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Strawflower ( Helichrysum bracteatum , Asteraceae) , an annual or biennial herb, is one of the most popular flowers in the world because of the colorful flowers and the long flowering period. However, the ornamental plants belonging to Asteraceae are susceptible to numerous viruses such as cucumber mosaic virus (CMV) ( Cucumovirus , Bromoviridae) , potato virus Y ( Potyvirus , Potyviridae), tomato mosaic virus (ToMV) ( Tobamovirus , Virgaviridae), tobacco mosaic virus (TMV) ( Tobamovirus , Virgaviridae), chrysanthemum virus B (CVB) ( Carlavirus , Betaflexiviridae), tomato aspermy virus (TAV) ( Cucumovirus , Bromoviridae), tomato spotted wilt virus (TSWV) ( Orthotospovirus tomatomaculae , Tospoviridae), and impatiens necrotic spot virus (INSV) ( Orthotospovirus impatiensnecromaculae , Orthotospovirus) resulting in severe yield loss (Verma et al. 2003; Raj et al. 2007; Kondo et al. 2011; Liu et al. 2014; Marys et al. 2014; Min et al. 2020; Gautam et al. 2021; Read et al. 2022; Supakitthanakorn et al. 2022). Among these viruses, the TSWV, a thrips-transmitted negative-stranded RNA virus, is well known to cause viral disease in several plant species while is less reported in Helichrysum , especially in China. In April 2021, viral attack symptoms were detected on the leaves of H. bracteatum during our routine checks in the greenhouse located at Shunyi District, Beijing, China, such as wilting, shrinking, chlorotic blotches, chlorotic ring spots. To investigate the virus infecting H. bracteatum , in total of 25 symptomatic and 5 asymptomatic leaves were sampled and tested by the effective double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using antisera against CMV, PVY/PVX, ToMV, TMV, CVB, TAV, TSWV, INSV, separately (Agdia, USA). Only the TSWV showed positive in symptomatic samples, and asymptomatic samples were all negative, which implied TSWV infection. To further confirm the virus type of TSWV isolated from H. bracteatum samples, the genomic RNA of the virus was isolated using reverse transcription and polymerase chain reaction (RT-PCR), and then was cloned, sequenced and analyzed. Total RNA of five symptomatic leaves (ELISA-positive) were extracted using the FastPure Plant Total RNA Isolation Kit (Vazyme, China), and then were reverse transcribed by HiScript II Reverse Transcriptase (Vazyme, China). Each genome segments were amplified using Phanta Max Super-Fidelity DNA Polymerase (Vazyme, China) with TSWV-specific primers newly designed and listed in Table S1. The PCR setup was as follow: 95°C for 30 s, followed by 35 cycles at 95°C for 30 s, 55°C for 30 s, and 72°C for 1.5 min, with a final extension at 72°C for 10 min. All PCR products were cloned into the TA/Blunt-Zero vector (Vazyme, China) and sequenced (GENEWIZ, Inc.). We assembled and then analyzed the evolutionary relationship of three genomic fragments, that is, TSWV-BJFC-Hb S (2923 bp), M (4785 bp) and L (8971 bp) using the BLAST tools. The results showed high similarity with TSWV-henan isolated from pepper in China (99.6% to TSWV-S (MT799179.1), 99.8 % to TSWV-M (MT799178.1) and 99.8 % TSWV-L (MT799177.1)). These sequences have been submitted to the GenBank (OM982910, OM982911 and OM937131). Taking all of these evidences together, the viral disease observed in H. bracteatum was closely associated with TSWV. TSWV is currently widespread in China, infecting Nasturtium , Chrysanthemum and cowpea (Xiao et al. 2015; Hu et al. 2018; Yu et al. 2021). Epidemics of TSWV have also been reported in several other countries such as Korea, North Carolina, Turkey and India (Renukadevi et al. 2015; Koehler et al. 2016; Kwak et al. 2021; Erilmez, S. 2022). This is the first report of TSWV infection on H. bracteatum in China. Due to the fast spread and serious economic losses of TSWV, the rapid detection may be the essential way to prevent this viral disease among crops (Macharia et al. 2014).

