Tomato brown rugose fruit virus: An emerging and rapidly spreading plant RNA virus that threatens tomato production worldwide

Optimizing ozone treatment for pathogen removal and disinfection by-product control for potable reuse at pilot-scale

Reclaimed water poses environmental and human health risks due to residual organic micropollutants and pathogens. Ozonation of reclaimed water to control pathogens and trace organics is an important step in advanced water treatment systems for potable reuse of reclaimed water. Ensuring efficient pathogen reduction while controlling disinfection byproducts remains a significant challenge to implementing ozonation in reclaimed water reuse applications. This study aimed to investigate ozonation conditions using a plug flow reactor (PFR) to achieve effective pathogen removal/inactivation while minimizing bromate and N-Nitrosodimethylamine (NDMA) formation. The pilot scale study was conducted using three doses of ozone (0.7, 1.0 and 1.4 ozone/total organic carbon (O3/TOC) ratio) to determine the disinfection performance using actual reclaimed water. The disinfection efficiency was assessed by measuring total coliforms, Escherichia coli (E. coli), Pepper Mild Mottle Virus (PMMoV), Tomato Brown Rugose Fruit Virus (ToBRFV) and Norovirus (HNoV). The ozone CT values ranged from 1.60 to 13.62 mg min L-1, resulting in significant reductions in pathogens and indicators. Specifically, ozone treatment led to concentration reductions of 2.46-2.89, 2.03-2.18, 0.46-1.63, 2.23-2.64 and > 4 log for total coliforms, E. coli, PMMoV, ToBRFV, and HNoV, respectively. After ozonation, concentrations of bromate and NDMA increased, reaching levels between 2.8 and 12.0 μg L-1, and 28-40.0 ng L-1, respectively, for average feed water bromide levels of 86.7 ± 1.8 μg L-1 and TOC levels of 7.2 ± 0.1 mg L-1. The increases in DBP formation were pronounced with higher ozone dosages, possibly requiring removal/control in subsequent treatment steps in some potable reuse applications.

Engineered Resistance to Tobamoviruses

Tobacco mosaic virus (TMV) was the first virus to be studied in detail and, for many years, TMV and other tobamoviruses, particularly tomato mosaic virus (ToMV) and tobamoviruses infecting pepper (Capsicum spp.), were serious crop pathogens. By the end of the twentieth and for the first decade of the twenty-first century, tobamoviruses were under some degree of control due to introgression of resistance genes into commercial tomato and pepper lines. However, tobamoviruses remained important models for molecular biology, biotechnology and bio-nanotechnology. Recently, tobamoviruses have again become serious crop pathogens due to the advent of tomato brown rugose fruit virus, which overcomes tomato resistance against TMV and ToMV, and the slow but apparently inexorable worldwide spread of cucumber green mottle mosaic virus, which threatens all cucurbit crops. This review discusses a range of mainly molecular biology-based approaches for protecting crops against tobamoviruses. These include cross-protection (using mild tobamovirus strains to 'immunize' plants against severe strains), expressing viral gene products in transgenic plants to inhibit the viral infection cycle, inducing RNA silencing against tobamoviruses by expressing virus-derived RNA sequences in planta or by direct application of double-stranded RNA molecules to non-engineered plants, gene editing of host susceptibility factors, and the transfer and optimization of natural resistance genes.

Slime molds (Myxomycetes) causing a "disease" in crop plants and cultivated mushrooms

Myxomycetes (plasmodial slime molds) are eukaryotic protist predators that are associated with wood, leaf litter, and soil in forests, where they feed on bacteria, protozoans, and (to a more limited extent) fungi. The health of crop plants is essential because they represent a primary food source for humans. However, when myxomycetes produce numerous fruiting bodies on the stems and leaves of crop plants, which is herein referred to as a myxomycete colonization, this has the potential of interfering with plant photosynthesis, transpiration and respiration by blocking out light and covering stomata. Myxomycetes are not pathogens, but their occurrence on plants can be mistakenly interpreted as some type of infection. However, this phenomenon has been largely ignored. This paper provides a comprehensive overview of the taxonomic and economic diversity of the organisms involved in myxomycete colonization. In addition, the various types of myxomycete colonization reported in the literature are described and discussed, a number of images provided, and cultural and chemical prevention and control measures are summarized. The latter should be of significant relevance for local production of crops and plant protective stations. While myxomycetes are not pathogens of crop plants, some species can seriously impact commercially grown mushrooms. Reports of myxomycetes affecting mushrooms are also described in this paper.

Getting Hold of the Tobamovirus Particle-Why and How? Purification Routes over Time and a New Customizable Approach

This article develops a multi-perspective view on motivations and methods for tobamovirus purification through the ages and presents a novel, efficient, easy-to-use approach that can be well-adapted to different species of native and functionalized virions. We survey the various driving forces prompting researchers to enrich tobamoviruses, from the search for the causative agents of mosaic diseases in plants to their increasing recognition as versatile nanocarriers in biomedical and engineering applications. The best practices and rarely applied options for the serial processing steps required for successful isolation of tobamoviruses are then reviewed. Adaptations for distinct particle species, pitfalls, and 'forgotten' or underrepresented technologies are considered as well. The article is topped off with our own development of a method for virion preparation, rooted in historical protocols. It combines selective re-solubilization of polyethylene glycol (PEG) virion raw precipitates with density step gradient centrifugation in biocompatible iodixanol formulations, yielding ready-to-use particle suspensions. This newly established protocol and some considerations for perhaps worthwhile further developments could serve as putative stepping stones towards preparation procedures appropriate for routine practical uses of these multivalent soft-matter nanorods.

Synthesis of Planar Chiral Compounds Containing α-Amino Phosphonates for Antiplant Virus Applications against Potato Virus Y

An unprecedented study of the application of planar chiral compounds in antiviral pesticide development is reported. A class of multifunctional planar chiral ferrocene derivatives bearing α-amino phosphonate moieties was synthesized. These compounds, exhibiting superior optical purities, were subsequently subjected to antiviral evaluations against the notable plant pathogen potato virus Y (PVY). The influence of the absolute configurations of the planar chiral compounds on their antiviral bioactivities was significant. A number of these enantiomerically enriched planar chiral molecules demonstrated superior anti-PVY activities. Specifically, compound (Sp, R)-9n displayed extraordinary curative activities against PVY, with a 50% maximal effective concentration (EC50) of 216.11 μg/mL, surpassing the efficacy of ningnanmycin (NNM, 272.74 μg/mL). The protective activities of compound (Sp, R)-9n had an EC50 value of 152.78 μg/mL, which was better than that of NNM (413.22 μg/mL). The molecular docking and defense enzyme activity tests were carried out using the planar chiral molecules bearing different absolute configurations to investigate the mechanism of their antiviral activities against PVY. (Sp, R)-9n, (Sp, R)-9o, and NMM all showed stronger affinities to the PVY-CP than the (Rp, S)-9n. Investigations into the mechanisms revealed that the planar chiral configurations of the compounds played pivotal roles in the interactions between the PVY-CP molecules and could augment the activities of the defense enzymes. This study contributes substantial insights into the role of planar chirality in defending plants against viral infections.

