Global status of tospovirus epidemics in diverse cropping systems: Successes achieved and challenges ahead

Bacillus endophytes for sustainable management of tomato spotted wilt virus and yield production

BACKGROUND

Tomato-spotted wilt virus (TSWV) from the Tospovirus genus affects over 1000 plant species, including key crops, and traditional control methods often prove inadequate. This study investigates the effectiveness of Bacillus amyloliquefaciens and Bacillus subtilis in reducing TSWV infection, enhancing plant growth, and strengthening defense in Nicotiana benthamiana. The aim is to assess Bacillus as a sustainable biocontrol alternative, offering an eco-friendly solution for managing TSWV disease in agriculture.

RESULTS

Here, we report the efficacy of five Bacillus isolates (out of 15 tested) - B. amyloliquefaciens (DJB5, YN48, YN28, Mg6) and B. subtilis L1-21 - significantly reducing TSWV copies per gram in N. benthamiana leaves, using a half-leaf assay. In glasshouse trials, isolates DJB5, YN48, and Mg6 decreased TSWV copies per gram by 75.7%, 83.6%, and 88.2%, with biocontrol efficacy rates of 91.2%, 94.1%, and 95.7% respectively. All the isolates consistently mitigated the symptoms of TSWV, reduced the disease severity, and area under the disease progress curve (AUDPC) at 21 days post-inoculation. Additionally, these isolates enhanced plant growth parameters, including shoot and root length, leaf number, area, and biomass. The application of endophytes in the infected plants activated antioxidant defense enzymes by elevating the activities of polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), and chitinase. However, defense-related enzymes, such as malondialdehyde (MDA), catalase (CAT), phenylalanine ammonia-lyase (PAL), total phenol, and β-1,3-glucanase decreased as TSWV infection reduced in the leaves.

CONCLUSION

Our findings indicate that B. amyloliquefaciens isolates, DJB5, YN48, and Mg6, effectively manage TSWV by activating plant defense, reducing virus load, reducing TSWV symptoms, and promoting plant growth. © 2024 Society of Chemical Industry.

Induction of innate immunity and plant growth promotion in tomato unveils the antiviral nature of bacterial endophytes against groundnut bud necrosis virus

Tomato is an important crop worldwide, but groundnut bud necrosis virus (GBNV) often hampers its growth. This study investigates the antiviral potential of bacterial endophytes, including Brucella melitensis CNEB54, Bacillus licheniformis CNEB4, Bacillus velezensis CNEB26, and Bacillus vallismortis BAVE5 against GBNV, as well as their ability to enhance immunity and growth in tomato. All four bacterial isolates demonstrated a significant delay in GBNV symptom development 10 days post-inoculation, with disease incidence ranging from 18% to 36% compared to 84% in control. DAC-ELISA results indicated a noteworthy reduction in virus titer (0.32-0.96 OD) in treated tomato plants versus the control (3.26 OD). In addition, qPCR analysis revealed decreased viral copy numbers in plants treated with bacterial endophytes (1.3-3.1 × 105) as against in untreated inoculated control (2.4 × 106). Furthermore, these endophytes upregulated the expression of defense-associated genes, such as MAPKK1, PAL, PPO, LOX1, JAR1, and PDF 1.2. Field experiments with the application of B. melitensis and B. velezensis exhibited improved growth, with an average plant height of 123.70 cm, 14.87 flowers per plant, and a fruit weight of 549.3 g per plant, with a disease incidence of 18.1%. In comparison, the untreated control plants only reached a height of 104.73 cm, produced 11.17 flowers per plant, and yielded 267 g of fruit per plant, with a disease incidence of 30.1%. These findings strongly support the use of bacterial endophytes to reduce disease incidence and severity, enhance plant immunity and promote plant growth, resulting in overall crop productivity in sustainable agriculture.IMPORTANCEThe infection of GBNV in crops such as tomatoes, peanuts, and pulses leads to significant yield loss. Applying insecticides to control vector populations, can limit the spread of viruses carried by these vectors. The present study envisages a novel strategy to combat GBNV, with the help of bacterial endophytes. These bacterial endophytes have tremendously reduced the symptom expression of GBNV, induced the expression of defense genes during the tri-trophic interaction and promoted plant growth in tomatoes under field conditions. Hence, these bacteria are identified to be involved in immunity boosting, viral suppression and growth promotion.

Visualizing Tomato Spotted Wilt Virus Protein Localization: Cross-Kingdom Comparisons of Protein-Protein Interactions

Tomato spotted wilt virus (TSWV) is an orthotospovirus that infects both plants and insect vectors, and understanding its protein localization and interactions is crucial for unraveling the infection cycle and host-virus interactions. We investigated and compared the localization of TSWV proteins. The localization between plant and insect cells was overall consistent, indicating a similar mechanism is utilized by the virus in both types of cells. However, a change in localization over time was associated with the viral proteins that did not contain signal peptides and transmembrane domains such as N, NSs, and NSm, which only occurred in the plant cells and not in the insect cells. We also tested the localization of the proteins during an active plant infection using free red fluorescent protein (RFP) as a marker to highlight the nucleus and cytoplasm. Voids in the cytoplasm were shown only during infection, and N, NSs, NSm, and to a lesser extent GN and GC were surrounding these areas, suggesting it may be a site of replication or morphogenesis. Furthermore, we tested the interactions of viral proteins using both bimolecular fluorescence complementation (BiFC) and membrane-based yeast two-hybrid (MbY2H) assays. These revealed self-interactions of NSm, N, GN, GC, and NSs. We also identified interactions between different TSWV proteins, indicating their possible roles, such as between NSs and GC and N and GC, which may be necessary during the replication and assembly processes, respectively. This research expands our knowledge of TSWV infection and elaborates on the intricate relationships between viral proteins, cellular dynamics, and host responses. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Resistance-breaking strains of tomato spotted wilt virus hamper photosynthesis and protein synthesis pathways in a virus accumulation-dependent manner in Sw5-carrying tomatoes

Tomato spotted wilt virus (TSWV; Orthotospovirus tomatomaculae) is one of the major horticultural threats due to its worldwide distribution and broad host range. In Italy, TSWV is widely spread in tomato (Solanum lycopersicum) crops and causes severe yield losses. In the last decades, several tomato varieties carrying the Sw-5b gene for resistance to TSWV have been released. We investigated the interaction between Sw-5b-carrying tomatoes and Sw5-Resistance-Breaking (SRB) TSWV to elucidate the molecular mechanisms underlying resistance breakage. Transcriptome sequencing (RNA-Seq) was used to analyze 18 tomato leaf samples collected from a field crop naturally infected by SRB TSWV in Italy. An increase in virus accumulation level in leaf tissues (titer) resulted in a higher number of differentially expressed genes (DEGs), ranging from 33 to 44% of the whole transcriptome, when the samples with the lowest and the highest virus titer were compared to the asymptomatic sample, respectively. Photosynthesis and protein biosynthesis were the main down-regulated biological processes, while enzyme families such as oxidoreductases and transferases, genes related to the response to biotic stimuli, solute transport, and vesicle trafficking were overall up-regulated. Remarkably, the expression of around 45% of genes (ca. 14000) of the whole transcriptome was significantly (P < 0.05) correlated (positively or negatively) to the virus titer, and in 6% of cases (about 2000 genes) the correlation was high (i.e., absolute value of R2 > 0.85). This phenomenon was also verified on 15 genes by a quantitative reverse transcription PCR assay on a greenhouse experiment with a different Sw-5b-tomato variety artificially inoculated with another SRB TSWV strain. In conclusion, the tomato transcriptome was considerably rearranged upon TSWV infection, with deregulation of photosynthesis, protein biosynthesis, and induction of defense pathways. Finally, this research demonstrated that the magnitude of transcriptional changes was proportional to the virus accumulation level in the leaves.

Structural and Functional Analysis of Groundnut bud necrosis virus (GBNV) Using Computational and Biochemical Approaches

Groundnut bud necrosis virus (GBNV) belonging to the genus Orthotospovirus is transmitted by its vector Thrips palmi. It is a tri-segmented RNA virus that consists of L, M, and S RNA segments. We analysed the secondary structure features of GBNV proteins through various software and predicted the transmembrane helix, glycosylation, and signal peptidase sites within the GBNV protein sequences (GN, GC, N, NSm, and NSs). In glycoprotein sequence, extended strands are predominant (52.87%) whereas the N protein sequence mostly contains alpha helices (47.46%). The random coils are present in movement protein (43.97%) and structural protein (39.41%). We generated the 3D structure of GN and N protein using SWISS MODEL software and quality is validated through PROCHECK and PDBsum software. We also expressed the GBNV proteins (GN, GC, N, NSm, and NSs) in bacterial expression system. The recombinant proteins were used to raise polyclonal antibodies in mice. Our study will be useful in understanding GBNV protein structures in further detail by analysing the important domains that interact with the thrips proteins. This will further aid us in understanding virus-vector relationship through the application of protein-protein interaction and other immunodiagnostic techniques.

