Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 212 - Pathogens and Nematodes Affecting Plants | 920 - Orange | 1160 - Pathology | 40% |
| 212 - Pathogens and Nematodes Affecting Plants | 999 - Citrus, general/other | 1160 - Pathology | 40% |
| 212 - Pathogens and Nematodes Affecting Plants | 910 - Grapefruit | 1160 - Pathology | 20% |
This research project is focused on huanglongbing (HLB) and the extremely invasive pathogen Ca. Liberibacter asiaticus and another potentially invasive but uncharacterized pathogen, a presumed virus that causes citrus chlorotic dwarf (CCD) in Turkey. The pathogen has not been described, but it is transmitted by a whitefly already widespread in the United States and thus has very high potential for invasiveness. We will conduct basic and applied research which will lead to improved understanding of the biology and etiology of these diseases and provide the basis for improved diagnostic and research methods. Microarray studies of sweet orange trees infected with Ca. Liberibacter asiaticus and other phloem-limited pathogens will lead to the identification of novel host genes associated with general disease responses triggered by phloem-limited pathogens and specific disease responses triggered by Ca. Liberibacter asiaticus. Recombinant antibodies developed by bacteriophage display will be used to develop diagnostic procedures for Ca. Liberibacter asiaticus and as research tools. We will analyze data obtained from deep sequencing technology to characterize the virus causing citrus chlorotic dwarf. This information will be used to develop PCR and serologically based assays for this pathogen. The products of this research project will improve both scientific knowledge of invasive pathogens of citrus and provide novel assays useful or their detection and management.
This is a final report for project 8042-22000-281-00D, "Invasive Pathogens of Citrus." The goal of this project was to prevent the introduction or spread within the citrus industry of a number of graft- transmissible and invasive pathogens of citrus. Due to quarantine considerations this work is carried out at Beltsville, Maryland. MPPL has continued their study of how several of the diseases of interest effect the expression of genes in infected citrus, and have identified families of genes that are differentially expressed in sweet orange trees infected by Citrus tristeza virus and �Ca. Liberibacter asiaticus�. We have moved on from assays with trees infected by pathogens one by one and continued with �deep sequencing� of RNA in trees simultaneously infected with Citrus tristeza virus and �Ca. Liberibacter asiaticus. We have analyzed the data which will give a more precise understanding of how gene expression varies in trees infected by these two important citrus pathogens. Gene expression analysis of the doubly- infected plants will provide information on the specificity of gene expression in response to different pathogens, and is also reflective of real-world conditions. Because these genes are plant genes, expression is likely to be more uniform than is the distribution of the pathogens themselves, and the resulting assays to reveal the pattern of plant gene expression in response to the pathogen may be more reliable. The data have been analyzed and the manuscripts have been submitted for publication. We have also worked with an antibody against the critically important pathogen that causes citrus greening disease, �Ca. Liberibacter asiaticus�. We have raised and purified this antibody from rabbits and have used them in �tissue print� assays to reveal the presence of the pathogen in infected citrus tissues. This has never been done before with this pathogen, and allows us to both detect the pathogen and study its distribution in infected citrus trees. MPPL has also worked on projects to identify novel pathogens of citrus and establish the causes of diseases of citrus. In cooperation with researchers at the University of Florida and at Ft. Detrick, Maryland, we have characterized a group of novel pararetroviruses that are associated with citrus blight disease. Citrus blight has been a serious problem for Florida citrus growers since at least the 1880's but the cause has always eluded researchers. We have developed evidence that an endogenous pararetrovirus is associated with the disease. This group of viruses may be integrated in the genome of citrus and under certain environmental or stress conditions may become active and cause disease. We continue to work on this important disease problem. Accomplishments 01 New method to detect citrus greening. ARS scientists in Beltsville, Maryland, in cooperation with Chinese visiting scientists identified surface antigens on the pathogen, cloned and expressed and purified the proteins in E. coli and raised antibodies. The antibodies were successfully used in tissue printing for detection of the pathogen in plants. This is the first and only serologically based detection assay for this pathogen of global significance.