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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Subtropical Plant Pathology Research

2012 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 research is related to inhouse project objective 3a. Develop and use stochastic models to test various disease control strategies for huanlongbing (HLB), Asiatic citrus canker (ACC), citrus black spot (CBS) and diseases caused by other exotic pathogens.

The intent of this study is to examine the effect of windbreaks, copper sprays to reduce infection, and leafminer treatments to determine their individual and combined effects on control of citrus canker in Brazilian commercial citrus and the applicability of this strategy to the U.S. commercial citrus industry. Via a USDA/ARS specific cooperative agreement with the University of Sao Paulo, and the Brazilian cooperator, new replicated plots have now been established at the IAPAR farm, in Xambrê, Parana state, located 350 km west from Londrina and 250 km west from Maringá. The plots consist of the cultivar Pêra on Rangpur lime, two years of age at the beginning of the experiment. Windbreaks have been completed and plants were be established in Mid April 2010. Plots are progressing and the following treatments are being applied:.
1)no sprays (control),.
2)Cu++ sprays to reduce citrus canker incidence, and.
3)insecticide sprays to inhibit infestations of Asian leafminer (secondary effects). Main effects are windbreak versus no windbreaks. Citrus canker incidence is being estimated on multiple branches on each tree treated as the number of leaves per branch infected. Data collection is currently underway. We anticipate running these plots for 2-3 more years. The development of the programmable leaf wetness controller (PLWC) software was written, debugged, is complete, and the control program is working well. New leaf wetness sensors were designed and constructed. Calibration has been tricky as this is a new type of sensor we are developing and has never been used before by any other research group. The new design of the leaf wetness controller has much greater sensitivity and provides better environmental control, but with these benefits comes added complexity in electronics. A circuit to control the leaf wetness sensor and another to control fans that facilitate wind generation in ambient environments have been completed, tested and calibrated. Initial trials have demonstrated some glitches that we are currently addressing. Once completed, we will continue with studies to examine the survival characteristics of bacterial pathogens under field conditions.

Last Modified: 4/18/2014
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