N Protein of Tomato Spotted Wilt Virus Proven to Be Antagonistic Against Tomato Yellow Leaf Curl Virus in Nicotiana benthamiana

Two phylogenetically unrelated viruses transmitted by different insect vectors, tomato spotted wilt virus (TSWV) and tomato yellow leaf curl virus (TYLCV), are major threats to tomato and other vegetable production. Although co-infections of TSWV and TYLCV on the same host plant have been reported on numerous occasions, there is still lack of research attempting to elucidate the mechanisms underlying the relationship between two viruses when they coexist in the same tomato or other plants. After assessing the effect of four TSWV-coded proteins on suppressing TYLCV in TSWV N transgenic Nicotiana benthamiana seedlings, the TSWV N protein proved to be effective in reducing TYLCV quantity and viral symptoms. Western blot analysis indicated that TSWV N was involved in down-regulating the expression level of the V1, C3, and C4 proteins of TYLCV, among which V1 was the most significantly suppressed one. Moreover, TSWV N was confirmed to reduce TYLCV V1 within both nucleus and cytoplasm, but a greater suppression was observed in cytoplasm. The co-immunoprecipitation and mass spectrometry identified 244 differential proteins from the TYLCV-infected TSWV N transgenic N. benthamiana seedling. These proteins pertaining to energy metabolism pathways were enriched, suggesting that TSWV N could inhibit TYLCV through competing for energy or regulating energy-related metabolism. The evidence presented here offers a novel perspective that will facilitate a comprehensive understanding of virus-virus and virus-host interactions, as well as a potential strategy for plant virus control through using TSWV N in the near future.

Integrated Biological Experiments and Proteomic Analyses of Nicotiana tabacum Xylem Sap Revealed the Host Response to Tomato Spotted Wilt Orthotospovirus Infection

The plant vascular system is not only a transportation system for delivering nutrients but also a highway transport network for spreading viruses. Tomato spotted wilt orthotospovirus (TSWV) is among the most destructive viruses that cause serious losses in economically important crops worldwide. However, there is minimal information about the long-distance movements of TSWV in the host plant vascular system. In this this study, we confirm that TSWV virions are present in the xylem as observed by transmission electron microscopy (TEM). Further, a quantitative proteomic analysis based on label-free methods was conducted to reveal the uniqueness of protein expression in xylem sap during TSWV infection. Thus, this study identified and quantified 3305 proteins in two groups. Furthermore, TSWV infection induced three viral structural proteins, N, Gn and Gc, and 315 host proteins differentially expressed in xylem (163 up-regulated and 152 down-regulated). GO enrichment analysis showed up-regulated proteins significantly enriched in homeostasis, wounding, defense response, and DNA integration terms, while down-regulated proteins significantly enriched in cell wall biogenesis/xyloglucan metabolic process-related terms. KEGG enrichment analysis showed that the differentially expressed proteins (DEPs) were most strongly associated with plant-pathogen interaction, MAPK signaling pathway, and plant hormone signal transduction. Cluster analysis of DEPs function showed the DEPs can be categorized into cell wall metabolism-related proteins, antioxidant proteins, PCD-related proteins, host defense proteins such as receptor-like kinases (RLKs), salicylic acid binding protein (SABP), pathogenesis related proteins (PR), DNA methylation, and proteinase inhibitor (PI). Finally, parallel reaction monitoring (PRM) validated 20 DEPs, demonstrating that the protein abundances were consistent between label-free and PRM data. Finally, 11 genes were selected for RT-qPCR validation of the DEPs and label-free-based proteomic analysis concordant results. Our results contribute to existing knowledge on the complexity of host plant xylem system response to virus infection and provide a basis for further study of the mechanism underlying TSWV long-distance movement in host plant vascular system.

Rapid detection of Impatiens necrotic spot virus from thrips vectors using reverse transcription-recombinase polymerase amplification

The plant virus, Impatiens necrotic spot virus (INSV), is an economically important pathogen of vegetables, fruits, and ornamental crops. INSV is vectored by the western flower thrips, Frankliniella occidentalis, a small insect pest that is globally distributed. In recent years, INSV outbreaks have reached epidemic levels in the Salinas Valley of California-an agriculturally rich region where most of the lettuce (Lactuca sativa) is produced in the United States. Due to the obligate nature in which virus transmission occurs, new tools that could rapidly detect INSV from thrips vectors would enhance our ability to predict where virus outbreaks may occur. Here, we report on the development of a reverse transcription-recombinase polymerase amplification (RT-RPA) assay that can detect INSV from individual thrips. The assay uses crude extraction methods, is performed at a single temperature of 42 °C, can be completed in 25 min, and provides sensitivity levels that are comparable to other available detection methods. When the assay was used on field populations of thrips, INSV was successfully identified and quantified from individual larvae and adults. The work provides a new cost-effective surveillance tool that can rapidly detect INSV from its insect vector and from plants.

Tomato Spotted Wilt Virus Suppresses the Antiviral Response of the Insect Vector, Frankliniella occidentalis, by Elevating an Immunosuppressive C18 Oxylipin Level Using Its Virulent Factor, NSs

Orthotospovirus tomatomaculae (tomato spotted wilt virus, TSWV) is transmitted by the western flower thrips, Frankliniella occidentalis. Epoxyoctadecamonoenoic acids (EpOMEs) function as immune-suppressive factors, particularly in insects infected by viral pathogens. These oxylipins are produced by cytochrome P450 monooxygenases (CYPs) and are degraded by soluble epoxide hydrolase (sEH). In this study, we tested the hypothesis that TSWV modulates the EpOME level in the thrips to suppress antiviral responses and enhance its replication. TSWV infection significantly elevated both 9,10-EpOME and 12,13-EpOME levels. Following TSWV infection, the larvae displayed apoptosis in the midgut along with the upregulated expression of four caspase genes. However, the addition of EpOME to the viral treatment notably reduced apoptosis and downregulated caspase gene expressions, which led to a marked increase in TSWV titers. The CYP and sEH genes of F. occidentalis were identified, and their expression manipulation using RNA interference (RNAi) treatments led to significant alternations in the insect's immune responses and TSWV viral titers. To ascertain which viral factor influences the host EpOME levels, specialized RNAi treatments targeting genes encoded by TSWV were administered to larvae infected with TSWV. These treatments demonstrated that NSS expression is pivotal in manipulating the genes involved in EpOME metabolism. These results indicate that NSs of TSWV are crucially linked with the elevation of host insect EpOME levels and play a key role in suppressing the antiviral responses of F. occidentalis.

Different viral effectors hijack TCP17, a key transcription factor for host Auxin synthesis, to promote viral infection

Auxin is an important class of plant hormones that play an important role in plant growth development, biotic stress response, and viruses often suppress host plant auxin levels to promote infection. However, previous research on auxin-mediated disease resistance has focused mainly on signaling pathway, and the molecular mechanisms of how pathogenic proteins manipulate the biosynthetic pathway of auxin remain poorly understood. TCP is a class of plant-specific transcription factors, of which TCP17 is a member that binds to the promoter of YUCCAs, a key rate-limiting enzyme for auxin synthesis, and promotes the expression of YUCCAs, which is involved in auxin synthesis in plants. In this study, we reported that Tomato spotted wilt virus (TSWV) infection suppressed the expression of YUCCAs through its interaction with TCP17. Further studies revealed that the NSs protein encoded by TSWV disrupts the dimerization of TCP17, thereby inhibit its transcriptional activation ability and reducing the auxin content in plants. Consequently, this interference inhibits the auxin response signal and promotes the TSWV infection. Transgenic plants overexpressing TCP17 exhibit resistance against TSWV infection, whereas plants knocking out TCP17 were more susceptible to TSWV infection. Additionally, proteins encoded by other RNA viruses (BSMV, RSV and TBSV) can also interact with TCP17 and interfere with its dimerization. Notably, overexpression of TCP17 enhanced resistance against BSMV. This suggests that TCP17 plays a crucial role in plant defense against different types of plant viruses that use viral proteins to target this key component of auxin synthesis and promote infection.

An all-out assault on a dominant resistance gene: Local emergence, establishment, and spread of strains of tomato spotted wilt orthotospovirus (TSWV) that overcome Sw-5b-mediated resistance in fresh market and processing tomatoes in California

Tomato spotted wilt orthotospovirus (TSWV) causes substantial economic loss to tomato production, and the Sw-5b resistance gene is widely deployed for management. Here, we show (i) the emergence of resistance-breaking (RB) TSWV strains in processing and fresh market tomato production in California over the past ten years, and (ii) evolutionary relationships with RB strains from other areas. A specific RT-PCR test was used to show the C118Y RB strain that emerged in Fresno County in 2016 quickly became predominant in the central production area and remained so through this study. In 2021, the C118Y strain was detected in the Northern production area, and was predominant in 2022. However, in 2023, the C118Y strain was unexpectedly detected in fewer spotted wilt samples from resistant varieties. This was due to emergence of the T120N RB strain, previously known to occur in Spain. A specific RT-PCR test was developed and used to show that the T120N RB strain was predominant in Colusa and Sutter counties (detected in 75-80% of samples), and detected in ~50% of samples from Yolo County. Pathogenicity tests confirmed California isolates of the T120N strain infected Sw-5b tomato varieties and induced severe symptoms. Another RB strain, C118F, was associated with spotted wilt samples of Sw-5 varieties from fresh market tomato production in southern California. Phylogenetic analyses with complete NSm sequences revealed that the C118Y and T120N RB strains infecting resistant processing tomato in California emerged locally, whereas those from fresh market production were more closely related to isolates from Mexico. Thus, widespread deployment of this single dominant resistance gene in California has driven the local emergence of multiple RB strains in different tomato production areas and types. These results further emphasize the need for ongoing monitoring for RB strains, and identification of sources of resistance to these strains.

Occurrence and characterization of viruses infecting Amorphophallus in Yunnan, China

Viral diseases are becoming an important problem in Amorphophallus production due to the propagation of seed corms and their trade across regions. In this study, combined-High-Throughput Sequencing, RT-PCR, electron microscopy, and mechanical inoculation were used to analyze virus-like infected Amorphophallus samples in Yunnan province to investigate the distribution, molecular characterization, and diversity and evolution of Amorphophallus-infecting viruses including three isolates of dasheen mosaic virus and three orthotospoviruses: mulberry vein banding associated virus (MVBaV), tomato zonate spot virus (TZSV) and impatiens necrotic spot virus (INSV). The results showed that DsMV is the dominant virus infecting Amorphophallus, mixed infections with DsMV and MVBaV to Amorphophallus were quite common in Yunnan province, China. This is the first report on infection of Amorphophallus with MVBaV, TZSV, and impatiens necrotic spot virus (INSV) in China. This work will help to develop an effective integrated management strategy to control the spread of Amorphophallus viral diseases.

