by the canker eradication effort. These liners will be utilized in the Grosser/Gmitter/Bowman MAC project.

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