Carolee T. Bull, Ph.D.

Carolee T. Bull, Ph.D.

  • Professor of Plant Pathology and Systematic Bacteriology, Plant Pathology and Environmental Microbiology
108 Buckhout Lab (office)
University Park, PA 16802

Areas of Expertise

  • Phytobacteriology
  • Translational Taxonomy
  • Systematic Bacteriology
  • Biological Control
  • Sustainable and Organic Agriculture


  • B.S., Botany, Ohio University
  • M.S., Plant Pathology, Washington State University
  • Ph.D., Plant Pathology, Oregon State University

Other Affiliations

  • Extraordinary Professor, Department of Plant and Soil Sciences, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa (2021-2024)
  • Member, International Committee on Systematics of Prokaryotes (ICSP, 2005-present)
  • Secretary, Judicial Commission ICSP (2014 -2020), Member (2014-2023)
  • Convener, International Society of Plant Pathology Committee on Taxonomy of Plant Pathogenic Bacteria (2006-present; Member 2000-2022)
  • Inaguaral Director, Penn State Microbiome Center (2016-2022)

Feature Stories

Bull steps down at Microbiome Center, looks forward to future innovation, October 3, 2022

Bull elected fellow of American Phytopathological Society, August 24, 2020

Plant Pathologist Aid Investigation of Lettuce Disease, May 28, 2020

Mighty Microbiome, Ag Science Magazine. March 2020

Trailblazers: Carolee Bull Investigates the Microbiome, September 18, 2019

Plant pathologist awarded grant to aid global study of seedborne pathogens, October 3, 2019

College of Agricultural Sciences Department Head Honored by Alma Mater by Amy Duke, November 1, 2017.

Bull Gives Doidge Memorial Lecture at SASPP Congress and Collaborates at FABI, January 17, 2017.

Current Research in the Bull Lab by Carolee Bull, December 19, 2016.

Recap of “How to Be Your Own Best Mentor" Workshop with Dr. Carolee Bull by Kelly Marie Ness, March 9, 2016.

Other Stories

Penn State Microbiome Center and GALT Enter Collaboration, August 4, 2020.


  • Fellow, American Phytopathological Society, (August 2020). Bull was recognized for contributions in translational taxonomy, including the use or development of taxonomic frameworks and methods for identification, classification and description of novel bacterial plant and mushroom pathogens; improved detection methods; descriptions of natural and artificial host ranges; and development of integrated disease management systems in conventional and organic systems.
  • USDA Secretary's Honor Award for Outreach, Diversity, and Equal Opportunity (2013). The USDA Secretary's Honor Award is the highest award in agriculture for service to the nation.
  • Administrator's Outreach, Diversity, and Equal Opportunity Award, USDA/ARS (2012).
  • Mentor of the Year Award, Undergraduate Research Opportunities Center at California State University Monterey Bay (inaugural; 2012).
  • Science and Technology Hall of Fame Inductee, Sewickley Academy (inaugural; 2015).
  • Outreach, Diversity, and Equal Opportunity Award, USDA/ARS/PWA (2012).
  • Research Fellow, Office for Economic Cooperation and Development (2004).
  • Special Service Award, USDA/ARS, HCRL Fresno, CA (1997).
  • Postdoctoral Fellow, National Science Foundation, Washington, DC (1991).
  • Savoury Outstanding Graduate Student, College of Agricultural Science, Oregon State University, Corvallis (1992): for outstanding scholarship and university service.
  • Nellie Townley Heald Scholarship, Department of Plant Pathology, Washington State University, Pullman (1987): for outstanding contributions to the department.
  • Young Botanist Award, Botanical Society of America, St. Louis, MO (1985).
  • Elizabeth Lash Brague Memorial Scholarship, Ohio University, Athens (1982).
  • James Cavalier Scholarship, Sewickley Academy, Sewickley, PA (1980).

