Progress 09/15/07 to 09/14/11
Outputs
OUTPUTS: This research is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of the H. schachtii suppressiveness exhibited by a southern California soil. This research will enhance the sustainability of U.S. agriculture, food safety, and the exportability of agricultural products by leading to the development of new and more sustainable strategies to manage nematode pathogens. This research will enhance the sustainability of U.S. agriculture, food safety, and the exportability of agricultural products by leading to the development of a more effective predictive tool for making sugar beet planting decisions. A publication in progress, to be submitted in 2012, will describe the relationships between the amounts of the fungus Dactylella oviparasitica and the nematode Heterodera schachtii (Yang, Jiue-in, Rocha, Fernando, Becker, J. Ole, Borneman, J. 2012, in progress). This work develops new models enabling better crop management decisions for the sugar beet industry, by not only using both the amounts of H. schachtii and D. oviparasitica. A publication in progress, to be submitted in 2012, will describe how the fungus Dactylella oviparasitica parasitizes the nematode Heterodera schachtii. This work examines which life cycle stages of the nematode are attractive to and parasitized by the fungus. A publication in progress, to be submitted in 2012, will describe the fact that the ARF-18 fungus, known to be an effective biocontrol agent against the soybean cysts nematode (Heterodera glycines), is phylogenetically related to Dactylella oviparasitica. In addition, we show that this clade, which contains several nematophagous fungi, has members with worldwide distribution. Thus, this group of fungi may have considerable potential for controlling various cyst nematodes throughout the planet. PARTICIPANTS: James Borneman J. Ole Becker TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
In prior research, we identified key microorganisms that suppress the sugarbeet cyst nematode (Heterodera schachtii) in a naturally suppressive soil. The objective of this research project is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of this H. schachtii suppressiveness. Toward this goal, we performed the following research and/or obtained the following findings. We developed a model system with the host/pathogen combination Arabidopsis thaliana and H. schachtii to evaluate the ability of D. oviparasitica to suppress cyst nematode reproduction under gnotobiotic conditions. The fungus reduced the average number of females developing on A. thaliana seedlings by almost 80%. On water agar, hyphae of D. oviparasitica did not exhibit distal attraction to roots or developing juveniles. However, once the fungus came in contact with a developing juvenile it grew densely, often forming an infection cushion on the surface of the nematode. Juvenile males were not susceptible to fungal infection once they had reached the J3 stage. No viable eggs developed in parasitized females. All infected females were eventually killed by the fungus. The fungus was never observed within the root, and consequently, cyst nematodes did not become infected until they broke through the root surface and were exposed to the rhizosphere. Viable eggs of H. schachtii were not susceptible to infection by the fungus in vitro, while heat- or freeze-killed eggs were rendered almost completely susceptible. Even when placed directly on mycelium of D. oviparasitica on water agar plates, the majority of undifferentiated eggs obtained from white (young) cyst nematode females developed into juveniles and were not infected by the fungus. Between 5 to 10% of eggs from aseptically reared females fail to develop into juveniles when placed on water agar plates. Thus, the number of non-treated undifferentiated eggs infected by D. oviparasitica correlated to the proportion of metabolically inactive eggs in females. A fungal strain with morphological characteristics very similar to D. oviparasitica, Arkansas Fungus 18 (ARF-18), was reported as a parasite of Heterodera glycines (Kim and Riggs, 1991). Our preliminary experiments with excised white females of H. schachtii indicated that ARF18 showed the same infectivity pattern as D. oviparasitica. Molecular analysis of the rRNA ITS region from ARF-18 indicated that the strain is most closely related to D. oviparasitica (AY185771). ARF-18 grew at twice the rate of D. oviparasitica on PDA agar and tolerated higher temperatures, up to 33C. However, in contrast to D. oviparasitica, ARF18 grew very poorly on water agar and in soil. We determined the relationships between the amounts of the fungus Dactylella oviparasitica and the plant-parasitic nematode Heterodera schachtii. We anticipate that monitoring both the Dactylella oviparasitica and Heterodera schachtii population levels will lead the development of a more effective predictive tool for making sugar beet planting decisions. See Outputs Section for additional publications in progress.
