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David Ritchie

Professor and Extension Specialist

Bacterial and fungal pathogens of fruit and vegetable crops

Gardner Hall 2406


Dr. Ritchie is no longer accepting students into his program.


My program focuses on both discovery and problem-solving research dealing with bacterial and fungal plant pathogens that cause diseases of fruit and vegetable crops. Emphasis is on the population biology and evolutionary mechanisms and dynamics that lead to the defeat of host resistance and the characterization of pathogens that have gained virulence. The goal of this research is to develop knowledge that leads to more durable disease resistance and disease management strategies. The crop and pathogen system used is pepper and Xanthomonas euvesicatoria causal agent of the disease, bacterial spot. Problem-solving and integrated disease management research also is conducted on two fungal diseases of peaches, brown rot and peach scab. A major focus on peaches and other Prunus spp. is in the area of epidemiology and management of bacterial spot of stone fruits caused by Xanthomonas arboricolapv. pruni.


PP501 (3 credits) Biology of Plant Pathogens – teach bacteriology section 2004 to present. Course coordinator 2007 – present.

PP 502 (2 credits) Methods in Plant Pathology – 2005 to present. Two labs using pepper andXanthomonas euvesicatora to demonstrate the gene-for-gene concept.

PP590U (2 credits) Plant pathology in the field (mid-May-early August course). 2008 and 2010. My portion involves spending 1 full day in the field with the class visiting the Sandhills Research Station and surrounding agricultural area exploring diseases and culture of peaches and agricultural produced in sandy soils.

International – co-taught a 2-credit graduate level course on “phytobacteriology” at the Universidad de Buenos Aires, Argentina, October 8-13, 2007.

Brown rot of stone fruits.Ritchie, D.F. 2000 (updated 2005). The Plant Health Instructor. APSnet Education Center. DOI:10.1094/PHI-I-2000-1025-01.

Bacterial spot of pepper and tomato. Ritchie, D.F. 2000 (updated 2007). The Plant Health Instructor. APSnet Education Center. DOI:10.1094/PHI-I-2000-1027-01.

Selected Publications


  • Yang, N., G. Reighard, D. Ritchie, W. Okie, and K. Gasic. 2012. Mapping quantitative trait loci associated with resistance to bacterial spot (Xanthomonas arboricola pv. pruni) in peach. Tree Genetic & Genomes 9(2):573-586..
  • R.J. Worthington, S.A. Rogers, R.W. Huigens III, C. Melander, D.F. Ritchie. 2012. Foliar applied small molecule that suppresses biofilm formation and enhances control of copper-resistant Xanthomonas euvesicatoria on peppers. Plant Dis. 96:1638-1644.
  • J.F. Pothier, M.C. Pagani, C. Pelludat, D.F. Ritchie, and B. Duffy.  2011. A duplex-PCR method for species and pathovar-level identification and detection of the quarantine plant pathogen Xanthomonas arboricola pv. pruni. J. Microbiol. Methods. 86:16-24.
  • Wichmann, G., Ritchie, D., Kousik, C.S., Bergelson, J. 2005. Reduced genetic variation occurs among genes of the highly clonal plant pathogen Xanthomonas axonopodis pv. vesicatoria, including the effector gene avrBs2. Appl. Environ. Microbiol. 71:2418-2432.
  • Romero, A.M. and Ritchie, D.F. 2004. Systemic acquired resistance delays race shifts to major resistance genes in bell pepper. Phytopathology 94:1376-1382.
  • Romero, A.M., Kousik, C.S., and Ritchie, D.F. 2002. Temperature sensitivity of the hypersensitive response of bell pepper to Xanthomonas axonopodis pv. vesicatoria. Phytopathology 92:197-203.
  • Romero, A.M., Kousik, C.S., and Ritchie, D.F. 2001. Resistance to bacterial spot in bell pepper induced by acibenzolar-S-methyl. Plant Dis. 85:189-194.
  • Kousik, C.S., and Ritchie, D.F. 1999. Development of bacterial spot on near-isogenic lines of bell pepper carrying gene pyramids composed of defeated major resistance genes. Phytopathology 89:1066-1072.
  • Kousik, C.S., and Ritchie, D.F. 1998. Response of bell pepper cultivars to bacterial spot pathogen races which individually overcome major resistance genes. Plant Dis. 82:181-186.
  • Kousik, C.S. and D.F. Ritchie. 1996. Disease potential of pepper bacterial spot pathogen races that overcome the Bs2 gene for resistance. Phytopathology 86:1336-1343.
  • Kousik, C.S. and D.F. Ritchie. 1996. Race shift in Xanthomonas campestris pv. vesicatoria within a season in field-grown pepper. Phytopathology 86:952-958.
  • Kousik, C.S., D.C. Sanders, and D.F. Ritchie. 1996. Mixed genotypes combined with copper sprays to manage bacterial spot of bell peppers. Phytopathology 86:502-508.
  • Ritchie, D.F., Werner, D.J., and Hammerschlag, F.A. 1993. Field evaluation of tissue culture-derived peach trees for susceptibility to bacterial spot (Xanthomonas campestris pv. pruni). Acta Horticulturae 336:155-169. 2nd Intl. Soc. Hort. Sci. Symp. on “In vitro culture and horticultural breeding”, 28 June- 2 July. Baltimore, MD.
  • Dittapongpitch, V., and D.F. Ritchie. 1993. Indigenous miniplasmids in strains of Xanthomonas campestris pv. vesicatoria. Phytopathology 83:959-964.
  • Ritchie, D.F., and V. Dittapongpitch. 1991. Copper- and streptomycin-resistant strains and host differentiated races of Xanthomonas campestris pv. vesicatoria in North Carolina. Plant Dis. 75:733-736.
  • Ritchie, D.F. 1989. Improved peach tree longevity with use of fenamiphos in peach tree short-life locations. Plant Dis. 73:160-163.
  • Werner, D.J., D.F. Ritchie, D.W. Cain, and E.I. Zehr. 1986. Susceptibility of peaches and nectarines, plant introductions, and other Prunus species to bacterial spot. HortScience 21:127-130.