Current External Funding

  • Project Director: USDA NIFA SCRI - Integrated Management of Emerging Seedborne Bacterial Diseases of Cucurbits and Chenopods, $3,760,000 + equivalent matching (2019 - 2024).
  • Co-PI (German Sandoya, PI), USDA AMS Specialty Crop Multi-State Program, Improving Lettuce Cultivars against Bacterial Leaf Spot (BLS) Through Breeding,Genetics, and Study of the BLS-Lettuce Interaction. $850,816 (2020 - 2023).
  • Co-PI (Kevin Hockett, PI), USDA NIFA Equipment Grants Program, Prospecting Microbial Diversity and FunctionsAssociated with Agricultural, Environmental, and Food Systems via the Prospector Instrument. $130,875 (2020 - 2021).
  • Co-PI (David Beyer, PI), USDA NIFA OREI, Collaborative Research and Extension Network Addressing Challenges for Sustainable Organic Mushroom Production, $959,991 (2017 - 2021)

Undergraduate Research Leading to Publications

Former undergraduate researchers supervised by C.T. Bull are listed in bold)

  • Bull, C. T., Gebben, S. J., Goldman, P. H., Trent, M. A., Hayes, R. J. 2015. Host genotype and hypersensitive reaction influence population levels of Xanthomonas campestris pv. vitians in lettuce. Phytopathology, 105:316-324.
  • Bull, C. T., Ortiz-Lytle, M. C., Ibarra, A. G., du Toit, L. J., and Reynolds G. J. 2015. First report of bacterial blight of crucifers caused by Pseudomonas cannabina pv. alisalensis in Minnesota on arugula (Eruca vesicaria subsp. sativa). Plant Disease, 99:415.
  • Hayes, R. J., Trent, M., Mou, B. Simko, I., Gebben, S. J. and Bull, C. T. 2014. Baby leaf lettuce germplasm enhancement: developing diverse populations with resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vitians. HortScience, 49:679-687.
  • Rubio, I., Hiddink, G., Asma, M. and Bull, C. T. 2012. First report of the crucifer pathogen Pseudomonas cannabina pv. alisalensis causing bacterial blight on radish (Raphanus sativus) in Germany. Plant Disease, 96:904.
  • Schofield, D. A., Bull, C. T., Rubio, I., Wechter, W. P., Westwater, C., Molineux, I. J. 2012. Development of an engineered bioluminescent reporter phage for the detection of bacterial blight of crucifers. Applied and Environmental Microbiology, 78:3592–3598.
  • Jardini, T. M., Koike, S.T., and Bull, C.T. 2011. First report of bacterial streak of fennel (Foeniculum vulgare) in California caused by Pseudomonas syringae pv. apii. Plant Disease, 96:285.
  • Bull, C. T. and Rubio, I. 2011. First report of bacterial blight of crucifers caused by Pseudomonas cannabina pv. alisalensis in Australia. Plant Disease, DOI: 10.1094/PDIS-11-10-0804.
  • Bull, C. T., Clarke, C. R., Cai, R., Vinatzer, B. A., Jardini, T. M., Koike, S. T. 2011. Multilocus sequence typing of Pseudomonas syringae sensu lato confirms previously described genomospecies and permits rapid identification of P. syringae pv. coriandricola and P. syringae pv. apii causing bacterial leaf spot on parsley. Phytopathology, 101:847-858.
  • Mauzey, S. J., Koike, S. T. and Bull, C. T. 2010. First report of bacterial blight of cabbage (Brassica oleracea var. capitata L.) caused by Pseudomonas cannabina pv. alisalensis in California. Plant Disease, 95:71
  • Bull, C. T., Mauzey, S. J. and Koike, S. T. 2010. First report of bacterial blight of Brussels sprouts (Brassica oleracea L. var. gemmifera) caused by Pseudomonas cannabina pv. alisalensis in California. Plant Disease, 94:1375 DOI: 10.1094/PDIS-07-10-0538.
  • Bull, C. T., Huerta A. I., Koike, S. T. 2009. First report of blossom blight of strawberry (Fragaria x ananassa Duch.) caused by Pseudomonas marginalis in California. Plant Disease, 12: 1350. DOI: 10.1094/PDIS-93-12-1350B.


