2011 Annual Report 1a.Objectives (from AD-416) ARS is interested in studying the interaction between ‘Ca. Liberibacter asiaticus’ and sweet orange trees. Our Project Plan has one objective that directly relates to this agreement: Objective 5. ‘Characterize, using microarray hybridizations and other approaches, host plant gene expression patterns in response to infection by ‘Ca. Liberibacter spp. (presumptive citrus greening pathogens)’. The University of Florida is interested in the same area of research. The University of Florida has the expertise and infrastructure (microarray processing core facility) to effectively assist ARS in the collection and analysis of this data. 1b.Approach (from AD-416) ARS will acquire the basic knowledge related to the expression of citrus genes in response to infection by ‘Ca. Liberibacter asiaticus’. The University of Florida will assist in the acquisition of the knowledge. Both parties will use the data to develop novel diagnostic or control methods for huanglongbing disease. 3.Progress Report RNA has been collected from orange trees infected with ‘Ca. Liberibacter asiaticus’ and other phloem limited pathogens of citrus. The RNA has been used for microarray analysis of differential expression of host genes in response to infection by these pathogens. Further experiments are in progress. This research is monitored by communication between the cooperating investigators and ARS. Communication is by e-mail, telephone, face-to-face meetings held at scientific meetings, and workshops that the researchers attend.