Single amino acid change in tomato brown rugose fruit virus breaks virus-specific resistance in new resistant tomato cultivar

Introduction

Tomato cultivation across the world is severely affected by emerging plant viruses. An effective method for protection of commercial crops against viral threats is the use of cultivars harboring resistance genes. Tomato brown rugose fruit virus (ToBRFV), a recently emerged tobamovirus, is able to overcome the dominant Tm-22 resistance that is present in the majority of commercial tomato cultivars. In an effort to alleviate the severe consequences of ToBRFV on tomato production, tomato breeding companies are developing new cultivars with varying levels of resistance against ToBRFV.

Methods

In the present study, cultivars with a new resistant phenotype against ToBRFV were screened against a wild-type isolate of ToBRFV, and subsequently, their performance under commercial greenhouse conditions was monitored. Following the identification of ToBRFV symptoms in a commercial greenhouse-where both new resistant and susceptible cultivars were interplanted-these cultivars were more closely examined.

Results

The presence of ToBRFV was molecularly confirmed on both cultivar types suggesting that the new resistance had been broken. High-throughput sequencing (HTS) was used to study the complete genomes of viral isolates present in the two cultivar types. The analysis revealed a single amino acid change at position 82 of the movement protein of ToBRFV in the isolate present in the new resistant cultivar compared with the isolate identified in the susceptible cultivar.

Discussion

A screening bioassay, that was performed to compare the infectivity of the two ToBRFV isolates, confirmed that only the isolate with this specific amino acid change could successfully infect the resistant cultivar, overcoming the new resistance against ToBRFV.

Molecular characterization and host reaction to tomato mottle mosaic virus isolated from sweet pepper seeds in Japan

Many countries have identified tomato mottle mosaic virus (ToMMV) as a serious threat to tomato production. Here, we constructed and characterized infectious clones of ToMMV isolated from Japanese sweet pepper seeds. The genome of the Japanese isolate is 6399 nucleotides in length and exhibits the highest identity with previously characterized isolates. For example, it is 99.7% identical to that of the Mauritius isolate, which occurs worldwide. Phylogenetic analysis based on complete genome sequences revealed that the Japanese isolates clustered in the same clade as those from other countries. When homozygous tomato cultivars with tobamovirus resistance genes were inoculated with an infectious cDNA clone of ToMMV, the virus systemically infected tomato plants with symptoms typical of Tm-1-carrying tomato cultivars. In contrast, tomato cultivars carrying Tm-2 or Tm-22 showed symptoms only on the inoculated leaves. Furthermore, when commercial cultivars of Tm-22 heterozygous tomato were inoculated with ToMMV, systemic infections were observed in all cultivars, with infection frequencies ranging from 25 to 100%. Inoculation of heterozygous sweet pepper cultivars with tobamovirus resistance genes (L1, L3, and L4) with ToMMV resulted in an infection frequency of about 70%, but most of the infected L1, L3, and L4 cultivars were symptomless, and 10-20% showed symptoms of necrosis and yellowing. Tomato mosaic virus strain L11A, an attenuated virus, did not provide cross-protection against ToMMV and led to systemic infection with typical symptoms. These results suggest that ToMMV might cause extensive damage to existing tomato and sweet pepper cultivars commonly grown in Japan.

Transcriptome Analysis of Tomato Leaves Reveals Candidate Genes Responsive to Tomato Brown Rugose Fruit Virus Infection

Tomato brown rugose fruit virus (ToBRFV) is a newly-emerging tobamovirus which was first reported on tomatoes in Israel and Jordan, and which has now spread rapidly in Asia, Europe, North America, and Africa. ToBRFV can overcome the resistance to other tobamoviruses conferred by tomato Tm-1, Tm-2, and Tm-22 genes, and it has seriously affected global crop production. The rapid and comprehensive transcription reprogramming of host plant cells is the key to resisting virus attack, but there have been no studies of the transcriptome changes induced by ToBRFV in tomatoes. Here, we made a comparative transcriptome analysis between tomato leaves infected with ToBRFV for 21 days and those mock-inoculated as controls. A total of 522 differentially expressed genes were identified after ToBRFV infection, of which 270 were up-regulated and 252 were down-regulated. Functional analysis showed that DEGs were involved in biological processes such as response to wounding, response to stress, protein folding, and defense response. Ten DEGs were selected and verified by qRT-PCR, confirming the reliability of the high-throughput sequencing data. These results provide candidate genes or signal pathways for the response of tomato leaves to ToBRFV infection.

A Novel Tiled Amplicon Sequencing Assay Targeting the Tomato Brown Rugose Fruit Virus (ToBRFV) Genome Reveals Widespread Distribution in Municipal Wastewater Treatment Systems in the Province of Ontario, Canada

Tomato Brown Rugose Fruit Virus (ToBRFV) is a plant pathogen that infects important Solanaceae crop species and can dramatically reduce tomato crop yields. The ToBRFV has rapidly spread around the globe due to its ability to escape detection by antiviral host genes which confer resistance to other tobamoviruses in tomato plants. The development of robust and reproducible methods for detecting viruses in the environment aids in the tracking and reduction of pathogen transmission. We detected ToBRFV in municipal wastewater influent (WWI) samples, likely due to its presence in human waste, demonstrating a widespread distribution of ToBRFV in WWI throughout Ontario, Canada. To aid in global ToBRFV surveillance efforts, we developed a tiled amplicon approach to sequence and track the evolution of ToBRFV genomes in municipal WWI. Our assay recovers 95.7% of the 6393 bp ToBRFV RefSeq genome, omitting the terminal 5' and 3' ends. We demonstrate that our sequencing assay is a robust, sensitive, and highly specific method for recovering ToBRFV genomes. Our ToBRFV assay was developed using existing ARTIC Network resources, including primer design, sequencing library prep, and read analysis. Additionally, we adapted our lineage abundance estimation tool, Alcov, to estimate the abundance of ToBRFV clades in samples.

Evaluation of Tomato Germplasm against Tomato Brown Rugose Fruit Virus and Identification of Resistance in Solanum pimpinellifolium

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.

