First Detection of Faba bean necrotic yellow virus in Spain

Novel nanovirus and associated alphasatellites identified in milk vetch plants with chlorotic dwarf disease in Iran

Members of the family Nanoviridae are multi-component single-stranded DNA viruses that infect a variety of plant species. Using a combination of conventional PCR and high throughput sequencing-based approach, we identified a novel nanovirus infecting two symptomatic milk vetch plants (Astragalus myriacanthus Boiss.; family Fabaceae) showing marginal leaf chlorosis, little leaves and dwarfing in Iran. All eight segments (DNA-C, DNA-M, DNA-N, DNA-R, DNA-S, DNA-U1, DNA-U2 and DNAU4) were recovered and Sanger sequenced. The genome of this new nanovirus, hereby referred to as milk vetch chlorotic dwarf virus (MVCDV), shares 62.2-74.7 % nucleotide pairwise identity with the genomes of other nanoviruses. DNA-C, DNA-M, DNA-N, DNA-S components are most closely related to those of black medic leaf roll virus (BMLRV), sharing between 67.8-81.2 % identity. We also identified three nanoalphasatellites (family Alphasatellitidae) associated with the nanovirus which belong to species Faba bean necrotic yellows alphasatellite 1 (genus Subclovsatellite), Faba bean necrotic yellows alphasatellite 2 (genus Fabenesatellite) and Sophora yellow stunt alphasatellite 5 (genus Clostunsatellite). Given the significant diversity of Astragalus spp. in Iran, it is likely that there could be more nanoviruses circulating in these plants and that these may play a role in the spread of these nanovirus to cultivated fabaceous hosts.

Eukaryotic Circular Rep-Encoding Single-Stranded DNA (CRESS DNA) Viruses: Ubiquitous Viruses With Small Genomes and a Diverse Host Range

While single-stranded DNA (ssDNA) was once thought to be a relatively rare genomic architecture for viruses, modern metagenomics sequencing has revealed circular ssDNA viruses in most environments and in association with diverse hosts. In particular, circular ssDNA viruses encoding a homologous replication-associated protein (Rep) have been identified in the majority of eukaryotic supergroups, generating interest in the ecological effects and evolutionary history of circular Rep-encoding ssDNA viruses (CRESS DNA) viruses. This review surveys the explosion of sequence diversity and expansion of eukaryotic CRESS DNA taxonomic groups over the last decade, highlights similarities between the well-studied geminiviruses and circoviruses with newly identified groups known only through their genome sequences, discusses the ecology and evolution of eukaryotic CRESS DNA viruses, and speculates on future research horizons.

Genome diversity and evidence of recombination and reassortment in nanoviruses from Europe

The recent identification of a new nanovirus, pea necrotic yellow dwarf virus, from pea in Germany prompted us to survey wild and cultivated legumes for nanovirus infections in several European countries. This led to the identification of two new nanoviruses: black medic leaf roll virus (BMLRV) and pea yellow stunt virus (PYSV), each considered a putative new species. The complete genomes of a PYSV isolate from Austria and three BMLRV isolates from Austria, Azerbaijan and Sweden were sequenced. In addition, the genomes of five isolates of faba bean necrotic yellows virus (FBNYV) from Azerbaijan and Spain and those of four faba bean necrotic stunt virus (FBNSV) isolates from Azerbaijan were completely sequenced, leading to the first identification of FBNSV occurring in Europe. Sequence analyses uncovered evolutionary relationships, extensive reassortment and potential remnants of mixed nanovirus infections, as well as intra- and intercomponent recombination events within the nanovirus genomes. In some virus isolates, diverse types of the same genome component (paralogues) were observed, a type of genome complexity not described previously for any member of the family Nanoviridae. Moreover, infectious and aphid-transmissible nanoviruses from cloned genomic DNAs of FBNYV and BMLRV were reconstituted that, for the first time, allow experimental reassortments for studying the genome functions and evolution of these nanoviruses.

Control of plant virus diseases in cool-season grain legume crops

Cool-season grain legume crops become infected with a wide range of viruses, many of which cause serious diseases and major yield losses. This review starts by discussing which viruses are important in the principal cool-season grain legume crops in different parts of the world, the losses they cause and their economic impacts in relation to control. It then describes the main types of control measures available: host resistance, phytosanitary measures, cultural measures, chemical control, and biological control. Examples are provided of successful deployment of the different types of measures to control virus epidemics in cool-season grain legume crops. Next it emphasizes the need for integrated approaches to control because single control measures used alone rarely suffice to adequately reduce virus-induced yield losses in these crops. Development of effective integrated disease management (IDM) strategies depends on an interdisciplinary team approach to (i) understand the ecological and climatic factors which lead to damaging virus epidemics and (ii) evaluate the effectiveness of individual control measures. In addition to using virus-resistant cultivars, other IDM components include sowing virus-tested seed stocks, selecting cultivars with low seed transmission rates, using diverse phytosanitary or cultural practices that minimize the virus source or reduce its spread, and using selective pesticides in an environmentally responsible way. The review finishes by briefly discussing the implications of climate change in increasing problems associated with control and the opportunities to control virus diseases more effectively through new technologies.

Virus diseases of peas, beans, and faba bean in the Mediterranean region

In the Mediterranean region, pea, bean, and faba bean production is affected by around 17 major viruses. These viruses do not have the same ecology and consequently require a variety of different preventive measures to control them. Some of these viruses have a narrow host range, such as Faba bean necrotic yellows virus (FBNYV), and others, such as Alfalfa mosaic virus (AMV) and Cucumber mosaic virus (CMV), a very wide host range. Such features are important when identifying sources of virus inoculum in a region, and the vectors can transmit viruses from natural reservoirs to the crop plants. Some of these viruses are seed borne and, consequently, can be disseminated long distances through infected seeds. Crop losses caused by these viruses are variable, depending on the sensitivity and susceptibility of the crop to infection. Host resistance genes have been identified for some of these viruses, but in others, such as FBNYV, no resistance genes in faba bean have been identified yet. Significant progress was made in developing precise methods for the identification of these viruses, and new virus problems are being identified every year. This chapter is not intended to be a review for pea, bean, and faba bean viruses, but rather focuses on the major viruses which affect these crops in the Mediterranean basin with focus on the progress made over the past two decades.