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. 1. To test for he unlikely but increasing possibility that HLB is transmitted by extracellular vectors, we isolated DNA from HLB leaves and inject these into 2 year old Valencia trees. The trees are being kept in a greenhouse and are under observation. Samples of nectar, honey, pollen, albedo, flavedo and flowers were collected in spring time and now being analyzed. 2. Experiments for objective 2 are well under way. Two trees (one healthy and one HLB+) were root grafted in three different locations and placed in special pots large enough to accommodate the 2 trees. The trees have been placed in a greenhouse and continue currently under observation. At the moment, symptoms have appeared and PCR will be performed soon. 3. Grafted trees with HLB material are being monitored weekly using Narrow-band imaging under polarized illumination. 4. Trees have been grafted for a substantial amount of time and some started showing HLB symptoms. However, given that analysis of this objective destroys the trees, more time is needed to be certain that HLB has taken root.