Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants | 920 - Orange | 1000 - Biochemistry and biophysics | 50% |
| 204 - Plant Product Quality and Utility (Preharvest) | 999 - Citrus, general/other | 1080 - Genetics (excludes breeding) | 50% |
Sustainability of the U.S. citrus industry, especially in Florida, is currently threatened by Huanglongbing (HLB), a disease associated with the bacterium Candidatus Liberibacter asiaticus (CLas) and its vector, the Asiatic citrus psyllid. HLB debilitates trees, reduces yield, ruins fruit quality, and eventually kills trees. Young trees are particularly susceptible to HLB, making the establishment of new orchards challenging. The foundation of sustainable citrus production in the face of HLB will be cultivars, both scion and rootstock, that are able to survive to bearing age and that produce high quality fruit for the fresh and juice markets. Identification of citrus types resistant or tolerant to HLB and acceptable to the market will require research at various stages of tree development; however, young tree survival, by default, is the first step in the process. If trees can survive to bearing age, the next step in the evaluation of promising genotypes is horticultural performance including susceptibility to other diseases, cropping ability, and fruit quality. Evaluation of fruit quality for genotypes which survive and produce a crop is essential to determine if new hybrids or transgenic plants meet established standards. Finally, when promising selections have been identified, replicated field trials will be the conducted to determine worthiness for eventual release. Protection and preservation of the invaluable advanced selections and breeding lines which exist only in the U.S. Horticultural Research Laboratory citrus breeding program are essential to this program; novel methods for pathogen elimination, scion evaluation, and germplasm conservation will be tested. Enhanced production efficiency, health, and value of the U.S. citrus crop will be outcomes of this research.
For Objective 1, numerous citrus scions, both newly released and advanced selections in the breeding program were propagated on multiple rootstocks in preparation for field trials. New field trials were established with grower cooperators using trees that had been produced in the previous FY. These trials were evaluated for mortality and overall health. The effects of citrus rootstocks on fruit and juice quality were evaluated for the third year of a multi-year trial. For Objective 2, trees were propagated to use in studies to determine how trees affected by Huanglongbing (HLB) disease respond to drought stress. A ten month greenhouse study was initiated to determine the kinetics of infection of Valencia oranges with Candidatus Liberibacter asiaticus (CLas) (causal organism of HLB disease). Trees were exposed to Asian citrus psyllids infected CLas for periods of 2 and 4 months. Following exposure trees were transferred to a greenhouse free of Asian citrus psyllids and tested for infection in leaves and roots. This experiment continues into the project 6618-21000-016-00D that was initiated 3/1/2014. Experiments to estimate proportions of live/dead CLas in various citrus tissues and in response to treatments that eliminate infections with the pathogen have continued. A field trial was conducted to determine whether spraying HLB-affected trees with various combinations of plant growth regulators, amino acids, phosphorus, and atrazine would have therapeutic effects. Data on tree health and growth were collected, leaf samples were analyzed to determine titer of CLas, ribonucleic acid and protein was extracted and provided to collaborator for transcriptomic and proteomic analysis. Accomplishments 01 Release of two new mandarin scion varieties. Development of new high quality mandarin varieties is essential for the U.S. citrus industry to remain competitive in the global market. Good flavor and color, ease of peeling, low seed counts, and resistance to plant pathogens are important characteristics that are necessary for new varieties to be successful in the market place. ARS researchers at the U.S. Horticultural Research Laboratory, Fort Pierce, Florida have released two new mandarin varieties, 'US Furr' and 'US Furr-ST'. 'US Furr' was produced by hybridizing 'Murcott' tangor (Florida Honey tangerine) with the Clementine mandarin. This selection has outstanding flavor and color and is mature around mid-December. 'US Furr-ST' was produced by irradiation of 'US Furr' seeds. Although essentially identical to 'US Furr', one of the plants resulting from irradiated seed was less prone to develop citrus scab than were others. These new mandarin varieties provide citrus growers the opportunity to diversify their cultivar mix and provide consumers with tasty alternatives to standard mandarins.