IntroductionTomato yellow leaf curl virus (TYLCV, Begomovirus coheni), a whitefly-transmitted begomovirus, causes serious economic losses to tomato crops globally. Over the past three decades, several genetic sources of TYLCV resistance have been identified and incorporated into tomato breeding. Among these is a recessive source of resistance known as ty-5.MethodsIn this study, we conducted a global transcriptome analysis to compare gene expression in a ty-5 near isogenic tomato line and its susceptible recurrent parent at various stages of TYLCV infection.ResultsWe identified 1,394 differentially expressed genes, including numerous defense-related genes and genes involved in RNA-mediated DNA methylation. In addition, the expression of key regulatory genes such as protein kinases (PKs) and transcription factors (TFs) was also significantly altered. To explore the function of one upregulated TF encoding an APETALA2/Ethylene Responsive Factor (AP2/ERF), tomato plants overexpressing this gene were generated and demonstrated to confer resistance to TYLCV.DiscussionThese results lead us to hypothesize that ty-5-mediated TYLCV resistance not only involves a pelota gene but is a product of two major pathways acting in concert: a typical host-disease resistance pathway and RNA-directed DNA methylation. Understanding the mechanism underlying ty-5 resistance will facilitate the development of tomato germplasm with more durable TYLCV resistance.

Cucurbit crops including watermelon (Citrullus lanatus), melon (Cucumis melo), cucumber (Cucumis sativus), squash, and pumpkin (Cucurbita spp.) make important nutritional and flavorful contributions to the human diet. The primary challenge for US cucurbit production is disease caused by numerous fungal, oomycete, bacterial, and viral pathogens that reduce crop yield and quality and engender costly control measures. The USDA National Institute of Food and Agriculture–Specialty Crop Research Initiative funded CucCAP (Cucurbit Coordinated Agricultural Project) projects “CucCAP: Leveraging applied genomics to improve disease resistance in cucurbit crops” and “CucCAP2: Harnessing genomic resources for disease resistance and management in cucurbit crops–Bringing the tools to the field” brought together members of the cucurbit community across the country with expertise in genomics, bioinformatics, breeding, genetics, plant pathology, integrated disease management, and economics to address these disease challenges. Collectively, the projects produced extensive genomic resources and bioinformatic tools including genome assemblies and pan-genomes for cucurbit species; genetically characterized the full US National Plant Germplasm System (NPGS) collections for watermelon, melon, cucumber, and squash; developed deeply resequenced core populations for these crops; identified single nucleotide polymorphism and structural variants; and developed the Cucurbit Genomics database (CuGenDB, http://cucurbitgenomics.org/v2/). New sources of resistance were identified for 17 cucurbit crop/disease combinations; quantitative trait loci were mapped and molecular markers developed for 24 combinations; and 15 breeding lines with resistances to various diseases were released. New detection methodology was developed for several pathogens; extensive disease monitoring and multilocation disease management trials and resistance tests were performed; a centralized web portal (https://cuccap.org) was developed to provide cucurbit disease information in English and Spanish; and disease management information was shared with growers, commodity groups and industry organizations through publications and presentations at conferences, field days, and extension schools delivered at more than 100 venues in 24 states. The CucCAP projects were carried out through joint efforts among 26 university and USDA coinvestigators and their research groups along with valued input and assistance from NPGS cucurbit crop curators, seed industry collaborators, cucurbit growers, external evaluators, and international collaborators. In addition to the specific genomic, breeding, and disease management outputs, the CucCAP projects have had broader impacts including use of the new genomic tools to provide insights into cucurbit biology, synergistic effects resulting from a more cohesive cucurbit community, and scientific training of a cadre of students and postdoctoral researchers.