Tomato leaf disease recognition based on multi-task distillation learning

Introduction

Tomato leaf diseases can cause major yield and quality losses. Computer vision techniques for automated disease recognition show promise but face challenges like symptom variations, limited labeled data, and model complexity.

Methods

Prior works explored hand-crafted and deep learning features for tomato disease classification and multi-task severity prediction, but did not sufficiently exploit the shared and unique knowledge between these tasks. We present a novel multi-task distillation learning (MTDL) framework for comprehensive diagnosis of tomato leaf diseases. It employs knowledge disentanglement, mutual learning, and knowledge integration through a multi-stage strategy to leverage the complementary nature of classification and severity prediction.

Results

Experiments show our framework improves performance while reducing model complexity. The MTDL-optimized EfficientNet outperforms single-task ResNet101 in classification accuracy by 0.68% and severity estimation by 1.52%, using only 9.46% of its parameters.

Discussion

The findings demonstrate the practical potential of our framework for intelligent agriculture applications.

Development and application of monoclonal antibody-based dot-ELISA and colloidal gold immunochromatographic strip for rapid, specific, and sensitive detection of tomato brown rugose fruit virus

Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus that has become a great concern to tomato production industry. Due to the lack of resistant cultivars, precise detection of ToBRFV is essential to prevent the spread of ToBRFV. In this study, we produced highly sensitive and specific monoclonal antibodies against ToBRFV and established dot-enzyme-linked immunosorbent assay (dot-ELISA) and colloidal gold immunochromatographic strip (CGICS)-based methods for ToBRFV detection. These two methods could specifically detect ToBRFV without cross-reaction with seven tested tobamoviruses and three frequently occurring tomato-infecting viruses. Sensitivity analysis showed that the limit of detection of the established dot-ELISA and CGICS methods reached up to 1:6400 and 1:10,000 (w/v, g/mL) dilution of ToBRFV-infected tomato tissue, respectively. Further analyses using field-collected tomato foliar and fruit samples showed that the results obtained by dot-ELISA and CGICS were consistent with those obtained by reverse transcription polymerase chain reaction. The established methods here allow for specific, sensitive, and robust detection of ToBRFV, and will be helpful for precise monitoring and early warning of ToBRFV.

Co-Infection of Tomato Brown Rugose Fruit Virus and Pepino Mosaic Virus in Grocery Tomatoes in South Florida: Prevalence and Genomic Diversity

Tomato brown rugose fruit virus (ToBRFV) is an economically important seed and mechanically transmitted pathogen of significant importance to tomato production around the globe. Synergistic interaction with pepino mosaic virus (PepMV), another seed and mechanically transmitted virus, and long-distance dissemination of these two viruses via contaminated tomato fruits through global marketing were previously suggested. In 2019, we detected both viruses in several grocery store-purchased tomatoes in South Florida, USA. In this study, to identify potential sources of inoculum, co-infection status, prevalence, and genomic diversity of these viruses, we surveyed symptomatic and asymptomatic imported tomatoes sold in ten different groceries in four cities in South Florida. According to the product labels, all collected tomatoes originated from Canada, Mexico, or repacking houses in the United States. With high prevalence levels, 86.5% of the collected samples were infected with ToBRFV, 90% with PepMV alone, and 73% were mixed-infected. The phylogenetic study showed no significant correlations between ToBRFV genomic diversity and the tomato label origin. Phylogenetic analysis of PepMV isolates revealed the prevalence of the PepMV strains, Chilean (CH2) and recombinant (US2). The results of this study highlight the continual presence of PepMV and ToBRFV in imported tomatoes in Florida grocery stores.

One-Step Reverse-Transcription Recombinase-Aided Amplification CRISPR/Cas12a-Based Lateral Flow Assay for Fast Field Screening and Accurate Differentiation of Four Major Tobamoviruses Infecting Tomato and Pepper

Several tobamoviruses cause substantial economic losses to tomato and pepper crops globally, especially the pepper mild mosaic virus (PMMoV), tomato brown rugose fruit virus (ToBRFV), tomato mosaic virus (ToMV), and tomato mottle mosaic virus (ToMMV). A fast and accurate detection method is essential for virus identification. An all-in-one reaction method combining a one-step reverse-transcription recombinase-aided amplification (RT-RAA) and CRISPR/Cas12a-based lateral flow assay in one mixture was developed to rapidly screen and accurately differentiate among these four tobamoviruses for field detection in tomato and pepper plants. With a generic RT-RAA primer set and a mix of four specific crRNAs, along with a portable metal incubator and the use of a crude extraction method, this method screened for PMMoV, ToBRFV, ToMV, and ToMMV concurrently in less than 1 h, enabling field workers to take action immediately. The accurate differentiation of these four viruses could be achieved by later adding a single specific crRNA.

Advances and Prospects of Virus-Resistant Breeding in Tomatoes

Plant viruses are the main pathogens which cause significant quality and yield losses in tomato crops. The important viruses that infect tomatoes worldwide belong to five genera: Begomovirus, Orthotospovirus, Tobamovirus, Potyvirus, and Crinivirus. Tomato resistance genes against viruses, including Ty gene resistance against begomoviruses, Sw gene resistance against orthotospoviruses, Tm gene resistance against tobamoviruses, and Pot 1 gene resistance against potyviruses, have been identified from wild germplasm and introduced into cultivated cultivars via hybrid breeding. However, these resistance genes mainly exhibit qualitative resistance mediated by single genes, which cannot protect against virus mutations, recombination, mixed-infection, or emerging viruses, thus posing a great challenge to tomato antiviral breeding. Based on the epidemic characteristics of tomato viruses, we propose that future studies on tomato virus resistance breeding should focus on rapidly, safely, and efficiently creating broad-spectrum germplasm materials resistant to multiple viruses. Accordingly, we summarized and analyzed the advantages and characteristics of the three tomato antiviral breeding strategies, including marker-assisted selection (MAS)-based hybrid breeding, RNA interference (RNAi)-based transgenic breeding, and CRISPR/Cas-based gene editing. Finally, we highlighted the challenges and provided suggestions for improving tomato antiviral breeding in the future using the three breeding strategies.

Breaking Boundaries: The Perpetual Interplay Between Tobamoviruses and Plant Immunity

Plant viruses of the genus Tobamovirus cause significant economic losses in various crops. The emergence of new tobamoviruses such as the tomato brown rugose fruit virus (ToBRFV) poses a major threat to global agriculture. Upon infection, plants mount a complex immune response to restrict virus replication and spread, involving a multilayered defense system that includes defense hormones, RNA silencing, and immune receptors. To counter these defenses, tobamoviruses have evolved various strategies to evade or suppress the different immune pathways. Understanding the interactions between tobamoviruses and the plant immune pathways is crucial for the development of effective control measures and genetic resistance to these viruses. In this review, we discuss past and current knowledge of the intricate relationship between tobamoviruses and host immunity. We use this knowledge to understand the emergence of ToBRFV and discuss potential approaches for the development of new resistance strategies to cope with emerging tobamoviruses.