La Mancha Bacteriana en Hojas de Lechuga., Bull, Carolee, 2022

Judicial Opinions 103–111
International Journal of Systematic Bacteriology, Arahal, David R., Busse, Hans Jürgen, Bull, Carolee T., Christensen, Henrik, Chuvochina, Maria, Dedysh, Svetlana N., Fournier, Pierre Edouard, Konstantinidis, Konstantinos T., Parker, Charles T., Rosselló-Móra, Ramon, Ventosa, Antonio, Göker, Markus, 2022

Lettuce (Lactuca sativa L.) germplasm resistant to bacterial leaf spot caused by race 1 of Xanthomonas hortorum pv. vitians (Brown 1918) Morinière et al. 2020
Journal of Plant Pathology, Sandoya, Germán V., Rosenthal, Emma, Simko, Ivan, Rodrigues-Porto, Lis N., Wadlington, William H., Bull, Carolee T., Carroll, Amanda, 2022

Judicial Opinions 112–122
International Journal of Systematic Bacteriology, Arahal, David, Busse, Hans-Jürgen, Bull, Carolee T., Christensen, Henrik, Chuvochina, Maria, Dedysh, Svetlana, Fournier, Pierre-Edouard, Konstantinidis, Konstantinos, Parker, Charles, Rossello-Mora, Ramon, Ventosa, Antonio, Göker, Markus, 2022

Predators of soil bacteria in plant and human health
Phytobiomes journal, Martins, Samuel, Taerum, Stephen, Triplett, Lindsay, Emerson, Joanne, Zasada, Inga, de Toledo, Beatriz, Kovac, Jasna, Martin, Kendall, Bull, Carolee, 2022

Ewingella americana: an Emerging Multifaceted Pathogen of Edible Mushrooms.
Phytopathology, Hamidizade, Mozhde, Taghavi, S. Mohsen, Moallem, Mahsa, Aeini, Milad, Fazliarab, Amal, Abachi, Hamid, Herschlag, Rachel, Hockett, Kevin, Bull, Carolee, Osdaghi, Ebrahim, 2022

Bacterial Leaf Spot of Cucurbits, Beets, and Swiss Chard, Garcia Rodriguez, Raymond, Gugino, B, Bull, Carolee, 2021

Lettuce Bacterial Leaf Spot, Gorgo-Gourovitch, M, Rosenthal, Emma, Bull, Carolee, 2021

Species of dickeya and pectobacterium isolated during an outbreak of blackleg and soft rot of potato in northeastern and north central united states
Microorganisms, Curland, R, Mainello, A, Perry, Keith L., Hao, Jianjun, Charkowski, Amy O., Bull, Carolee T., McNally, Ryan R., Johnson, Steven B., Rosenzweig, Noah, Secor, Gary A., Larkin, Robert P., Gugino, Beth, Ishimaru, Carol A., 2021

First Report of Brown Spot on White Button Mushroom (Agaricus bisporus) Caused by Cedecea neteri in Iran
Plant Disease, Hamidzade, Mozhde, Hamidizade, Mozhde, Mohsen Taghavi, S., Taghavi, Moshen, Taghavi, S., Mafakheri, Hamzeh, Herschlag, Rachel, Martins, Samuel, Hockett, Kevin, Bull, Carolee, Osdaghi, Ebrahim, 2021

Clarifying the taxonomy of the causal agent of bacterial leaf spot of lettuce through a polyphasic approach reveals that Xanthomonas cynarae Trébaol et al. 2000 emend. Timilsina et al. 2019 is a later heterotypic synonym of Xanthomonas hortorum Vauterin et al. 1995
Systematic and Applied Microbiology, Morinière, Lucas, Burlet, Alexandre, Rosenthal, Emma R., Nesme, Xavier, Portier, Perrine, Bull, Carolee T., Lavire, Céline, Fischer-Le Saux, Marion, Bertolla, Franck, 2020