Tomato (Solanum lycopersicum L.), one of the most widely grown vegetables in the world, has been seriously impacted in the past decade by the emerging tomato brown rugose fruit virus (ToBRFV). ToBRFV is a seed-borne tobamovirus, with ability to overcome the commonly used Tm-22 resistance gene in tomato. The objective of this study was to conduct quantitative trait locus (QTL) mapping and identify single-nucleotide polymorphism (SNP) markers associated with ToBRFV resistance in tomato. Two F2 populations were used for QTL mapping: One derived from a cross between S. pimpinellifolium USVL333 (PI 390718) × USVL332 (PI 390717) and another from ‘Moneymaker’ × USVL332 (PI 390717), with population sizes of 195 and 79 plants, respectively. The resistance trait was derived from the S. pimpinellifolium accession USVL332 (PI 390717). A major QTL for ToBRFV resistance was identified on chromosome 11 (SL4.0ch11), with the peak located at approximately 46.84 Mbp. This QTL spans a 22-kb interval between 46,825,788 bp and 46,847,421 bp, as determined through both genome-wide association study (GWAS) and QTL linkage mapping. Three SNP markers, SL4.0ch11_46825788, SL4.0ch11_46847421, and SL4.0ch11_46850215, demonstrated the most significant association with high LOD values (LOD = 13 in the Blink model) in GWAS analysis. In this genomic region, two disease resistance gene analogs, Solyc11g062150 (TIR-NBS-LRR resistance protein, Toll-Interleukin receptor) and Solyc11g062180 (disease resistance protein, leucine-rich repeat), were identified, which may serve as candidates for ToBRFV resistance. The QTL identified in this study could be valuable for plant breeders in facilitating tomato breeding with ToBRFV resistance.

Soil salinity is a significant abiotic factor that impedes sustainable crop production in key agricultural regions worldwide. Saline cultivation adversely affects soil quality, whereas the use of saline water for irrigation disrupts the physiological and biochemical processes of plants. Continuous irrigation with high salt concentrations leads to a gradual buildup of soil salinity, thus hindering optimal plant growth and development. Consequently, there is a growing emphasis on breeding salinity-tolerant cultivars of various crops. In this study, 71 tomato accessions sourced from 20 countries and provided by the US Department of Agriculture were evaluated under controlled greenhouse conditions and subjected to saline stress (200 mM NaCl). The experiment used a split-plot design, with the salt treatment serving as the main plot and the tomato accession as the subplot, which were arranged in a completely randomized design with three replications. Results identified nine accessions (PI 109837, PI 127820, PI 270256, PI 634828, PI 636205, PI 636255, PI 647143, PI 647528, and PI 647556) as salt-tolerant. Additionally, high broad-sense heritability was observed for the leaf injury score and leaf chlorophyll content. Furthermore, positive correlations were found among parameters related to the leaf injury score and leaf chlorophyll content (soil plant analysis development value). These findings offer valuable insights for tomato breeding programs, particularly those focused on enhancing salt tolerance of elite cultivars of this crucial crop.

The genetic diversity and population structure of tomato (Solanum lycopersicum) were investigated to support breeding strategies and germplasm conservation. A total of 276 accessions from the USDA-GRIN collection were analyzed using single-nucleotide polymorphisms (SNPs) generated through genotyping by sequencing (GBS). After stringent filtering, 5162 high-quality polymorphic SNPs were retained for analysis. Population structure analysis revealed three distinct genetic groups (Q1, Q2, and Q3) among the accessions. Accessions from the USA, Asia, and Central and South America were assigned to all three groups, while accessions from Europe and Oceania were predominantly clustered within Q2. Genetic diversity indices, including major allele frequency, heterozygosity, and polymorphism information content (PIC), indicated moderate-to-high levels of genetic variation. These findings provide essential insights into the genetic diversity and population structure of tomato, offering valuable information for breeding programs aimed at improving traits such as yield, stress tolerance, and disease resistance. The results further underscore the role of global germplasm exchange in shaping the genetic landscape of tomato accessions.

The tobamovirus tomato brown rugose fruit virus (ToBRFV) has recently emerged, causing significant damage to the tomato industry in various regions worldwide, including the US. ToBRFV evades the widely used Tm-22 resistance gene, which encodes a nucleotide-binding leucine-rich repeat (NLR) class immune receptor with an N-terminal coiled-coil (CC) domain that confers resistance to the tomato mosaic virus (ToMV). In this study, we tested a transgenic tomato line (tomatoNN) expressing the Nicotiana glutinosa N gene, which encodes an NLR with a Toll-Interleukin 1 homology domain (TIR) at the N-terminus, for resistance to ToBRFV. Our results demonstrate that tomatoNN is resistant to ToBRFV, evidenced by the necrotic local lesions observed on the inoculated leaves and the absence of symptoms on systemic leaves. This correlates with very low to non-detectable virus levels in double antibody sandwich enzyme-linked immunosorbent (DAS-ELISA) and quantitative reverse transcription-polymerase chain reaction (RT-qPCR) assays. Furthermore, our findings reveal that tomatoNN is resistant to ToBRFV at 22 °C, but not at 30 °C, showing that the temperature-sensitive nature of N-mediated resistance also extends to ToBRFV resistance in tomato. These results highlight the significant potential of using tomatoNN to breed tomato cultivars resistant to ToBRFV, offering a new approach to managing the global pandemic caused by this emerging virus.

