Transmission of Tomato spotted wilt virus isolates able and unable to overcome tomato or pepper resistance by its vector Frankliniella occidentalis

[EN] Tomato spotted wilt virus (TSWV) causes serious diseases of many economically important crops. Disease control has been achieved by breeding tomato and pepper cultivars with the resistance genes Sw-5 and Tsw, respectively. However, TSWV isolates overcoming these genetic resistances have appeared in several countries. To evaluate the risk of spread of these resistance-breaking isolates, we tested their ability of transmission by the main vector of TSWV, the thrips Frankliniella occidentalis. We compared the transmission rate by thrips of six TSWV isolates of different biotype (able or unable to overcome this resistance in pepper and tomato), and with divergent genotype (A and B). Our results indicate that the transmission rate was related to the amount of virus accumulated in thrips but not to virus accumulation in the source plants on which thrips acquired the virus. No correlation was found between transmission efficiency by thrips and the genotype or between transmission efficiency and the ability of overcoming both resistances. This result suggests that resistance-breaking isolates have the same potential to be transmitted as the isolates unable to infect resistant tomato and pepper cultivars.This work was supported by grants RTA2008-00010-C03 and FEDER, and ACOMP/2009/103 financed by INIA and Generalitat Valenciana, respectively. D. E. D. was recipient of a FPU predoctoral fellowship from the Spanish Ministry of Science and Education and B. B. was supported by an INIA-CCAA contract. Fito´ and Seminis kindly provided the seeds of the tomato and pepper cultivars used in the experiment. We would like to thank Debora Mart ´ ´ınez and Dolores Com´ın for technical assistance, as well as Dr D. Peters (Wageningen University, the Netherlands) and Dr J. Contreras (Universidad Politecnica de Cartagena, Spain) ´ for kindly providing the TSWV isolate BR01 and a thrips colony, respectively. Drs E. Carbonell and J. Perez- Panades (IVIA) are thanked for statistical advice. Two anonymous referees improved a previous version of the manuscript.Debreczeni, DE.; Rubio, L.; Aramburu, J.; López Del Rincón, C.; Galipienso, L.; Soler Aleixandre, S.; Belliure, B. (2014). Transmission of Tomato spotted wilt virus isolates able and unable to overcome tomato or pepper resistance by its vector Frankliniella occidentalis. Annals of Applied Biology. 164:182-189. https://doi.org/10.1111/aab.12090S18218916

First report of cucurbit chlorotic yellows virus infecting watermelon and zucchini in the Canary Islands, Spain

This work was funded by grants from Spanish Ministerio de Econolnia, industria y competitividad (RTA2017-00061-C03-02) and from Instituto Valenciano de Investigaciones Agrarias (IVlA) (51912), both co-funded by the European Regional Development Fund (ERDF).Alfaro Fernández, AO.; Espino De Paz, AI.; Botella-Guillen, M.; Font San Ambrosio, MI.; Sanauja, E.; Galipienso, L.; Rubio, L. (2022). First report of cucurbit chlorotic yellows virus infecting watermelon and zucchini in the Canary Islands, Spain. Plant Disease. 106(7):1-1. https://doi.org/10.1094/PDIS-10-21-2296-PDN11106

Nucleotide sequence and genome organization of Dweet mottle virus and its relationship to members of the family Betaflexiviridae

The nucleotide sequence of Dweet mottle virus (DMV) was determined and compared to sequences of members of the families Alphaflexiviridae and Betaflexiviridae. The DMV genome has 8,747 nucleotides (nt) excluding the 3′ poly-(A) tail. DMV genomic RNA contains three putative open reading frames (ORFs) and untranslated regions of 73 nt at the 5′ and 541 nt at 3′ termini. ORF1 potentially encoding a 227.48-kDa polyprotein, which has methyltransferase, oxygenase, endopeptidase, helicase, and RNA-dependent RNA polymerase (RdRP) domains. ORF2 encodes a movement protein of 40.25 kDa, while ORF3 encodes a coat protein of 40.69 kDa. Protein database searches showed 98–99% matches of DMV ORFs with citrus leaf blotch virus (CLBV) sequences. Phylogenetic analysis based on the RdRP core domain revealed that DMV is closely related to CLBV as a member of the genus Citrivirus. DMV did not satisfy the molecular criteria for demarcation of an independent species within the genus Citrivirus, family Betaflexiviridae, and hence, DMV can be considered a CLBV isolate

RNA2-encoded VP37 protein of Broad bean wilt virus 1 is a determinant of pathogenicity, host susceptibility, and a suppressor of post-transcriptional gene silencing

Broad bean wilt virus 1 (BBWV-1, genus Fabavirus, family Secoviridae) is a bipartite, single-stranded positive-sense RNA virus infecting many horticultural and ornamental crops worldwide. RNA1 encodes proteins involved in viral replication whereas RNA2 encodes two coat proteins (the large and small coat proteins) and two putative movement proteins (MPs) of different sizes with overlapping C-terminal regions. In this work, we determined the role played by the small putative BBWV-1 MP (VP37) on virus pathogenicity, host specificity, and suppression of post-transcriptional gene silencing (PTGS). We engineered a BBWV-1 35S-driven full-length cDNA infectious clone corresponding to BBWV-1 RNA1 and RNA2 (pBBWV1-Wt) and generated a mutant knocking out VP37 (pBBWV1-G492C). Agroinfiltration assays showed that pBBWV1-Wt, as the original BBWV-1 isolate, infected broad bean, tomato, pepper, and Nicotiana benthamiana, whereas pBBWV1-G492C did not infect pepper and tomato systemically. Also, pBBWV1-G492C induced milder symptoms in broad bean and N. benthamiana than pBBWV1-Wt. Differential retrotranscription and amplification of the (+) and (−) strands showed that pBBWV1-G492C replicated in the agroinfiltrated leaves of pepper but not in tomato. All this suggests that VP37 is a determinant of pathogenicity and host specificity. Transient expression of VP37 through a potato virus X (PVX) vector enhanced PVX symptoms and induced systemic necrosis associated with programmed cell death in N. benthamiana plants. Finally, VP37 was identified as a viral suppressor of RNA silencing by transient expression in N. benthamiana 16c plants and movement complementation of a viral construct based on turnip crinkle virus (pTCV-GFP)

