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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Research Project #434734

Research Project: Genetic Improvement of Citrus for Enhanced Resistance to Huanglongbing Disease and Other Stresses

Location: Subtropical Insects and Horticulture Research

Project Number: 6034-21000-018-00-D
Project Type: In-House Appropriated

Start Date: Jul 3, 2018
End Date: Jul 2, 2023

Objective:
1. Develop and release new citrus rootstock and scion cultivars with traits urgently needed for successful commercial fruit production, especially resistance or tolerance to Huanglongbing (HLB). 1.A. Develop and select promising candidates and assess performance in multiyear field trials, leading to release of outstanding new cultivars. 1.B. Select promising candidates and assess huanglongbing resistance and tolerance in the greenhouse. 2. Introduce new useful traits into USDA citrus breeding populations by sexual hybridization, mutation, and genetic transformation, and recombine traits as needed to obtain desired new types. 2.A. Use hybridization to create new germplasm from diverse parental types with useful horticultural characteristics. 2.B. Create new scions with useful traits through mutation. 2.C. Create scions and rootstocks resistant to huanglongbing and other citrus diseases via genetic modification technologies. 3. Improve the methodology to create, select, propagate, and evaluate new citrus rootstock and scion cultivars for valued traits, especially tolerance or resistance to huanglongbing, and employ these methods for the development and commercialization of new cultivars. 3.A. Refine and evaluate methods to assess huanglongbing tolerance/resistance, and apply appropriate methods to select superior individuals. 3.B. Evaluate rootstocks propagated by seed, cuttings, and micropropagation for horticultural performance and genetic fidelity suitable for large-scale nursery production and commercial field use. 4. Develop in vitro, molecular markers, model systems, and other technology that facilitates the project goals. 4.A. Develop rapid in-vitro methods to accelerate assessment of citrus huanglongbing resistance. 4.B. Develop populations to identify molecular markers associated with resistance or tolerance to huanglongbing.

Approach:
This project will focus on development of new citrus rootstock and scion cultivars with traits urgently needed for commercial production, especially tolerance and resistance to huanglongbing (HLB). These new rootstock and scion cultivars will enhance the competitiveness of the U.S. citrus industry by improving production efficiency, plant health, and value of the U.S. citrus crop. Breeding citrus for resistance to HLB is particularly difficult because of the long life cycle of citrus, predominant apomixis among most important cultivars, and lack of significant HLB resistance in the important cultivated citrus scion cultivars. The primary objectives of this project are to generate new citrus genotypes through conventional breeding, mutation, and genetic modification technologies; evaluate them as candidate cultivars for commercial use; and release new superior cultivars. Due to the very long-term cycle for development of new citrus cultivars, a significant portion of the project is focused on the multiyear evaluation of hybrids created under previous projects, and creating new hybrids for future evaluation and based on the best available knowledge. These components of the project focus on creation and evaluation of germplasm and are not hypothesis-driven research. Under this project, improved methods will be developed for genetic modification of citrus, since current methods are notably inefficient and result in plants containing many foreign sequences and difficult to commercialize. Plant responses to HLB will be investigated, and increased knowledge will be used to design strategies for creation and more rapid selection of tolerant and resistant cultivars. Development of improved screening methods will increase the efficiency of new cultivar development with these traits. Among global efforts to develop new citrus cultivars with HLB resistance and tolerance, this program has the unique advantage of numerous advanced breeding lines, produced by more than a century of interbreeding and introgression, which contain alleles for resistance or tolerance to HLB from related species and genera, combined with other critical traits.