Research Interests:

Dr. Roberts' research interests include: (1) the genetic and physiologic basis of colonization of seeds and roots by plant-beneficial bacteria; (2) the role of colonization by plant- beneficial bacteria in the suppression of soilborne plant pathogens; and (3) the manipulation of colonization by plant- beneficial bacteria for enhanced suppression of soilborne plant pathogens; and (4) development of biological controls for suppression of soilborne pathogens of vegetables.

Summary of Ongoing Projects:

Dr. Roberts' research projects involve the delivery of beneficial microorganisms (bacteria and fungi) to the spermosphere and rhizosphere for effective biological control of plant pathogens. The picture above is an example of biological control of damping-off of cucumber caused by Pythium ultimum with the plant-beneficial bacterium Enterobacter cloacae. Cucumber seeds treated with E. cloacae were sown in potting mix with and without sporangia of the pathogen P. ultimum. HCK (healthy check) seeds were not treated with E. cloacae and were sown in noninfested potting mix. PATH CK (pathogen check) nontreated cucumber seeds were sown in potting mix infested with P. ultimum. 501R3 + PU, cucumber seeds were treated with E. cloacae strain 501R3 and sown in potting mix infested with the same level of P. ultimum as in the PATH CK. 501R3, cucumber seeds were treated with E. cloacae strain 501R3 and sown in noninfested potting mix. Various aspects of the process to deliver biocontrol agents are being investigated from the development of seed treatments compatible with farm equipment, to the development of methods to visualize the distribution of beneficial microorganisms in the spermosphere and rhizosphere, to understanding the genetic and physiologic basis of colonization by beneficial organisms.

A method which couples image processing and genetic-tagging of beneficial bacteria was developed to analyze the spatial distribution of specific bacteria in the rhizosphere. In this image, the plant- beneficial bacterium E. cloacae, genetically tagged with bioluminescence, is depicted in association with a cucumber root system.

E. cloacae on cucumber roots is in green, E. cloacae in the soil is in white, the cucumber root system is brown and the soil is black.

Recent Publications

Roberts, D.P., Yucel, I., and Larkin, R.P. Genetic approaches for analysis and manipulation of rhizosphere colonization by bacterial biocontrol agents, pp. 415-431. IN G.J. Boland and L.D. Kuykendall (eds.) Plant-Microbe Interactions and Biological Control. Marcel Dekker, Inc. 1998.

Larkin, R.P., Roberts, D.P., and Gracia-Garza, J.A. Biological Control of Fungal Diseases, pp. 149-191. IN D. Hutson and J. Miyamoto (eds.) Fungicidal Activity: Chemical and Biological Approaches to Plant Protection. John Wiley and Sons, New York. 1998.

Kobayashi, D.Y., Roberts, D.P., and Holtman, M.A. A 6 kb fragment involved in general metabolism in Enterobacter cloacae strain 501. Genbank accession number:AF098509. 1998.

Meyer S.F.M., Roberts, D.P., and Wergin, W.P. Association of the plant-beneficial fungus Verticillium lecanii with soybean roots and rhizosphere. J. Nematology 30:451-460. 1998.

Roberts, D.P., Kobayashi, D.Y., Dery, P.D., and Short, N.M., Jr. An image analysis method for determination of spatial colonization patterns of bacteria in plant rhizosphere. Applied Microbiol. and Biotechnol. 51:653-658. 1999.

Roberts, D.P., P.D. Dery, I. Yucel, J.S. Buyer, M.A. Holtman, and D.Y. Kobayashi. Role of pfkA and general carbohydrate catabolism in seed colonization by Enterobacter cloacae. Appl. Environ. Microbiol. 65:2513-2519. 1999.

Stromberg, E.L., D.P.Roberts, G.H.Lacy, P.D.Dery, and J.S.Buyer. Field evaluation of selected bacterial isolates and seed tratment fungicides for the control of Take-all in Jackson Soft Red Winter wheat, 1998. Bio. Cult. Tests Control Plant Dis. 14:127-129. 1999.

Buyer, J.S., Roberts,D.P., and Russek-Cohen, E. Microbial community structure and function as affected by soil and seed type. Can. J. Microbiol. 45:138-144. 1999.

Roberts, D.P., E.L. Stromberg, G.H. Lacy, and J.S. Buyer. Biological disease control: considerations for seed treatment and stand establishment. Acta Horticulturae 504:69-74. 1999.

Roberts, D.P., P.D. Dery, I. Yucel, and J.S. Buyer. Importance of pfkA for rapid growth during colonization of crop seeds by Enterobacter cloacae. Appl. Environ. Microbiol. 66:87-91. 2000.

Stromberg, E.L. D.P.Roberts, G.H.Lacy, P.D.Dery, and J.S.Buyer. Field evaluation of selected bacterial isolates and seed treatment fungicides for the control of Take-all in Jackson Soft Red Winter wheat, 1999. Biol. Cult. Tests Control Plant Dis. 15:135-139.