Tomato Brown Rugose Fruit Virus Pandemic

Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus. It was first reported in 2015 in Jordan in greenhouse tomatoes and now threatens tomato and pepper crops around the world. ToBRFV is a stable and highly infectious virus that is easily transmitted by mechanical means and via seeds, which enables it to spread locally and over long distances. The ability of ToBRFV to infect tomato plants harboring the commonly deployed Tm resistance genes, as well as pepper plants harboring the L resistance alleles under certain conditions, limits the ability to prevent damage from the virus. The fruit production and quality of ToBRFV-infected tomato and pepper plants can be drastically affected, thus significantly impacting their market value. Herein, we review the current information and discuss the latest areas of research on this virus, which include its discovery and distribution, epidemiology, detection, and prevention and control measures, that could help mitigate the ToBRFV disease pandemic.

The Past Is Present: Coevolution of Viruses and Host Resistance Within Geographic Centers of Plant Diversity

Understanding the coevolutionary history of plants, pathogens, and disease resistance is vital for plant pathology. Here, I review Francis O. Holmes's work with tobacco mosaic virus (TMV) framed by the foundational work of Nikolai Vavilov on the geographic centers of origin of plants and crop wild relatives (CWRs) and T. Harper Goodspeed's taxonomy of the genus Nicotiana. Holmes developed a hypothesis that the origin of host resistance to viruses was due to coevolution of both at a geographic center. In the 1950s, Holmes proved that genetic resistance to TMV, especially dominant R-genes, was centered in South America for Nicotiana and other solanaceous plants, including Capsicum, potato, and tomato. One seeming exception was eggplant (Solanum melongena). Not until the acceptance of plate tectonics in the 1960s and recent advances in evolutionary taxonomy did it become evident that northeast Africa was the home of eggplant CWRs, far from Holmes's geographic center for TMV-R-gene coevolution. Unbeknownst to most plant pathologists, Holmes's ideas predated those of H.H. Flor, including experimental proof of the gene-for-gene interaction, identification of R-genes, and deployment of dominant host genes to protect crop plants from virus-associated yield losses.

Tobamoviruses Show Broad Host Ranges and Little Genetic Diversity Among Four Habitat Types of a Heterogeneous Ecosystem

Host ranges of plant viruses are poorly known, as studies have focused on pathogenic viruses in crops and adjacent wild plants. High-throughput sequencing (HTS) avoids the bias toward plant-virus interactions that result in disease. Here we study the host ranges of tobamoviruses, important pathogens of crops, using HTS analyses of an extensive sample of plant communities in four habitats of a heterogeneous ecosystem. Sequences of 17 virus operational taxonomic units (OTUs) matched references in the Tobamovirus genus, eight had narrow host ranges, and five had wide host ranges. Regardless of host range, the OTU hosts belonged to taxonomically distant families, suggesting no phylogenetic constraints in host use associated with virus adaptation, and that tobamoviruses may be host generalists. The OTUs identified as tobacco mild green mosaic virus (TMGMV), tobacco mosaic virus (TMV), pepper mild mottle virus, and Youcai mosaic virus had the largest realized host ranges that occurred across habitats and exhibited host use unrelated to the degree of human intervention. This result is at odds with assumptions that contact-transmitted viruses would be more abundant in crops than in wild plant communities and could be explained by effective seed-, contact-, or pollinator-mediated transmission or by survival in the soil. TMGMV and TMV had low genetic diversity that was not structured according to habitat or host plant taxonomy, which indicated that phenotypic plasticity allows virus genotypes to infect new hosts with no need for adaptive evolution. Our results underscore the relevance of ecological factors in host range evolution, in addition to the more often studied genetic factors. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Advances in detecting fruit aroma compounds by combining chromatography and spectrometry

Fruit aroma is produced by volatile compounds, which can significantly enhance fruit flavor. These compounds are highly complex and have remarkable pharmacological effects. The synthesis, concentration, type, and quantity of fruit aroma substances are affected by various factors, both abiotic and biotic. To fully understand the aroma substances of various fruits and their influencing factors, detection technology can be used. Many methods exist for detecting aroma compounds, and approaches combining multiple instruments are widely used. This review describes and compares each detection technology and discusses the potential use of combined technologies to provide a comprehensive understanding of fruit aroma compounds and the factors influencing their synthesis. These results can inform the development and utilization of fruit aroma substances. © 2023 Society of Chemical Industry.

Activation of Tm-22 resistance is mediated by a conserved cysteine essential for tobacco mosaic virus movement

The tomato Tm-22 gene was considered to be one of the most durable resistance genes in agriculture, protecting against viruses of the Tobamovirus genus, such as tomato mosaic virus (ToMV) and tobacco mosaic virus (TMV). However, an emerging tobamovirus, tomato brown rugose fruit virus (ToBRFV), has overcome Tm-22 , damaging tomato production worldwide. Tm-22 encodes a nucleotide-binding leucine-rich repeat (NLR) class immune receptor that recognizes its effector, the tobamovirus movement protein (MP). Previously, we found that ToBRFV MP (MPToBRFV ) enabled the virus to overcome Tm-22 -mediated resistance. Yet, it was unknown how Tm-22 remained durable against other tobamoviruses, such as TMV and ToMV, for over 60 years. Here, we show that a conserved cysteine (C68) in the MP of TMV (MPTMV ) plays a dual role in Tm-22 activation and viral movement. Substitution of MPToBRFV amino acid H67 with the corresponding amino acid in MPTMV (C68) activated Tm-22 -mediated resistance. However, replacement of C68 in TMV and ToMV disabled the infectivity of both viruses. Phylogenetic and structural prediction analysis revealed that C68 is conserved among all Solanaceae-infecting tobamoviruses except ToBRFV and localizes to a predicted jelly-roll fold common to various MPs. Cell-to-cell and subcellular movement analysis showed that C68 is required for the movement of TMV by regulating the MP interaction with the endoplasmic reticulum and targeting it to plasmodesmata. The dual role of C68 in viral movement and Tm-22 immune activation could explain how TMV was unable to overcome this resistance for such a long period.

What Can Be Learned by a Synoptic Review of Plant Disease Epidemics and Outbreaks Published in 2021?

