Sugarbelle appears to be one of the most HLB tolerant scion varieties and UFR-4 is a rootstock that does not suffer from HLB-induced root loss. Valencia and Swingle are susceptible to HLB damage. This project has two main goals based on different graft combinations of these two scion and two rootstock varieties. First is to determine if there is a benefit to only half of a grafted tree being tolerant or if both scion and rootstock need to be tolerant to ameliorate some of the physiological effects of HLB. Second is to identify the mechanism of UFR-4 resistance to HLB-induced root loss and to identify the systemic signal of HLB-induced root loss with the hope of finding CRISPR targets to move this resistance into other rootstock varieties. These experiment will use a previously developed split root rhizotron system to maintain CLas infected and uninfected root systems on the same tree Rootstock seedlings (Swingle) and cuttings (UFR-4) have been selected from our greenhouse for grafting of SugarBelle and Valencia. The first round of grafting had an unexpectedly low success rate, so a new source of budwood was found and trees were regrafted. In both grafting events combinations containing Sugarbelle or UFR-4 had much lower success rates than the standard Valencia on Swingle. This has led to a delay in the initial inoculation until Spring to allow trees to caliper up and avoid inoculations during the winter, which have more unpredictable CLas movement. Meanwhile we are starting propagation of trees for the second experiment, to stay on track overall. This may require the production of more than expected aluminum rhizotrons.