Identifying Onion Fields at Risk of Iris Yellow Spot Virus in New York

Iris yellow spot virus (IYSV) poses a significant threat to dry bulb onion, Allium cepa L., production and can lead to substantial yield reductions. IYSV is transmitted by onion thrips, Thrips tabaci (Lindeman), but not via seed. Transplanted onion fields have been major early season sources of IYSV epidemics. As onion thrips tend to disperse short distances, seeded onion fields bordering transplanted onion fields may be at greater risk of IYSV infection than seeded fields isolated from transplanted ones. Additionally, seeded onion fields planted early may be at greater risk of IYSV infection than those seeded later. In a 2-year study in New York, we compared IYSV incidence and onion thrips populations in seeded onion fields relative to their proximity to transplanted onion fields. In a second study, we compared IYSV incidence in onion fields with either small or large plants during midseason. Results showed similar IYSV incidence and onion thrips populations in seeded onion fields regardless of their proximity to transplanted onion fields, while IYSV incidence was over four times greater in large onion plants than in small ones during midseason. These findings suggest a greater risk of onion thrips-mediated IYSV infection in onion fields with large plants compared with small ones during midseason and that proximity of seeded fields to transplanted ones is a poor indicator of IYSV risk. Our findings on IYSV spread dynamics provided valuable insights for developing integrated pest and disease management strategies for New York onion growers.

Multigenic Hairpin Transgenes in Tomato Confer Resistance to Multiple Orthotospoviruses Including Sw-5 Resistance-Breaking Tomato Spotted Wilt Virus

Tomato spotted wilt virus (TSWV) and related thrips-borne orthotospoviruses are a threat to food and ornamental crops. Orthotospoviruses have the capacity for rapid genetic change by genome segment reassortment and mutation. Genetic resistance is one of the most effective strategies for managing orthotospoviruses, but there are multiple examples of resistance gene breakdown. Our goal was to develop effective multigenic, broad-spectrum resistance to TSWV and other orthotospoviruses. The most conserved sequences for each open reading frame (ORF) of the TSWV genome were identified, and comparison with other orthotospoviruses revealed sequence conservation within virus clades; some overlapped with domains with well-documented biological functions. We made six hairpin constructs, each of which incorporated sequences matching portions of all five ORFs. Tomato plants expressing the hairpin transgene were challenged with TSWV by thrips and leaf-rub inoculation, and four constructs provided strong protection against TSWV in foliage and fruit. To determine if the hairpin constructs provided protection against other emerging orthotospoviruses, we challenged the plants with tomato chlorotic spot virus and resistance-breaking TSWV and found that the same constructs also provided resistance to these related viruses. Antiviral hairpin constructs are an effective way to protect plants from multiple orthotospoviruses and are an important strategy in the fight against resistance-breaking TSWV and emerging viruses. Targeting of all five viral ORFs is expected to increase the durability of resistance, and combining them with other resistance genes could further extend the utility of this disease control strategy. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Emerging challenges in the management of Orthotospoviruses in Indian agriculture

Orthotospoviruses, a genera of negative-sense ssRNA viruses transmitted by thrips, have gained significant attention in recent years due to their detrimental impact on diverse crops, causing substantial economic losses and posing threats to food security. Orthotospoviruses are characterised by a wide range of symptoms in plants, including chlorotic/necrotic spots, vein banding, and fruit deformation. Seven species, including four definite and three tentative species in the genus Orthotospovirus, have so far been documented on the crops of the Indian subcontinent. Management of Orthotospoviruses under field conditions is challenging since they have a wide host range, adaptation to versatile environmental conditions, a lack of promising resistance sources, and the ubiquitous nature of thrips and their transmission through a propagative manner. Our present review elucidates the significance, molecular biology and evolutionary relationship of Orthotospoviruses; vector population; and possible management strategies for Orthotospoviruses and their vectors in the scenario of the Indian subcontinent.

Harnessing Nanoencapsulated Bacillus spp. Consortia To Combat Groundnut Bud Necrosis Orthotospovirus in Tomato

Tomato (Solanum lycopersicum L.), a globally significant vegetable crop, faces a substantial threat from viral diseases, specifically Groundnut bud necrosis orthotospovirus (GBNV). Traditional approaches such as removal of infected plants, use of barrier crops, and insecticides have been employed but they have not proven to be consistently effective. Consequently, an alternative approach involving the stimulation of host resistance through the Plant Growth Promoting Rhizobacteria (PGPR) was adopted. From the previous study, B. subtilis (BST8), B. subtilis (Bbv57), and B. amyloliquefaciens (Ka1) were found to be effective against GBNV in cowpea. To enhance the shelf life of Bacillus spp. and improve the water retention capacity of tomato leaf surfaces, these bacteria were encapsulated within nanosilica, an identified host defense inducer. An effective inverse Pickering emulsion with a 2.5% (w/v) silica concentration was developed and characterized using diverse techniques, viz., phase contrast, scanning electron microscopy, confocal microscopy, contact angle goniometry, and variable angle ellipsometry. The prepared emulsion was then tested for its antiviral efficacy against GBNV in cowpea and tomatoes. Nanoencapsulated Bacillus consortia significantly reduced GBNV lesions in cowpea to 0.63 per leaf compared to the control (6.63). DAC-ELISA revealed a virus titer of 0.75 (3.33 times lower than the control), indicating antiviral efficacy. In tomato (var. PKM1), the consortia achieved an impressive 77.91% disease reduction (19% DSI) at 14 days post-inoculation (DPI), surpassing both nanoemulsion and consortia alone (DSIs: 67 and 30%, respectively). Nanoencapsulated Bacillus consortia demonstrated the lowest GBNV titer in tomatoes (0.86 vs control-3.32) through DAC-ELISA. This study introduces a promising strategy for the effective management of GBNV in cowpea and tomatoes using nanoencapsulated Bacillus consortia, underscoring its potential as an effective solution in crop protection.

Genetic Diversity and DNA Barcoding of Thrips in Bangladesh

Thrips are economically important pests, and some species transmit plant viruses that are widely distributed and can damage vegetables and cash crops. Although few studies on thrips species have been conducted in Bangladesh, the variation and genetic diversity of thrips species remain unknown. In this study, we collected thrips samples from 16 geographical locations throughout the country and determined the nucleotide sequences of the mitochondrial cytochrome c oxidase subunit 1 (mtCOI) gene in 207 thrips individuals. Phylogenetic analysis revealed ten genera (Thrips, Haplothrips, Megalothrips, Scirtothrips, Frankliniella, Dendrothripoides, Astrothrips, Microcephalothrips, Ayyaria, and Bathrips) and 19 species of thrips to inhabit Bangladesh. Among these, ten species had not been previously reported in Bangladesh. Intraspecific genetic variation was diverse for each species. Notably, Thrips palmi was the most genetically diverse species, containing 14 haplotypes. The Mantel test revealed no correlation between genetic and geographical distances. This study revealed that thrips species are expanding their host ranges and geographical distributions, which provides valuable insights into monitoring the diversity of and control strategies for these pests.

Phytochemistry and Pharmacological Activity of Malva sylvestris L: A Detailed Insight

Malva sylvestris L., is commonly referred to as Mallow and is found in Europe, Asia and Africa. This has been traditionally used for inflammation, gastrointestinal disturbances, skin disorders, menstrual pains, and urological disorders. This review covers phytoconstituents and Pharmacological activities of M. sylvestris. The plant contains a large number of phytochemical constituents having diverse pharmacological activities. The plant contains many phenolic compounds responsible for its strong antioxidant activity. Coumarins from Mallow have a potential anticancer activity. Malva sylvestris also contains essential as well as non-essential elements and minerals. Many researchers have provided evidence that Malva sylvestris is a good candidate for use as a medicinal herb and has good nutritional value. The leaves, in particular, offer properties like anticancer, skin whitening, and anti-aging. Furthermore, the aqueous extract was recently shown to have an anti-ulcerogenic effect. Malva sylvestris has a high potential for use in cosmetics such as skin whitening and anti-aging treatments. Methanolic extracts of Malva sylvestris leaves, and flowers showed strong antibacterial activity against a common plant pathogen bacterium. The plant also contains Malvone A, which is responsible for antibacterial action. The plant also possesses anti-inflammatory, analgesic, wound healing properties and various other activities.

Invasive flower thrips, Thrips parvispinus (Karny) occurrence, host expansion and genetic diversification in a tropical poly-crop ecosystem

BACKGROUND

Invasive black flower thrips Thrips parvispinus (Karny) has recently emerged as a significant threat to Indian chilli production. Identifying T. parvispinus became difficult due to the complex presence of thrips species in Indian chilli and allied ecosystems. Pest management success depends on assessing invasive pests genetic populations and their distribution in newly habituated areas.

METHODS AND RESULTS

The current study investigated the genetic diversity and phylogeographic structure of T. parvispinus across major chilli-growing zones representing different agro-climatic conditions in Tamil Nadu. The species-specific chaetotaxy characteristics of T. parvispinus and molecular analysis of the mtCOI gene were used to confirm that the species T. parvispinus has expanded rapidly in three regions (North Western, Western and Cauvery delta), sparsely in one (Southern) and absent from two (hilly and high rainfall). Fifteen allied crops in chilli/capsicum growing tracts served as host plants for T. parvispinus. A shrub species, namely Littleleaf boxwood, Buxus microphylla Siebold & Zucc., is described as a host plant for the first time. On capsicum and chilli, T. parvispinus and Scirtothrips dorsalis coexisted. Thrips palmi, T. tabaci, Frankliniella schultzei, and Microcephalothrips abdominalis co-occurring alongside T. parvispinus on allied crops.