Transfer of Xanthomonas campestris pv. arecae and X. campestris pv. musacearum to X. vasicola (Vauterin) as X. vasicola pv. arecae comb. nov. And X. vasicola pv. musacearum comb. nov. And description of X. vasicola pv. vasculorum pv. nov.
Phytopathology, Studholme, David J., Wicker, Emmanuel, Abrare, Sadik Muzemil, Aspin, Andrew, Bogdanove, Adam, Broders, Kirk, Dubrow, Zoe, Grant, Murray, Jones, Jeffrey B., Karamura, Georgina, Lang, Jillian, Leach, Jan, Mahuku, George, Nakato, Gloria Valentine, Coutinho, Teresa, Smith, Julian, Bull, Carolee T., 2020

Bacterial brown pit, a new disease of edible mushrooms caused by mycetocola sp.
Plant Disease, Hamidizade, Mozhde, Taghavi, S. Mohsen, Martins, Samuel J., Herschlag, Rachel A., Hockett, Kevin L., Bull, Carolee T., Osdaghi, Ebrahim, 2020

Identification of Pseudomonas isolates associated with bacterial canker of stone fruit trees in the Western Cape, South Africa
Plant Disease, Bophela, Khumbuzile N., Petersen, Yolanda, Carolee, T. Bull, Teresa, A. Coutinho, 2020

Comparing approaches for capturing bacterial assemblages associated with symptomatic (Bacterial Blotch) and asymptomatic mushroom (Agaricus bisporus) caps
Phytobiomes Journal, Martins, Samuel, Trexler, Ryan, Vieira, Fabricio R., Pecchia, John A., Kandel, Prem, Hockett, Kevin L., Bell, Terrence H., Bull, Carolee T., 2020

The emergence of microbiome centres
Nature Microbiology, Martiny, Jennifer, Whiteson, Katrine, Bohannan, Brendan, David, Lawrence, Hynson, Nicole, McFall-Ngai, Margaret, Rawls, John, Schmidt, Thomas, Abdo, Zaid, Blaser, Martin, Bordenstein, Seth, Bréchot, Christian, Bull, Carolee T., Dorrestein, Pieter, Eisen, Jonathan, Garcia-Pichel, Ferran, Gilbert, Jack, Hofmockel, Kirsten, Holtz, Mary, Knight, Rob, Mark Welch, David, McDonald, Daniel, Methé, Barbara, Mouncey, Nigel, Mueller, Noel, Pfister, Catherine, Proctor, Lita, Sachs, Joel, 2020

Genetic analysis of resistance to bacterial leaf spot in the heirloom lettuce cultivar Reine des Glaces
Molecular Breeding, Sandoya, Germán V., Maisonneuve, Brigitte, Truco, Maria Jose, Bull, Carolee T., Simko, Ivan, Trent, Mark, Hayes, Ryan J., Michelmore, Richard W., 2019

Translational taxonomy for bacterial blotch management.
Mushroom News, Bull, Carolee, 2019

Observation of Drippy Nut Disease on Oak In Southeastern NY in 2017-2018
Phytopathology, Mainello, Amanda, Daughtrey, Margery, Bull, Carolee, 2019

Request for revision of the statutes of the international committee on systematics of prokaryotes
International Journal of Systematic Bacteriology, Whitman, William B., Bull, Carolee T., Busse, Hans Jürgen, Fournier, Pierre Edouard, Oren, Aharon, Ventura, Stefano, 2019

Corrigendum: Inference of convergent gene acquisition among pseudomonas syringae strains isolated from watermelon, cantaloupe, and squash (Frontiers in Microbiology (2019) 10 (270) DOI: 10.3389/fmicb.2019.00270)
Frontiers in Microbiology, Newberry, Eric A., Ebrahim, Mohamed, Timilsina, Sujan, Zlatković, Nevena, Obradoví, Aleksa, Bull, Carolee T., Goss, Erica M., Huguet-Tapia, Jose C., Paret, Mathews L., Jones, Jeffrey B., Potnis, Neha, 2019

100 years since Tolaas: Bacterial blotch of mushrooms in the 21st century
Plant Disease, Osdaghi, Ebrahim, Martins, Samuel, Ramos-Sepulveda, Laura, Vieira, Fabrício Rocha, Rocha Vieira, Fabrício, Pecchia, John A., Beyer, David, Bell, Terrence H., Yang, Yinong, Hockett, Kevin L., Bull, Carolee T., 2019