Salinity is a major constraint on tomato production, increasingly intensified by climate change. This study aimed to develop superior salt-tolerant tomato cultivars by evaluating genetic variation in salt tolerance, identifying associated single-nucleotide polymorphism (SNP) markers through genome-wide association studies (GWAS), and applying genomic prediction (GP). A total of 265 tomato accessions from the USDA germplasm collection were evaluated at the seedling stage under controlled greenhouse conditions with saline stress (200 mM NaCl). Nineteen accessions were identified as salt-tolerant, exhibiting a leaf injury score (LIS) ≤ 3.0 (on a 1–7 scale) and less than 40

The solanaceous-infecting tobamoviruses are closely related and hence it can be challenging to detect them using serological or molecular methods, particularly when present in a mixed infection. Tomato mottle mosaic virus (ToMMV) is a newly identified tobamovirus that poses serious risk to tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.) production worldwide. Species-specific identification is crucial to prevent the entry and establishment of plant pathogens and protect the billion-dollar tomato industry. In this study, we report the validation of a previously described reverse transcription polymerase chain reaction (RT-PCR) assay that amplifies a 289 bp fragment of the coat protein coding region of ToMMV genome. This assay has 100% specificity for ToMMV. Inclusivity tests were performed against a diverse collection of six ToMMV isolates in North America. Exclusivity tests showed no cross reaction with eleven non-target viruses and seven viroids commonly found on tomato and pepper host plants. The detection limit of the one-step RT-PCR was determined to be at 10-5 (or 0.25pg/μl) dilution in plant samples, with its amplicon sequence confirmed by Sanger sequencing. The RT-PCR can detect ToMMV consistently on contaminated seed or leaf tissues. This validated assay could serve as a standard method for detecting ToMMV in seed health testing and for plant disease diagnosis, thus to prevent inadvertent introduction and spread of this emerging and economically important tobamovirus in tomato and pepper fields.

Drought, a crucial abiotic stressor, markedly reduces the growth and yield of tomato crops (Solanum lycopersicum L.). Consequently, adopting drought-resistant cultivars and implementing breeding programs to enhance drought tolerance have emerged as enduring solutions to alleviate the adverse effects of drought in various tomato cultivation regions. In this study, 68 United States Department of Agriculture (USDA) tomato accessions were assessed in a controlled greenhouse experiment, encompassing both water deficit treatment and a control group subjected to standard watering conditions. The experiment was arranged in a randomized complete block design with three replications. The results of this study pinpointed four accessions, PI 365956, PI 584456, PI 390510, and PI 370091, as drought-tolerant accessions. Additionally, high broad-sense heritability was revealed for leaf wilting, leaf rolling, and SPAD chlorophyll content (total leaf chlorophyll). Furthermore, positive correlations were found among parameters associated with leaf wilting, leaf rolling, and SPAD chlorophyll content. The findings offer valuable insights for tomato breeding initiatives, especially those focused on enhancing drought tolerance in elite cultivars. Future studies will expand the evaluation to include a larger pool of tomato accessions and conduct a genome-wide association study to identify single nucleotide polymorphism (SNP) markers for molecular breeding in tomatoes.

Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus infecting tomatoes and peppers, resulting in a pandemic in recent years. In addition to its abilities of being seed-borne, transmitted mechanically and overcoming current resistance, we speculated other factors may also contribute to such catastrophic effect on tomato production in a hydroponic greenhouse. The objective of this study was to evaluate whether ToBRFV can be transmissible through recirculating hydroponic systems and, more importantly, search for an effective approach to contain its spread. We not only detected ToBRFV in the runoff water samples collected from three greenhouses but also determined the virus’ infectivity through a bioassay. We then conducted a water treatment using cold plasma ozone to assess its efficacy in inactivating ToBRFV. The results showed that, with a high concentration of ToBRFV (inoculum in 1:100 dilution), a prolonged exposure (72 min) to two higher ozone concentrations (0.6 mg/L and 1.0 mg/L) achieved partial effects. With a medium virus concentration (inoculum in 1:1000 dilution), an exposure to ozone for 48 min was sufficient to completely suppress the virus’ infectivity. However, with a low virus concentration (inoculum in 1:10,000 dilution), the virus was completely inactivated even with just a short ozone exposure (24 min). Future work will need to confirm the efficacy of the ozone treatment against ToBRFV as well as its impact on tomato plants in a hydroponic greenhouse.