CONCLUSION

Molecular characterization and haplotype identification help define the genetic composition of T. parvispinus and serve as a foundation for efficient monitoring and creation of Integrated Pest Management (IPM) strategies. As a result, the genetic data presented in this work strongly argues that T. parvispinus as a population is resolving itself towards a fixed state through natural selection that spans its native range globally along with low genetic diversity [Hd: 0.771].

Eco-Friendly Cinnamic Acid Derivatives Containing Glycoside Scaffolds as Potential Antiviral Agents

Natural products are a crucial source in the development of new eco-friendly antiviral agents to control plant viral diseases. In our previous studies, some ferulic acid derivatives with good antiviral activity were obtained as an immune activator. To continue the discovery of eco-friendly antiviral agents, different monosaccharides were introduced into cinnamic acid skeletons by an activity-based strategy to obtain a series of cinnamic acid derivatives containing glycoside scaffolds, and their antiviral activities against tobacco mosaic virus (TMV) and tomato spotted wilt virus (TSWV) were evaluated. Among them, compound 8d showed the greatest protective activities against TMV and TSWV, with the EC50 values of 128.5 and 236.8 μg mL-1, respectively, which were superior to those of ningnanmycin (238.5 and 315.7 μg mL-1, respectively). Moreover, compound 8d could significantly improve the defense enzyme activities of peroxidase, chitinase, and β-1,3-glucanase. Proteomic and transcriptome analyses indicated that compound 8d regulated gene transcription and protein expression levels involved in the defense response to resist virus infection. The present study revealed that compound 8d is a potential lead candidate for the development of novel, eco-friendly, and natural-product-based antiviral agents.

A novel tomato spotted wilt virus isolate encoding a noncanonical NSm C118F substitution associated with Sw-5 tomato gene resistance breaking

The nonstructural protein NSm of tomato spotted wilt virus (TSWV) has been identified as the avirulence determinant of the tomato single dominant Sw-5 resistance gene. Although Sw-5 effectiveness has been shown for most TSWV isolates, the emergence of resistance-breaking (RB) isolates has been observed. It is strongly associated with two point mutations (C118Y or T120N) in the NSm viral protein. TSWV-like symptoms were observed in tomato crop cultivars (+Sw-5) in the Baja California peninsula, Mexico, and molecular methods confirmed the presence of TSWV. Sequence analysis of the NSm 118-120 motif and three-dimensional protein modelling exhibited a noncanonical C118F substitution in seven isolates, suggesting that this substitution could emulate the C118Y-related RB phenotype. Furthermore, phylogenetic and molecular analysis of the full-length genome (TSWV-MX) revealed its reassortment-related evolution and confirmed that putative RB-related features are restricted to the NSm protein. Biological and mutational NSm 118 residue assays in tomato (+Sw-5) confirmed the RB nature of TSWV-MX isolate, and the F118 residue plays a critical role in the RB phenotype. The discovery of a novel TSWV-RB Mexican isolate with the presence of C118F substitution highlights a not previously described viral adaptation in the genus Orthotospovirus, and hence, the necessity of further crop monitoring to alert the establishment of novel RB isolates in cultivated tomatoes.

Novel strains of a pandemic plant virus, tomato spotted wilt orthotospovirus, increase vector fitness and modulate virus transmission in a resistant host

Tomato spotted wilt orthotospovirus (TSWV) is one of the most successful pandemic agricultural pathogens transmitted by several species of thrips in a persistent propagative manner. Current management strategies for TSWV heavily rely on growing single-gene resistant cultivars of tomato ("Sw-5b" gene) and pepper ("Tsw" gene) deployed worldwide. However, the emergence of resistance-breaking strains (RB) in recent years has compounded the threat of TSWV to agricultural production worldwide. Despite this, an extensive study on the thrips transmission biology of RB strains is currently lacking. It is also unclear whether mutualistic TSWV-thrips interactions vary across different novel strains with disparate geographical origins. To address both critical questions, we studied whether and how four novel RB strains of TSWV (two sympatric and two allopatric), along with a non-RB strain, impact western flower thrips (WFT) fitness and whether this leads to differences in TSWV incidence, symptom severity (virulence), and virus accumulation in two differentially resistant tomato cultivars. Our findings show that all RB strains increased WFT fitness by prolonging the adult period and increasing fecundity compared to non-RB and non-viruliferous controls, regardless of the geographical origin of strains or the TSWV titers in individual thrips, which were substantially low in allopatric strains. TSWV accumulation in thrips varied at different developmental stages and was unrelated to the infected tissues from which thrips acquired the virus. However, it was significantly positively correlated to that in WFT-inoculated susceptible plants, but not the resistant ones. The TSW incidences were high in tomato plants infected with all RB strains, ranging from 80% to 90% and 100% in resistant and susceptible plants, respectively. However, TSW incidence in the non-RB-infected susceptible tomato plants was 80%. Our findings provide new insights into how novel strains of TSWV, by selectively offering substantial fitness benefits to vectors, modulate transmission and gain a potential epidemiological advantage over non-RB strains. This study presents the first direct evidence of how vector-imposed selection pressure, besides the one imposed by resistant cultivars, may contribute to the worldwide emergence of RB strains.

Unraveling the Mechanisms of Virus-Induced Symptom Development in Plants

Plant viruses, as obligate intracellular parasites, induce significant changes in the cellular physiology of host cells to facilitate their multiplication. These alterations often lead to the development of symptoms that interfere with normal growth and development, causing USD 60 billion worth of losses per year, worldwide, in both agricultural and horticultural crops. However, existing literature often lacks a clear and concise presentation of the key information regarding the mechanisms underlying plant virus-induced symptoms. To address this, we conducted a comprehensive review to highlight the crucial interactions between plant viruses and host factors, discussing key genes that increase viral virulence and their roles in influencing cellular processes such as dysfunction of chloroplast proteins, hormone manipulation, reactive oxidative species accumulation, and cell cycle control, which are critical for symptom development. Moreover, we explore the alterations in host metabolism and gene expression that are associated with virus-induced symptoms. In addition, the influence of environmental factors on virus-induced symptom development is discussed. By integrating these various aspects, this review provides valuable insights into the complex mechanisms underlying virus-induced symptoms in plants, and emphasizes the urgency of addressing viral diseases to ensure sustainable agriculture and food production.

NLRs derepress MED10b- and MED7-mediated repression of jasmonate-dependent transcription to activate immunity

Plant intracellular nucleotide-binding domain, leucine-rich repeat-containing receptors (NLRs) activate a robust immune response upon detection of pathogen effectors. How NLRs induce downstream immune defense genes remains poorly understood. The Mediator complex plays a central role in transducing signals from gene-specific transcription factors to the transcription machinery for gene transcription/activation. In this study, we demonstrate that MED10b and MED7 of the Mediator complex mediate jasmonate-dependent transcription repression, and coiled-coil NLRs (CNLs) in Solanaceae modulate MED10b/MED7 to activate immunity. Using the tomato CNL Sw-5b, which confers resistance to tospovirus, as a model, we found that the CC domain of Sw-5b directly interacts with MED10b. Knockout/down of MED10b and other subunits including MED7 of the middle module of Mediator activates plant defense against tospovirus. MED10b was found to directly interact with MED7, and MED7 directly interacts with JAZ proteins, which function as transcriptional repressors of jasmonic acid (JA) signaling. MED10b-MED7-JAZ together can strongly repress the expression of JA-responsive genes. The activated Sw-5b CC interferes with the interaction between MED10b and MED7, leading to the activation of JA-dependent defense signaling against tospovirus. Furthermore, we found that CC domains of various other CNLs including helper NLR NRCs from Solanaceae modulate MED10b/MED7 to activate defense against different pathogens. Together, our findings reveal that MED10b/MED7 serve as a previously unknown repressor of jasmonate-dependent transcription repression and are modulated by diverse CNLs in Solanaceae to activate the JA-specific defense pathways.

Mitochondrial genetic diversity of Thrips tabaci (Thysanoptera: Thripidae) in onion growing regions of the United States

Onion thrips (Thrips tabaci Lindeman, Thysanoptera: Thripidae) causes severe damage to many horticultural and agronomic crops worldwide. It also acts as a vector of several plant viruses. T. tabaci is a key pest of Allium cepa in the United States. However, there is limited information available on the genetic variation within and between T. tabaci populations in the United States and its key evolutionary parameters. In the current study, 83 T. tabaci specimens were collected from A. cepa from 15 different locations comprising four states of the United States. A total of 92 mtCOI gene sequences of T. tabaci from A. cepa were analyzed to understand the genetic diversity and structure of T. tabaci collected from onion host. Seven distinct haplotypes of T. tabaci infesting A. cepa were identified from the current collection, while nine T. tabaci sequences retrieved from GenBank comprised 5 haplotypes. Overall, 15 haplotypes of T. tabaci infesting A. cepa were identified in the world that includes the ten haplotypes in the United States. In the phylogenetic analysis, all the populations collected during the study clustered with thelytokous lineage, while T. tabaci sequences retrieved from GenBank corresponded to leek-associated arrhenotokous lineage. The highest genetic variation was found in Elba and Malheur populations with 3 haplotypes identified in each. The results suggest that haplotypes 1 and 7 are more frequently prevailing haplotypes in the north-western United States, with haplotype 1 being the predominant all over the country. The eastern United States appears to have a more diverse group of haplotypes. The populations from Hungary constituted distinct haplotypes and a haplotype from Kingston linked it with the predominant haplotype.

