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United States Department of Agriculture

Agricultural Research Service

Research Project: Alternative disease management strategies for soilborne pathogens of cucumber
2013 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.


3.Progress Report:
Work reported here is from the first partial year of the project which is currently under OSQR review. Seven Trichoderma isolates were found to control damping-off of cucumber caused by Rhizoctonia solani compared to the nontreated control when applied in-furrow as a granular formulation (Sub-obj. 1A). Work investigating ethanol extracts from Serratia marcescens N4-5 that effectively suppressed Pythium ultimum on cucumber was continued (Sub-obj. 1B). These extracts, when co-applied as seed treatments, were stable, did not inhibit seed germination after a three-month storage period, and were compatible with fungal biological control agents. Shelf-life and compatibility with other biologically based technologies are important qualities for commercialization. Work determining the role of the regulatory proteins Crc and Vfr of Pseudomonas protegens Pf-5 in colonization of plant seeds and roots was continued by scientists at USDA-ARS, Beltsville in collaboration with scientists at USDA-ARS, Corvallis and Rutgers University (Sub-obj. 1C). It was found that Crc plays a critical role in colonization of cucumber seeds by P. protegens Pf-5. Proteomic work identifying proteins regulated by the global regulator Vfr was completed. Vfr has a role in polyamine uptake and transport of glycine betain, compounds associated with survival and colonization by bacteria in the rhizosphere. Vfr also regulates antibiotics involved in suppression of important soilborne plant pathogens. These studies suggest a role for Vfr in disparate traits important to colonization and disease suppression by P. protegens. A paper written by scientists at USDA-ARS, Corvallis in collaboration with scientists at Rutgers University and USDA-ARS, Beltsville, which detailed the impact of the cucumber seed environment on expression of genes in biological control bacteria, including genes involved in stress responses and biological control, was published. A number of cold-tolerant Trichoderma strains have been isolated that have demonstrated antagonism toward the plant pathogens R. solani and Fusarium culmorum in vitro and in growth chamber pot studies with cucumber and wheat plants. These strains were isolated and tested in collaborative work between scientists at the All-Russian Research Institute of Phytopathology, Bolshiye Vyazyomy, Russia and the USDA-ARS, Beltsville. A paper written by scientists at USDA-ARS, Beltsville in collaboration with scientists at the Oil Crops Research Institute, Wuhan, People's Republic of China, regarding the development of Bacillus megaterium for sustainable production of oilseed rape was accepted for publication.


Review Publications
Hu, X., Roberts, D.P., Xie, L., Maul, J.E., Yu, C., Li, Y., Zhang, S., Liao, X. 2013. Development of a biologically based fertilizer, incorporating Bacillus megaterium A6, for improved phosphorus nutrition of oilseed rape. Canadian Journal of Microbiology. 59:231-236.

Lakshman, D.K., Roberts, D.P., Alkharouf, N., Mitra, A., Natarajan, S.S. 2012. Gene expression profiling of the plant pathogenic basidiomycetous fungus Rhizoctonia solani AG 4 reveals putative virulence factors. Phytopathology. 104(5):1020-1035.

Last Modified: 4/22/2015
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