A synoptic review of plant disease epidemics and outbreaks was made using two complementary approaches. The first approach involved reviewing scientific literature published in 2021, in which quantitative data related to new plant disease epidemics or outbreaks were obtained via surveys or similar methodologies. The second approach involved retrieving new records added in 2021 to the CABI Distribution Database, which contains over a million global geographic records of organisms from over 50,000 species. The literature review retrieved 186 articles, describing studies in 62 categories (pathogen species/species complexes) across more than 40 host species on six continents. Pathogen species with more than five articles were Bursaphelenchus xylophilus, 'Candidatus Liberibacter asiaticus', cassava mosaic viruses, citrus tristeza virus, Erwinia amylovora, Fusarium spp. complexes, F. oxysporum f. sp. cubense, Magnaporthe oryzae, maize lethal necrosis co-infecting viruses, Meloidogyne spp. complexes, Pseudomonas syringae pvs., Puccinia striiformis f. sp. tritici, Xylella fastidiosa, and Zymoseptoria tritici. Automated searches of the CABI Distribution Database identified 617 distribution records new in 2021 of 283 plant pathogens. A further manual review of these records confirmed 15 pathogens reported in new locations: apple hammerhead viroid, apple rubbery wood viruses, Aphelenchoides besseyi, Biscogniauxia mediterranea, 'Ca. Liberibacter asiaticus', citrus tristeza virus, Colletotrichum siamense, cucurbit chlorotic yellows virus, Erwinia rhapontici, Erysiphe corylacearum, F. oxysporum f. sp. cubense Tropical race 4, Globodera rostochiensis, Nothophoma quercina, potato spindle tuber viroid, and tomato brown rugose fruit virus. Of these, four pathogens had at least 25% of all records reported in 2021. We assessed two of these pathogens-tomato brown rugose fruit virus and cucurbit chlorotic yellows virus-to be actively emerging in/spreading to new locations. Although three important pathogens-'Ca. Liberibacter asiaticus', citrus tristeza virus, and F. oxysporum f. sp. cubense-were represented in the results of both our literature review and our interrogation of the CABI Distribution Database, in general, our dual approaches revealed distinct sets of plant disease outbreaks and new records, with little overlap. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Development of axially chiral urazole scaffolds for antiplant virus applications against potato virus Y

BACKGROUND

Potato virus Y (PVY) was first discovered by Smith in 1931 and is currently ranked as the fifth most significant plant virus. It can cause severe damage to plants from the family Solanaceae, which results in billions of dollars of economic loss worldwide every year. To discover new antiviral drugs, a class of multifunctional urazole derivatives bearing a stereogenic CN axis were synthesized with excellent optical purities for antiviral evaluations against PVY.

RESULTS

The absolute configurations of the axially chiral compounds exhibited obvious distinctions in antiviral bioactivities, with several of these enantio-enriched axially chiral molecules showing excellent anti-PVY activities. In particular, compound (R)-9f exhibited remarkable curative activities against PVY with a 50% maximal effective concentration (EC₅₀ ) of 224.9 μg mL^-1 , which was better than that of ningnanmycin (NNM), which had an EC₅₀ of 234.0 μg mL^-1 . And the EC₅₀ value of the protective activities of compound (R)-9f was 462.2 μg mL^-1 , which was comparable to that of NNM (442.0 μg mL^-1 ). The mechanisms of two enantiomer of the axially chiral compounds 9f were studied by both molecule docking and defensive enzyme activity tests.

CONCLUSION

Mechanistic studies demonstrated that the axially chiral configurations of the compounds played significant roles in the molecule PVY-CP (PVY Coat Protein) interactions and could enhance the activities of the defense enzymes. The (S)-9f showed only one carbon-hydrogen bond and one π-cation interaction between the chiral molecule and the PVY-CP amino acid sites. In contrast, the (R)-enantiomer of 9f exhibited three hydrogen bonding interactions between the carbonyl groups and the PVY-CP active sites of ARG157 and GLN158. The current study provides significant information on the roles that axial chiralities play in plant protection against viruses, which will facilitate the development of novel green pesticides bearing axial chiralities with excellent optical purities. © 2023 Society of Chemical Industry.

Tobamovirus infection aggravates gray mold disease caused by Botrytis cinerea by manipulating the salicylic acid pathway in tomato

Botrytis cinerea is the causative agent of gray mold disease, and infects more than 1400 plant species, including important crop plants. In tomato, B. cinerea causes severe damage in greenhouses and post-harvest storage and transport. Plant viruses of the Tobamovirus genus cause significant damage to various crop species. In recent years, the tobamovirus tomato brown rugose fruit virus (ToBRFV) has significantly affected the global tomato industry. Most studies of plant-microbe interactions focus on the interaction between the plant host and a single pathogen, however, in agricultural or natural environments, plants are routinely exposed to multiple pathogens. Here, we examined how preceding tobamovirus infection affects the response of tomato to subsequent infection by B. cinerea. We found that infection with the tobamoviruses tomato mosaic virus (ToMV) or ToBRFV resulted in increased susceptibility to B. cinerea. Analysis of the immune response of tobamovirus-infected plants revealed hyper-accumulation of endogenous salicylic acid (SA), upregulation of SA-responsive transcripts, and activation of SA-mediated immunity. Deficiency in SA biosynthesis decreased tobamovirus-mediated susceptibility to B. cinerea, while exogenous application of SA enhanced B. cinerea symptoms. These results suggest that tobamovirus-mediated accumulation of SA increases the plants' susceptibility to B. cinerea, and provide evidence for a new risk caused by tobamovirus infection in agriculture.

Tomato brown rugose fruit virus in aqueous environments - survival and significance of water-mediated transmission

Tomato brown rugose fruit virus (ToBRFV) has recently emerged as a major disease of tomatoes and peppers. ToBRFV is a seed- and contact-transmitted virus. In Slovenia, ToBRFV RNA was detected in samples of wastewater, river, and water used to irrigate plants. Even though the source of detected RNA could not be clearly established, this raised the question of the significance of the detection of ToBRFV in water samples and experimental studies were performed to address this question. The data presented here confirm that the release of virus particles from the roots of infected plants is a source of infectious ToBRFV particles in water and that the virus can remain infective up to four weeks in water stored at room temperature, while its RNA can be detected for much longer. These data also indicate that irrigation with ToBRFV-contaminated water can lead to plant infection. In addition, it has been shown that ToBRFV circulated in drain water in commercial tomato greenhouses from other European countries and that an outbreak of ToBRFV can be detected by regular monitoring of drain water. A simple method for concentrating ToBRFV from water samples and a comparison of the sensitivity of different methods, including the determination of the highest ToBRFV dilution still capable of infecting test plants, were also investigated. The results of our studies fill the knowledge gaps in the epidemiology and diagnosis of ToBRFV, by studying the role of water-mediated transmission, and provide a reliable risk assessment to identify critical points for monitoring and control.