Genetic and physiological determinants of lettuce partial resistance to Impatiens necrotic spot virus

Introduction

Impatiens necrotic spot virus (INSV) is a major pathogen currently threatening lettuce (Lactuca sativa L.) production in the coastal areas of California. The virus is transmitted by the western flower thrips (Frankliniella occidentalis Pergande).

Methods

We have tested a diversity panel of almost 500 lettuce accessions for disease incidence (DI) in 12 field experiments performed over 7 years. This set of accessions was also assessed for thrips feeding damage (TFD), the rate of plant development (PD), and the content of chlorophyll (SPAD) and anthocyanins (ACI) to determine their effect on resistance to INSV. In addition, recombinant inbred lines from two biparental mapping populations were also evaluated for DI in field experiments.

Results

The mean DI in 14 field experiments ranged from 2.1% to 70.4%. A highly significant difference in DI was observed among the tested accessions, with the overall lowest DI detected in the red color cultivars, Outredgeous Selection, Red Splash Cos, Infantry, Sweet Valentine, Annapolis, and Velvet. Multiple linear regression models revealed a small but significant effect (p < 0.005) of the four analyzed determinants on DI. Accessions with lower DI values had slower plant development (PD, r = 0.352), higher ACI content (r = -0.284), lower TFD (r = 0.198), and lower SPAD content (r = 0.125). A genome-wide association study revealed 13 QTLs for DI located on eight out of the nine lettuce chromosomes (the exception was chr. 8). The most frequently detected QTL (qINSV2.1) was located on chr. 2. Several of the QTLs for DI were in the same genomic areas as QTLs for PD, ACI, and SPAD. Additional three QTLs for DI on chr. 5 and 8 were identified using linkage mapping performed on two biparental mapping populations.

Conclusions

The work highlights the genetic basis of partial resistance to INSV and reveals the relationship between resistance, the host physiology, and the thrips vector. Results of this study are an important steppingstone toward developing cultivars with increased resistance against INSV.

Obstructor, a Frankliniella occidentalis protein, promotes transmission of tomato spotted wilt orthotospovirus

Tomato spotted wilt orthotospovirus (TSWV) causes substantial economic losses to vegetables and other crops. TSWV is mainly transmitted by thrips in a persistent and proliferative manner, and its most efficient vector is the western flower thrips, Frankliniella occidentalis (Pergande). In moving from the thrips midgut to the salivary glands in preparation for transmission, the virions must overcome multiple barriers. Although several proteins that interact with TSWV in thrips have been characterized, we hypothesized that additional thrips proteins interact with TSWV and facilitate its transmission. In the current study, 67 F. occidentalis proteins that interact with G_N (a structural glycoprotein) were identified using a split-ubiquitin membrane-based yeast 2-hybrid (MbY2H) system. Three proteins, apolipoprotein-D (ApoD), orai-2-like (Orai), and obstructor-E-like isoform X2 (Obst), were selected for further study based on their high abundance and interaction strength; their interactions with G_N were confirmed by MbY2H, yeast β-galactosidase and luciferase complementation assays. The relative expressions of ApoD and Orai were significantly down-regulated but that of Obst was significantly up-regulated in viruliferous thrips. When interfering with Obst in larval stage, the TSWV acquisition rate in 3 independent experiments was significantly decreased by 26%, 40%, and 35%, respectively. In addition, when Obst was silenced in adults, the virus titer was significantly decreased, and the TSWV transmission rate decreased from 66.7% to 31.9% using the leaf disk method and from 86.67% to 43.33% using the living plant method. However, the TSWV acquisition and transmission rates were not affected by interference with the ApoD or Orai gene. The results indicate that Obst may play an important role in TSWV acquisition and transmission in Frankliniella occidentalis.

Advances in omics research on peanut response to biotic stresses

Peanut growth, development, and eventual production are constrained by biotic and abiotic stresses resulting in serious economic losses. To understand the response and tolerance mechanism of peanut to biotic and abiotic stresses, high-throughput Omics approaches have been applied in peanut research. Integrated Omics approaches are essential for elucidating the temporal and spatial changes that occur in peanut facing different stresses. The integration of functional genomics with other Omics highlights the relationships between peanut genomes and phenotypes under specific stress conditions. In this review, we focus on research on peanut biotic stresses. Here we review the primary types of biotic stresses that threaten sustainable peanut production, the multi-Omics technologies for peanut research and breeding, and the recent advances in various peanut Omics under biotic stresses, including genomics, transcriptomics, proteomics, metabolomics, miRNAomics, epigenomics and phenomics, for identification of biotic stress-related genes, proteins, metabolites and their networks as well as the development of potential traits. We also discuss the challenges, opportunities, and future directions for peanut Omics under biotic stresses, aiming sustainable food production. The Omics knowledge is instrumental for improving peanut tolerance to cope with various biotic stresses and for meeting the food demands of the exponentially growing global population.

Interspecies/Intergroup Complementation of Orthotospovirus Replication and Movement through Reverse Genetics Systems

Orthotospoviruses, the plant-infecting bunyaviruses, cause serious diseases in agronomic crops and pose major threats to global food security. The family of Tospoviridae contains more than 30 members that are classified into two geographic groups, American-type and Euro/Asian-type orthotospovirus. However, the genetic interaction between different species and the possibility, during mixed infections, for transcomplementation of gene functions by orthotospoviruses from different geographic groups remains underexplored. In this study, minireplicon-based reverse genetics (RG) systems have been established for Impatiens necrotic spot virus (INSV) (an American-type orthotospovirus) and for Calla lily chlorotic spot virus and Tomato zonate spot virus (CCSV and TZSV) (two representative Euro/Asian orthotospoviruses). Together with the earlier established RG system for Tomato spotted wilt virus (TSWV), a type species of the Orthotospovirus American-clade, viral replicase/movement proteins were exchanged and analyzed on interspecies transcomplementation. Whereas the homologous RNA-dependent RNA polymerase (RdRp) and nucleocapsid (N) protein supported the replication of orthotospoviruses from both geographic groups, heterologous combinations of RdRp from one group and N from the other group were unable to support the replication of viruses from both groups. Furthermore, the NSm movement protein (MP), from both geographic groups of orthotospoviruses, was able to transcomplement heterologous orthotospoviruses or a positive-strand Cucumber mosaic virus (CMV) in their movement, albeit with varying efficiency. MP from Rice stripe tenuivirus (RSV), a plant-infecting bunyavirus that is distinct from orthotospoviruses, or MP from CMV also moves orthotospoviruses. Our findings gain insights into the genetic interaction/reassortant potentials for the segmented plant orthotospoviruses. IMPORTANCE Orthotospoviruses are agriculturally important negative-strand RNA viruses and cause severe yield-losses on many crops worldwide. Whereas the emergence of new animal-infecting bunyaviruses is frequently associated with genetic reassortants, this issue remains underexposed with the plant-infecting orthotospovirus. With the development of reverse genetics systems for orthotospoviruses from different geographic regions, the interspecies/intergroup replication/movement complementation between American- and Euro/Asian-type orthotospoviruses were investigated. Genomic RNAs from American orthotospoviruses can be replicated by the RdRp and N from those of Euro/Asia-group orthotospoviruses, and vice versa. However, their genomic RNAs cannot be replicated by a heterologous combination of RdRp from one geographic group and N from another geographic group. Cell-to-cell movement of viral entity is supported by NSm from both geographic groups, with highest efficiency by NSm from viruses belonging to the same group. Our findings provide important insights into the genetic interaction and exchange ability of viral gene functions between different species of orthotospovirus.

Epidemiology and Economic Impact of Impatiens Necrotic Spot Virus: A Resurging Pathogen Affecting Lettuce in the Salinas Valley of California

The Orthotospovirus impatiens necrotic spot virus (INSV) is a thrips-transmitted pathogen of lettuce that has rapidly emerged as a serious threat to production in the Salinas Valley of Monterey County, California. As a first step toward understanding the severity of the virus, we utilized Spatial Analysis by Distance IndicEs (SADIE) to characterize the distribution and progression of INSV outbreaks and thrips infestations in two commercial lettuce fields. In both fields, INSV incidence rapidly increased from 15.86% ± 1.77 to 80.24% ± 2.60 over the course of 7 weeks and aggregated at specific edges in both fields as early as 3 weeks after planting (Ia = 1.63, Pa = 0.0100, and Ia = 1.53, Pa = 0.0300). In one of the fields, thrips populations aggregated in areas that also experienced the most INSV (Ia = 1.2435, Pa = 0.0400, week 3; Ia = 1.4815, Pa < 0.0001, week 6; Ia = 1.5608, Pa < 0.0001, week 9), while in the second field, thrips were distributed randomly despite the aggregated effects that were observed for INSV incidence. Economic analysis estimated that the virus accounted for over $475,000 in losses for the two fields, while stakeholder surveys documented over 750 fields that experienced INSV infection during the 2021 season in Monterey County alone. These studies enhance our knowledge on the epidemiology of thrips and INSV under current lettuce production practices in the Salinas Valley, while elucidating the economic consequences and broader challenges that are associated with managing thrips-transmitted viruses.

Matrine-Type Alkaloids with Anti-Tomato Spotted Wilt Virus Activity from the Root of Sophora tonkinensis Gagnep

As a continuation of our research on the development of pesticide active quinolizidine alkaloids (QAs) from the family Fabaceae, the chemical constituents of the root of Sophora tonkinensis Gagnep. were systematically investigated. Seventeen new matrine-type alkaloids (1-17), including one new naturally occurring compound (17), along with 20 known ones were isolated from the EtOH extract of S. tonkinensis. Notably, compound 5 possessed an unprecedented 6/6/5/4/6/6 hexacyclic system. Their structures were confirmed via comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS), ECD calculation, and X-ray crystallography. Biological tests indicated that compounds 1, 4, 10, 12, 13, and 30 displayed significant anti-tomato spotted wilt virus (TSWV) activities compared with the positive control ningnanmycin. Moreover, compound 12 strongly inhibited the expression of the TSWV N, NSs, and NSm genes and TSWV NSs protein in plant host. Furthermore, compounds 4, 10, 12, 20, and 22 exhibited moderate insecticidal activities against TSWV thrip vector (Frankliniella occidentalis).