Bacterial wilt (BW), caused by Ralstonia solanacearum, is one of the devastating diseases in tomatoes (Solanum lycopersicum L.). The use of resistant cultivars and breeding for genetic resistance is the most effective, economical, and environmentally friendly management strategy for this disease. It is necessary to screen diverse germplasm and cultivated genotypes to identify resistant resources and to develop resistant cultivars in tomatoes to combat the changing pathogen isolates. This study evaluated 40 United States Department of Agriculture (USDA) tomato accessions for their BW resistance to the R. solanacearum isolate P822 under greenhouse conditions. The tomato plants were inoculated and visually assessed to observe their symptoms, and the disease severity was scored on a scale of 0 to 4 (0 = no leaf wilted, 1 = 25% of leaves wilted, 2 = 50% leaves wilted, 3 = 75% of leaves wilted, and 4 = 100% leaves wilted). Five accessions (PI 645370, PI 647306, PI 600993, PI 355110, and PI 270210) were observed as BW resistance, with PI 645370 showing the greatest resistance. The broad-sense heritability for BW resistance was estimated as 59.9% and 42.8% based on a 0–4 scale of disease incidence and the disease severity index, respectively. Two distinct clusters (sub-populations) were detected among 39 of the 40 accessions. The five identified BW-resistant accessions were distributed in both clusters, suggesting a likely difference in the genetic base among the five resistance accessions. The resistant accessions will contribute significantly to the tomato breeding program to develop new cultivars with BW resistance.

Sweetpotato (Ipomoea batatas L.) is an important staple crop cultivated in over 100 countries, and the storage roots and vines provide food for humans and livestock. Sweetpotato consumption and demand for its value-added products have increased significantly in the last two decades and have led to new cultivar development, expansion in acreage, and increased demand in the United States and its export markets. Despite the known nutritional components and other health benefits, further research is needed to characterize the genetic diversity and chemical composition related to their storage root qualities, essential in developing consumer-preferred cultivars that offer host plant resistance against pests and pathogens. There is a critical need for research on non-pesticidal control approaches that can provide safe, effective, economical, sustainable, and environmentally sound pest and disease management techniques, especially for socially disadvantaged small farmers in the United States. Moreover, climate change can significantly impact future production practices and yield and may directly or indirectly affect crop pests, weeds, and diseases. In this review, we discuss the current status, challenges, and future approaches associated with sweetpotato production practices; health-promoting properties of sweetpotato cultivars; value-added products; genetic diversity and germplasm; pest and disease management; weed and water management; pollination ecology; and other agronomic and cultural practices that may impact sustainable sweetpotato production by small-scale, organic, and large-scale growers. Sweetpotato (Ipomoea batatas L.) is an important staple crop cultivated in over 100 countries. US sweetpotato industry faces many production challenges, including pest and diseases, as well as climate change extremes. A comprehensive review by subject matter experts on the challenges of US sweetpotato industry is not available. This review evaluates the current situation, challenges, and future approaches for improving sweetpotato production. Also, current and future impacts of climate change on global sweetpotato production and demand are discussed.

Summary Bottle gourd (Lagenaria siceraria (Mol.) Strandl.) is an economically important vegetable crop and one of the earliest domesticated crops. However, the population history and genomic diversification of bottle gourd have not been extensively studied. We generated a comprehensive bottle gourd genome variation map from genome sequences of 197 world‐wide representative accessions, which enables a genome‐wide association study for identifying genomic loci associated with resistance to zucchini yellow mosaic virus, and constructed a bottle gourd pangenome that harbors 1534 protein‐coding genes absent in the reference genome. Demographic analyses uncover that domesticated bottle gourd originated in Southern Africa c. 12 000 yr ago, and subsequently radiated to the New World via the Atlantic drift and to Eurasia through the efforts of early farmers in the initial Holocene. The identified highly differentiated genomic regions among different bottle gourd populations harbor many genes contributing to their local adaptations such as those related to disease resistance and stress tolerance. Presence/absence variation analysis of genes in the pangenome reveals numerous genes including those involved in abiotic/biotic stress responses that have been under selection during the world‐wide expansion of bottle gourds. The bottle gourd variation map and pangenome provide valuable resources for future functional studies and genomics‐assisted breeding.

