This proposal is aimed at following previous work in CRDF-710 and CRDF-818 with a series of precise experiments that will: 1. Elucidate the nature of the HLB signal(s) 2. Provide additional evidence on its transmission in terms of movement across tissues and between trees though underground organs. 3. Determine the progression of physical symptoms from its inception. 4. Examine the in-tree variation in CLas titer. Research commenced addressing objective 4, due to natural timing of events. Fifteen trees were selected for having branches with at least 11 leaves. This number of leaves was needed for analysis of CLas transport in both directions. The middle leaf of all 15 trees was disc grafted with HLB material and placed in the greenhouse until the presence of HLB symptoms. Experiments for objective 2 are in under way. Trees, both HLB-affected and healthy, have been selected and special pots purchased. For this experiments, a healthy and a HLB tree will be root grafted and placed in a larger, flexible pot until HLB symptoms appear.