First report of tomato chlorosis virus (ToCV) and detection of other viruses in field-grown tomatoes in North-Western region of India

Tomato crop is known to be infected by large number of viruses across the globe causing severe losses in its yield. Accurate information on the distribution and incidence of different viruses is essential to implement virus control strategies. This study provides information on prevalence and distribution of different viruses infecting tomato crop in North-western region of India. Leaf samples of 76 symptomatic tomato and 30 symptomatic and asymptomatic plants of Chenopodium sp. (weed) were collected from eight villages. DAS-ELISA and/or RT-PCR/PCR were used to detect occurrence of nineteen viruses and one viroid in tomatoes. Nine viruses viz. cucumber mosaic virus, groundnut bud necrosis virus, potato virus M, potato virus S, potato virus X, potato virus Y, tomato chlorosis virus, tomato leaf curl New Delhi virus and tomato mosaic virus were detected in 58 of 76 tomato samples. Detection of viruses was confirmed by cloning of specific amplicons followed by sequencing and submission of sequences to the GenBank database. None of the targeted pathogens were found in collected weed samples. Tomato leaf curl New Delhi virus (ToLCNDV) was the most prevalent virus (64.47%) followed by potato virus Y (PVY) (23.68%). Double, triple, quadruple and quintuple infections were also noticed. Phylogenetic analysis of nucleotide sequences was also carried out. Nine viruses infecting tomato crop from North-western region of India were detected. ToLCNDV was most prevalent with highest incidence. To the best of our knowledge, this is the first report of ToCV on tomato from India.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-022-00801-y.

The phytochemical profiling, pharmacological activities, and safety of malva sylvestris: a review

Malva sylvestris is a plant commonly found in Europe, Asia, and Africa. The leaves and flowers of this plant have been used for centuries in traditional medicine to treat various ailments such as cough, cold, diarrhoea, and constipation. Google Scholar, PubMed, Scopus, and Web of Science were used to search for relevant material on the phytochemical profiling and pharmacologic activities of Malva sylvestris. The techniques used in phytochemical profiling and the pharmacologic activity of each compound were extracted from the included studies, including in vitro, in vivo, and clinical studies. The phytochemical analysis of Malva sylvestris revealed that the leaves and flowers are the most commonly used parts of the plant and contain various bioactive compounds such as flavonoids, mucilages, terpenoids, phenol derivatives, coumarins, sterols, tannins, saponins, and alkaloids. These phytochemicals are responsible for the many pharmacological activities of Malva sylvestris, such as anti-inflammatory, antimicrobial, hepatoprotective, laxative, antiproliferative and antioxidant properties. This review has presented an overview of the antinociceptive and anti-inflammatory activities and the cytotoxic effects of Malva sylvestris on different types of cancer cells. It has also summarised the work on developing copper oxide nanoparticles using Malva sylvestris leaf extract and its potential use in food and medicine. This review aims to highlight the traditional uses, phytochemistry, pharmacological activities, and safety of Malva sylvestris.

Analysis of lysine acetylation in tomato spot wilt virus infection in Nicotiana benthamiana

Introduction

Kac is a model for all acylation modification studies. Kac plays a critical role in eukaryotes and prokaryotes. It is mainly involved in six major biological functions: gene expression, signal transduction, cell development, protein conversion, metabolism, and metabolite transport.

Method

We investigated and compared the acetylation modification of proteins in healthy and tomato spot wilt virus (TSWV)-infected Nicotiana benthamiana leaves.

Result

We identified 3,418 acetylated lysine sites on 1962 proteins acetylation of proteins in the TSWV-infected and control groups were compared; it was observed that 408 sites on 294 proteins were upregulated and 284 sites on 219 proteins (involved in pentose phosphate, photosynthesis, and carbon fixation in photosynthesis) were downregulated after the infection. Overall, 35 conserved motifs were identified, of which xxxkxxxxx_K_ Rxxxxxxxxx represented 1,334 (31.63%) enrichment motifs and was the most common combination. Bioinformatic analysis revealed that most of the proteins with Kac sites were located in the chloroplast and cytoplasm. They were involved in biological processes, such as cellular and metabolic processes.

Discussion

In conclusion, our results revealed that Kac may participate in the regulation of TSWV infection in N. benthamiana.

Plant Viruses of Agricultural Importance: Current and Future Perspectives of Virus Disease Management Strategies

Plant viruses cause significant losses in agricultural crops worldwide, affecting the yield and quality of agricultural products. The emergence of novel viruses or variants through genetic evolution and spillover from reservoir host species, changes in agricultural practices, mixed infections with disease synergism, and impacts from global warming pose continuous challenges for the management of epidemics resulting from emerging plant virus diseases. This review describes some of the most devastating virus diseases plus select virus diseases with regional importance in agriculturally important crops that have caused significant yield losses. The lack of curative measures for plant virus infections prompts the use of risk-reducing measures for managing plant virus diseases. These measures include exclusion, avoidance, and eradication techniques, along with vector management practices. The use of sensitive, high throughput, and user-friendly diagnostic methods is crucial for defining preventive and management strategies against plant viruses. The advent of next-generation sequencing technologies has great potential for detecting unknown viruses in quarantine samples. The deployment of genetic resistance in crop plants is an effective and desirable method of managing virus diseases. Several dominant and recessive resistance genes have been used to manage virus diseases in crops. Recently, RNA-based technologies such as dsRNA- and siRNA-based RNA interference, microRNA, and CRISPR/Cas9 provide transgenic and nontransgenic approaches for developing virus-resistant crop plants. Importantly, the topical application of dsRNA, hairpin RNA, and artificial microRNA and trans-active siRNA molecules on plants has the potential to develop GMO-free virus disease management methods. However, the long-term efficacy and acceptance of these new technologies, especially transgenic methods, remain to be established.

Activity Patterns, Population Dynamics, and Spatial Distribution of the Stick Tea Thrips, Dendrothrips minowai, in Tea Plantations

The stick tea thrips, D. minowai Priesner (Thysanoptera: Thripidae), is one of the most economically significant thrips pests of tea (Camellia sinensis (L.) O. Ktze.) in China. Here, we sampled D. minowai in tea plantations from 2019 to 2022 to characterize its activity patterns, population dynamics, and spatial distribution. A large proportion of D. minowai individuals were caught in traps placed at heights ranging from 5 cm below to 25 cm above the position of tender leaves at the top of the tea plant, and the greatest number of individuals were captured at a height of 10 cm from the position of tender leaves at the top of the tea plant. Thrips were most abundant from 10:00 to 16:00 h in the spring and from 06:00 to 10:00 h and from 16:00 to 20:00 h on sunny days in the summer. The spatial distribution of D. minowai females and nymphs was aggregated on leaves according to Taylor's power law (females: R² = 0.92, b = 1.69 > 1; nymphs: R² = 0.91, b = 2.29 > 1) and Lloyd's patchiness index (females and nymphs: C > 1, Ca > 0, I > 0, M*/m > 1). The D. minowai population was dominated by females, and male density increased in June. Adult thrips overwintered on the bottom leaves, and they were most abundant from April to June and from August to October. Our findings will aid efforts to control D. minowai populations.

The effects of the E3 ubiquitin-protein ligase UBR7 of Frankliniella occidentalis on the ability of insects to acquire and transmit TSWV

The interactions between plant viruses and insect vectors are very complex. In recent years, RNA sequencing data have been used to elucidate critical genes of Tomato spotted wilt ortho-tospovirus (TSWV) and Frankliniella occidentalis (F. occidentalis). However, very little is known about the essential genes involved in thrips acquisition and transmission of TSWV. Based on transcriptome data of F. occidentalis infected with TSWV, we verified the complete sequence of the E3 ubiquitin-protein ligase UBR7 gene (UBR7), which is closely related to virus transmission. Additionally, we found that UBR7 belongs to the E3 ubiquitin-protein ligase family that is highly expressed in adulthood in F. occidentalis. UBR7 could interfere with virus replication and thus affect the transmission efficiency of F. occidentalis. With low URB7 expression, TSWV transmission efficiency decreased, while TSWV acquisition efficiency was unaffected. Moreover, the direct interaction between UBR7 and the nucleocapsid (N) protein of TSWV was investigated through surface plasmon resonance and GST pull-down. In conclusion, we found that UBR7 is a crucial protein for TSWV transmission by F. occidentalis, as it directly interacts with TSWV N. This study provides a new direction for developing green pesticides targeting E3 ubiquitin to control TSWV and F. occidentalis.