The tomato is one of the most important vegetable crops grown worldwide. Tomato brown rugose fruit virus (ToBRFV), a seed-borne tobamovirus, poses a serious threat to tomato production due to its ability to break the resistant genes (Tm-1, Tm-2, Tm-22) in tomatoes. The objective of this work was to identify new resistant source(s) of tomato germplasm against ToBRFV. To achieve this aim, a total of 476 accessions from 12 Solanum species were tested with the ToBRFV US isolate for their resistance and susceptibility. As a result, a total of 44 asymptomatic accessions were identified as resistant/tolerant, including thirty-one accessions of S. pimpinellifolium, one accession of S. corneliomulleri, four accessions of S. habrochaites, three accessions of S. peruvianum, and five accessions of S. subsection lycopersicon hybrid. Further analyses using serological tests identified four highly resistant S. pimpinellifolium lines, PI 390713, PI 390714, PI 390716, and PI 390717. The inheritance of resistance in the selected lines was verified in the next generation and confirmed using RT-qPCR. To our knowledge, this is a first report of high resistance to ToBRFV in S. pimpinellifolium. These new genetic resources will expand the genetic pool available for breeders to develop new resistant cultivars of tomato against ToBRFV.

This study aimed to determine gene pool structure in the tomato (Solanum lycopersicum) along with the relationships of populations in different regions. To do so, it leveraged 276 diverse cultivated accessions representing 35 countries, obtained via the USDA-GRIN tomato germplasm collection. Single nucleotide polymorphisms (SNPs) in these accessions were detected by sequencing, and genetic diversity, population structure, and phylogenetic relationships were estimated from the SNP alleles. The results of model-based ancestry analysis, phylogenetic tree construction, and principal component analysis supported these accessions as representing three well-differentiated genetic populations. Phylogenetic analyses traced the accessions back to their regions of origin, highlighting Central and South America as the primary center of domestication, with secondary centers in Europe and North America. This study provides a comprehensive analysis of the genetic variation in and relationships among cultivated tomato genotypes. The findings are of benefit to curators, researchers, and breeders in understanding, utilizing, conserving, and managing the collection, and in thereby contributing more efficiently to international tomato research.

Bottle gourd (Lagenaria siceraria L.) belongs to the cucurbit family and has a long history of cultivation in tropical and subtropical regions worldwide, both for food and medicine. Popularized by its unique fruit shapes, gourds are used to make ornaments and musical instruments. However, there is limited information on volatile organic compounds (VOCs) in the bottle gourd fruit. In the present study, we conducted a comparative analysis of VOCs profiled in two accessions (USVL5 and USVL10) with distinct fruit shapes: bottle and cylinder. While USVL5 only produced long cylinder fruits, USVL10 produced two fruit types, cylinder (USVL10CYN) and bottle (USVL10A and USVL10B). VOCs in each line were analyzed using headspace solid-phase microextraction–gas chromatography/mass spectrometry (HS-SPME-GC/MS). Aliphatic aldehydes and alcohols were the most abundant compounds found in these bottle gourd accessions. Based on the functional profile of the identified VOCs, our results reveal the suitability of our tested line (USVL10), enriched in functionally important VOCs such as hexanal (abundance = 381.07), nonanal (abundance = 9.85), 2-methoxy-2-methylpropane (abundance = 21.26) and D-limonene (abundance = 31.48). The VOCs profiling and functional analyses support the notion that the bottle gourd accession USVL10 can be a good candidate for its use in agriculture, the health care industry and domestic uses.

Tomato yellow leaf curl virus (TYLCV), a monopartite begomovirus in the family Geminiviridae, is efficiently transmitted by the whitefly, Bemisia tabaci, and causes serious economic losses to tomato crops around the world. TYLCV-infected tomato plants develop distinctive symptoms of yellowing and leaf upward cupping. In recent years, excellent progress has been made in the characterization of TYLCV C4 protein function as a pathogenicity determinant in experimental plants, including Nicotiana benthamiana and Arabidopsis thaliana. However, the molecular mechanism leading to disease symptom development in the natural host plant, tomato, has yet to be characterized. The aim of the current study was to generate transgenic tomato plants expressing the TYLCV C4 gene and evaluate differential gene expression through comparative transcriptome analysis between the transgenic C4 plants and the transgenic green fluorescent protein (Gfp) gene control plants. Transgenic tomato plants expressing TYLCV C4 developed phenotypes, including leaf upward cupping and yellowing, that are similar to the disease symptoms expressed on tomato plants infected with TYLCV. In a total of 241 differentially expressed genes identified in the transcriptome analysis, a series of plant development-related genes, including transcription factors, glutaredoxins, protein kinases, R-genes and microRNA target genes, were significantly altered. These results provide further evidence to support the important function of the C4 protein in begomovirus pathogenicity. These transgenic tomato plants could serve as basic genetic materials for further characterization of plant receptors that are interacting with the TYLCV C4.