Li, W., Roberts, D.P., Dery, P.D., Mock, N.M., Baker, C.J., and Buyer, J.S. Effect of decreased catabolic capability of Enterobacter cloacae strain A-11 on root colonization and suppression of damping-off by Pythium ultimum on cucumber. Proceedings of the 5th International PGPR Workshop, Cordoba, Argentina. http://www.ag.auburn.edu/argentina. 2000.

Roberts, D.P. Seedling diseases, pp. 895-896. In O.C. Malloy and T.D. Murray, Encyclopedia of Plant Pathology, John Wiley and Sons, New York, NY. 2000.

Roberts, D.P. Seedling blight, pp. 894-895. In O.C. Malloy and T.D. Murray, Encyclopedia of Plant Pathology, John Wiley and Sons, New York, NY. 2000.

Roberts, D.P. Preemergence damping-off, pp.826-827. In O.C. Malloy and T.D. Murray, Encyclopedia of Plant Pathology, John Wiley and Sons, New York, NY. 2000.

Roberts, D.P. Postemergence damping-off, pp. 796-797. In O.C. Malloy and T.D. Murray, Encyclopedia of Plant Pathology, John Wiley and Sons, New York, NY. 2000.

Roberts, D.P. and D.Y. Kobayashi. Hyphal lysis, pp. 558-559. In O.C. Malloy and T.D. Murray, Encyclopedia of Plant Pathology, John Wiley and Sons, New York, NY. 2000.

Meyer, S.L.F., Massoud, S.I., Chitwood, D.J., and Roberts, D.P. Evaluation of Trichoderma virens and Burkholderia cepacia for antagonistic activity against root-knot nematode, Meloidogyne incognita. Nematology 2: 865-873. 2001.

Buyer, J.S., Roberts, D.P., Millner, P., and Russek-Cohen, E. Analysis of fungal communities by sole carbon source utilization profiles. J. Microbial Meth. 45: 53-60. 2001.

Meyer, S.L.F., Roberts, D.P., Chitwood, D.J., Carta, L.K., Lumsden, R.D., and Mao, W. Application of Burkholderia cepacia and Trichoderma virens, alone and in combinations, against Meloidogyne incognita on bell pepper. Nematropica 31: 75-86. 2001.

Stromberg. E.L., D.P. Roberts, G.H. Lacy, P.D. Dery, and J.S. Buyer. Field evaluation of selected bacterial isolates and seed treatment fungicides for the control of take-all in Madison soft red winter wheat, 2000. Biol. Cult. Tests Control Plant Dis. Report 2001:S25. 2001.

Li, W., D.P. Roberts, P.D. Dery, S.L.F. Meyer, S. Lohrke, R.D. Lumsden, and K.P. Hebbar. 2001. Broad spectrum anti-biotic activity and disease suppression by the potential biocontrol agent Burkholderia ambifaria BC-F. Crop Protection 21:129-135.

Baker, C.J., N. Mock, E.W. Orlandi, K.L. Deahl, and D.P. Roberts. 2001. Oxygen metabolism in plant/bacteria interactions: characterization of the oxygen uptake response of plants to bacteria. Physiol. Molec. Plant Pathol. 59:17-23.

Meyer, S.L.F., and D.P. Roberts. 2002. Combinations of biocontrol agents for management of plant-parasitic nematodes and soilborne plant-pathogenic fungi. J. Nematol. 34:1-8.

Lohrke, S.M., P.D. Dery, W. Li, R. Reedy, D.Y. Kobayashi, and D.P. Roberts. 2002. Mutation in an rpiA homologue in Enterobacter cloacae decreases colonization and biocontrol of damping-off on cucumber caused by Pythium ultimum. Mol. Plant-Microbe Interact. 15:817-825.

Roberts, D.P., S.M. Lohrke, and S. Chung. 2002. Current Research in Biological Control of Plant Diseases. Monthly Agriculture and Horticulture (Korean Magazine). Monthly Agriculture and Horticulture (Korean Magazine), August, 2002, pp. 124-125.

Stromberg, E.L., D.P. Roberts, G.H. Lacy, S.M. Lohrke, W. Li, and J.S. Buyer. 2002. Field evaluation of selected bacterial isolates and seed treatment fungicides for the control of take-all in Roane soft red winter wheat in Virginia, 2001. Biol. and Cult. Tests Control Plant Dis. 17:508.

Buyer, J.S., D.P. Roberts, and E. Russek-Cohen. 2002. Soil and plant effects on microbial community structure. Can. J. Microbiol. 48:955-964.

Roberts, D.P., and S.M. Lohrke. 2003. USDA_ARS research programs in biological control of plant diseases. Pest Manag. Sci. 59:654-664.

Zhou, H., F. Yao, P. Knittle, D.P. Roberts, and T.G. Lessie. 2003. AHL-deficient mutants of Burkholderia ambifaria BC-F have decreased anti-fungal activity. Curr. Microbiol. 47:174-179.

Xiaojia, H., S. Liu, and D.P. Roberts. Rhizosphere colonization of Oilseed Rape by Pseudomonas alcaligenes A9(lacZ). Chinese Journal of Oil Crops Sciences. In Press.