Location: Emerging Pests and Pathogens Research
Project Number: 8062-22410-007-029-I
Project Type: Interagency Reimbursable Agreement
Start Date: Oct 1, 2022
End Date: Sep 14, 2024
Solutions to solving citrus green disease (HLB) is perhaps the most pressing need in U.S. agriculture. The HLB disease complex, the Asian Citrus Psyllid (ACP) and ‘Candidatus Liberibacter asiaticus’ (CLas) bacterium, has devastated Florida citrus production. The societal impact is massive as thousands of people have lost their jobs, farms and processors have gone bankrupt, and consumer industries inter-connected to citrus industry workers have also been negatively economically impacted. The causative microbe and its insect vector, CLas and ACP, are now found in California and Texas citrus trees. Growers have no options to block transmission of CLas by ACP, and tools are desperately needed in this area. Furthermore, transmission blocking tools must be tailored to the unique needs of the citrus growing states and the needs of juice, fresh fruit, and organic growers. Solutions must include protecting existing and newly planted trees, as well as delivery in an economical format suitable to each industry sector. As an insect-vector borne pathogen, methods to block transmission represent a dead end for the bacteria and a novel solution for huanglongbing in all areas where the insect vector is found. The identification of psyllid genes that block CLas transmission has been a major focus of ARS Ithaca, NY location (and others) for the past 8 years. Moreover, ARS has published studies that show some ACP transmit CLas very efficiently and others not at all. We showed that the ability or inability to transmit the pathogen is passed on from parents to offspring for several generations. The chromosomal length assembly of the psyllid genome, a novel method to directly sequence CLas from ACP, and a streamlined bioassay to measure CLas acquisition by psyllids are recent advances that make this project possible. ARS PI’s are working on two different molecular delivery strategies that can be used to modulate ACP gene expression, alone or in combination. Silvec Biologics have discovered a tiny plant virus called Citrus yellow vein associated virus (CYVaV). The team developed this virus into a stable infectious clone that delivers silencing signals to the plant phloem under a grant funded by the ECDRE program. The ARS PI’s have developed a novel plant SymbiontTM to deliver molecules, such as peptides and silencing signals into the tree. Commercialization of these strategies is underway by both teams. It is unknown whether SymbiontsTM can deliver viruses such as CVYaV into citrus, and that will be a focus of this work.
The four major research questions that will be addressed in this grant proposal include: 1. Which ACP genes can be turned off using gene silencing with the CYVaV vector to block CLas transmission? 2. Can we use the natural variation in ACP to discover new ACP genes involved in transmission? 3. Can CYVaV be delivered to trees using SymbiontTM technology? 4. Can we develop a viral sequence so CYVaV can be used as a vector to deliver antimicrobial and other peptides?