  • Roberts, J. and D. Ritchie. 2013. Impact of antimicrobial compounds on etiolation of creeping bentgrass putting green turf. Phytopathology (Suppl.) 103:S2.122.
  • Smith, A.M. and D.F. Ritchie. 2013. Bacteriophage ecological niches and potential role in coevolution of Xanthomonas arboricola pv. pruni. Phytopathology (Suppl. 2) 103:S2.135.
  • Yang, N., G. Reighard, D. Ritchie, W. Okie and K. Gasic.  2011.  Development of a Genetic Linkage Map for Identification of Molecular Markers Associated with Resistance to Bacterial Spot (Xanthomonas arboricola pv. pruni) in Peach.  Abstracts of XIII Eucarpia Symposium on Fruit Breeding and Genetics. Warsaw, Poland. Sept. 11-15, 2011.  Abstract 99. Page 207.
  • Yang, N., G. Reighard, D. Ritchie, W. Okie and K. Gasic. 2010.  Development of a genetic linkage map for identification of molecular markers associated with resistance to bacterial spot in peach. 5th International Rosaceae Genomics Conference. Stellenbosch, S. Africa.  Abstract P56.
  • Pagani, C.M., Leoni, C., Silvera, E., and Ritchie, D.F. 2001. Characterization of fruit infection periods for bacterial spot on peach. Phytopathology 91:(Suppl.) S68.
  • Wangsomboondee, T., and Ritchie, D.F. 2001. Competitiveness and aggressiveness of Xanthomonas axonopodis pv. vesicatoria strains with mutations in the avrBs2 locus. Phytopathology 91:(Suppl.) S93.
  • Kent, S.J., M.E. Daub, and D.F. Ritchie. 1996. Gallic acid production protects Xanthomonas campestris pv. pruni from cytotoxic effects of hydrogen peroxide. Phytopathology 86:S16 (Abst.).
  • Pagani, M.C., D.F. Ritchie, P.B. Lindgren, D.J. Werner, and C.S. Kousik. 1995. Identification of a DNA fragment that differentiates strains of Xanthomonas campestris pv. pruni. Phytopathology 85:1194. (Abst.).
  • Plant Disease Management Reports: 2007 – 2012


  • D.F. Ritchie and A.M. Smith. 2012. Evaluation of packaged pre-mixed fungicides for peach brown rot control, 2011. Plant Disease Management Reports 6:STF012.
  • D.F. Ritchie and A.M Smith. 2012. Evaluation of fungicides for control of peach scab, 2011.Plant Disease Management Reports 6:STF014.
  • D.F. Ritchie and A.M. Smith. 2012. Efficacy of pre-mixed fungicides for fruit rot control of peaches, 2011. Plant Disease Management Reports 6:STF015.
  • D.F. Ritchie. 2011. Efficacy of pre-mixture fungicides in cover sprays for control of peach scab, 2010. Plant Disease Management Reports 5:STF011.
  • D.F. Ritchie. 2011. Efficacy of preharvest fungicides for brown rot control of peaches, 2010.Plant Disease Management Reports 5:STF012.
  • D.F. Ritchie. 2011. Actigard applied as peach soil drench and drip compared to standard foliar sprays – 2009, 2010. Plant Disease Management Reports 5:STF013.
  • D.F. Ritchie. 2010. Efficacy of fungicides for control of peach scab, 2009. Plant Disease Management Reports 4:STF001.
  • D.F. Ritchie. 2010. Efficacy of fungicides for control of brown rot and peach scab, 2009. Plant Disease Management Reports 4:STF002.
  • D.F. Ritchie. 2010. Control of peach fruit rots with preharvest sprays, 2009. Plant Disease Management Reports 4:STF003.
  • D.F. Ritchie. 2009. Efficacy of Quash and V-10135 for control of brown rot and peach scab, 2008. Plant Disease Management Reports 3:STF014.
  • D.F. Ritchie. 2009. LEM17 for control of brown rot and peach scab, 2008. Plant Disease Management Reports 3:STF015.
  • D.F. Ritchie. 2008. Evaluation of materials and application schedules for bacterial spot management on peach, 2007.  Plant Disease Management Reports 2:STF010.
  • D.F. Ritchie. 2007. Potential bacterial spot control with copper, oxytetracycline, biologicals, and plant-defense activators, 2006. Plant Disease Management Reports 1:STF012.
  • D.F. Ritchie. 2007. Preharvest fungicide sprays for control of brown rot on peaches, 2006. Plant Disease Management Reports 1:STF013.
  • D. F. Ritchie. 2007. Comparison of two tebuconazole formulations (KFD-10-01 and Elite) for brown rot control on peaches, 2006.  Plant Disease Management Reports 1:STF014.


  • D.F. Ritchie. 2012. Actigard 50WG drip and foliar sprays and other selected compounds for bacterial spot control on pepper, 2011.Plant Disease Management Reports 6:V091.
  • D.F. Ritchie. 2009. Comparison of materials and rates for controlling bacterial spot on bell peppers, 2008. Plant Disease Management Reports 3:V015.
  • D.F. Ritchie and T. Abernethy. 2007. Use of bactericides and host resistance for bacterial spot management on bell peppers, 2006.  Plant Disease Management Reports 2:V003.


B.A, Biology, Goshen College
M.S., Plant Pathology, Michigan State University
Ph.D, Plant Pathology, Michigan State University