Statistical inference for spatial models of infectious disease spread is often very computationally expensive. These models are generally fitted in a Bayesian Markov chain Monte Carlo (MCMC) framework, which requires multiple iterations of the computationally cumbersome likelihood function. We here propose a method of inference based on so-called emulation techniques. Once again the method is set in a Bayesian MCMC context, but avoids calculation of the computationally expensive likelihood function by replacing it with a Gaussian process approximation of the likelihood function built from simulated data. We show that such a method can be used to infer the model parameters and underlying characteristics of the spatial disease system, and this can be done in a computationally efficient manner. The Canadian Journal of Statistics 44: 480-501; 2016 © 2016 Statistical Society of Canada [ABSTRACT FROM AUTHOR]

Tospovirus is a tripartite negative stranded RNA virus and is considered as one of the most devastating plant viruses. Successful virus infection in plant requires many host factors. To date, very few host factors have been identified as important in Tospovirus infection in plants. We reported earlier that NSm protein encoded by Tomato spotted wilt virus (TSWV), a type species of the genus Orthotospovirus, plays critical roles in viral cell-to-cell and long-distance movement. In this study, we determined that molecular co-chaperone NbSGT1 interacted with TSWV NSm in Nicotiana benthamiana. TSWV infection significantly upregulated the expression of NbSGT1 gene and transient overexpression of NbSGT1 in N. benthamiana leaves accelerated TSWV infection. In contrast, silencing the NbSGT1 gene expression using a virus-induced gene silencing (VIGS) approach strongly inhibited TSWV NSm cell-to-cell movement, as well as TSWV local and systemic infection in N. benthamiana plants. Furthermore, NbSGT1 was found to regulate the infection of both American and Euro/Asia type tospoviruses in N. benthamiana plant. Collectively, our findings presented in this paper and the results published previously indicated that molecular co-chaperone NbSGT1 plays important roles in modulating both positive stranded and tripartite negative stranded RNA virus infection in plants.

Tomato spotted wilt virus (TSWV) is one of the most destructive viral pathogens of plants. Recently, a single dominant gene conferring complete resistance to TSWV (RTSW) was identified in Nicotina alata and introgressed into cultivated tobacco (N. tabacum). However, whether the TSWV carries an avirulence (Avr) factor directed against RTSW remains obscure. In the present study, we identified the non-structural protein (NSm), the movement protein of TSWV, which is an RTSW-specific Avr factor, by using two different transient expression systems. Using amino acid (aa) substitution mutants, we demonstrated the ability to induce RTSW-mediated hypersensitive response (HR) of NSm is independent of its movement function. Moreover, key substitutions (C118Y and T120N), a 21-aa viral effector epitope, and different truncated versions of NSm, which are responsible for the recognition of the Sw-5b resistance gene of tomato, were tested for their ability to trigger HR to TSWV in tobacco. Together, our results demonstrated that RTSW-mediated resistance is triggered by NSm in the same way as by Sw-5b, however, via different elicitor active sites. Finally, an Avr gene-based diagnostic approach was established and used to determine the presence and effectiveness of resistance genes in tobacco.

Plant viruses are inducers and targets of antiviral RNA silencing. To condition susceptibility, most plant viruses encode silencing suppressor proteins that interfere with antiviral RNA silencing. The NSs protein is an RNA silencing suppressor in orthotospoviruses, such as the tomato spotted wilt virus (TSWV). The mechanism of RNA silencing suppression by NSs and its role in virus infection and movement are poorly understood. Here, we cloned and tagged TSWV NSs and expressed it from a GFP-tagged turnip mosaic virus (TuMV-GFP) carrying either a wild-type or suppressor-deficient (AS9) helper component proteinase (HC-Pro). When expressed in cis, NSs restored pathogenicity and promoted systemic infection of suppressor-deficient TuMV-AS9-GFP in Nicotiana benthamiana and Arabidopsis thaliana. Inactivating mutations were introduced in NSs RNA-binding domain one. A genetic analysis with active and suppressor-deficient NSs, in combination with wild-type and mutant plants lacking essential components of the RNA silencing machinery, showed that the NSs insert is stable when expressed from a potyvirus. NSs can functionally replace potyviral HC-Pro, condition virus susceptibility, and promote systemic infection and symptom development by suppressing antiviral RNA silencing through a mechanism that partially overlaps that of potyviral HC-Pro. The results presented provide new insight into the mechanism of silencing suppression by NSs and its effect on virus infection.

