Dr. Evan Johnson

Dr. Evan Johnson

Program Emphasis

Our research focuses the effects and interactions of systemic citrus pathogens with the root system for better understanding of the belowground pathology and for management of root health. This includes study of synergistic interactions of these pathogens with soil-borne root pathogens and pests of citrus.


  • Ph. D. Plant Pathology, Cornell University, Ithaca NY
  • B. A. Biology, Chemistry, Wabash College, Crawfordsville IN

Past Positions

Postdoctoral Associate, 2008-2013. CREC, University of Florida, Lake Alfred FL

Graduate Research Fellow, 2001-2007. Cornell University, Ithaca NY

Refereed Papers

J. K. Parker, S. R. Wisotsky, E. G. Johnson, F. M. Hijaz, N. Killiny, M. E. Hilf, L. De La Fuente.  2013.  Viability of ‘Candidatus Liberibacter asiaticus’ prolonged by addition of citrus juice to culture medium Phytopathology, DOI: 10.1094/PHYTO-05-13-0119-R

E. G. Johnson, J. Wu, D. B. Bright, J. H. Graham.  2013.  Root loss on presymptomatic Huanglongbing affected trees is preceded by Candidatus Liberibacter asiaticus root infection but not phloem plugging.  Plant Pathology, DOI: 10.1111/ppa.12109

J. H. Graham, E. G. Johnson, T. R. Gottwald, M. Irey.  2013.  Pre-symptomatic fibrous root decline in citrus trees caused by Huanglongbing and potential synergistic interaction with Phytophthora spp.  Plant Disease, DOI: 10.1094/PDIS-01-13-0024-RE

E. Pathak, F. E. El-Borai, R. Campos-Herrera, R. J. Stuart, E. G. Johnson, J. H. Graham, L. W. Duncan. 2012. Use of real-time PCR to discriminate predatory and saprophagous behavior by nematophagous fungi. Fungal Biology 112:563-573.

S. M. Barry, J. A. Kers, E. G. Johnson, B. Patel, S. B. Krasnoff, B. R. Crane, D. M. Gibson, G. L. Challis, R. Loria.  2012  Regiospecific cytochrome P450-catalysed nitration of L-tryptophan in thaxtomin phytotoxin biosynthesis.  Nature Chemical Biology 8 (10):814-816.

Graham, J. H., Johnson E. G., Bright, D. B., Irey, M. S. 2011. Lack of development of huanglongbing in seedlings from citrus seed. Proc. Fla. State Hort. Soc. 124:65-68.

J. Cubero, I. Gell, E. G. Johnson, A. Redondo, J. H. Graham.  2011.  Use of unstable green fluorescence protein variants for studies of survival of Xanthomonas citri subsp. citri on citrus.  Plant Pathology, 60 (5):977-985.

R. Campos-Herrera, E. G. Johnson, F. E. El-Borai, R. J. Stuart, J. H. Graham, and L. W. Duncan.  2011. Long-term stability of entomopathogenic nematode spatial patterns in soil as measured by sentinel insects and real-time PCR assays. Annals of Applied Biology, 158 (1):55-68.

E. G. Johnson*, S. B. Krasnoff*, D. R. D. Bignell*, W. Chung, T. Tao, R. J. Parry, R. Loria, D. M. Gibson.  2009.  4-Nitrotryptophan is a substrate for the non-ribosomal peptide synthetase TxtB in the thaxtomin A biosynthetic pathway.  Molecular Microbiology, 73(3):409-418. *Authors contributed equally

R. Loria, D. R. Bignell, S. Moll, J. C. Huguet-Tapia, M. V. Joshi, E. G. Johnson, R. F. Seipke, D. M. Gibson.  2008.  Thaxtomin biosynthesis: The path to plant pathogenicity in the genus Streptomyces.  Antonie van Leeuwenhoek International Journal of General and Molecular Microbiology, 94(1):3-10.

E. G. Johnson, J. P. Sparks, B. Dzikovski, B. R. Crane, D. M. Gibson, R. Loria.  2008.  Plant-pathogenic Streptomyces species produce nitric oxide synthase derived nitric oxide in response to host signals.  Chemistry and Biology, 15(1):43-50.

E. G. Johnson, M. V. Joshi, D. M. Gibson, R. Loria.  2007.  Cello-oligosaccharides released from host plants induce pathogenicity in scab-causing Streptomyces species.  Physiological and Molecular Plant Pathology, 71:18-25.
M. V. Joshi, D. R. D. Bignell, E. G. Johnson, Jed P. Sparks, D. M. Gibson, R. Loria.  2007.  The AraC/XylS regulator TxtR modulates thaxtomin biosynthesis and virulence in Streptomyces scabies.  Molecular Microbiology, 66(3):633-642.