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Abstract: Viruses cause a big fraction of economically important diseases in major crops, including tomato. In the past decade (2011–2020), many emerging or re-emerging tomato-infecting viruses were reported worldwide. In this period, 45 novel viral species were identified in tomato, 14 of which were discovered using high-throughput sequencing (HTS). In this review, we first discuss the role of HTS in these discoveries and its general impact on tomato virome research. We observed that the rate of tomato virus discovery is accelerating in the past few years due to the use of HTS. However, the extent of the post-discovery characterization of viruses is lagging behind and is greater for economically devastating viruses, such as the recently emerged tomato brown rugose fruit virus. Moreover, many known viruses still cause significant economic damages to tomato production. The review of databases and literature revealed at least 312 virus, satellite virus, or viroid species (in 22 families and 39 genera) associated with tomato, which is likely the highest number recorded for any plant. Among those, here, we summarize the current knowledge on the biology, global distribution, and epidemiology of the most important species. Increasing knowledge on tomato virome and employment of HTS to also study viromes of surrounding wild plants and environmental samples are bringing new insights into the understanding of epidemiology and ecology of tomato-infecting viruses and can, in the future, facilitate virus disease forecasting and prevention of virus disease outbreaks in tomato.
Published in DiRROS: 05.08.2024; Views: 58; Downloads: 64
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Abstract: Pepino mosaic virus (PepMV) has caused great concern in the greenhouse tomato industry after it was found causing a new disease in tomato in 1999. The objective of this paper is to investigate alternative hosts and compare important biological characteristics of the three PepMV strains occurring in Europe when tested under different environmental conditions. To this end we compared the infectivity and symptom development of three, well characterized isolates belonging to three different PepMV strains, EU-tom, Ch2 and US1, by inoculating them on tomato, possible alternative host plants in the family Solanaceae and selected test plants. The inoculation experiments were done in 10 countries from south to north in Europe. The importance of alternative hosts among the solanaceous crops and the usefulness of test plants in the biological characterization of PepMV isolates are discussed. Our data for the three strains tested at 10 different European locations with both international and local cultivars showed that eggplant is an alternative host of PepMV. Sweet pepper is not an important host of PepMV, but potato can be infected when the right isolate is matched with a specific cultivar. Nicotiana occidentalis 37B is a useful indicator plant for PepMV studies, since it reacts with a different symptomatology to each one of the PepMV strains.
Keywords: Pepino mosaic virus, potexvirus, strains, host plants, test plants
Published in DiRROS: 26.07.2024; Views: 98; Downloads: 112
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Abstract: Waterborne and seedborne Pepino mosaic virus (PepMV) and Potato spindle tuber viroid (PSTVd) pose serious threats to tomato production due to seed transmission and mechanical transmission, coupled with their long-term stability outside the host plant. Therefore, rapid and sensitive diagnostic procedures are needed to prevent the spread of these quarantine pathogens. In particular, water and seed contamination are difficult to detect and confirm without efficient concentration methods. This study presents procedures that improve detection of PSTVd from tomato seeds and leaf tissue, and PepMV from water and tomato leaf tissue. For efficient concentration of PepMV from water samples, a procedure was optimized using convective interaction media monolithic chromatography columns, which provides concentration by three orders of magnitude. For concentration of PSTVd from seed extracts, an easy-to-use and efficient method was developed based on RNA binding to positively charged anion-exchange resin beads that provides up to 100-fold more sensitive detection in comparison with procedures without a concentration step. This thus allows confirmation of RT-qPCR results with sequencing of RT-PCR products in samples with low viroid levels. In addition, reverse-transcription loop-mediated isothermal amplification assays for detection of PSTVd and PepMV were optimized and adapted to both laboratory and on-site testing requirements. This allows rapid detection of these pathogens in crude leaf homogenates, in under 30 min. These procedures of concentration and detection are shown to be efficient and to fill the gaps in diagnostics of PepMV and PSTVd, especially when these pathogens are present at low levels in difficult matrices such as water and seeds.
