About

Frank Louws is a William Neal Reynolds Distinguished Professor and former Department Head of Horticulture Science at NC State University. He is a Fellow of the American Phytopathology Society (APS) and has received awards including the APS Excellence in Extension and APS Excellence in Regulatory Affairs and Crop Security. His work emphasizes the linkage between basic science and translative outcomes that benefit farmers, companies, and citizens involved in horticultural plant cultivation. Dr. Louws has secured over $42 million in external funding to support research and extension activities focused on horticultural crop production systems, particularly in strawberry and vegetable production with an emphasis on sustainability and disease management. His research and extension programs aim to improve horticultural practices through scientific advancements.

Research topics

• Biology
• Horticulture
• Microbiology
• Biotechnology
• Ecology
• Agronomy
• Materials science
• Engineering
• Philosophy
• Nanotechnology
• Virology
• Linguistics
• Genetics
• Botany

Selected publications

• Neopestalotiopsis spp., an invasive fungal pathogen, is a major threat to strawberry production: the current status, challenges, and future directions

  Frontiers in Plant Science · 2026-01-28 · 1 citations

  articleOpen access

  Pestalotioid fungi have traditionally been regarded as secondary or opportunistic pathogens of strawberries, which has led to limited research attention. However, recent outbreaks of Neopestalotiopsis have demonstrated its potential to act as a primary pathogen, posing a significant threat to strawberry production worldwide. Current management strategies primarily involve propagation of pathogen-free plants, cultural practices such as field sanitation, crop rotation, and the removal of infected plants, supplemented by the application of biocontrol agents and fungicides. Advances in molecular diagnostic tools have improved early detection and monitoring of Neopestalotiopsis spp. Furthermore, initial efforts have begun to identify sources of genetic resistance in strawberry, thereby supporting future breeding programs. Despite these advancements, a considerable gap remains in our understanding of the host’s defense mechanisms, the pathogen’s infection strategies, the dynamics of their interactions, and the pathogen’s ecology. The taxonomy’s complexity and the variability in virulence among its isolates further complicate diagnosis and control efforts. Addressing these challenges is crucial to developing sustainable, integrated disease management strategies and advancing resistance breeding, thereby ensuring the long-term productivity and resilience of the strawberry industry. This review consolidates the current understanding of Neopestalotiopsis spp., evaluates the available diagnostic tools and management strategies, discusses recent progress in genetics and genomics for breeding resistance to this pathogen, and identifies areas for further research.

  PublisherOA PDFDOI

• Assessing Tomato Lines with <i>Bwr-6</i> and <i>Bwr-12</i> Loci for Resistance to <i>Ralstonia solanacearum</i> Species Complex Phylotypes I and II from North Carolina

  PhytoFrontiers™ · 2026-03-01

  articleOpen access

  Bacterial wilt (BW), caused by members of the Ralstonia solanacearum species complex (RSSC), is a devastating disease affecting many crops, including tomato. Among the management practices implemented to combat BW, developing host resistance is the most effective approach. Therefore, it is crucial to identify sources of resistance within the available tomato germplasm. In this study, we evaluated 10 tomato lines from the World Vegetable Center in Taiwan, each possessing either the Bwr-6-linked or the Bwr-12-linked marker gene for BW resistance. We used two RSSC strains in our experiments: phylotype I strain NG-RL01 and phylotype II strain K60, both isolated from North Carolina. The two independent experiments were conducted simultaneously in a greenhouse using a split-plot design with six replications. Five-week-old plants were drenched and inoculated in the wounded root zone with a suspension of a 2-day-old bacterial culture. Disease severity was assessed daily using a standard disease rating scale, and the area under the disease progress curve was calculated. The results showed significant differences between the two bacterial strains, the tomato lines, and their interactions. Furthermore, K60 was more aggressive than NG-RL01. Most of the tomato lines were resistant to strain NG-RL01; however, none of the tested lines showed resistance to strain K60. Interestingly, a few plants, specifically AVTO2102, showed some resistance to K60. The findings indicate that the BW resistance-linked markers Bwr-6 and/or Bwr-12 confer considerable resistance to strain NG-RL01 but are ineffective against strain K60, emphasizing the need for research to enhance resistance across different RSSC strains. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

