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United States Department of Agriculture

Agricultural Research Service

Research Project: Spatial and Temporal Incidence of CA Liberibacter in Citrus and Psyllids Detected Using Real-Time PCR
2012 Annual Report


1a.Objectives (from AD-416):
1) Assess seasonal patterns of pathogen incidence in citrus trees and psyllid vector populations in regions of high huanglongbing (HLB) incidence;.
2)Evaluate the influence of cultural factors that affect incidence and titer of Liberibacter in citrus trees and psyllid populations including tree age, variety, rootstock, block size, surroundings and HLB management practices such as tree removal and vector control; and.
3)refine and update management recommendations based upon seasonal and cultural effects on pathogen incidence and intensity.


1b.Approach (from AD-416):
Objective 1: Seasonal fluctuations in psyllid numbers, in symptom expression in citrus trees and incidence and intensity of Liberibacter infection in both psyllids and plant tissue will be assessed over time in insecticide free blocks located at the SWFREC, Immokalee, FL. Nymphs will be collected from flush tissue and adults by sweep net. Trees will be visually evaluated monthly using a disease severity scale for symptoms of HLB. Foliage and psyllids will be assayed using real time PCR for presence of HLB. Objective 2: Large field plots will be established within citrus groves of different sizes and management practices in blocks of different varieties of citrus. Psyllids will be monitored and collected as previously described in Obj. 1. Fruit production and quality will be evaluated using grower-supplied yield data supplemented by analysis of fruit quality (size, color, density, and blemish criteria) obtained from the pilot plant, CREC, Lake Alfred where a color vision system is now in operation. Juice quality including acid content and BRIX will also be evaluated. Objective 3: Measures such as vector control and rouging of symptomatic trees are designed to reduce HLB incidence and the spread of greening, to ameliorate the impact of greening on the grove, and ultimately to increase production and maintain a healthy profit margin. Vector management will be most effective when the greatest number of infective psyllids can be suppressed at least cost and collateral damage to beneficial organisms. The information obtained here will provide data on the incidence of infection in vectors related to seasonal and cultural factors to enable growers to optimize their management practices.


3.Progress Report:

This is the final report for this project. The research is related to objective 3A of the parent project, "Recover citrus germplasm exposed to Huanglongbing (HLB) and citrus canker, and evaluate citrus relatives for tolerance or resistance to psyllids and/or HLB". The purpose of this research is to assess seasonal patterns of pathogen incidence in citrus and psyllid populations in regions of high HLB incidence, to evaluate the influence of cultural factors that affect incidence and titer of Ca. Liberibacter in citrus and psyllids, and to develop information needed to improve recommendations for the management of HLB. Psyllids were collected approximately weekly from suction traps, and identified in Gainesville. Beginning in 2011, all Diaphorina citri have been tested singly for presence or absence of the HLB pathogen. There were positive samples collected from all three short (2 meter tall) suction traps. There was no difference in the numbers of positives by trap. This can be attributed to the fact that citrus greening disease is widespread and common in the Immokalee area. Preliminary data indicates that neither nutritional nor insecticidal sprays impacted the disease progress of HLB, either because the treatments were initiated during the long lag time between inoculation/symptom expression or for some other reason. Recent yield data indicates that trees in plots receiving nutritionals and insecticide are benefiting by increased yields.


Last Modified: 12/21/2014
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