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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Research Project #430055

Research Project: Huanglongbing (HLB) Resistance and Tolerance in Citrus Scion Breeding

Location: Subtropical Insects and Horticulture Research

Project Number: 6034-21000-018-02-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Oct 1, 2015
End Date: Sep 30, 2018

To produce citrus scion genotypes which are resistant to huanglongbing using conventional plant breeding and non-transgenic biotechnology.

In the USDA breeding program several hybrids display tolerance to huanglongbing (HLB), with plants testing positive for Liberibacter, but continuing to grow and crop well. Among commercial cultivars, Temple has the best hunaglongbing-resistance in initial tests. In this study, we will quantify the huanglongbing-resistance/tolerance of priority material to determine its value in commercial Florida citrus production. We will also develop tissue culture derived material in which resistant genotypes form the vascular system and standard varieties produce the fruit quality layers. Such chimeras exist as commercial cultivars in China. Like scions on rootstocks, these chimeras use genotypes for their best traits in each plant portion, with proven methodology. The tissue culture "internal grafting" procedure to produce periclinal chimeras was developed by Ohtsu (Ann. Phytopath. Soc. Japan 60:82-88) and further demonstrated by Sugawara et al. (HortScience 30:1276 -1278) in Japan. Since the tissue layer forming the phloem and xylem contribute little to the juice vesicles, use of an hunaglongbing-resistant internal layer may provide a rapid and sustainable solution to huanglongbing using established fruiting types. Material displaying promise will be further tested for fruit quality and other characteristics, while being field tested against standards to assess huanglongbing resistance. A field trial of diverse mandarins associated with tolerance will be planted & tested. Ribonucleic acid seq indicates marked upregulation of defense genes in Jackson (tolerant) vs. Marsh (suscept.). In this project we will conduct RNAseq of five tolerant and closely related susceptibles to refine markers. Differences in resistance genes between susceptible and tolerant/resistant members of the citrus gene pool will be determined and initial steps will be taken to modify susceptible types through gene editing (CRISPR-CAS).