Identification and management of tomato brown rugose fruit virus in greenhouses in Mexico

Tomato brown rugose fruit virus (ToBRFV) has become a cause of great concern in the global tomato agro-industry since its first report in Israel in 2014. Global tomato production is affected by ToBRFV, and management practices are being evaluated. We tested seed lots from international producers as well as greenhouse substrates and water wells as possible sources of virus contamination. We identified a second introduction of ToBRFV in Mexico by a strain closely resembling isolates from the Netherlands and the Middle East. ToBRFV was detected by RT-PCR in seed coats and epicotyls (from commercial seeds and seedlings obtained from infected tomato plants), indicating a transmission rate of 9%. Virus-like particles (VLPs) were found in wells used for irrigation in greenhouses, but these exhibited low infectivity. These findings suggest that water sources could serve as ToBRFV reservoirs. We evaluated four chemical and six thermal methods for sanitizing substrates, plasticware, and other greenhouse utensils, using detached leaf bioassays in Nicotiana rugosa. The most effective chemical sanitization method was treatment with glutaraldehyde plus quaternary ammonium salts and pentapotassium salts. The most effective heat treatment was at 92°C for 30 minutes, which inactivated the virus. Tomato producers could implement these sanitization methods to control ToBRFV.

In-depth study of tomato and weed viromes reveals undiscovered plant virus diversity in an agroecosystem

BACKGROUND

In agroecosystems, viruses are well known to influence crop health and some cause phytosanitary and economic problems, but their diversity in non-crop plants and role outside the disease perspective is less known. Extensive virome explorations that include both crop and diverse weed plants are therefore needed to better understand roles of viruses in agroecosystems. Such unbiased exploration is available through viromics, which could generate biological and ecological insights from immense high-throughput sequencing (HTS) data.

RESULTS

Here, we implemented HTS-based viromics to explore viral diversity in tomatoes and weeds in farming areas at a nation-wide scale. We detected 125 viruses, including 79 novel species, wherein 65 were found exclusively in weeds. This spanned 21 higher-level plant virus taxa dominated by Potyviridae, Rhabdoviridae, and Tombusviridae, and four non-plant virus families. We detected viruses of non-plant hosts and viroid-like sequences and demonstrated infectivity of a novel tobamovirus in plants of Solanaceae family. Diversities of predominant tomato viruses were variable, in some cases, comparable to that of global isolates of the same species. We phylogenetically classified novel viruses and showed links between a subgroup of phylogenetically related rhabdoviruses to their taxonomically related host plants. Ten classified viruses detected in tomatoes were also detected in weeds, which might indicate possible role of weeds as their reservoirs and that these viruses could be exchanged between the two compartments.

CONCLUSIONS

We showed that even in relatively well studied agroecosystems, such as tomato farms, a large part of very diverse plant viromes can still be unknown and is mostly present in understudied non-crop plants. The overlapping presence of viruses in tomatoes and weeds implicate possible presence of virus reservoir and possible exchange between the weed and crop compartments, which may influence weed management decisions. The observed variability and widespread presence of predominant tomato viruses and the infectivity of a novel tobamovirus in solanaceous plants, provided foundation for further investigation of virus disease dynamics and their effect on tomato health. The extensive insights we generated from such in-depth agroecosystem virome exploration will be valuable in anticipating possible emergences of plant virus diseases and would serve as baseline for further post-discovery characterization studies. Video Abstract.

A Novel Platform for Root Protection Applies New Root-Coating Technologies to Mitigate Soil-Borne Tomato Brown Rugose Fruit Virus Disease

Tomato brown rugose fruit virus (ToBRFV) is a soil-borne virus showing a low percentage of ca. 3% soil-mediated infection when the soil contains root debris from a previous 30–50 day growth cycle of ToBRFV-infected tomato plants. We designed stringent conditions of soil-mediated ToBRFV infection by increasing the length of the pre-growth cycle to 90–120 days, adding a ToBRFV inoculum as well as truncating seedling roots, which increased seedling susceptibility to ToBRFV infection. These rigorous conditions were employed to challenge the efficiency of four innovative root-coating technologies in mitigating soil-mediated ToBRFV infection while avoiding any phytotoxic effect. We tested four different formulations, which were prepared with or without the addition of various virus disinfectants. We found that under conditions of 100% soil-mediated ToBRFV infection of uncoated positive control plants, root-coating with formulations based on methylcellulose (MC), polyvinyl alcohol (PVA), silica Pickering emulsion and super-absorbent polymer (SAP) that were prepared with the disinfectant chlorinated-trisodium phosphate (Cl-TSP) showed low percentages of soil-mediated ToBRFV infection of 0%, 4.3%, 5.5% and 0%, respectively. These formulations had no adverse effect on plant growth parameters when compared to negative control plants grown under non ToBRFV inoculation conditions.

Nanopore Technology Applied to Targeted Detection of Tomato Brown Rugose Fruit Virus Allows Sequencing of Related Viruses and the Diagnosis of Mixed Infections

Tomato (Solanum lycopersicum) plants from a commercial glasshouse were identified with symptoms compatible with a tomato brown rugose fruit virus (ToBRFV) infection. Reverse transcription-PCR and quantitative PCR confirmed the presence of ToBRFV. Subsequently, the same RNA sample and a second from tomato plants infected with a similar tobamovirus, tomato mottle mosaic virus (ToMMV), were extracted and processed for high-throughput sequencing with the Oxford Nanopore Technology (ONT). For the targeted detection of ToBRFV, the two libraries were synthesized by using six ToBRFV sequence-specific primers in the reverse transcription step. This innovative target enrichment technology enabled deep coverage sequencing of ToBRFV, with 30% of the total reads mapping to the target virus genome and 57% mapping to the host genome. The same set of primers applied to the ToMMV library generated 5% of the total reads mapping to the latter virus, indicating that sequencing of similar, non-target viral sequences was also allowed. Further, the complete genome of pepino mosaic virus (PepMV) was also sequenced from the ToBRFV library, thus suggesting that, even using multiple sequence-specific primers, a low rate of off-target sequencing can usefully provide additional information on unexpected viral species coinfecting the same samples in an individual assay. These results demonstrate that targeted nanopore sequencing can specifically identify viral agents and has sufficient sensitivity towards non-target organisms to provide evidence of mixed virus infections.

