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.
3. Progress Report
Six subobjectives of the Project Plan were scheduled to be worked on during this annual report cycle. For three of these subobjectives, studies were to be continued to determine 1) the impact of soil texture on suppression of Phytophthora capsici by biological control agents, 2) the impact of soil texture on suppression of Pythium ultimum by the biocontrol bacterium Pseudomonas fluorescens Pf-5, and 3) the impact of soil texture on colonization of roots by P. fluorescens Pf-5. Soils with varying textures were identified and collected from different locations at the Beltsville Agricultural Research Center for use in work detailed under these three subobjectives. Five isolates of Trichoderma virens were shown to suppress P. capsici on bell pepper in a single soil type. Pilot experiments are being conducted to determine the impact of the different soil types on disease severity by P. capsici and P. ultimum in preparation for disease suppression assays with these biological control isolates. A manuscript for submission to a peer-reviewed journal has been prepared based on some of this work. For the fourth subobjective, the metabolic activity of plant-beneficial bacteria in various soil environments was to be studied. It was demonstrated that seed type and nutrients released from seeds significantly impact metabolic activity by the plant-beneficial bacterium Enterobacter cloacae. A manuscript regarding this work was published in a peer-reviewed journal. The fifth subobjective scheduled to be worked on during this annual report cycle dealt with the impact of various soils on expression of genes in plant-beneficial bacteria that are involved in disease suppression. Experiments have been initiated in collaboration with scientists at USDA-ARS, Corvallis and at Rutgers University to use microarray technology to obtain a snapshot of expression of all genes within the plant-beneficial bacterium Pseudomonas fluorescens Pf5 influenced by two different soil environments. To date, experiments have been completed that demonstrated the feasibility of this research approach. Disease suppression experiments are being conducted to look at the impact of combining cover crops with biological control agents (Trichoderma virens) on suppression of P. capsici on bell pepper to satisfy the sixth subobjective. The cover crops sorghum sudangrass, sunnhemp, and velvet bean have been applied alone, and in combination with five Trichoderma isolates, in these experiments. No cover crop has been shown to suppress P. capsici on bell pepper in the absence of Trichoderma.
1. Metabolic activity of plant-beneficial bacteria is significantly impacted by nutrient inputs from plants. Methods are needed to determine the impact of both soil environmental conditions and disease management strategies on the performance of plant-beneficial microorganisms when in soil in association with plants. Methods were developed to determine the impact of seeds with dramatically different nutrient release rates on the plant-beneficial bacterium Enterobacter cloacae. This study demonstrated for the first time that seeds and nutrient inputs from seeds dramatically influence overall metabolic activity of plant-beneficial bacteria in soil. Metabolic activity is being developed as a metric of performance by plant-beneficial bacteria. This information will be useful to scientists devising methods to determine the influence of soil environmental conditions on performance of plant-beneficial bacteria.
2. Development of a collection of Trichoderma isolates with disease suppression capabilities against Phytophthora capsici on bell pepper. Due to the phase-out of methyl bromide use in the United States control measures are needed for the important soil-borne pathogen Phytophthora capsici. The objective of this study was to identify genetically distinct isolates of Trichoderma with disease suppressive capabilities against this pathogen on bell pepper. Five genetically distinct isolates of Trichoderma were found which significantly reduced disease on bell pepper caused by this pathogen in greenhouse pot assays. These isolates will be used by scientists in future studies where combinations containing these isolates are analyzed for suppression of Phytophthora blight on pepper in a number of different soil environments.
Roberts, D.P., Baker, C.J., Mckenna, L.F., Liu, S., Buyer, J.S., Kobayashi, D.Y. 2009. Influence of host seed on metabolic activity by Enterobacter cloacae in the spermosphere. Soil Biology and Biochemistry. 41:754-761.