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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETIC IMPROVEMENT OF CITRUS
2008 Annual Report


1a.Objectives (from AD-416)
Develop new citrus scion and rootstock cultivars with needed horticultural traits, including enhanced tolerance of environmental stress, resistance to diseases and pests, and improved fruit quality and yield.


1b.Approach (from AD-416)
Create new genetic combinations of citrus germplasm via conventional breeding, mutation, and transformation. Screen germplasm for important traits, such as fruit quality, yield, tree size, tolerance of cold and drought, and resistance to Citrus Tristeza Virus, Citrus Bacterial Canker, and Huanglongbing. Select and propagate superior individuals. Evaluate selections for field performance and other traits. Release promising new scion and rootstock varieties for commercial use.


3.Progress Report
This project replaces Project 6618-21000-012-00D, which terminated in April, 2008. Progress on this new project since April included making crosses for new hybrids, growing hybrid seedlings, planting field trials for evaluation of new hybrids, and collecting performance information from trials for new selections. A study was completed on seed transmission of Huanglongbing and submitted for publication. Studies were initiated on citrus tristeza virus resistance of new hybrids using reverse grafts. Greenhouse tests were completed to evaluate germplasm resistance to Huanglongbing disease. Data was collected on Huanglongbing infection in selected field trials to evaluate potential cultivar influence on Huanglongbing-related decline. The rootstock cultivars US-812 and US-802 were transformed with the anti-microbial peptide D4E1 and transgenic plants established in the greenhouse. All these areas of progress directly relate to the National Program 301 Plant Genetic Resources, Genomics, and Genetic Improvement, Component 3 Genetic Improvement of Crops, Problem Area 3C Germplasm Enhancement/Release of Improved Genetic Resources and Varieties.


4.Accomplishments
1. Improving Transition of Transgenics to Greenhouse. A method was developed to micrograft transgenic shoots directly onto greenhouse seedlings, thereby eliminating the extended time needed to transition plants from sterile culture into soil in the greenhouse. This modification of the process for producing transgenic citrus effectively shortens the time until greenhouse or field testing can begin on these plants by at least 3 months. The development of new cultivars with improved characteristics relates to the National Program 301 Plant Genetic Resources, Genomics, and Genetic Improvement, Component 3 Genetic Improvement of Crops, Problem Area 3C Germplasm Enhancement/Release of Improved Genetic Resources and Varieties.

2. Transgenic Rootstocks. Thirty independent transgenic plants, transformed with the anti-microbial peptide D4E1, have been created and established in the greenhouse from the rootstock cultivars US-802 and US-812. These transgenic plants may possess resistance to disease and are being prepared for propagation and controlled testing with Huanglongbing and citrus bacterial canker. The development of cultivars resistant to Huanglongbing and citrus canker relates to the National Program 301 Plant Genetic Resources, Genomics, and Genetic Improvement, Component 3 Genetic Improvement of Crops, Problem Area 3C Germplasm Enhancement/Release of Improved Genetic Resources and Varieties.


5.Significant Activities that Support Special Target Populations
None.


6.Technology Transfer

None

Last Modified: 11/26/2014
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