Applicability of Different Methods for Quantifying Virucidal Efficacy Using MENNO Florades and Tomato Brown Rugose Fruit Virus as an Example

After entry of a quarantine/regulated pathogen, infected plants shall be destroyed, and the cultivated area (e.g., greenhouse) shall be disinfected. Therefore, the selection of an effective disinfectant plays an important role. With the availability of different methods for virus quantification, we investigated the application of quantitative ELISA (qELISA), RT-qPCR (reverse transcription-quantitative polymerase chain reaction), and bioassays for the quantification of disinfectant efficacy. Therefore, we estimated the titer reduction in tomato brown rugose fruit virus (ToBRFV), a regulated pathogen, in plant sap and on germ carriers after treatment with MENNO Florades 4% for 16 h. The virus load before and after the treatment was measured with the mentioned methods. The RT-qPCR and qELISA methods showed very low efficacy in the presence of the disinfectant. Although bioassays are time-consuming, need purified particles for establishing the quantification models, and are less sensitive than RT-qPCR, they were able to quantify the differences in virus titer in the presence/absence of disinfectant. Interestingly, the bioassays reached at least the lower limit sensitivity of a qELISA. By being less sensitive to the presence of the disinfectant, bioassays proved to be the only technique for the determination of the disinfectant efficacy against ToBRFV on different germ carriers as well as on virus-infected plant sap.

Recent Achievements in Antiviral Agent Development for Plant Protection

Plant virus disease is the second most prevalent plant diseases and can cause extensive loss in global agricultural economy. Extensive work has been carried out on the development of novel antiplant virus agents for preventing and treating plant virus diseases. In this review, we summarize the achievements of the research and development of new antiviral agents in the recent five years and provide our own perspective on the future development in this highly active research field.

Tomato brown rugose fruit virus Mo gene is a novel microbial source tracking marker

Microbial source tracking (MST) identifies sources of fecal contamination in the environment using fecal host-associated markers. While there are numerous bacterial MST markers, there are few viral markers. Here we design and test novel viral MST markers based on tomato brown rugose fruit virus (ToBRFV) genomes. We assembled eight nearly complete genomes of ToBRFV from wastewater and stool samples from the San Francisco Bay Area in the United States of America. Next, we developed two novel probe-based RT-PCR assays based on conserved regions of the ToBRFV genome, and tested the markers’ sensitivities and specificities using human and non-human animal stool as well as wastewater. TheToBRFV markers are sensitive and specific; in human stool and wastewater, they are more prevalent and abundant than a currently used marker, the pepper mild mottle virus (PMMoV) coat protein (CP) gene. We applied the assays to detect fecal contamination in urban stormwater samples and found that the ToBRFV markers matched cross-assembly phage (crAssphage), an established viral MST marker, in prevalence across samples. Taken together, ToBRFV is a promising viral human-associated MST marker.

Importance

Human exposure to fecal contamination in the environment can cause transmission of infectious diseases. Microbial source tracking (MST) can identify sources of fecal contamination so that contamination can be remediated and human exposures can be reduced. MST requires the use of fecal host-associated MST markers. Here we design and test novel MST markers from genomes of tomato brown rugose fruit virus (ToBRFV). The markers are sensitive and specific to human stool, and highly abundant in human stool and wastewater samples.

Comparison of Models for Quantification of Tomato Brown Rugose Fruit Virus Based on a Bioassay Using a Local Lesion Host

Considering the availability of serological and molecular biological methods, the bioassay has been paled into insignificance, although it is the only experimental method that can be used to demonstrate the infectivity of a virus. We compared goodness-of-fit and predictability power of five models for the quantification of tomato brown rugose fruit virus (ToBRFV) based on local lesion assays: the Kleczkowski model, Furumoto and Mickey models I and II, the Gokhale and Bald model (growth curve model), and the modified Poisson model. For this purpose, mechanical inoculations onto Nicotiana tabacum L. cv. Xanthi nc and N. glutionosa L. with defined virus concentrations were first performed with half-leaf randomization in a Latin square design. Subsequently, models were implemented using Python software and fitted to the number of local lesions. All models could fit to the data for quantifying ToBRFV based on local lesions, among which the modified Poisson model had the best prediction of virus concentration in spike samples based on local lesions, although data of individual indicator plants showed variations. More accurate modeling was obtained from the test plant N. glutinosa than from N. tabacum cv. Xanthi nc. The position of the half-leaves on the test plants had no significant effect on the number of local lesions.

Optimal reduced-mixing for an SIS infectious-disease model

Which reduced-mixing strategy maximizes economic output during a disease outbreak? To answer this question, we formulate an optimal-control problem that maximizes the difference between revenue, due to healthy individuals, and medical costs, associated with infective individuals, for SIS disease dynamics. The control variable is the level of mixing in the population, which influences both revenue and the spread of the disease. Using Pontryagin's maximum principle, we find a closed-form solution for our problem. We explore an example of our problem with parameters for the transmission of Staphylococcus aureus in dairy cows, and we perform sensitivity analyses to determine how model parameters affect optimal strategies. We find that less mixing is preferable when the transmission rate is high, the per-capita recovery rate is low, or when the revenue parameter is much smaller than the cost parameter.

Insight into Population Structure and Evolutionary Analysis of the Emerging Tomato Brown Rugose Fruit Virus

A total of 112 symptomatic tomatoes (Solanum lycopersicum L.) and 83 symptomatic pepper (Capsicum spp.) samples were collected in Ankara, Eskişehir, Bartın, and Zonguldak provinces of Turkey during 2020-2021. Six tomatoes and one pepper sample (3.6%) tested positive for tomato brown rugose fruit virus (ToBRFV, genus Tobamovirus) infection by DAS-ELISA and RT-PCR. ToBRFV-positive tomato and pepper plants were removed from greenhouses as soon as possible, and the greenhouses and tools were disinfected completely. Phylogenetic analysis on the complete CP sequences suggested the clustering of 178 GenBank isolates and 7 novel isolates into three groups. A study using DnaSP software showed very low genetic variation among current global ToBRFV isolates. All four ORFs of the virus genome were under strong negative evolutionary constraints, with a ω value range of 0.0869-0.2066. However, three neutrality tests indicated that most populations of the newly identified ToBRFV are currently expanding by assigning statistically significant negative values to them. The very low F_ST values (0.25 or less) obtained by all comparisons of the isolates from Europe, the Middle East, China, and America concluded that there is no clear genetic separation among currently known isolates from different geographic origins. The divergence time of ToBRFV was estimated to be in the middle of the course of the evolution of 11 tested tobamoviruses. The time to the most recent common ancestors (TMRCAs) of ToBRFV were calculated to be 0.8 and 1.87 with the genetically closest members of Tobamovirus. The results of this study could improve our understanding on the population structure of the emerging ToBRFV.

