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Virginia O. Stockwell

Virginia Stockwell

Associate Professor (Courtesy) Ph.D.,1984, Colorado State University



Office/Lab: USDA Horticultural Crops Research Unit
Phone: 541-738-4023

Research Area

Integrated management of bacterial plant diseases with an emphasis in biological control.

Description of Research

My research focuses on utilizing biological control agents as a disease management tool. A guiding tenet of my research is that we can optimize biological control by understanding of the sources of variation in establishment, growth, and activity of antagonists. My model system is the biological control of the bacterial disease fire blight of pear and apple. We documented an increased prevalence of antibiotic-resistant isolates of the pathogen Erwinia amylovora in the Pacific Northwest, which has diminished the effectiveness of chemicals for disease control and sparked interest in biocontrol. In field experiments, we evaluated the influence of weather conditions, indigenous microorganisms, orchard management practices, and stress tolerance on the establishment and growth of bacterial biological control agents on pear and apple trees. Using molecular techniques, we are enhancing the antagonistic activity of mixtures of biological control organisms to optimize suppression of fire blight.


BOT 692 Selected Topics in Plant Pathology/ Phytobacteriology


Loper, J.E.,  Hassan, K.A., Mavrodi, D., Davis II, E.W.,  Lim, C.K., Shaffer, B.T.,  Elbourne, L.D.H., Stockwell, V.O.,  Hartney, S.L., Breakwell, K., Henkels, M.D., Tetu, S.G, Rangel, L.I., Kidarsa, T.A., Wilson, N.L., van Mortel, J., Song, C., Blumhagen, R., Radune, D., Hostetler, J.B., Brinkac, L.M., Durkin, A.S., Kluepfel, D.A., Wechter. W.P., Anderson, A.J., Kim, Y.C., Pierson III, L.S., Pierson, E.A., Lindow, S.E., Raaijmakers, J.M., Weller, D.M., Thomashow, L.S., Allen, A.E., and Ian T. Paulsen, I.T. 2012. Comparative genomics of plant-associated Pseudomonas spp.: Insights into diversity and inheritance of traits involved in multitrophic interactions. PloS Genetics: in press.

Stockwell, V.O., and Duffy, B. 2012. Use of antibiotics in plant agriculture. World Organisation for Animal Health, OIE Scientific and Technical Review; Special Issue: Antimicrobial Resistance in Animal and Public Health, accepted Vol. 31(1).

Rezzonico, F., Stockwell, V.O., Tonolla, M., Duffy, B., and Smits, T.H.M. 2012. Pantoea clinical isolates cannot be accurately assigned to species based on metabolic profiling. Transplant Infectious Disease, in press. (doi:10.1111/j.1399-3062.2011.00684.x).

Kamber, T., Lansdell, T.A., Stockwell, V.O., Ishimaru, C.A., Smits, T.H.M., and Duffy, B. 2012. Characterization of the antibacterial peptide herbicolin I biosynthetic operon in Pantoea vagans biocontrol strain C9-1 and incidence in Pantoea species. Appl. Environ. Microbiol. 78:4412-4419.

Pusey, P.L., V.O. Stockwell, C. Reardon, T.H.M. Smits, and B. Duffy. 2011. Antibiotic production by Pantoea agglomerans biocontrol strain E325 and activity against Erwinia amylovora on apple flower stigmas. Phytopathology 101:1234-1241.

Smits, T.H.M., F. Rezzonico, T. Kamber, A. Goesmann, C.A. Ishimaru, J.E. Frey, V.O. Stockwell, and B. Duffy. 2011. Metabolic versatility and antibacterial metabolite biosynthesis are distinguishing genomic features of the fire blight antagonist Pantoea vagans C9-1. PLoS One 6(7):e22247 (doi:10.1371/journal.pone.0022247).

Stockwell, V.O., Johnson, K., Sugar, D., and Loper, J. 2011.  Mechanistically compatible mixtures of bacterial antagonists improves biological control of fire blight of pear. Phytopathology 101:113-123.

Carey, A.B., Pusey, P.L., Smith, T.J., Loper, J.E., and Stockwell, V.O. 2011. Plasmid content of isolates of Erwinia amylovora from orchards in Washington and Oregon in the USA.  Acta Hort. 896:123-126.

Braun-Kiewnick, A., Lehmann, A., Duffy, B., Dreo, T., Ravnikar, M., and Stockwell, V.O. 2011. Detection of Erwinia amylovora in orchards using quantitative PCR and lateral-flow immunography. Acta Hort. 896:73-76.

Philion, V., Toussaint, V., Svircev, A., and Stockwell, V.O. 2011.  Antagonistic interaction between the biocontrol agent BlightBan C9-1 and the plant defense elicitor Actigard. Acta Hort. 896: 437-440.

Stockwell, V.O., Johnson, K.B., Sugar, D., and Loper, J.E. 2010. Control of fire blight by Pseudomonas fluorescens A506 and Pantoea vagans C9-1 applied as single strains and mixed inocula.  Phytopathology 100:1330-1339.

Smits, T.H.M., Rezzonico, F., Kamber,T.,  Goesmann, A., Ishimaru, C.A., Stockwell, V.O., Frey, J.E., and Duffy, B. 2010. Genome sequence of the biocontrol agent Pantoea vagans strain C9-1. J.  Bacteriol. 192:6486–6487.

