Location: Subtropical Plant Pathology Research
Project Number: 6034-22000-045-033-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jan 1, 2025
End Date: Nov 30, 2027
Objective:
The main deliverable from this project will be an assessment of ACP and HLB risk to cold-hardy citrus. This will be important information for growers interested in moving citrus production northward. The results of the project will allow us to determine the risk for ACP infestation and the associated risk of HLB transmission to cold-hardy citrus. The specific objectives are:
Objective 1: ACP and HLB distribution and risk assessment survey for North FL, GA and North CA
Objective 2: ACP feeding preferences, and performance on different fresh market cold hardy citrus varieties.
Objective 3: Investigate CLas transmission on cold-hardy citrus, and persistence of CLas within these varieties after freezing events.
Objective 4. Investigate mechanisms in cold acclimation and cold resistance of ACP and its dispersal potential.
Objective 5: Model of area climate suitability for ACP and HLB in cold-hardy citrus.
Approach:
Objective 1: A regional survey will be conducted by the PD and co-PDs in with collaborators and county Extension agents. Yellow sticky traps will be deployed in select citrus groves for 2 years to capture ACP. There will be 5 traps per location and up to 2 locations per county. The traps will be changed weekly and moved to a different location after 2 months in order to sample a maximum of locations. In each grove where ACP is sampled, 50 trees will also be sampled for HLB detection. In addition, canine detection (Gottwald et al. 2020) will be used to survey citrus groves for HLB in a north-south transect starting from Gainesville, FL to Macon, GA. The geographical distribution of ACPs, and HLB trees will be correlated to the biotic and abiotic characteristics of each sampling location (citrus variety, latitudinal coordinates, cultivated area in a 2 km radius, organic or conventional, etc.). Objective 2: Cold hardy citrus species for ACP preference and performance will include lemon, Sugar bell, Tango and Satsuma mandarin. The varieties will be compared to ‘Valencia’ orange, used as a control. On each of the varieties we will evaluate female oviposition preference, immature development, adult survival, and feeding performance under laboratory conditions. Objective 3: Seedlings of each variety will be exposed to a CLas infected ACP colony for 18 months. Once a month, leaves from each plant will be collected and CLas infection determined with a standardized q-PCR test. In addition, CLas-infected citrus will be exposed to freezing temperatures of a range of intensity. CLas titer in citrus will be compared before and after the freezing treatments to investigate how cold affects the titer of the pathogen. Objective 4: ACP will be exposed to non-lethal freezing temperature. The adaptation of the offspring will be investigated to determine if there are any epigenic elements associated with cold resistance of ACP. In addition, ACP will be selected for cold resistance traits to investigate the genetic basis of cold resistance. Expression of genes involved in cold resistance in Hemiptera will be investigated. Objective 5: Based on the literature already available and on the data collected with the proposed investigation, a risk model will be established for cold-hardy citrus regions. Our goal is to model the potential distribution of ACP and HLB in northern latitudes and establish if there exists a ‘safe zone’ where citrus can still be produced commercially, but ACP and HLB are unlikely to become established.