  PublisherDOI

• Genomic insights and comparative analysis of Colletotrichum species associated with anthracnose fruit rot and crown rot of strawberry in North Carolina

  Frontiers in Microbiology · 2025-02-10 · 4 citations

  articleOpen accessSenior author

  Colletotrichum is a large genus of fungal phytopathogens responsible for significant economic losses in numerous crops globally. These pathogens exhibit varying host specificities; some have a broad host range, while others are more limited. To explore the genetic composition and underlying factors of fungal virulence and pathogenicity, we sequenced the genomes of seven isolates of Colletotrichum spp.: three from the C. acutatum and four from the C. gloeosporioides . These isolates were sourced from anthracnose fruit rot and crown rot of strawberry in North Carolina. Phylogenetic and phylogenomic analyses classified the isolates within the C. acutatum as C. nymphaeae , while those in the C. gloeosporioides were identified as C. siamense . The genome sizes of the C. nymphaeae isolates ranged from 50.3 Mb to 50.7 Mb, with 14,235 to 14,260 predicted protein-coding gene models. In contrast, the genome sizes of the C. siamense isolates ranged from 55.7 Mb to 58.6 Mb, with predicted protein-coding gene models ranging from 17,420 to 17,729. The GC content across all genomes spanned from 51.9 to 53.7%. The predicted gene models included effectors (339 to 480), secondary metabolic gene clusters (67 to 90), and carbohydrate-active enzymes (800 to 1,060), with C. siamense isolates exhibiting the highest numbers in these categories. The genomic resources from this study will aid in resolving taxonomic challenges associated with Colletotrichum spp., elucidate their evolutionary history, and enhance the understanding of fungal biology and ecology, which is crucial for developing effective disease management strategies.

  PublisherOA PDFDOI

• High-Quality Complete Genomes of Three Phylotype IIA <i>Ralstonia solanacearum</i> Strains Isolated from Tomatoes in North Carolina

  PhytoFrontiers™ · 2025-05-28 · 1 citations

  articleOpen access

  Ralstonia solanacearum ( R. sol) is a destructive bacterial plant pathogen and the causal agent of bacterial wilt in various crops, including tomatoes, blueberries, and eucalyptus. The type strain for this pathogen species is K60, isolated in North Carolina in 1953, and is one of two high-quality closed genomes for R. sol phylotype IIA strains in public databases. To enhance resources that support investigations into the genotypic diversity of R. sol in the United States, three complete, high-quality phylotype IIA R. sol genomes for strains isolated from tomatoes in North Carolina were generated using hybrid long- and short-read sequencing technologies. These new genomes have high and low CheckM scores for completeness and contamination, respectively, and provide valuable resources for studying R. sol evolution, epidemiology, and virulence, particularly in the context of U.S. pathogen populations. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

  PublisherDOI

• Genome Sequence Resource of Four <i>Botrytis cinerea</i> Isolates from North Carolina

  PhytoFrontiers™ · 2025-01-03 · 2 citations

  articleOpen accessSenior author

  Botrytis cinerea is a fungal pathogen that affects over 1,400 plant species and causes significant damage to crops. It is also responsible for causing gray mold in small fruits, such as blueberries and strawberries. In this study, four isolates of B. cinerea were collected (two from blueberry and two from strawberry) in North Carolina. Their genomes were sequenced using Illumina paired-end sequencing. The core genome of the isolates was analyzed for carbohydrate-active enzymes, secretomes, effectors, and secondary metabolite repertoires. The genome assembly of the four isolates ranged from 41.9 Mb for NC5 to 44.9 Mb for KC33. Based on Benchmarking Universal Single-Copy Orthologs analysis, all of the genomes had high levels of completeness, ranging from 98.2 to 99.1%. The annotation revealed the presence of 500 to 565 carbohydrate-active enzymes, 649 to 688 secreted proteins, and 162 to 181 potential fungal effectors. This study not only provides valuable genomic resources for B. cinerea but also significantly contributes to the existing resources available for understanding host–pathogen interactions and the factors that affect disease development in the host. [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 .