Grafting to Manage Infections of the Emerging Tomato Leaf Curl New Delhi Virus in Cucurbits

Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging begomovirus (Geminiviridae family) listed in the EPPO Alert List 2, present in the Mediterranean area and in Italy, where it was reported in 2015 in Sicilian courgette. The virus is widespread in cucurbits where it causes up to 100% production losses. In 2018, ToLCNDV was isolated in Apulia (southern Italy) in commercial fields of zucchini squash and since then its recurrent outbreaks generated justified concern among growers. Thus, a sustainable and environmentally friendly approach must be adopted. Genetic resistances have been identified in Cucurbita moschata and Luffa cylindrica but, compared to genetic resistance, grafting could provide a faster and more flexible solution because the graft wounding induces tolerance rather than resistance against airborne virus infection. Compared to tolerance, the up-regulation of resistance genes requires energy resources mobilized at the expense of primary metabolism, plant growth, and development. Results of screening among twenty-one local cucurbit cvs. ecotypes and accessions to evaluate tolerance levels against rub-inoculation of ToLCNDV led to the identification of potential rootstocks to attain suitable levels of tolerance against the virus in commercial cucurbit varieties. Cucurbit plants were challenged by a ToLCNDV isolated in Apulia denoted ToLCNDV-Le and evaluated for disease symptoms development and viral DNA accumulation up to 28 days after inoculation. On the basis of disease symptoms developed, plants were classified as tolerant, moderately tolerant, moderately susceptible, and susceptible. Cucumis melo cv. Barattiere did not show any detectable disease symptoms and very low levels of viral DNA accumulation was recorded; thus, it was used as rootstock for some of the remaining cucurbit genotypes that were used as scions. The tolerance trait was transmitted to the otherwise susceptible and moderately susceptible cucurbit genotypes grafted onto the cv. Barattiere. The results of this study suggest practical implications of the approach described.

RNA Viruses Linked to Eukaryotic Hosts in Thawed Permafrost

Arctic permafrost is thawing due to global warming, with unknown consequences on the microbial inhabitants or associated viruses. DNA viruses have previously been shown to be abundant and active in thawing permafrost, but little is known about RNA viruses in these systems. To address this knowledge gap, we assessed the composition of RNA viruses in thawed permafrost samples that were incubated for 97 days at 4°C to simulate thaw conditions. A diverse RNA viral community was assembled from metatranscriptome data including double-stranded RNA viruses, dominated by Reoviridae and Hypoviridae, and negative and positive single-stranded RNA viruses, with relatively high representations of Rhabdoviridae and Leviviridae, respectively. Sequences corresponding to potential plant and human pathogens were also detected. The detected RNA viruses primarily targeted dominant eukaryotic taxa in the samples (e.g., fungi, Metazoa and Viridiplantae) and the viral community structures were significantly associated with predicted host populations. These results indicate that RNA viruses are linked to eukaryotic host dynamics. Several of the RNA viral sequences contained auxiliary metabolic genes encoding proteins involved in carbon utilization (e.g., polygalacturosase), implying their potential roles in carbon cycling in thawed permafrost. IMPORTANCE Permafrost is thawing at a rapid pace in the Arctic with largely unknown consequences on ecological processes that are fundamental to Arctic ecosystems. This is the first study to determine the composition of RNA viruses in thawed permafrost. Other recent studies have characterized DNA viruses in thawing permafrost, but the majority of DNA viruses are bacteriophages that target bacterial hosts. By contrast RNA viruses primarily target eukaryotic hosts and thus represent potential pathogenic threats to humans, animals, and plants. Here, we find that RNA viruses in permafrost are novel and distinct from those in other habitats studied to date. The COVID-19 pandemic has heightened awareness of the importance of potential environmental reservoirs of emerging RNA viral pathogens. We demonstrate that some potential pathogens were detected after an experimental thawing regime. These results are important for understanding critical viral-host interactions and provide a better understanding of the ecological roles that RNA viruses play as permafrost thaws.

Silencing of Thrips palmi UHRF1BP1 and PFAS Using Antisense Oligos Induces Mortality and Reduces Tospovirus Titer in Its Vector

Thrips palmi (Thysanoptera: Thripidae) is an important pest of vegetables, legumes, and ornamentals. In addition, it transmits several plant viruses. T. palmi genes associated with innate immunity, endocytosis-related pathways, and cuticular development are highly enriched in response to Groundnut bud necrosis orthotospovirus (GBNV, genus Orthotospovirus, family Tospoviridae) infection. As the previous transcriptomic study suggested the involvement of T. palmi UHRF1BP1 and PFAS in GBNV infection, these two genes were targeted for silencing using antisense oligonucleotides (ASOs), and the effects on thrips’ fitness and virus acquisition were observed. Phosphorothioate modification of ASOs was carried out by replacing the nonbridging oxygen atom with a sulfur atom at the 3′ position to increase nuclease stability. The modified ASOs were delivered orally through an artificial diet. Exposure to ASOs reduced the target mRNA expression up to 2.70-fold optimally. Silencing of T. palmi UHRF1BP1 and PFAS induced 93.33% mortality that further increased up to 100% with an increase in exposure. Silencing of T. palmi UHRF1BP1 and PFAS also produced morphological deformities in the treated T. palmi. GBNV titer in T. palmi significantly declined post-exposure to ASOs. This is the first-ever report of silencing T. palmi UHRF1BP1 and PFAS using modified ASO to induce mortality and impair virus transmission in T. palmi. T. palmi UHRF1BP1 and PFAS would be novel genetic targets to manage thrips and restrict the spread of tospovirus.

Repellency, contact toxicity, and anti-oviposition effects of three ethanol-extracted plant essential oils on Bemisia tabaci (Hemiptera: Aleyrodidae)

There are more than 1200 species of whiteflies found across the globe. Due to the high level of resistance of whitefly against synthetic insecticides, alternate pest management measures have their significance. Plant essential oils (EOs) affect insect pests in many ways, such as via stimulatory, deterrent, toxic, and hormonal effects. This study was designed to determine the repellency of EOs, toxicity, and oviposition deterrent activities of Allium ascalonicum, Cinnamomum camphora, and Mentha haplocalyx against adult whiteflies. In repellency determination experiments, a single tomato plant was treated with 10 ml of ethanol-extracted EO with 1000 ppm concentration. Results showed that C. camphora EO was the most repellent for whitefly compared to M. haplocalyx and A. ascalonicum. The oviposition deterrent experiments revealed that C. camphora has the highest oviposition deterrent effect, followed by M. haplocalyx and A. ascalonicum. A single plant treatment method was used to assess the contact toxicity of three EOs against whitefly after 12, 24, 48, and 72 h of exposure. The results revealed that C. camphora is more toxic to whitefly than M. haplocalyx and A. ascalonicum. After determining the antagonistic effects of these EOs, the oils were analyzed using gas chromatography/mass spectrometry to identify the chemical components. It can be concluded that C. camphora is the most effective oil EO in terms of toxicity, repellence, and oviposition deterrence, followed by M. haplocalyx and A. ascalonicum under greenhouse conditions. Our results introduce some new eco-friendly plant EOs to control whiteflies.

Seed Transmission of Tomato Spotted Wilt Orthotospovirus in Peppers

Tomato spotted wilt orthotospovirus (TSWV) severely damaged agricultural production in many places around the world. It is generally believed that TSWV transmits among plants via their insect vector. In this study, we provide evidence on the seed-borne transmission of TSWV in pepper (Capsicum annuum L.) plants. RT-PCR, RT-qPCR, and transmission electron microscopy data demonstrate the seed transmission ability of TSWV in peppers. Endosperm, but not the embryo, is the abundant virus-containing seed organ. TSWV can also be detected in the second generation of newly germinated seedlings from virus-containing seed germination experiments. Our data are useful for researchers, certification agencies, the seed industry, and policy makers when considering the importance of TSWV in vegetable production all over the world.

Quinolizidine Alkaloids with Antitomato Spotted Wilt Virus and Insecticidal Activities from the Seeds of Thermopsis lanceolata R. Br

As part of our ongoing investigation of pesticide active quinolizidine alkaloids (QAs) from the family Fabaceae, the chemical constituents of the seeds of Thermopsis lanceolata R. Br. were systematically investigated. Bioassay-guided fractionation and purification of the crude extract led to the isolation of seventeen new QAs (1-17), including three new naturally occurring compounds (15-17), along with 15 known compounds (18-32). Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, NMR, and HRESIMS) and quantum chemistry calculations (¹³C NMR and ECD). The antitomato spotted wilt virus activities and insecticidal activities against Aphis fabae, Nilaparvata lugens (Stal), and Tetranychus urticae of compounds 1-32 were screened using the lesion counting method, spray method, and rice-stem dipping method, respectively. Biological tests indicated that compounds 6, 9, 10, and 18 displayed significant anti-TSWV activities compared with the positive control ningnanmycin. Compounds 3, 4, and 5 showed better insecticidal activities against A. fabae with LC₅₀ values of 10.07, 12.07, and 6.56 mg/L, respectively. Moreover, compounds 5, 18, and 24 exhibited moderate insecticidal activities against N. lugens (Stal) with LC₅₀ values of 37.91, 53.44, and 31.21 mg/L, respectively. Furthermore, compounds 9 and 10 exhibited moderate insecticidal activities against T. urticae.

The Effect of Species Soybean Vein Necrosis Orthotospovirus (SVNV) on Life Table Parameters of Its Vector, Soybean Thrips (Neohydatothrips variabilis Thysanoptera: Thripidae)

Simple Summary

Soybean vein necrosis, caused by soybean vein necrosis virus (SVNV) is an important viral disease of soybeans that can be seed borne or insect vectored. This plant viral disease affects seed qualitative parameters, including seed oil content. Increased damage is observed in late planted soybeans. The disease is widespread, and almost all soybean-growing states in USA are affected. Globally, SVNV is reported in Canada, the United States, Egypt and Pakistan. In order to manage the disease, it is important to understand the vector’s biology and the effect of SVNV on life table parameters (survival, longevity, mortality, doubling time, generation, rate of intrinsic increase) of vector soybean thrips, which can help to establish pest management predictive models. We used an age-stage two-sex life table estimation model to define the effect of SVNV on the life parameters of male and female soybean thrips. Overall, we found that SVNV infection increased viruliferous thrips survival, longevity, gross reproduction rate, life expectancy and decreased population doubling time. Overall viruliferous thrips benefit from SVNV infection and transmission due to better survival, longevity and increased fitness.

