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United States Department of Agriculture

Agricultural Research Service

Research Project: RESEARCH ON THE EPIDEMIOLOGY OF CITRUS HUANGLONGBING AND OTHER EXOTIC PATHOGENS
2011 Annual Report


1a.Objectives (from AD-416)
The overall objective of this research project is to conduct a series of epidemiological studies to elucidate those biological factors that are not well understood. Utilizing this new information, develop enhanced control strategies for citrus HLB. The sub objectives employed in support of the over-arching main objective are: 1. Develop new real time PCR diagnostic methodologies for Ca. Liberibacter asiaticus and Liberibacter americanus to the use for detection in both plants and insect vectors. 2. Conduct greenhouse epidemic trials using both pathogens, L. asiaticus and L. americanus, studying their spatiotemporal dynamics and interactions between the isolates. 3. Using spatiotemporal analyses monitor and estimate HLB epidemics in commercial orchards. 4. Determine acquisition and inoculation. It's a L. americanus and L. asiaticus for Diaphorina citri. 5. Examine the effect of temperature in geographic regions on HLB progress. 6. Determine the geographic distribution of the two HLB bacterial strains in the state of São Paulo Brazil. 7. Sam the progress and colonization of the two HLB strains in various citrus cultivars. 8. Determine the infectivity D. citri in commercial orchards for the two bacterial strains. 9. Based on information extracted from the above objectives, develop augmented and potentially new strategies for HLB control in commercial orchards.


1b.Approach (from AD-416)
Develop a coordinated, multiphased research effort on exotic citrus diseases of common concern to the US and Brazilian citrus industries with the Fundação de Estudos Agrários Luiz de Queiroz (FEALQ), Piracicaba, SP, Brazil and ARS personnel USDA, ARS, Horticultural Research Laboratory, Fort Pierce, Florida. The cooperative agreement will be developed to implement the research effort between these parties within the USA and abroad for research that cannot be performed in the U.S., or more easily facilitated outside the U.S.


3.Progress Report

This project is related to Objective 3: Develop or improve comprehensive integrated disease management strategies.

The objective of the project in part was to determine the regional Huanglongbing (HLB) management on the effectiveness of local strategies of inoculum reduction and vector control. The effectiveness of local strategies of inoculum reduction and vector control on HLB progress were studied in São Paulo (E1-Oct/05; E2-May/06). Regional HLB management was present for E1 and absent for E2. Local inoculum reduction levels for E1 were every 4, 8, and 16 weeks, and for E2, every 2, 4, 12, and 26 weeks. Local vector control levels for E1 were no control, program A (PA), and program B (PB), and for E2, no control and program C (PC). Psyllid control was done with two 56-day-interval applications of systemic insecticides during the rainy season, and in the rest of the year, with contact insecticide sprays every 28 days for PA, and every 14 days for PB and PC. The beginning of the HLB epidemic was delayed 10 months by regional HLB management but wasn’t affected by different local strategies in both experiments. After 60 and 53 months, HLB incidence and progress rate weren’t affected by different frequencies of local inoculum reduction in both experiments, and were different only in plots with and without local vector control in E2. Regional HLB management reduced HLB incidence (90% less for E1) and progress rate (75% less for E1) in both plots with and without vector control. Smaller psyllid populations and lower frequency of infected psyllid in E1 than in E2 explained these reductions.

Progress was monitored via through direct involvement in lab and field activities, research meetings, telephone calls and email communications.


Last Modified: 12/24/2014
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