  PublisherOA PDFDOI

• Diversification of an emerging bacterial plant pathogen; insights into the global spread of Xanthomonas euvesicatoria pv. perforans

  PLoS Pathogens · 2025-04-09 · 6 citations

  articleOpen access

  Emerging and re-emerging plant diseases continue to present multifarious threats to global food security. Considerable recent efforts are therefore being channeled towards understanding the nature of pathogen emergence, their spread and evolution. Xanthomonas euvesicatoria pv. perforans (Xep), one of the causal agents of bacterial spot of tomato, rapidly emerged and displaced other bacterial spot xanthomonads in many tomato production regions around the world. In less than three decades, it has become a dominant xanthomonad pathogen in tomato production systems across the world and presents a compelling example for understanding diversification of recently emerged bacterial plant pathogens. Although Xep has been continuously monitored in Florida since its discovery, the global population structure and evolution at the genome-scale is yet to be fully explored. The objectives of this work were to determine genetic diversity globally to ascertain if different tomato production regions contain genetically distinct Xep populations, to examine genetic relatedness of strains collected in tomato seed production areas in East Asia and other production regions, and to evaluate variation in type III secretion effectors, which are critical pathogenicity and virulence factors, in relationship to population structure. We used genome data from 270 strains from 13 countries for phylogenetic analysis and characterization of type III effector gene diversity among strains. Our results showed notable genetic diversity in the pathogen. We found genetically similar strains in distant tomato production regions, including seed production regions, and diversification over the past 100 years, which is consistent with intercontinental dissemination of the pathogen in hybrid tomato production chains. Evolution of the Xep pangenome, including the acquisition and loss of type III secreted effectors, is apparent within and among phylogenetic lineages. The apparent long-distance movement of the pathogen, together with variants that may not yet be widely distributed, poses risks of emergence of new variants in tomato production.

  PublisherDOI

• Genome assembly and comparative analysis of Alternaria linariae reveal novel genes associated with host colonization and virulence

  BMC Genomics · 2025-07-07 · 1 citations

  articleOpen access

  Early blight (EB) is one of the most economically devastating diseases affecting tomato production, leading to significant yield losses. Traditionally, EB has been associated with the fungus Alternaria solani. However, recent evidence indicates that A. linariae (previously known as A. tomatophila) is the main causative agent. This revised understanding improves diagnostic accuracy and underscores A. linariae as a valuable resource for studying host-pathogen interactions, host adaptation, and evolutionary mechanisms within the Alternaria genus due to its distinct pathogenic profile and host specificity. The A. linariae strain 25, isolated from EB-infected tomatoes in Swain County, North Carolina, United States, was confirmed through analyses of its asexual morphs, cultural characteristics, and PCR-based identification. Nonetheless, the genomic structure and genetic factors influencing host specificity in A. linariae on tomatoes remain poorly understood. To address this knowledge gap, we sequenced the complete genome of A. linariae. This study will help elucidate its structure, compare its genomic features with those of other Alternaria spp., and identify the genetic basis for its host specificity. These insights are crucial for understanding its pathogenicity and host adaptation and for developing effective disease management strategies. The genome of A. linariae strain 25 has been fully assembled and spans 33.1 Mb. It comprises 18 rRNA genes and 117 tRNA genes, and approximately 272,542 base pairs (0.8%) of repetitive elements. The genome features 11,768 predicted gene models, with 221 genes identified as potential candidate effector proteins that may play a role in host colonization and specificity. Additionally, the genome encodes 573 carbohydrate-active enzymes (CAZymes) and 37 secondary metabolite gene clusters, which are likely involved in pathogenicity and interactions with the host. A comparative genomic analysis of effector genes across different Alternaria spp. revealed that the A. linariae strain 25 possesses unique effectors, which may enhance its ability to colonize and adapt precisely to tomato plants. These findings lay the groundwork for further investigation into the molecular mechanisms that drive host specificity and pathogenicity in A. linariae and provide a foundation for developing targeted strategies to control early blight in tomato crops.

  PublisherOA PDFDOI

• First Report of <i>Ralstonia pseudosolanacearum</i> Phylotype I Sequevar 14 Causing Bacterial Wilt on Tomato (<i>Solanum lycopersicum</i>) and Eggplant (<i>Solanum melongena</i>) in North Carolina, U.S.A.