Rezzonico, F., Stockwell, V., and Duffy, B. 2009. Plant-agricultural streptomycin formulations do not carry antibiotic resistance genes. Antimicrobial Agents and Chemotherapy 53: 3173–3177.

Stockwell, V. O., Hockett, K. and Loper, J. E. 2009.  Role of RpoS in stress tolerance and environmental fitness of the phyllosphere bacterium Pseudomonas fluorescens strain Pf-122.  Phytopathology 99:689-695.

Hagen, M., Stockwell, V., Whistler, C., Johnson, K., and Loper, J. 2009. Stress tolerance and environmental fitness of Pseudomonas fluorescens A506 which has a mutation in rpoS.  Phytopathology 99:679-688.

Pusey, P. L., Stockwell, V. O., and Mazzola, M. 2009. Epiphytic bacteria and yeasts on apple blossoms and their potential as antagonists of Erwinia amylovora. Phytopathology 99:571-581.

Johnson, K. B., Sawyer, T. L., Stockwell, V. O. and Temple, T. N. 2009. Implications of pathogenesis by Erwinia amylovora on rosaceous stigmas to biological control of fire blight.  Phytopathology 99:128-138.

Pusey, P. L., Stockwell, V.O., and Rudell, D.R. 2008.  Antibiosis and acidification by Pantoea agglomerans strain E325 may contribute to suppression of Erwinia amylovora. Phytopathology 98:1136-1143.

Stockwell, V. O. and Stack, J. P. 2007. Using Pseudomonas spp. for integrated biological control. Phytopathology 97: 244-249.

Gross, H., Stockwell, V.O., Henkels, M. D., Nowak-Thompson, B., Loper, J. E. and Gerwick, W. H. 2007. The genomisotopic approach:  A systematic method to isolate the products of orphan biosynthetic gene clusters. Chemistry and Biology 14:53-63.

Bubán, Tamas, T. Lakatos, Tímea Tóth, L. Dorgai, Ildikó Hudák, Mária Hevesi and Virginia O. Stockwell. 2007. Comparison of the efficacy of various bacterium strains antagonistic to Erwinia amylovora . Növényvédelem 43: 531-538.

Temple , T. N., Stockwell, V. O., Pusey, P. L., and Johnson, K. B. 2007. Evaluation of likelihood of co-occurrence of Erwinia amylovora with mature fruit of winter pear.  Phytopathology 97: 1263-1273.

Stockwell, V.O., Johnson, K.B., and Johnson, V.W. 2006. Colonization of flowers by Pseudomonas fluorescens A506 formulated in a biopolymer gel. Acta Hort 704: 293-299.

Temple , T.N., Stockwell, V.O., Johnson, K.B., and Loper, J.E. 2006. Relative availability of iron to Pseudomonas fluorescens A506 on pome fruit blossoms. Acta Hort 704: 301-305.

Stockwell, V. O., and Loper, J. E. 2005. The sigma factor RpoS is required for stress tolerance and environmental fitness of Pseudomonas fluorescens Pf-5. Microbiology 151: 3001-3009.

Temple , T.N., Stockwell, V.O., Loper, J.E. and Johnson, K.B. 2004. Bioavailability of iron to Pseudomonas fluorescens A506 on flowers of pear and apple. Phytopathology 94:1286-1294.

Anderson, L. M., Stockwell, V. O., and Loper, J. E. 2004. An extracellular protease of Pseudomonas fluorescens inactivates antibiotics of Pantoea agglomerans. Phytopathology 94:1228-1234.

Johnson, K.B., Stockwell, V.O. and Sawyer, T.L. 2004. Adaptation of fire blight forecasting to optimize the use of biological controls. Plant Disease 88:41-48.

Stockwell, V.O., Johnson, K.B., Sugar, D., and Loper, J. E. 2002. Antibiosis contributes to biological control of fire blight by Pantoea agglomerans strain Eh252 in orchards. Phytopathology 92: 1202- 1209. 

McManus, P. S., Stockwell, V. O., Sundin, G. W., and Jones, A. L. 2002. Antibiotic use in plant agriculture. Annual Review of Phytopathology 40: 443-465. 

Stockwell, V. O., Johnson, K. B., and Loper, J. E. 2002. Biological control of fire blight: Understanding interactions among introduced and indigenous microbial communities. Pages 225-239. In: Phyllosphere Microbiology. S. E. Lindow, E. I. Hecht-Poinar, and V.J. Elliot, eds. APS Press, St. Paul, MN. 

McManus, P.S. and Stockwell, V.O. 2001. Antibiotic use for plant disease management in the United States. Plant Health Progress Doi:10.1094/PHP-2001-0327-01-RV. 

Stockwell, V. O., McLaughlin, R. J., Henkels, M. D., Loper, J. E., Sugar, D. and Roberts, R. G. 1999. Epiphytic colonization of pear stigmas and hypanthia by bacteria during primary bloom. Phytopathology 89:1162-1168

Johnson, K. B. and Stockwell, V. O. 1998. Management of fire blight: A case study in microbial ecology. Annual Review of Phytopathology 36:227-248.

Stockwell, V. O., Johnson, K. B., and Loper, J. E. 1998. Establishment of bacterial antagonists of Erwinia amylovora on pear and apple blossoms as influenced by inoculum preparation. Phytopathology 88: 506-513.