Publications
- Rocha, F.S., J. Smith Becker, S. Benecke, D.R. Jeske, J. Borneman, and J.O. Becker 2009. Influence of population densities of Dactylella oviparasitica and Heterodera schachtii on sugarbeet cyst nematode population suppression. J. Nematology 41:375.
- Smith Becker, J., J. Yang, J. Borneman, P. Timper, R.R. Riggs, and J.O. Becker 2011. Investigations into the relatedness of the nematophagous fungi Dactylella oviparasitica and ARF-L. J. Nematology 43: (in press).
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Progress 09/15/09 to 09/14/10
Outputs
OUTPUTS: This research is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of the H. schachtii suppressiveness exhibited by a southern California soil. This research will enhance the sustainability of U.S. agriculture, food safety, and the exportability of agricultural products by leading to the development of new and more sustainable strategies to manage nematode pathogens. PARTICIPANTS: Training on molecular biology and nematology were provided for Jiue-in Yang (PhD student) and Fernando Rocha (Postdoc). TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Suppressive soils hold considerable potential for managing soilborne pathogens. When the suppressiveness has a biological origin, the crucial steps in realizing this potential are to identify the causal organisms and then understand the agronomic and environmental factors that enable them to function. In prior research, we identified key microorganisms that suppress the sugarbeet cyst nematode (Heterodera schachtii) in a naturally suppressive soil. The objective of this research project is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of this H. schachtii suppressiveness. To define these relationships, we will examine a series of factors that influence the level of suppressiveness, while simultaneously monitoring the population densities of the beneficial organisms and H. schachtii over time and space. Various levels of suppressiveness will be created using different crops and amounts of the nematode and beneficial microorganisms. We will measure the population densities of the beneficial microorganisms and H. schachtii in key sites including roots and different life-cycle-stages of the nematode. We will also employ microscopic techniques to examine the morphological structures of and spatial relationships among the organisms. In year one, we performed a series of experiments to examine the relationships between the initial numbers of the beneficial fungus Dactylella parasitica, the initial numbers of the nematode pathogen (H. schachtii), and the "final" numbers of H. schachtii after several nematode generations. These experiments showed that the final numbers of nematodes was dependent upon both the initial numbers of the fungus and nematode. Statistical analysis has led to predictive models of these relationships. In year two, we performed a series of experiments that measured the population densities of D. oviparasitica in various life-cycle-stages of the nematode throughout the development of the H. schachtii suppressiveness. Because of considerable variation in the results of these experiments, likely due to plant growth irregularities, we are repeating this set of experiments. We have also performed a series of experiments examining the relationship between soil temperature and the ability of D. oviparasitica to suppress nematode populations. These experiments have been completed and the data are currently being analyzed. We have also performed experiments that have shown that although the fungus very quickly colonizes and parasitizes nematode females and cysts, D. oviparasitica levels decrease to below detectable levels in the cysts sometime after the cysts detach from the roots and enter the soil. Finally, we have determined that two different strains of D. oviparasitica inhabit the soil in our study site, and that these two fungi are representative of the strains that have been reported worldwide. We are currently in the process of isolating the new strain. Once this is accomplished, we will perform experiments to assess the relative abilities of the two strains to control H. schachtii populations.