  Plant Disease · 2025-03-04 · 5 citations

  articleOpen access

  Ralstonia solanacearum species complex (RSSC) consists of three species, including R. solanacearum, R. pseudosolanacearum, and R. syzygii. The K60-type strain of R. solanacearum was isolated from a wilted 'Marglobe' tomato in Raleigh, North Carolina (NC) in 1953 (Kelman 1954). It is classified as phylotype IIA, sequevar 7 (Prior and Fegan 2005). In July 2023, during a field visit in Eastern NC, patches of >50 eggplant (Solanum melongena cv. Pingtung Oriental) and tomato (Solanum lycopersicum cv. Saybrook) plants showing wilt symptoms were observed in a 1 ha field. Two plants from each host were collected from this site and tested positive for bacterial streaming in sterile deionized water for 2 min. One plant from each host was used for bacterial isolation by plating a 10 μl aliquot of the resulting bacterial streaming suspension on triphenyl tetrazolium chloride (TZC) medium (Kelman 1954) and incubated at 28°C for 48 hr. Multiple fluidal white colonies with a pink center and irregularly round morphology reminiscent of strains in the RSSC were observed on all plates. Only one colony from each plant host, NG-RL and EP-RL from tomato and eggplant, respectively, was selected for molecular characterization. Neither strain amplified the 357 bp band and was not R. solanacearum Select Agent (Opina et al. 1997). Genomic DNA from both NG-RL and EP-RL generated the 280 bp and 144 bp bands and confirmed as R. pseudosolanacearum phylotype I using the RSSC multiplex PCR (Fegan and Prior 2005). To determine sequevar, the primers Endo-F/Endo-R (Poussier et al. 2000; Fegan and Prior 2005) were used to sequence the partial endoglucanase (egl) gene from EP-RL and NG-RL (GenBank accessions: PQ554799 and PQ554800). These sequences were compared to publicly available egl sequences from GenBank and Cellier et al. (2023). A maximum likelihood phylogenetic tree showed that both NG-RL and EP-RL clustered with reference strains PSS81, MLI71-15, and Zo4 with 100% identity, confirming NG-RL and EP-RL are R. pseudosolanacearum phylotype I sequevar 14. To fulfill Koch's postulates, NG-RL and EP-RL inoculant was prepared from 48 h cultures grown on TZC plates at 28°C. Plates were flooded with sterile deionized water and then transferred to a falcon tube, adjusting O.D. 600 to 0.2 (~1×108 CFU/ml). The roots of six-week-old eggplants (cv. Black Beauty) and tomatoes (cv. Bonny Best) were wounded by running a scalpel through the soil 2 cm from the stem. This was repeated on six plants for both NG-RL and EP-RL. Mock-inoculated plants treated with sterile deionized water (SDW) served as controls. Plants incubated at 28°C in the greenhouse showed bacterial wilt symptoms nine days post-inoculation. R. pseudosolanacearum phylotype I sequevar 14 was confirmed from all bacteria-inoculated plants using the multiplex PCR and egl sequencing methods described above. No symptoms or bacteria were isolated from SDW mock-inoculated plants. There have been no prior reports of R. pseudosolanacearum phylotype I in North Carolina. To our knowledge, this is the first report on R. pseudosolanacearum phylotype I and the sequevar 14 in both tomato and eggplant in NC. This phylotype I is endemic to Asia and was first reported in the US in 2003 on pepper in Florida (Ji et al. 2006) and in 2015 on tomatoes in Louisiana (Jimenez Madrid et al. 2019). This finding highlights the need for a nationwide RSSC survey program, which can undoubtedly inform pathogen spread and management for crops in NC and beyond.

  PublisherOA PDFDOI

• Genome‐wide association study identifies quantitative trait loci associated with resistance to <i>Verticillium dahliae</i> race 3 in tomato