Genome-based evolutionary history of Pseudomonas spp
Environmental Microbiology, Hesse, Cedar, Schulz, Frederik, Bull, Carolee T., Shaffer, Brenda T., Yan, Qing, Shapiro, Nicole, Hassan, Karl A., Varghese, Neha, Elbourne, Liam D.H., Paulsen, Ian T., Kyrpides, Nikos, Woyke, Tanja, Loper, Joyce E., 2018

First report of black rot caused by Xanthomonas campestris on arugula in California
Plant Disease, Rosenthal, E. R., Sepulveda, L. Ramos, Bull, C. T., Koike, S. T., 2018

Genetic diversity and virulence of wheat and barley strains of xanthomonas translucens from the upper midwestern United States
Phytopathology, Curland, Rebecca D., Gao, Liangliang, Bull, Carolee T., Vinatzer, Boris A., Dill-Macky, Ruth, Van Eck, Leon, Ishimaru, Carol A., 2018

Bacterial gall of Loropetalum chinense caused by Pseudomonas amygdali pv. loropetali pv. nov.
Plant Disease, Harmon, Carrie Lapaire, Timilsina, Sujan, Bonkowski, John, Jones, Debra D., Sun, Xiaoan, Vallad, Gary E., Sepulveda, Laura Ramos, Bull, Carolee, Jones, Jeffrey B., 2018

Genetic diversity and virulence of wheat and barley strains of Xanthomonas translucens from the Upper Midwestern United States.
Phytopathology, Currland, Rebecca, Gao, Liangliang, Bull, Carolee, Von Eck, Leon, Vinatzer, Boris, Dill-Macky, Ruth, Ishimaru, Carol, 2017

First report of bacterial leaf spot caused by Pseudomonas syringae pv. Tomato on kale in california
Plant Disease, Koike, S. T., Alger, E. I., Ramos Sepulveda, L., Bull, C. T., 2017

Detection of Pseudomonas pathogens from crucifers, Koike, S, Bull, Carolee, 2017

Plant pathogenic prokaryotes, Bull, Carolee, Koike, S, Huerta, A, Jardini, T, Mauzey, S, Rubio, I, Zacaroni, A, 2017

Angular leaf spot of cucurbits is associated with genetically diverse pseudomonas syringae strains
Plant Disease, Newberry, E. A., Jardini, T. M., Rubio, I., Roberts, P. D., Babu, B., Koike, S. T., Bouzar, H., Goss, E. M., Jones, J. B., Bull, C. T., Paret, M. L., 2016

The U.S. Culture Collection Network lays the foundation for progress in preservation of valuable microbial resources
Phytopathology, McCluskey, Kevin, Alvarez, Anne, Bennett, Rick, Bokati, Deepak, Boundy-Mills, Kyria, Brown, Daniel, Bull, Carolee T., Coffey, Michael, Dreaden, Tyler, Duke, Clifford, Dye, Greg, Ehmke, Erin, Eversole, Kellye, Fenstermacher, Kristi, Geiser, David, Glaeser, Jessie A., Greene, Stephanie, Gribble, Lisa, Griffith, M. Patrick, Hanser, Kathryn, Humber, Richard, Johnson, Barbara W., Kermode, Anthony, Krichevsky, Micah, Laudon, Matt, Leach, Jan, Leslie, John, May, Meghan, Melcher, Ulrich, Nobles, David, Fonseca, Natalia Risso, Robinson, Sara, Ryan, Matthew, Scott, James, Silflow, Carolyn, Vidaver, Anne, Webb, Kimberly M., Wertz, John E., Yentsch, Sara, Zehr, Sarah, 2016

Multilocus sequence typing of strains of bacterial spot of lettuce collected in the United States
Phytopathology, Fayette, Joubert, Raid, Richard, Roberts, Pamela D., Jones, Jeffrey B., Pernezny, Ken, Bull, Carolee T., Goss, Erica M., 2016

Host genotype and hypersensitive reaction influence population levels of Xanthomonas campestris pv. vitians in lettuce
Phytopathology, Bull, Carolee T., Gebben, Samantha J., Goldman, Polly H., Trent, Mark, Hayes, Ryan J., 2015