Abstract

Soybean vein necrosis orthotospovirus (SVNV: Tospoviridae: Orthotospovirus), the causal agent of soybean vein necrosis disease, is vectored by soybean thrips Neohydatothrips variabilis (Beach, 1896), and to a lesser extent by five other thrips species. There is increasing incidence of soybean vein necrosis (SVN) disease in all soybean growing states in the United States, Canada, Egypt and Pakistan, necessitating a study of the system’s ecology and management. We addressed the effect of SVNV on the life table parameters of the vector. We used an ‘age-stage two-sex’ life table approach, which provided detailed life stage durations of each larval instar and adults (both sexes). Our results showed that the intrinsic rate of increase (r), finite rate of increase (λ) and mortality index (qx) were higher in the infected population, while the net reproduction rate (Ro), cumulative probability of survival (lx) and gross reproduction rate (GRR) were lower in the uninfected population. Overall, in both infected and uninfected populations, the number of eggs producing haploid males via arrhenotoky ranged from 9–12 per female. Male to female ratio was female biased in the infected population. Overall, our study provided evidence that virus infection, by decreasing the population doubling time, could enhance the virus and vector populations in soybeans.

EFSA Panel on Plant Health (PLH), Bragard C, Baptista P, Chatzivassiliou E, Gonthier P, Jaques Miret JA, Justesen AF, MacLeod A, Magnusson CS, Milonas P, Navas‐Cortes JA, Parnell S, Potting R, Reignault PL, Stefani E, Thulke H, Van der Werf W, Vicent Civera A, Yuen J, Zappalà L, Dehnen‐Schmutz K, Migheli Q, Vloutoglou I, Czwienczek E, Streissl F, Carluccio AV, Chiumenti M, Di Serio F, Rubino L, Reignault PL. Pest categorisation of Capsicum chlorosis virus

The EFSA Panel on Plant Health conducted a pest categorisation of Capsicum chlorosis virus (CaCV) for the EU territory. The identity of CaCV, a member of the genus Orthotospovirus (family Tospoviridae), is established and reliable detection and identification methods are available. The pathogen is not included in the EU Commission Implementing Regulation 2019/2072. CaCV has been reported in Australia, China, India, Iran, Taiwan, Thailand and USA (Hawaii). In the EU, it has been reported once in Greece (Crete Island). The NPPO of Greece reported that CaCV is no longer present in Greece. CaCV infects plant species in the family Solanaceae (i.e. pepper, tomato) and several species of other families, including ornamentals. It may induce severe symptoms on its hosts, mainly on leaves and fruits, which may become unmarketable. The virus is transmitted in a persistent propagative mode by the thrips Ceratothripoides claratris, Frankliniella schultzei, Microcephalothrips abdominalis and Thrips palmi. C. claratris and T. palmi are EU quarantine pests. M. abdominalis is known to be present in several EU member states and it is not regulated in the EU. Plants for planting, parts of plants, fruits and cut flowers of CaCV hosts, and viruliferous thrips were identified as the most relevant pathways for the entry of CaCV into the EU. Cultivated and wild hosts of CaCV are distributed across the EU. Should the pest enter and establish in the EU territory, impact on the production of cultivated hosts is expected. Phytosanitary measures are available to prevent entry and spread of the virus in the EU. CaCV fulfils the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

Design, Synthesis, Anti-Tomato Spotted Wilt Virus Activity, and Mechanism of Action of Thienopyrimidine-Containing Dithioacetal Derivatives

Currently, there is insufficient viricide to effectively control tomato spotted wilt virus (TSWV). To address this pending issue, a series of thienopyrimidine-containing dithioacetal derivatives were prepared and tested for their anti-TSWV activities. A subsequent three-dimensional quantitative structure-activity relationship was constructed to indicate the development of optimal compound 35. The obtained compound 35 had excellent anti-TSWV curative, protective, and inactivating activities (63.0, 56.6, and 74.1%, respectively), and the EC₅₀ values of protective and inactivating activities of compound 35 were 252.8 and 113.5 mg/L, respectively, better than those of ningnanmycin (284.8 and 144.7 mg/L) and xiangcaoliusuobingmi (624.9 and 300.0 mg/L). In addition, the anti-TSWV activity of compound 35 was associated with defense-related enzyme activities, enhanced photosynthesis, and reduced stress response, thereby enhancing disease resistance.

Efficient control of western flower thrips by plastid-mediated RNA interference

Plastid-mediated RNA interference (PM-RNAi) has emerged as a promising strategy for pest control. Expression from the plastid genome of stable double-stranded RNAs (dsRNAs) targeted against essential insect genes can effectively control some herbivorous beetles, but little is known about the efficacy of the transplastomic approach in other groups of pest insects, especially nonchewing insects that do not consume large amounts of leaf material. Here we have investigated the susceptibility of the western flower thrip (WFT, Frankliniella occidentalis), a notorious pest in greenhouses and open fields, to PM-RNAi. We show that WFTs ingest chloroplasts and take up plastid-expressed dsRNAs. We generated a series of transplastomic tobacco plants expressing dsRNAs and hairpin RNAs (hpRNAs) targeted against four essential WFT genes. Unexpectedly, we discovered plastid genome instability in transplastomic plants expressing hpRNAs, suggesting that dsRNA cassettes are preferable over hpRNA cassettes when designing PM-RNAi strategies. Feeding studies revealed that, unlike nuclear transgenic plants, transplastomic plants induced a potent RNAi response in WFTs, causing efficient suppression of the targeted genes and high insect mortality. Our study extends the application range of PM-RNAi technology to an important group of nonchewing insects, reveals design principles for the construction of dsRNA-expressing transplastomic plants, and provides an efficient approach to control one of the toughest insect pests in agriculture and horticulture.

Groundnut Bud Necrosis Virus Modulates the Expression of Innate Immune, Endocytosis, and Cuticle Development-Associated Genes to Circulate and Propagate in Its Vector, Thrips palmi

Thrips palmi (Thysanoptera: Thripidae) is the predominant tospovirus vector in Asia-Pacific region. It transmits economically damaging groundnut bud necrosis virus (GBNV, family Tospoviridae) in a persistent propagative manner. Thrips serve as the alternate host, and virus reservoirs making tospovirus management very challenging. Insecticides and host plant resistance remain ineffective in managing thrips–tospoviruses. Recent genomic approaches have led to understanding the molecular interactions of thrips–tospoviruses and identifying novel genetic targets. However, most of the studies are limited to Frankliniella species and tomato spotted wilt virus (TSWV). Amidst the limited information available on T. palmi–tospovirus relationships, the present study is the first report of the transcriptome-wide response of T. palmi associated with GBNV infection. The differential expression analyses of the triplicate transcriptome of viruliferous vs. nonviruliferous adult T. palmi identified a total of 2,363 (1,383 upregulated and 980 downregulated) significant transcripts. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed the abundance of differentially expressed genes (DEGs) involved in innate immune response, endocytosis, cuticle development, and receptor binding and signaling that mediate the virus invasion and multiplication in the vector system. Also, the gene regulatory network (GRN) of most significant DEGs showed the genes like ABC transporter, cytochrome P450, endocuticle structural glycoprotein, gamma-aminobutyric acid (GABA) receptor, heat shock protein 70, larval and pupal cuticle proteins, nephrin, proline-rich protein, sperm-associated antigen, UHRF1-binding protein, serpin, tyrosine–protein kinase receptor, etc., were enriched with higher degrees of interactions. Further, the expression of the candidate genes in response to GBNV infection was validated in reverse transcriptase-quantitative real-time PCR (RT-qPCR). This study leads to an understanding of molecular interactions between T. palmi and GBNV and suggests potential genetic targets for generic pest control.

Reproductive Isolation in the Cryptic Species Complex of a Key Pest: Analysis of Mating and Rejection Behaviour of Onion Thrips (Thrips tabaci Lindeman)

Simple Summary

The onion thrips (Thrips tabaci), which is a key pest worldwide, includes three characteristic, distinct groups (i.e., lineages) under the same species name. In the current report, we addressed the question of whether individuals from these lineages recognize and assess each other as potential mating partners. We demonstrated that at least two of these lineages do not belong to the same species, since under our laboratory conditions no mating occurred between them. Moreover, specimens from these cross pairings often exhibited an escape response upon contact with the other thrips, while most of the pairs from the same lineages readily mated at their first interaction. The behaviour of males clearly indicated that they can assess the mating status of a female and usually only try to copulate with virgins. Our findings are important not only because in agriculture it is vital to know whether morphologically similar entities belong to the same species, but also because knowledge about the communication of insects and the possible role of the cues involved can help the development of new plant protection techniques.

Abstract

Thrips tabaci Lindeman is a serious pest of various cultivated plants, with three, distinct lineages within a cryptic species complex. Despite the well-known significance of this pest, many attributes of these lineages are not yet fully understood, including their reproductive behaviour. We performed no-choice-design cross-mating experiments under a controlled laboratory environment with virgin adult individuals from all three lineages. The behaviour of thrips was recorded with a camera mounted on a stereomicroscope, and the recordings were analysed in detail. We found that the so-called leek-associated lineages of this cryptic species complex are reproductively isolated from the tobacco-associated lineage; therefore, they represent different species. Divergence in the behaviour of conspecific and heterospecific pairs became evident only after contact. There were no marked differences between the lineages in their precopulatory and copulatory behaviour, except in the duration of the latter. We confirmed mating between thelytokous females and arrhenotokous males; however, we assume some form of loss of function in the sexual traits of asexual females. The post-mating behaviour of males indicated the presence and role of an anti-aphrodisiac pheromone. We also demonstrated differences between lineages regarding their activity and their propensity for exhibiting an escape response upon interaction with heterospecific thrips.