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Project description

Examination of novel strategies to identify biological control organisms and to incorporate them into an avocado integrated pest management program. (01BC001)
Program UC IPM competitive research grants program
Principal
investigators 		J. Borneman, Plant Pathology, UC Riverside
J.A. Menge, Plant Pathology, UC Riverside
B.A. Faber, UCCE Ventura County
Host/habitat Avocados; Tree Crops
Pest Phytophthora cinnamomi
Disciplines Soil Microbiology, Plant Pathology
Beneficial
organism 		Unidentified bacteria/fungi
Review
panel 		Biological Controls
 Start year (duration)  2001 (Two Years)
Objectives Identify microorganisms associated with suppressiveness against Phytophthora cinnamomi using an in situ substrate utilization assay.

Compare several schemes to apply biological control agents: single versus mixed populations and annual versus frequent application.

Final report The ultimate goal of this research was to develop new strategies to control avocado root rot. We theorized that a thorough understanding of soils that naturally suppress Phytophthora cinnamomi will lead to new and effective strategies to control this pest. The study site for this project was an avocado grove where a P. cinnamomi epidemic created soils with varying levels of suppressiveness. To identify the organisms contributing to the suppressiveness, we utilized a method that identifies microorganisms that respond to the same nutrients that trigger root infection by the pathogen. We hypothesize that bacteria such as these will occupy a niche similar to that of the pathogen and contribute to suppressiveness through mechanisms such as nutrient competition and antibiosis. This approach led to the identification of several microorganisms that correlated with the pathogen suppressiveness. Greenhouse trials showed that one of these bacteria were able to reproduce the suppressiveness exhibited by the natural soil. This organism will be tested in field trials and the successful ones will be incorporated into an integrated management plan for controlling avocado root rot. These newly developed pest management strategies will be disseminated through UC Cooperative Extension newsletters, trade journals, scientific publications, DANR workgroup meetings, and CE training sessions.

Second-year
progress 		The ultimate goal of this research is to develop new strategies to control avocado root rot. We theorize a thorough understanding of soils that naturally suppress Phytophthora cinnamomi will lead to new and effective strategies to control this pest. Two different experimental approaches are being used to identify microorganisms that cause natural P. cinnamomi suppressiveness. For project 1, the study site is an avocado grove where a P. cinnamomi epidemic has created soils with varying levels of suppressiveness. To identify the organisms contributing to the suppressiveness, we have utilized a method that identifies microorganisms that respond to the same nutrients, which trigger root infection by the pathogen. Thus far, this work has identified several microorganisms that correlate with the pathogen suppressiveness. Preliminary greenhouse trials have shown that some of the bacteria can reproduce the suppressiveness exhibited by the natural soil. For project 2, we have identified a soil that has suppressed avocado root rot for several years. Newly developed tools that allow extensive analysis of microbial communities are being used to identify bacteria and fungi whose population levels correlate with suppressiveness. Such microorganisms are likely to contribute to the natural soil suppressiveness. Once these organisms have been identified, their abilities to reproduce P. cinnamomi suppressiveness will be assessed. The successful organisms will be incorporated into an integrated management plan for controlling avocado root rot. These newly developed pest management strategies will be disseminated through UC Cooperative Extension Newsletters, trade journals, scientific publications, DANR Workgroup meetings, and CE training sessions.
First-year
progress 		Towards the goal of improving biological control and integrated pest management, we are exploring new strategies to identify biological control agents for soilborne plant pathogens. If we can understand how natural soils inhibit P. cinnamomi, then we should be able to develop more effective means to control this pathogen. Our experimental approach is to identify the microorganisms that can utilize P. cinnamomi cell walls in soil or that can compete for substrates that are important to the pathogen. For this work, we have identified avocado groves where P. cinnamomi epidemics have created soils with varying levels of suppressiveness. Our work to date has identified several bacteria and fungi that correlate with the pathogen suppressiveness. We have isolated most of these organisms and are now testing their abilities to inhibit P. cinnamomi in laboratory assays. Once this process is completed, we will test their abilities to produce pathogen suppressiveness in nonsuppressive soils. After this is accomplished, these newly developed pest management strategies will be disseminated through UC Cooperative Extension Newsletters, trade journals, scientific publications, DANR Workgroup meetings, and CE training sessions.

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