Publications
- No publications reported this period
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Progress 09/15/08 to 09/14/09
Outputs
OUTPUTS: This research is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of the H. schachtii suppressiveness exhibited by a southern California soil. This research will enhance the sustainability of U.S. agriculture, food safety, and the exportability of agricultural products by leading to the development of new and more sustainable strategies to manage nematode pathogens. PARTICIPANTS: James Borneman and Ole Becker performed and coordinated the molecular microbial ecology and greenhouse portions of the work. The postdoctoral researcher (Fernando Rocha) performed most of the work. A staff research associate (John Oross) assisted with the experimentation. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Suppressive soils hold considerable potential for managing soilborne pathogens. When the suppressiveness has a biological origin, the crucial steps in realizing this potential are to identify the causal organisms and then understand the agronomic and environmental factors that enable them to function. In prior research, we identified key microorganisms that suppress the sugarbeet cyst nematode (Heterodera schachtii) in a naturally suppressive soil. The objective of this research project is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of this H. schachtii suppressiveness. To define these relationships, we will examine a series of factors that influence the level of suppressiveness, while simultaneously monitoring the population densities of the beneficial organisms and H. schachtii over time and space. Various levels of suppressiveness will be created using different crops and amounts of the nematode and beneficial microorganisms. We will measure the population densities of the beneficial microorganisms and H. schachtii in key sites including roots and different life-cycle-stages of the nematode. We will also employ microscopic techniques to examine the morphological structures of and spatial relationships among the organisms. In year one, we performed a series of experiments to examine the relationships between the initial numbers of the beneficial fungus Dactylella parasitica, the initial numbers of the nematode pathogen (H. schachtii), and the "final" numbers of H. schachtii after several nematode generations. These experiments showed that the final numbers of nematodes was dependent upon both the initial numbers of the fungus and nematode. Statistical analysis has led to predictive models of these relationships. In year two, we performed a series of experiments that measured the population densities of D. oviparasitica in various life-cycle-stages of the nematode throughout the development of the H. schachtii suppressiveness. Because of considerable variation in the results of these experiments, likely due to plant growth irregularities, we are repeating this set of experiments. We have also performed a series of experiments examining the relationship between soil temperature and the ability of D. oviparasitica to suppress nematode populations. These experiments have been completed and the data are currently being analyzed. We have also performed experiments that have shown that although the fungus very quickly colonizes and parasitizes nematode females and cysts, D. oviparasitica levels decrease to below detectable levels in the cysts sometime after the cysts detach from the roots and enter the soil. Finally, we have determined that two different strains of D. oviparasitica inhabit the soil in our study site, and that these two fungi are representative of the strains that have been reported worldwide. We are currently in the process of isolating the new strain. Once this is accomplished, we will perform experiments to assess the relative abilities of the two strains to control H. schachtii populations.
Publications
- No publications reported this period
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Progress 09/15/07 to 09/14/08
Outputs
OUTPUTS: This research is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of the H. schachtii suppressiveness exhibited by a southern California soil. This research will enhance the sustainability of U.S. agriculture, food safety, and the exportability of agricultural products by leading to the development of new and more sustainable strategies to manage nematode pathogens. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Suppressive soils hold considerable potential for managing soilborne pathogens. When the suppressiveness has a biological origin, the crucial steps in realizing this potential are to identify the causal organisms and then understand the agronomic and environmental factors that enable them to function. In prior research, we identified key microorganisms that suppress the sugarbeet cyst nematode (Heterodera schachtii) in a naturally suppressive soil. The objective of this research project is to elucidate the interactions among the beneficial microorganisms, nematode and crops that lead to the development and stability of this H. schachtii suppressiveness. To define these relationships, we will examine a series of factors that influence the level of suppressiveness, while simultaneously monitoring the population densities of the beneficial organisms and H. schachtii over time and space. Various levels of suppressiveness will be created using different crops and amounts of the nematode and beneficial microorganisms. We will measure the population densities of the beneficial microorganisms and H. schachtii in key sites including roots and different life-cycle-stages of the nematode. We will also employ microscopic techniques to examine the morphological structures of and spatial relationships among the organisms. In year one, we performed a series of experiments to examine the relationships between the initial numbers of the beneficial fungus Dactylella parasitica, the initial numbers of the nematode pathogen (H. schachtii), and the numbers of H. schachtii after several nematode generations. We are also performing experiments that measure the population densities of this fungus in various life-cycle-stages of the nematode throughout the development of the H. schachtii suppressiveness.
Publications
- No publications reported this period
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