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: 08/13/2018
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, approximately 150 new rootstock candidates from 2016 crosses stick-grafted with HLB-affected budwood; these included hybrids using Sugar Belle, pummelo, and trifoliate orange 50-7. We planted 100 new �gauntlet� trees (HLB+ Valencia on individual new rootstock candidates) at the USDA Picos Farm in Fort Pierce. This planting includes numerous tetraploid hybrids of a recently characterized HLB-tolerant tetraploid sour orange-like seed parent with HLB-tolerant hybrids of trifoliate orange 50-7. Finally, a small preliminary screening trial using left-over cuttings from �gauntlet� rootstock candidates (34 trees on 22 new rootstock hybrids), grafted with dark red grapefruit clone N11-7, was planted in the Indian River area. 2. Breeding of HLB tolerant/resistant processing sweet oranges and orange-like hybrids. Sensory and chemical analyses of fruit of tolerant sweet oranges and sweet orange-like hybrids were conducted, to understand the potential value of such fruit to the OJ business. Also, we planted approximately 500 triploid scion hybrids in CREC research blocks, with emphasis on hybrids designed to produce sweet orange-like fruit from HLB-tolerant parents. Finally, 140 new transgenic trees were planted at an APHIS-permitted site for field testing. These trees were mostly oranges containing either BG or another new AMP gene Lima B, under control of either constitutive or phloem-limited promoters. 3. Screening of the UF-CREC germplasm collection to identify and validate HLB tolerant or resistant selections. We continued to monitor our germplasm collection and breeding families for performance against HLB, and we contine our genomic selection efforts based on HLB-phenotype and SNP genotyping. Genomic regions identified contain putative disease resistance/defense genes. 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 finished off a very busy fruit season with collecting yield data from 2 field trial sites and determined fruit juice quality from 5 field trials; in these cases, data were collected on tree performance in the face of HLB. At least 15 grove sites throughout the state were visited to check the status of existing field trials, and to make certain that appropriate personnel within the cooperators� organizations were aware of our continued interest and commitment to their field trials with us. We have continued our efforts to develop cumulative reports over time of certain selected individual trials, to highlight the better performing combinations for yields and HLB tolerance. We are moving forward with plans to share these with the collaborative growers first, and then to make them available to the industry at large. Finally, a very substantial effort was undertaken 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 are being 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.

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