Tomato is an important vegetable in the United States and around the world. Recently, tomato brown rugose fruit virus (ToBRFV), an emerging tobamovirus, has impacted tomato crops worldwide and can result in fruit loss. ToBRFV causes severe symptoms, such as mosaic, puckering, and necrotic lesions on leaves; other symptoms include brown rugose and marbling on fruits. More importantly, ToBRFV can overcome resistance in tomato cultivars carrying the Tm-22 locus. In this study, we recovered ToBRFV sequences from tomato seeds, leaves, and fruits from the U.S., Mexico, and Peru. Samples were pre-screened using a real-time RT-PCR assay prior to high-throughput sequencing. Virus draft genomes from 22 samples were assembled and analyzed against more than 120 publicly available genomes. Overall, most sequenced isolates were similar to each other and did not form a distinct population. Phylogenetic analysis revealed three clades within the ToBRFV population. Most of the isolates (95%) clustered in clade 3. Genetic analysis revealed differentiation between the three clades indicating minor divergence occurring. Overall, pairwise identity showed limited genetic diversity among the isolates in this study with worldwide isolates, with a pairwise identity ranging from 99.36% and 99.97%. The overall population is undergoing high gene flow and population expansion with strong negative selection pressure at all ToBRFV genes. Based on the results of this study, it is likely that the limited ToBRFV diversity is associated with the rapid movement and eradication of ToBRFV-infected material between countries.

Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus infecting tomato and pepper crops. First identified in 2014 in the Middle East, ToBRFV has spread rapidly around the world. Being seed-borne, resistance breaking and easy mechanical transmission, ToBRFV can spread quickly in a greenhouse through plant handling. Thus, selecting an effective disinfectant that is capable of deactivating virus infectivity is important. We aimed to identify these effective disinfectants for ToBRFV management in greenhouse tomato production, particularly for total cleaning. A useful disinfectant should be effective against ToBRFV infectivity without major phytotoxic effect on the test plants. In this study, we evaluated 11 disinfectants at various concentrations and assessed their efficacy in ToBRFV treatment on tomato plants that were pretreated with or without SP2700, a known antiviral plant activator of Ningnanmycin. SP2700 treated-plants generated systemic acquired resistance with a delay in symptom expression for 2–3 weeks in comparison to the mock control. Overall, 1% Virocid, 2% Virkon S, 0.25% sodium hypochlorite (5% Clorox bleach), and 2.5% trisodium phosphate (TSP) achieved complete deactivation of ToBRFV with 15 min exposure. However, TSP presented serious phytotoxicity. Our results offer practical solutions to manage this emerging disease affecting tomato production in greenhouses.

Watermelon (Citrullus lanatus) is an important vegetable fruit crop, widely grown in many countries in the tropical and subtropical regions around the world. The narrow genetic base of cultivated watermelon makes it susceptible to many pests and diseases, especially viruses. However, genetic sources of resistance are available in wild relatives that could potentially be used to incorporate the resistance genes into watermelon cultivars. Ribosome-inactivating proteins (RIPs) are prevalent in many plant species and are known to have an important role in defence against bacteria, fungi, and viruses. The objective of this study was to identify RIP-like sequences in the watermelon genome and to conduct comparative measurement of RIP gene expression between the potyvirus-resistant Citrullus amarus 'PI 244019MODIFIER LETTER PRIME versus the susceptible watermelon (C. lanatus) 'Charleston Gray' in response to infection by papaya ringspot virus (PRSV). Taking advantage of the recently available genome sequences of 'PI 244019MODIFIER LETTER PRIME and 'Charleston Gray', in this study we mined out watermelon RIP genes and conducted comparative sequence and expression analyses of RIP-I and RIP-II between the genotypes. The RIP gene expression analysis revealed elevated RIP gene expression in resistant PI 244019 plants, but not in susceptible 'Charleston Gray' plants, in response to inoculation with PRSV, indicating a potential association of RIP gene expression and resistance to potyviruses in watermelon. This elevated expression of RIP genes in association with potyvirus resistance opens a new avenue to investigate the underlying mechanism of potyvirus resistance in watermelon.