Pepper is a very popular and profitable crop in Serbia and its production is growing rapidly as well as the importance of diseases caused by viruses. Virus infections interfere with development of pepper plants, reducing yield and fruit quality. More than 45 viruses have been isolated from pepper so far, and in our country the following are considered economically very important: Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), Alfalfa mosaic virus (AMV), Tomato spotted wilt virus (TSWV) and Potato virus Y (PVY). During 2009, an investigation was conducted regarding the presence and distribution of pepper viruses in Serbia, which included a survey of different localities of transplant production, and both greenhouse and open field pepper crops. Collected samples were tested utilizing a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with polyclonal antisera specific for the detection of economically important pepper viruses: PVY, AMV, CMV, TSWV, TMV and Potato virus X (PVX). In the collected samples, presence of the four viruses (PVY, CMV, TSWV and AMV) was confirmed in single and mixed infections. In tested transplant samples, the most frequently detected virus was CMV (18.18%), while PVY was the most frequent in samples collected in greenhouse and open field pepper crops (32.56% and 51.21% respectively). The presence of TSWV was detected only in greenhouse-grown pepper crops, while the presence of PVX and TMV was not detected during this investigation. The obtained results indicated that PVY and CMV were widely distributed and the most frequent viruses in pepper crops in Serbia. Future investigation should include their detailed biological and molecular characterization, as well as the implementation of appropriate control measures in pepper productions.

Reliable detection of plant pathogens does not only mean the development of sufficiently sensitive laboratory techniques for their routine testing. Regardless of the sensitivity of applied methods, the proper selection of samples to be tested has crucial influence on method reliability. Due to uneven distribution of Tomato spotted wilt virus (TSWV) in naturally infected systemic host plants, the collection and sampling of material for assaying is acritical moment upon which the reliability of laboratory procedure depends. The effect of irregular virus distribution on its serological detection was examined in tomato, pepper and four ornamental species, as its most important host plants in our country.The reliability of virus detection, depending on its uneven distribution, was assessed by serological testing of tomato and pepper symptomatic leaves and fruits, and symptomatic and asymptomatic young and old leaves, as well as flower petals of ornamentals. Although TSWV was detected using ELISA in the majority of plants included in the experiment, the tests indicated an uneven distribution and unequal concentrations of TSWV in different parts of the plants. The virus could not be detected in a certain number of subsamples, prepared from infected tomato and pepper fruits and older ornamental leaves. The virus also could not be detected in some ornamentals and tomato plants with intensive symptoms. Conversely, the virus was detected in three ornamental plants without any symptoms. Examining the virus distribution in different plant parts indicated that the reliability of ELISA could be reached not only by sampling younger ornamental leaves, but also by preparing compound samples with as much leaves as possible, or by testing a greater number of subsamples of the tested plant. Considering a small possibility of TSWV detection in tomato and pepper fruits, the infection of these should be established by testing their leaves. Besides, the data show that negative test results for the known host plants with characteristic symptoms require tests to be repeated using more sensitive methods than ELISA. These results are important as guidelines for growers and professionals who submit samples, as well as for laboratories performing routine testing.

Tomato spotted wilt virus (TSWV) has one of the largest host ranges among plant viruses and is widespread in all climates. TSWV is responsible for numerous epidemics in many parts of the world in different crops, mainly vegetables, tobacco and ornamentals. Its highly polyphagous nature, effectiveness of virus transmission by the thrips as its vectors, rapidity with which new variants arise, as well as difficulties in controlling the vectors make TSWV one of the most dangerous plant viruses. The ability of this virus to cause such severe losses on a broad range of crops, as well as its intriguing biological and molecular characteristics place TSWV amongst the most extensively studied plant viruses in the world at present. This paper provides a general overview of TSWV, encompassing all the major aspects of its biology and current knowledge on host range, symptomatology, molecular biology, vectorrelationship, control and diagnosis.