About

David Ritchie is a Professor and Extension Specialist in the Department of Entomology and Plant Pathology at North Carolina State University. His research focuses on discovery and problem-solving related to bacterial and fungal plant pathogens that cause diseases in fruit and vegetable crops. His work emphasizes understanding the population biology, evolutionary mechanisms, and dynamics that lead to the defeat of host resistance, as well as characterizing pathogens that have gained virulence. Ritchie's research aims to develop knowledge that results in more durable disease resistance and effective disease management strategies, particularly in systems involving pepper and Xanthomonas euvesicatoria, the causal agent of bacterial spot, and fungal diseases of peaches such as brown rot and peach scab. He also conducts problem-solving and integrated disease management research on these crops, with a focus on epidemiology and control methods. Ritchie teaches courses in plant pathology, including the biology of plant pathogens and methods in plant pathology, and has international teaching experience, notably co-teaching a graduate course on phytobacteriology at the Universidad de Buenos Aires. His extensive publication record and ongoing research projects contribute significantly to the understanding and management of plant diseases caused by bacterial and fungal pathogens.

Research topics

• Microbiology
• Horticulture
• Biology
• Botany
• Genetics
• Veterinary medicine

Selected publications

• Four decades of genomic stability and adaptive divergence in Xanthomonas phages: defining Duraznoxanthovirus arenicola and its evolutionary framework

  Frontiers in Microbiology · 2026-04-29

  articleOpen access

  Bacteriophages (phages) are abundant and ecologically significant, yet their diversity and roles in plant-associated ecosystems remain poorly understood, limiting their application in sustainable disease management. To address this gap, we characterized 15 phages infecting Xanthomonas arboricola pv. pruni , the causal agent of bacterial spot on peach, has been isolated for over four decades from North Carolina orchards. Comparative genomic and phylogenetic analyses revealed two temporally distinct clades with >95% nucleotide identity and 63 conserved core genes, forming a new genus and species, Duraznoxanthovirus arenicola . These findings challenge assumptions of pervasive genomic mosaicism, highlighting remarkable genomic stability alongside localized variability in accessory loci. Beyond genus-level characterization, our analyses support a broader taxonomic restructuring within the family Anamaviridae , introducing a new subfamily ( Terravirinae ) and two new genera ( Duraznoxanthovirus and Ralstopathovirus ). This work provides the a family-level framework for phages exclusively infecting plant-associated bacteria, offering evolutionary insights and a foundation for ecological studies and management strategies.

  PublisherDOI

• Table 4_Four decades of genomic stability and adaptive divergence in Xanthomonas phages: defining Duraznoxanthovirus arenicola and its evolutionary framework.xlsx

  Figshare · 2026-04-29

  datasetOpen access

  Bacteriophages (phages) are abundant and ecologically significant, yet their diversity and roles in plant-associated ecosystems remain poorly understood, limiting their application in sustainable disease management. To address this gap, we characterized 15 phages infecting Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot on peach, has been isolated for over four decades from North Carolina orchards. Comparative genomic and phylogenetic analyses revealed two temporally distinct clades with >95% nucleotide identity and 63 conserved core genes, forming a new genus and species, Duraznoxanthovirus arenicola. These findings challenge assumptions of pervasive genomic mosaicism, highlighting remarkable genomic stability alongside localized variability in accessory loci. Beyond genus-level characterization, our analyses support a broader taxonomic restructuring within the family Anamaviridae, introducing a new subfamily (Terravirinae) and two new genera (Duraznoxanthovirus and Ralstopathovirus). This work provides the a family-level framework for phages exclusively infecting plant-associated bacteria, offering evolutionary insights and a foundation for ecological studies and management strategies.

  PublisherDOI

• Table 3_Four decades of genomic stability and adaptive divergence in Xanthomonas phages: defining Duraznoxanthovirus arenicola and its evolutionary framework.xlsx

  Figshare · 2026-04-29

  datasetOpen access

  Bacteriophages (phages) are abundant and ecologically significant, yet their diversity and roles in plant-associated ecosystems remain poorly understood, limiting their application in sustainable disease management. To address this gap, we characterized 15 phages infecting Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot on peach, has been isolated for over four decades from North Carolina orchards. Comparative genomic and phylogenetic analyses revealed two temporally distinct clades with >95% nucleotide identity and 63 conserved core genes, forming a new genus and species, Duraznoxanthovirus arenicola. These findings challenge assumptions of pervasive genomic mosaicism, highlighting remarkable genomic stability alongside localized variability in accessory loci. Beyond genus-level characterization, our analyses support a broader taxonomic restructuring within the family Anamaviridae, introducing a new subfamily (Terravirinae) and two new genera (Duraznoxanthovirus and Ralstopathovirus). This work provides the a family-level framework for phages exclusively infecting plant-associated bacteria, offering evolutionary insights and a foundation for ecological studies and management strategies.

