ASHS 2024 Conference

Citrus greening (Huanglongbing, HLB) is considered one of the most devastating diseases affecting the global citrus industry. There is an urgent need to provide relief from HLB and restore profitable citrus production. Since 2005, over a billion dollars has been spent on research to find a solution to HLB. Trunk injection with the antibiotic oxytetracycline is the current treatment that Florida growers are using to manage the disease. To broaden the number of molecules available to growers to treat HLB a framework was developed to efficiently screen molecules in citrus groves, selecting those that enhance tree health over a season. The framework is based on the principles of the design-of-experiments (DOE). Utilizing the injection system developed by TJ Biotech (LLC), 88 molecules were injected into 8-year-old ‘Valencia’ sweet orange (Citrus × sinensis) trees grafted on ‘US-812’ (Citrus reticulata × Poncirus trifoliata) rootstock over a six-week period. The injections were divided into nine sets, with varying numbers of molecules injected in each set (12, 10, or 6). The injections were administered into the scion, approximately 5 cm above the graft union. Visual assessments of tree health index and canopy density were collected to evaluate changes in restoring tree horticultural traits. Ratings were recorded before injections and at 90 and180 days post-injections. In addition to health index and canopy density, a series of seven pictures were taken per tree on the injection day and subsequently at 30, 60, 90, and 180 days after injections. Pre-harvest fruit drops were measured by counting and removing any fruits on the ground beneath each tree. The total number of fruits on each tree was tallied at harvest to calculate the percentage of fruit drops for each tree. Yield, fruit, and juice quality were assessed at harvest. In this screening trial, trees injected with oxytetracycline have been used as a positive control to indicate enhancement in tree health. Results from the tree health index obtained at 90 and 180 days after injection showed that 17 molecules performed similarly or better than the oxytetracycline-treated positive control. We are partnering with regulatory consultants to identify those that are safe and affordable. New molecules for injection will require regulatory labeling.