Occurrence and Distribution of Tomato Brown Rugose Fruit Virus Infecting Tomato Crop in Saudi Arabia

During the growing season of 2021-2022, a total of 145 symptomatic tomato leaf and fruit samples were collected from different locations in Riyadh Region, Saudi Arabia, showing a moderate-to-severe mosaic with dark green wrinkling, blistering, narrowing, and deformation with necrosis spot on tomato leaves, while irregular brown necrotic lesions, deformation, and yellowing spots rendering the fruits non-marketable were observed on tomato fruits. These samples were tested serologically against important tomato viruses using enzyme-linked immunosorbent assay (ELISA), and the obtained results showed that 52.4% of symptomatic tomato samples were found positive for Tomato brown rugose fruit virus (ToBRFV), wherein 12 out of 76 samples were singly infected; however, 64 out of 145 had mixed infection. A sample with a single infection of ToBRFV was used for mechanical inoculation into a range of different host plants; symptoms were observed weekly, and the presence of the ToBRFV was confirmed by ELISA and reverse transcription-polymerase chain reaction (RT-PCR). A total RNA was extracted from selected ELISA-positive samples, and RT-PCR was carried out using specific primers F-3666 and R-4718, which amplified a fragment of 1052 bp. RT-PCR products were sequenced in both directions, and partial genome nucleotide sequences were submitted to GenBank under the following accession numbers: MZ130501, MZ130502, and MZ130503. BLAST analysis of Saudi isolates of ToBRFV showed that the sequence shared nucleotide identities (99-99.5%) among them and 99-100% identity with ToBRFV isolates in different countries. A ToBRFV isolate (MZ130503) was selected for mechanical inoculation and to evaluate symptom severity responses of 13 commonly grown tomato cultivars in Saudi Arabia. All of the tomato cultivars showed a wide range of symptoms. The disease severity index of the tested cultivars ranged between 52% and 96%. The importance ToBRFV disease severity and its expanding host range due to its resistance breaking ability was discussed.

N and N'-mediated recognition confers resistance to tomato brown rugose fruit virus

Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus that overcomes the Tm-2 ² resistance gene used in commercial tomato plants to protect against tobamoviruses. In this article, we show that ToBRFV is recognised through its P50 replicase fragment by the resistance gene N in N. tabacum , which triggers a hypersensitive response (HR). We also demonstrate that the N' gene provides protection against ToBRFV through recognition of the viral coat protein without triggering a typical HR in N. tabacum .

Pepper Plants Harboring L Resistance Alleles Showed Tolerance toward Manifestations of Tomato Brown Rugose Fruit Virus Disease

The tobamovirus tomato brown rugose fruit virus (ToBRFV) infects tomato plants harboring the Tm-2² resistance allele, which corresponds with tobamoviruses’ avirulence (Avr) gene encoding the movement protein to activate a resistance-associated hypersensitive response (HR). ToBRFV has caused severe damage to tomato crops worldwide. Unlike tomato plants, pepper plants harboring the L resistance alleles, which correspond with the tobamovirus Avr gene encoding the coat protein, have shown HR manifestations upon ToBRFV infection. We have found that ToBRFV inoculation of a wide range of undefined pepper plant varieties could cause a “hypersensitive-like cell death” response, which was associated with ToBRFV transient systemic infection dissociated from disease symptom manifestations on fruits. Susceptibility of pepper plants harboring L¹, L³, or L⁴ resistance alleles to ToBRFV infection following HRs was similarly transient and dissociated from disease symptom manifestations on fruits. Interestingly, ToBRFV stable infection of a pepper cultivar not harboring the L gene was also not associated with disease symptoms on fruits, although ToBRFV was localized in the seed epidermis, parenchyma, and endothelium, which borders the endosperm, indicating that a stable infection of maternal origin of these tissues occurred. Pepper plants with systemic ToBRFV infection could constitute an inoculum source for adjacently grown tomato plants.

New Weed Hosts for Tomato Brown Rugose Fruit Virus in Wild Mediterranean Vegetation

Tomato brown rugose fruit virus (ToBRFV; genus, Tobamovirus, family, Virgaviridae) was first reported in 2015 infecting tomatoes grown under protected cropping in the Jordan Valley. Since then, ToBRFV has been detected in tomatoes grown in both protected and open fields across Jordan. The increased incidence of ToBRFV prompted this investigation of the potential role of natural weed hosts in the dissemination of ToBRFV. A survey was conducted in the Jordan Valley and highlands to determine possible reservoir hosts of ToBRFV in fields and greenhouse complexes in which tomatoes were grown. Detection of ToBRFV infection was made by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and further confirmation by reverse-transcription polymerase chain reaction (RT-PCR), followed by DNA cloning and sequencing, and bioassays. Thirty weed species belonging to twenty-six genera from sixteen families were tested. Twelve species belonging to eight families were infected of which ten species are newly reported hosts for ToBRFV. Seed transmission of ToBRFV in Solanum nigrum was confirmed in a grow-out experiment. To our knowledge, this is the first report of the natural occurrence of ToBRFV on weed hosts. Identification of natural reservoirs of ToBRFV can help to develop management practices focused on weed plant species to prevent ToBRFV transmission. The extent to which ToBRFV survives in diverse alternate weed host species outside tomato growing seasons in different world regions requires further research in order to establish the risk associated with the possible contribution of weeds as a reservoir for primary infections in tomato crops.

Viruses of Economic Impact on Tomato Crops in Mexico: From Diagnosis to Management-A Review

Tomato is the most economically important vegetable crop worldwide and the second most important for Mexico. However, viral diseases are among the main limiting factors that affect the productivity of this crop, causing total losses in some cases. This review provides key information and findings on the symptoms, distribution, transmission, detection, and management of diseases caused by viruses of major importance in tomato crops in Mexico. Currently, about 25 viruses belonging to nine different families have been reported infecting tomato in Mexico, but not all of them cause economically significant diseases. Viruses of economic importance include tomato brown rugose fruit virus (ToBRFV), tomato spotted wilt virus (TSWV), tomato yellow leaf curl virus (TYLCV), pepino mosaic virus (PepMV), and tomato marchitez virus (ToMarV). The topics discussed here will provide updated information about the status of these plant viruses in Mexico as well as diverse management strategies that can be implemented according to the specific circumstances of each viral pathosystem. Additionally, a list of tomato-affecting viruses not present in Mexico that are continuous threats to the crop health is included.