The project entitled ‘Further characterization of HLB resistant clones of selected citrus varieties’ (project no. 758) is currently in its second year. The overall aim of the project is to study tolerance/resistance to Citrus huanglongbing. We have field data that indicates different levels of disease tolerance or resistance in certain citrus relative genera. In this project, we are further testing the resistance by conducting controlled experiments in green house conditions. In the current period (July 1- Oct 1, 2014), we have challenged about 70 plants with Liberibacter positive and negative psyllids in a no-choice situation. A representative part of the psyllids used for the experiment were checked for the presence of the bacterium and also the titer of Liberibacter was estimated. After a two week exposure of the plants to the Liberibacter containing (or, Liberibacter negative control psyllids), the individual psyllids were collected and checked again for the Liberibacter titer. The plants are then maintained in the greenhouse and observed for symptoms. We have also collected plant tissue at different times and conducted DNA extractions. In the past, we have used the plant DNA extractions for real-time PCR assay in order to determine the Liberibacter titer in the different treatments. At present, we have the capability of detecting very minute amounts of Liberibacter by conducting a droplet digital PCR assay. More sensitive than real time PCR, this method can give an absolute quantification of the pathogenic bacteria. We have standardized the assay to be used for the plant samples. We are in the process of testing plant samples using this methodology. This will enable us to determine the tolerant and resistant cultivars in our experiments with accuracy and will complement the other methods that we are using to test resistance or tolerance.