2011 Annual Report
1a.Objectives (from AD-416)
Evaluate the impact of soil environmental factors on the behavior (including disease suppression and colonization of plant surfaces) of biological control agents (BCAs). Evaluate the impact of interactions resulting from the combination of BCAs with other biologically or chemically based control measures on the performance of BCAs. Develop strategies to enhance compatibility between BCAs combined with other BCAs or cover crops in biologically based disease control strategies directed at controlling Pythium ultimum, Phytophthora capsici, and Meloidogyne incognita on cucumber and pepper. Develop strategies for combining chemical pesticides with biologically based disease control methods in integrated pest control strategies directed at controlling P. ultimum, P. capsici, and M. incognita on cucumber and pepper.
1b.Approach (from AD-416)
Use basic microbiology techniques to determine soil factors that negatively impact performance of biological control agents. Use techniques from molecular biology, biochemistry, and basic microbiology to identify genes to use as reporters for environmental conditions that negatively impact biological control performance. Multi-disciplinary collaboration in growth chamber and greenhouse studies will determine impacts of cover crops and chemical controls on performance of biological control agents.
A manuscript dealing with the impact of complex nutrients released from plants on the RpoE stress-response pathway was accepted for publication. A manuscript dealing with the identification of fungi with biological control activity against Phytophthora capsici on bell pepper was accepted for publication. A third manuscript is being prepared in collaboration with scientists at USDA-ARS, Corvallis and Rutgers University detailing the impact of the cucumber seed environment on expression of genes in biological control bacteria; including genes involved in stress responses and biological control. Work investigating combinations of cover crops and biological control bacteria with regard to suppression of Pythium ultimum on cucumber has been completed. Additive affects on suppression of this pathogen due to the combination of biological control bacteria with sorghum sudan grass or velvet bean were demonstrated. Jack bean and sunnhemp cover crops when used alone also provided disease suppression.
The cover crops sorghum sudan grass and velvet bean enhance disease suppression by biological control bacteria. Biological control microbes are being evaluated in combination with other biologically based technologies such as cover crops for enhanced control of soilborne plant pathogens. Strategies such as the combination of disease control tactics must be developed to overcome inconsistencies in biological control performance prior to commercial acceptance of these technologies. ARS scientists at Beltsville, MD demonstrated that combining the cover crops sorghum sudan grass or velvet bean with bacterial biological control agents resulted in control of Pythium ultimum damping-off of cucumber that was greater than any of these treatments applied alone. Knowledge of treatments that lead to increased biological control performance will allow scientists to devise strategies for more effective disease control in agricultural settings.
Roberts, D.P., Maul, J.E., Mckenna, L.F., Emche, S.E., Meyer, S.L., Collins, R.T., Bowers, J.H. 2010. Selection of genetically diverse trichoderma spp. isolates for suppression of phytophthora capsici on bell pepper. Canadian Journal of Microbiology. 56:864-873.
Roberts, D.P., Lohrke, S.M., Mckenna, L.F., Lakshman, D.K., Kong, H.N., Lydon, J. 2011. Mutation of a degS homologue in Enterobacter cloacae decreases colonization and biological control of damping-off caused by Pythium ultimum on cucumber. Microbiology. 101:271-280.
Bae, H., Roberts, D.P., Lim, H.S., Strem, M.D., Park, S., Ryu, C., Melnick, R., Bailey, B.A. 2011. Endophytic Trichoderma isolates from tropical environments delay disease onset and induce resistance against Phytophthora capsici in hot pepper using multiple mechanisms. Molecular Plant-Microbe Interactions. 24:336-351.
Roberts, D.P., Kobayashi, D.Y. 2011. Impact of the Spatial Heterogeneity of the Spermosphere and Rhizosphere on Performance of Bacterial Biological Control Agents. In: Maheshwari, D.K., editor. Bacteria in Agrobiology: Crop Ecosystems. Berlin Heidelberg: Springer. p. 111-130.