Novel primers and PCR protocols for the specific detection and quantification of Sphingobium suberifaciens in situ
Molecular and Cellular Probes, Bull, Carolee T., Goldman, Polly H., Martin, Kendall J., 2014

In memoriam--John M. Young (1942-2013).
International journal of systematic and evolutionary microbiology, Bull, Carolee, Coutinho, T, Denny, T, Firrao, G, Fischer-Le Saux, M, Li, X, Saddler, G, Scortichini, M, Stead, D, Takikawa, Y, 2014

Integrated Biological and Cultural Practices Can Reduce Crop Rotation Period of Organic Strawberries
Agroecology and Sustainable Food Systems, Muramoto, Joji, Gliessman, Stephen R., Koike, Steven T., Shennan, Carol, Bull, Carolee T., Klonsky, Karen, Swezey, Sean, 2014

Characterization and performance of 16 new inbred lines of lettuce
Hortscience: A Publication of the American Society for Hortcultural Science, Simko, Ivan, Hayes, Ryan J., Bull, Carolee T., Mou, Beiquan, Luo, Yaguang, Trent, Mark A., Atallah, Amy J., Ryder, Edward J., Sideman, Rebecca G., 2014

The inheritance of resistance to bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. Vitians in three lettuce cultivars
Horticulture Research, Hayes, Ryan J., Trent, Mark A., Truco, Maria Jose, Antonise, Rudie, Michelmore, Richard W., Bull, Carolee T., 2014

Baby leaf lettuce germplasm enhancement: Developing diverse populations with resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vitians
Hortscience: A Publication of the American Society for Hortcultural Science, Hayes, Ryan J., Trent, Mark A., Mou, Beiquan, Simko, Ivan, Gebben, Samantha J., Bull, Carolee T., 2014

Pseudomonas blight caused by Pseudomonas syringae on raspberry in California
Plant Disease, Koike, S. T., Bolda, M. P., Bull, C. T., 2014

First report of bacterial leaf blight on mustard greens (Brassica juncea) caused by Pseudomonas cannabina pv. alisalensis in Mississippi
Plant Disease, Wechter, W. P., Keinath, A. P., Smith, J. P., Farnham, M. W., Bull, C. T., Schofield, D. A., 2014

Characterization and performance of sixteen new inbred lines of lettuce developed by the USDA breeding program in Salinas, California
HortScience, Simko, I, Hayes, R, Bull, Carolee, Mou, B, Luo, Y, Trent, M, Atallah, A, Ryder, E, Sideman, R, 2014

List of new names of plant pathogenic bacteria (2011-2012)
Journal of Plant Pathology, Bull, C. T., Coutinho, T. A., Denny, T. P., Firrao, G., Fischer-Le Saux, M., Li, X., Saddler, G. S., Scortichini, M., Stead, D. E., Takikawa, Y., 2014

The organic research network project on the central coast of California, Muramoto, J., Gliessman, S. R., Shennan, C., Pisani Gareau, T., Monsen, K. L., Pedersen, S., Bolda, M. P., Daugovish, O., Bull, C. T., Li, C., Leap, J., Nieto, D., Bryer, J., Koike, S. T., Smith, R. F., Gaskell, M., Klonsky, K. M., Salas, W., Oomen, G. J.M., 2013

Comparative Genomics of Multiple Strains of Pseudomonas cannabina pv. alisalensis, a Potential Model Pathogen of Both Monocots and Dicots
PLoS One, Sarris, Panagiotis F., Trantas, Emmanouil A., Baltrus, David A., Bull, Carolee T., Wechter, William Patrick, Yan, Shuangchun, Ververidis, Filippos, Almeida, Nalvo F., Jones, Corbin D., Dangl, Jeffery L., Panopoulos, Nickolas J., Vinatzer, Boris A., Goumas, Dimitrios E., 2013

Notice of release of baby leaf romaine breeding lines of lettuce with resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vitians, Hayes, R, Trent, M, Mou, B, Simko, I, Bull, Carolee, 2013