A comparative study of viral infectivity, accumulation and symptoms induced by broad bean wilt virus 1 isolates

Broad bean wilt virus 1 (BBWV-1, genus Fabavirus, family Secoviridae) is a bipartite positive-sense single-stranded RNA virus distributed worldwide infecting many herbaceous species. Until now, scarce information regarding biological properties of BBWV-1 isolates is available. This work shows a comparative study on virus infectivity (proportion of infected plants over inoculated plants), virus accumulation and symptoms induced by four genetically different BBWV-1 isolates (Ben, B41/99, NSRV and PV0548) which were mechanically inoculated on several herbaceous hosts. The four BBWV-1 isolates infected broad bean, tomato, pepper and Nicotiana benthamiana plants, whereas none of them infected cucumber, common bean and melon. Infectivity ranged from 40 to 60% in tomato and from 75% to 95% in pepper, whereas it was 100% in broad bean and N. benthamiana for the four BBWV-1 isolates. Symptoms showed differences depending on the host plant, the viral isolate and the infection time. Virus accumulation was determined in broad bean and pepper plants and showed differences among host species and BBWV-1 isolates. No association between plant symptom manifestation and viral titre was observed

Citrus Leaf Blotch Virus: A New Citrus Virus Associated with Bud Union Crease on Trifoliate Rootstocks

Citrus leaf blotch virus (CLBV) was first detected in a Nagami kumquat, clone SRA-153 from Corsica (France), showing bud union crease when propagated on Troyer citrange. Citranges are important rootstocks in Spain, presently being used for about 50% of all commercial citrus trees. Therefore, dispersal of a graft-transmissible pathogen causing bud union crease on this rootstock could potentially cause important economic losses. CLBV has filamentous particles about 900×14 nm in size, with a single-stranded, positive sense, genomic RNA (gRNA) of 8,747nt, and a coat protein about 41 kDa. The gRNA contains three open reading frames (ORFs) and two untranslated regions of 73 and 541 nt at the 5’ and 3’ termini, respectively. Biological and molecular properties of CLBV support its inclusion in a new virus genus. The virus can be detected by graft-inoculation onto Dweet tangor seedlings, in which it induces chlorotic blotching in young leaves, but transmission is sometimes erratic and at least six indicator plants should be used in each test. We developed a quick detection procedure using RT-PCR with two sets of primers derived from sequences in ORF1 (a region containing motifs characteristic of an RNA polymerase) and ORF3 (the coat protein gene). Results with both sets of primers were similar. CLBV was readily detected in young leaves of infected Nagami kumquat or in Nules Clementine, Owari Satsuma, Eureka lemon, Marsh grapefruit or Newhall navel orange inoculated with kumquat SRA-153, but not in Pineapple sweet orange, a host that yielded more than 80% false negatives. Detection in field trees was less consistent, as the virus generally has low titer and is unevenly distributed. By this procedure CLBV was detected in two mandarins from Japan, a kumquat from New South Wales (Australia), and in various sweet orange trees showing bud union crease on citrange or citrumelo, from commercial citrus orchards in Valencia (Spain) and Florida (USA), but not in other trees in the same orchards showing similar symptoms. Our results indicate that CLBV is present in citrus varieties other than kumquat in several geographic areas. Failure to detect CLBV in some trees with bud union crease could be due to low titer or uneven distribution of the virus within the plant. Alternatively, a different agent could be involved

Broad bean wilt virus 1 encoded VP47 and SCP are suppressors of plant post-transcriptional gene silencing

Broad bean wilt virus 1 (BBWV-1, genus Fabavirus, family Secoviridae) is a bipartite positive single-stranded RNA (+ssRNA) virus infecting important horticultural and ornamental crops worldwide. RNA1 encodes proteins involved in virus replication, whereas RNA2 encodes the large and small coat proteins (LCP, and SCP, respectively) and two putative movement proteins with overlapping C-terminal but different sizes: 47.2 kDa (VP47) and 37 kDa (VP37). Post-transcriptional gene silencing (PTGS) is a mechanism of gene regulation and defense against pathogens such as viruses. However, most plant viruses encode proteins called viral suppressors of RNA silencing (VSRs) which able to inhibit PTGS. Previously, BBWV-1 VP37 was identified as VSR and here, we have demonstrated that VP47 and SCP, but not LCP, are also VSRs by two approaches: (i) transient expression in Nicotiana benthamiana 16c plants expressing the green fluorescent protein (GFP) constitutively, and (ii) movement complementation assays using a viral vector based on Turnip crinkle virus sequence containing GFP (pTCV-GFP). In contrast LCP but not SCP of Broad been wilt virus 2 (BBWV-2, genus Fabavirus, family Secoviridae) is a VSR, which illustrates that viruses of the same genus can interact differently with the host