  PublisherDOI

• Table 2_Four decades of genomic stability and adaptive divergence in Xanthomonas phages: defining Duraznoxanthovirus arenicola and its evolutionary framework.docx

  Figshare · 2026-04-29

  datasetOpen access

  Bacteriophages (phages) are abundant and ecologically significant, yet their diversity and roles in plant-associated ecosystems remain poorly understood, limiting their application in sustainable disease management. To address this gap, we characterized 15 phages infecting Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot on peach, has been isolated for over four decades from North Carolina orchards. Comparative genomic and phylogenetic analyses revealed two temporally distinct clades with >95% nucleotide identity and 63 conserved core genes, forming a new genus and species, Duraznoxanthovirus arenicola. These findings challenge assumptions of pervasive genomic mosaicism, highlighting remarkable genomic stability alongside localized variability in accessory loci. Beyond genus-level characterization, our analyses support a broader taxonomic restructuring within the family Anamaviridae, introducing a new subfamily (Terravirinae) and two new genera (Duraznoxanthovirus and Ralstopathovirus). This work provides the a family-level framework for phages exclusively infecting plant-associated bacteria, offering evolutionary insights and a foundation for ecological studies and management strategies.

  PublisherDOI

• Table 1_Four decades of genomic stability and adaptive divergence in Xanthomonas phages: defining Duraznoxanthovirus arenicola and its evolutionary framework.docx

  Figshare · 2026-04-29

  datasetOpen access

  Bacteriophages (phages) are abundant and ecologically significant, yet their diversity and roles in plant-associated ecosystems remain poorly understood, limiting their application in sustainable disease management. To address this gap, we characterized 15 phages infecting Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot on peach, has been isolated for over four decades from North Carolina orchards. Comparative genomic and phylogenetic analyses revealed two temporally distinct clades with >95% nucleotide identity and 63 conserved core genes, forming a new genus and species, Duraznoxanthovirus arenicola. These findings challenge assumptions of pervasive genomic mosaicism, highlighting remarkable genomic stability alongside localized variability in accessory loci. Beyond genus-level characterization, our analyses support a broader taxonomic restructuring within the family Anamaviridae, introducing a new subfamily (Terravirinae) and two new genera (Duraznoxanthovirus and Ralstopathovirus). This work provides the a family-level framework for phages exclusively infecting plant-associated bacteria, offering evolutionary insights and a foundation for ecological studies and management strategies.

  PublisherDOI

• <i>Xanthomonas citri</i> pv. <i>lagerstroemium</i>, Description of a New Pathovar Causing Leaf Spot on Crape Myrtle

  Plant Disease · 2025-03-11

  article

  Bacterial leaf spot caused by Xanthomonas was reported in 2014 as a new disease of crape myrtle. Unfortunately, this foundational strain was lost, preventing further experimentation, sequencing of the genome, and phylogenetic analysis. This work describes a collection of Xanthomonas strains isolated from angular leaf spot lesions on crape myrtle in North Carolina from 2014 to 2023. This study includes full reference genomes as well as refulfillment of Koch’s postulates. Genomes were obtained with hybrid whole genome sequencing using Illumina and Nanopore and assembled to develop robust genomic resources for these disease-causing strains. The completed genomes support inclusion of the strains in the X. citri species group; however, both phylogenetic analysis and the identification of a novel plant host suggest the creation of the new pathovar Xanthomonas citri pv. lagerstroemium.

  PublisherDOI

• Molecular Characterization of Copper Resistance Genes from <i>Xanthomonas arboricola</i> pv. <i>pruni</i>

  Phytopathology · 2025-12-09

  article

  Xanthomonas arboricola pv. pruni (XAP) causes bacterial spot in Prunus, and copper sprays have been widely used to manage this disease. Copper tolerance (≥150 µg/ml of copper sulfate pentahydrate [CSP]) is commonly found in XAP populations, but copper resistance (&gt;200 µg/ml of CSP) has not been previously reported. This study reports and characterizes the first copper-resistant strain of XAP (XAPCuR), which was isolated from diseased leaves of Prunus laurocerasus in North Carolina in 2017. Whole-genome sequence analysis of XAPCuR revealed an approximately 247-kb plasmid carrying a duplicated 17-kb cluster containing copper resistance candidate genes copL, copA, copB, copC, copD, copM, copG, copF, cusA, and cusB. The two copies of the copper resistance cluster did not increase the level of copper resistance compared with a single copy, but deletion of both copies led to the loss of resistance. Functional analysis of the cluster revealed that copL-D is the major contributor to copper resistance, allowing XAP to grow on nutrient agar containing up to 750 µg/ml of CSP. Removing copL from copL-D decreased the resistance level to 300 µg/ml of CSP. The copF and cusAB genes alone did not confer copper resistance; however, adding copF-cusB to copL-D increased the resistance level of XAP to 1,000 µg/ml of CSP. The resistance genotype and phenotype were able to be transferred from XAP to Xanthomonas perforans via conjugation. This plasmid has up to 99% identity to other copper resistance plasmids of closely related xanthomonads, indicating that horizontal transfer is driving its spread.

