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Project description

Community dynamics of microorganisms associated with Heterodera schachtii suppression. (00BC010)
Program UC IPM competitive research grants program
Principal
investigators 		J. Borneman, Plant Pathology, UC Riverside
J.O. Becker, Nematology, UC Riverside
Host/habitat Unspecified
Pest Sugarbeet Cyst Nematode Heterodera schachtii
Disciplines Nematology, Soil Microbiology
Beneficial
organism 		Bacteria; Fungi
Review
panel 		Biological Controls
 Start year (duration)  2000 (Three Years)
Objectives Identify bacteria and fungi associated with a soil suppressive against Heterodera schachtii by using a culture-independent, ribosomal RNA approach.

Compare two strategies to recreate the Heterodera suppression in nonsuppressive soils: application of microbial communities or application of single microorganisms.

Final report The goals of this project were to understand how a soil naturally suppresses the beet cyst nematode, Heterodera schachtii, and use this knowledge to develop new management strategies. The nematode suppressiveness has a biological origin as treatments such as fumigation remove this beneficial property. To identify the microorganisms causing the suppressiveness, the bacterial and fungal communities associated with the nematode cysts were examined. The cysts themselves were examined because they can transfer the suppressiveness to nonsuppressive soil, indicating the organisms causing the suppressiveness are associated with the cysts. These studies have led to the identification of one bacterium (Zoogloea ramigera) and two fungi (Dactylella oviparasiticaand Fusarium oxysporum) whose population levels correlated with suppressiveness. Greenhouse trials have shown that the Dactylella oviparasitica strain can reproduce the level of suppressiveness found in the natural soil. We are currently testing the ability of this strain to produce suppressiveness in field trials and in different soil types. After this is accomplished, we will endeavor to develop pest management strategies based on these findings. These data and management practices will be disseminated through UC Cooperative Extension newsletters, trade journals, scientific publications, DANR workgroup meetings, and CE training sessions.

Third-year
progress 		The goals of this project are to understand how a soil naturally suppresses the beet cyst nematode, Heterodera schachtii, and use this knowledge to develop new management strategies. The nematode suppressiveness has a biological origin as treatments such as fumigation remove this beneficial property. To identify the microorganisms causing the suppressiveness, the bacterial and fungal communities associated with the nematode cysts were examined. The cysts themselves were examined because they can transfer the suppressiveness to nonsuppressive soil, indicating the organisms causing the suppressiveness are associated with the cysts. These studies have led to the identification of one bacterium and two fungi whose population levels correlated with suppressiveness. These organisms are Dactylella oviparasitica, Fusarium oxysporum, and a Rhizobium sp. Greenhouse trials are currently underway to determine if these organisms can reproduce the nematode suppressiveness exhibited by the natural soil. The next step will be to confirm these results with field trials. After this is accomplished, we will attempt to develop pest management strategies based on these findings. These data and management practices will be disseminated through UC Cooperative Extension Newsletters, trade journals, scientific publications, DANR Workgroup meetings, and CE training sessions.
Second-year
progress 		We are investigating the biological factors associated with a soil that suppresses the beet cyst nematode, Heterodera schachtii. If we can understand how the soil inhibits H. schachtii, then we should be able to develop more effective means to control this pathogen. We know that this suppressiveness has a biological origin because treatments such as fumigation remove this beneficial property. To identify the microorganisms causing the suppressiveness, we are identifying shifts in microbial populations that correlate with the suppressiveness. This is being done by examining soils that possess varying levels of H. schachtii suppressiveness. Thus far, we have created such soils by transferring different amounts of the suppressive soil to nonsuppressive soils. We have also collected H. schachtii cysts that have developed in soils with varying levels of suppressiveness. From these samples, we have begun to identify microbial population shifts that correlate with the H. schachtii suppressiveness. Once this process has been completed, we will isolate the microorganisms and 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.

First-year
progress 		We are investigating the biological factors associated with a soil that suppresses the beet cyst nematode, Heterodera schachtii. We know that the pathogen suppressiveness is biological in origin because treatments such as fumigation remove this beneficial effect. To determine the biological factors associated with this "natural" pathogen suppression, we are applying new DNA-based strategies to identify the bacteria and fungi in this soil. As most microorganisms resist identification by traditional methods, we postulate that this new approach may represent a new investigative paradigm for biological control research since it will enable more comprehensive examinations of microbial communities. Thus far, we have established soils with varying degrees of suppressiveness against this pest by transferring different amounts of the beneficial soil to nonsuppressive soils. In addition, we are also in the process of collecting Heterodera. schachtii cysts that have developed in soils with varying levels of suppressiveness. Once these tasks are completed, we will be able to identify the important biological components by correlating the microbial populations with the differential levels of suppressiveness in these soils and cysts. The next step will be to use these microorganisms to recreate this beneficial effect in nonsuppressive soils.

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