  The Plant Genome · 2025-10-14 · 1 citations

  articleOpen accessSenior author

  Verticillium wilt (VW) disease, caused by Verticillium dahliae Kleb., is a major threat to tomato (Solanum lycopersicum L.) production. Identifying loci associated with VW resistance can accelerate breeding efforts and support sustainable disease management. Although the Ve1 and Ve2 genes confer resistance to V. dahliae races 1 and 2, the emergence of race 3 in the United States poses a new challenge. To investigate the genetic basis of quantitative resistance to the race 3 strain KJ14a, we evaluated 250 diverse tomato accessions. Disease severity and incidence were assessed weekly over 5 weeks, using chlorosis/necrosis percentage (CN_perc) and the number of symptomatic leaves (LC) as phenotypes. OmeSeq quantitative reduced-representation sequencing yielded 42,941 high-quality single nucleotide polymorphism and insertion-deletion markers. Genome-wide association study (GWAS) and local linkage disequilibrium analyses identified four candidate genes associated with VW resistance on chromosomes 3, 5, and 7, including two loci mapping to previously reported quantitative trait loci and two novel resistance loci on chromosome 5. The candidate genes are involved in plant defense and the modification of cell walls. To validate and assess the breeding potential of marker-trait associations, we applied GWAS-assisted best linear unbiased prediction (GWABLUP). Using an additive + dominance model and GWABLUP with top 100 associated markers, predictive ability for LC improved by 16.4% and 4.8%, and for CN_perc by 11.7% and 7.9%, compared to standard genomic best linear unbiased prediction using 100 and 18,000 genome-wide markers, respectively. These results offer valuable insights into the genetic architecture of VW resistance to race 3 and demonstrate the potential of combining GWAS and genomic prediction to accelerate tomato breeding for durable disease resistance.

  PublisherOA PDFDOI

• Elucidating the impact of organic amendments on soil bacterial communities and strawberry yield in North Carolina

  Frontiers in Sustainable Food Systems · 2025-03-19 · 3 citations

  articleOpen accessSenior author

  Strawberry ( Fragaria × ananassa Duchesne ex Rozier) is an important small fruit grown worldwide. Organic amendments can alter microbial communities and increase crop productivity. While research on organic amendments in strawberry cultivation has primarily focused on various regions in the U.S., especially the West Coast, there has been little to no investigation into their potential benefits in North Carolina (NC). A three-year trial was conducted from 2019 to 2022 at the Horticultural Crops Research Station in Castle Hayne, NC, U. S. A. The main objective of the study was to examine the effects of reduced rates of dried molasses (5.60 t/ha) and mustard meal (2.24 t/ha), a half-rate combination of both, a positive control (Pic Clor 60), and a negative control (no fumigated and no amended) on soil bacterial communities and strawberry yield. Our results from 16S microbiome amplicon sequencing showed significant variations in the composition of the soil bacterial community over time between the organic amendment treatments and the controls. The alpha diversity indices (Shannon index) of the soil bacterial microbiome were generally higher in plots with organic amendments than those treated with Pic Clor 60. Taxonomic classification revealed that the two phyla, Proteobacteria and Actinobacteriota , were prominent in the organic amendment treatments. The total marketable yield rankings for the three organic amendment treatments (dried molasses, mustard meal, and the half-rate combination of both) were comparable to those achieved through fumigation. The results indicated that bacterial structure and yield improved in the organic amendment plots, while microbial diversity decreased in the fumigation plots, and yields were lower in the untreated plots. This study will inform the selection of organic amendments to enhance microbial diversity and promote sustainability in strawberry farming in NC.

  PublisherOA PDFDOI

Frequent coauthors

• Doug Sanders

  North Carolina State University

  55 shared

• Jeffrey P. Mitchell

  University of California Division of Agriculture and Natural Resources

  54 shared

• Doug Monks

  North Central State College

  54 shared

• William Sciarappa

  Rutgers, The State University of New Jersey

  54 shared

• Peter Nitzsche

  Rutgers, The State University of New Jersey

  54 shared

• Bodie Pennisi

  54 shared

• William T. Hlubik

  54 shared

• Aref A. Abdul‐Baki

  54 shared

Labs

• Structural Pest Management Training & Research FacilityPI

Education

• Postdoctoral Fellow, Center for Microbial Ecology/ Department of Energy

  Michigan State University

  1996

• PhD, Plant Pathology

  Michigan State University

  1993

• M.Sc, Environmental Biology (Plant Pathology)

  University of Guelph

  1987

• B.Sc, Horticulture

  University of Guelph

  1986

Awards & honors

• Fellow of the American Phytopathology Society (APS)
• APS Excellence in Extension
• APS Excellence in Regulatory Affairs and Crop Security