  PublisherDOI

• <i>Xanthomonas citri</i> pv. <i>lagerstroemium</i> , description of a new pathovar causing leaf spot on crape myrtle

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-03-01

  preprintOpen access

  Abstract Bacterial leaf spot caused by Xanthomonas was reported in 2014 as a new disease of crape myrtle. Unfortunately, this foundational strain was lost, preventing further experimentation, sequencing of the genome, and phylogenetic analysis. This work describes a collection of Xanthomonas strains isolated from angular leaf spot lesions on crape myrtle in North Carolina from 2014 to 2023. This study includes full reference genomes, as well as re-fulfillment of Koch’s postulates. Genomes were obtained with hybrid whole genome sequencing using Illumina and Nanopore and assembled to develop robust genomic resources for these disease-causing strains. The completed genomes support inclusion of the strains in the X. citri species group; however, both phylogenetic analysis and the identification of a novel plant host suggest the creation of the new pathovar Xanthomonas citri pv. lagerstroemium .

  PublisherOA PDFDOI

• Genetically Similar <i>Xanthomonas arboricola</i> pv. <i>pruni</i> Strains and Associated Phages Display Phenotypic and Genotypic Variation Across 35 Years

  Phytobiomes Journal · 2024-07-24 · 2 citations

  articleOpen access

  Bacteriophages (phages), viruses that infect bacteria, have key ecological and evolutionary functions in the phytobiome. Despite the importance of phages as primary drivers for bacterial evolution, phage-bacteria interactions across spatiotemporal scales in natural, agricultural settings are underexplored. With increased interest in phage-based therapies to manage bacterial pathogens, an enhanced understanding of phage genetic and functional diversity at the population level and how this, in turn, impacts bacterial evolution and virulence, is necessary. This study presents data on the genetic similarity among Xanthomonas arboricola pv. pruni (Xap) strains isolated from different geographic locations that display different lytic phenotypes when challenged with a panel of six phage isolates collected in the same region over four decades. The minor yet significant genetic variation among this small population of Xap strains is structured by both geographic location and response to phage infection. Phage genomes are also highly similar, with conserved and diverse genomic loci that correspond to isolation year. The six phages characterized here cluster into the Kantovirinae subfamily and possibly form a new genus. Only future studies will elucidate the role of Xap and Xapφ phage genes identified here in the virulence and lysis of Xap and how these, in turn, impact bacterial spot disease outcomes. The research and tripartite pathosystem presented here provide a unique opportunity to investigate the coevolution of phage-phytobacterial pathogen-plant host in depth in an agricultural setting with the potential to monitor the rate at which phage populations contribute to bacterial genetic diversity across geographic and temporal scales. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

  PublisherDOI

• Whole-Genome Sequence Resources for <i>Pseudomonas amygdali</i> pv. <i>sesami</i> and <i>Xanthomonas arboricola</i> Isolated from Sesame (<i>Sesamum indicum</i>) in North Carolina in 2022

  PhytoFrontiers™ · 2024 · 1 citations

  • Biology
  • Botany
  • Microbiology

  Sesame ( Sesamum indicum) is a specialty crop with increasing interest as an alternative, rotational crop for U.S. agricultural systems. This crop is susceptible to several pathogens, including Pseudomonas and Xanthomonas species. Two bacterial isolates were recently cultured from sesame in North Carolina symptomatic of bacterial spot and identified as Pseudomonas amygdali pv. sesami (Pas) and Xanthomonas sp. These isolates were used for hybrid whole-genome sequencing and assembly using Illumina and PacBio to develop robust genomic resources for these disease-causing strains. The results provide the most complete Pas genome available and placed the Xanthomonas sp. isolate into the X. arboricola species designation. Improved genomic resources for pathogens of sesame are needed to accurately detect, characterize, and employ timely management of the disease. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

  PublisherDOI

Frequent coauthors

• James P. Kerns

  North Carolina State University

  15 shared

• Joseph Roberts

  Clemson University

  13 shared

• Joseph R. Doherty

  University of Maryland, College Park

  9 shared

• Megan Botti-Marino

  Michigan State University

  9 shared

• Dennis J. Werner

  North Carolina State University

  4 shared

• João Carlos Setúbal

  Universidade de São Paulo

  4 shared

• Prasanna Joglekar

  North Carolina State University

  4 shared

• Alejandra I. Huerta

  North Carolina State University

  4 shared

Labs

• David Ritchie LabPI

Education

• Ph.D., Entomology

  North Carolina State University

  1995

• M.S., Entomology

  North Carolina State University

  1990

• B.S., Entomology

  University of Georgia

  1987

Awards & honors

• CRISPR; Removal of Plant Pathogens (2021-2023)