Keywords: PSTVd, PepMV, seeds, water, concentration, loop-mediated isothermal amplification
Published in DiRROS: 24.07.2024; Views: 121; Downloads: 55
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Abstract: High-throughput sequencing has dramatically broadened the possibilities for plant virus research and diagnostics, enabling discovery of new or obscure viruses, and virus strains and rapid sequencing of their genomes. In this research, we employed high-throughput sequencing to discover a new virus infecting tomato, Henbane mosaic virus (Potyvirus, Potyviridae), which was first discovered at the beginning of 20th century in the United Kingdom in cultivated henbane. A field tomato plant with severe necrotic symptoms of unknown etiology was sampled in Slovenia and high-throughput sequencing analysis using small RNA and ribosomal RNA depleted total RNA approaches revealed a mixed infection with Potato virus M (Carlavirus, Betaflexiviridae), Southern tomato virus (Amalgavirus, Amalgamaviridae) and henbane mosaic virus in the sample. The complete genomic sequence of henbane mosaic virus was assembled from the sequencing reads. By re-inoculation of the infected material on selected test plants, henbane mosaic virus was isolated and a host range analysis was performed, demonstrating the virus was pathogenic on several plant species. Due to limited metadata in public repositories, the taxonomic identification of the virus isolate was initially putative. Thus, in the next step, we used small RNA sequencing to determine genomic sequences of four historic isolates of the virus, obtained from different virus collections. Phylogenetic analyses performed using this new sequence information enabled us to taxonomically position Henbane mosaic virus as a member of the Potyvirus genus within the chili veinal mottle virus phylogenetic cluster and define the relationship of the new tomato isolate with the historic ones, indicating the existence of at least four putative strains of the virus. The first detection of henbane mosaic virus in tomato and demonstration of its pathogenicity on this host is important for plant protection and commercial tomato production. Since the virus was initially present in a mixed infection, and its whole genome was not sequenced, it has probably been overlooked in routine diagnostics. This study confirms the applicability of a combination of high-throughput sequencing and classic plant virus characterization methods for identification and phylogenetic classification of obscure viruses and historical viral isolates, for which no or limited genome sequence data is available.
Keywords: henbane mosaic virus, Tomato, high-throughput sequencing, host range analysis, phylogeny, Potyvirus
Published in DiRROS: 24.07.2024; Views: 101; Downloads: 97
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Abstract: Hazelnut (Corylus avellana) is cultivated on 118 ha and ranks eighth in Slovenian fruit growing production, representing 2.8% of the total area of fruit plantations in the country. However, decline of some of the trees appeared in 2012 in two plantations located in eastern Slovenia. Together these orchards cover 5 ha, with around 1600 trees planted 12 to 15 years ago. By October 2018, ~12% of these trees had died, and an additional 12% showed decay symptoms. The dead and dying trees were scattered throughout both orchards, with no apparent pattern. The most affected cultivar was ‘Istrska dolgoplodna leska’. Using molecular diagnostic methods, we showed infection of symptomatic trees with three unrelated phytoplasmas: ‘Candidatus Phytoplasma fragariae’, of the 16SrXII-E phytoplasma subgroup, and phytoplasma of the 16SrV and 16SrIX groups. In 2018, the presence of ‘Ca. P. fragariae’ and/or phytoplasma of 16SrV group were confirmed in decayed hazelnut trees in eastern, north-eastern, central, south-eastern and western Slovenia. ‘Ca. P. fragariae’ has also been detected in a forest in south-western Slovenia, for Acer campestre, Carpinus betulus, Crataegus laevigata, Fraxinus ornus and Quercus petraea. All infected forest trees showed unusual dense proliferation of sprouts from roots and/or trunks. Molecular characterisations of partial 16S rRNA, secY, map and ribosomal protein genetic locus of hazelnut 16SrV phytoplasma isolates show that they are identical to isolates that can cause grapevine flavescence dorée disease. Here, the results of our recent study and the open questions on this burning issue for hazelnut production are presented.
Keywords: Corylus avellana, ʼCandidatus Phytoplasma fragariaeʼ, 16SrV phytoplasma group, 16SrIX phytoplasma group, decline
Published in DiRROS: 24.07.2024; Views: 79; Downloads: 55
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