Origin, world-wide dispersion, bio-geographical diversification, radiation and recombination: an evolutionary history of Yam mild mosaic virus (YMMV)

Molecular diversity of yam virus Y and identification of banana mild mosaic virus isolates infecting yam (Dioscorea spp.)

Two members of the family Betaflexiviridae associated with yam (Dioscorea spp.) have been described so far: yam latent virus (YLV) and yam virus Y (YVY). However, their geographical distribution and molecular diversity remain poorly documented. Using a nested RT-PCR assay, we detected YVY in D. alata, D. bulbifera, D. cayenensis, D. rotundata, and D. trifida in Guadeloupe, and in D. rotundata in Côte d'Ivoire, thus extending the known host range of this virus and geographical distribution. Using amplicon sequencing, we determined that the molecular diversity of YVY in the yam samples analyzed in this work ranged between 0.0 and 29.1% and that this diversity is partially geographically structured. We also identified three isolates of banana mild mosaic virus (BanMMV) infecting D. alata in Guadeloupe, providing the first evidence for BanMMV infection in yam.

Epidemiology of Yam Viruses in Guadeloupe: Role of Cropping Practices and Seed-Tuber Supply

The epidemiology of yam viruses remains largely unexplored. We present a large-scale epidemiological study of yam viruses in Guadeloupe based on the analysis of 1124 leaf samples collected from yams and weeds. We addressed the prevalence of cucumber mosaic virus (CMV), Cordyline virus 1 (CoV1), Dioscorea mosaic associated virus (DMaV), yam asymptomatic virus 1 (YaV1), yam mosaic virus (YMV), yam mild mosaic virus (YMMV), badnaviruses, macluraviruses and potexviruses, and the key epidemiological drivers of these viruses. We provide evidence that several weeds are reservoirs of YMMV and that YMMV isolates infecting weeds cluster together with those infecting yams, pointing to the role of weeds in the epidemiology of YMMV. We report the occurrence of yam chlorotic necrosis virus (YCNV) in Guadeloupe, the introduction of YMMV isolates through the importation of yam tubers, and the absence of vertical transmission of YaV1. We identified specific effects on some cropping practices, such as weed management and the use of chemical pesticides, on the occurrence of a few viruses, but no crop-related factor had a strong or general effect on the overall epidemiology of the targeted viruses. Overall, our work provides insights into the epidemiology of yam viruses that will help design more efficient control strategies.

Viruses of Yams (Dioscorea spp.): Current Gaps in Knowledge and Future Research Directions to Improve Disease Management

Viruses are a major constraint for yam production worldwide. They hamper the conservation, movement, and exchange of yam germplasm and are a threat to food security in tropical and subtropical areas of Africa and the Pacific where yam is a staple food and a source of income. However, the biology and impact of yam viruses remains largely unknown. This review summarizes current knowledge on yam viruses and emphasizes gaps that exist in the knowledge of the biology of these viruses, their diagnosis, and their impact on production. It provides essential information to inform the implementation of more effective virus control strategies.

A Review of Viruses Infecting Yam (Dioscorea spp.)

Yam is an important food staple for millions of people globally, particularly those in the developing countries of West Africa and the Pacific Islands. To sustain the growing population, yam production must be increased amidst the many biotic and abiotic stresses. Plant viruses are among the most detrimental of plant pathogens and have caused great losses of crop yield and quality, including those of yam. Knowledge and understanding of virus biology and ecology are important for the development of diagnostic tools and disease management strategies to combat the spread of yam-infecting viruses. This review aims to highlight current knowledge on key yam-infecting viruses by examining their characteristics, genetic diversity, disease symptoms, diagnostics, and elimination to provide a synopsis for consideration in developing diagnostic strategy and disease management for yam.

Lack of evidence for differences in the spread of classic (Lagovirus europaeus/GI.1) and novel (Lagovirus europaeus/GI.2) rabbit haemorrhagic disease viruses in Europe and North Africa

BACKGROUND

Fast-spreading diseases affecting wildlife populations threaten biodiversity. Two caliciviruses, Lagovirus europaeus/GI.1 and Lagovirus europaeus/GI.2, caused rabbit haemorrhagic disease virus (RHDV) in wild rabbits. Despite having different characteristics, these variants spread quickly, posing a threat to wild rabbit populations.

METHODS

In this study, we conducted a thorough review of the scientific literature and reports of international organisations of first detections of both variants of RHDV in the Euro-Mediterranean region. We concentrated on this area to avoid bias due to intentional human introductions.

RESULTS

The estimated mean spread rate of GI.2 was higher than that of GI.1 (GI.2: 479 km/year, range: 47-7346; GI.1: 330 km/year, 37-6248). These differences were not statistically significant. This lack of difference may be due to the interactions between each variant's virulence characteristics. Humans may have a dominant effect on their spread. Potential limitations associated with the observational process could have hindered our ability to identify statistical differences.

CONCLUSIONS

The lack of difference in the spread patterns of the two variants could be due to a biological cause, human facilitation or a lack of statistical power. Adapting protocols to detect diseases in wildlife using homogeneous criteria will be indispensable in the coming years.

Detection and diversity of viruses infecting African yam (Dioscorea rotundata) in a collection and F1 progenies in Côte d'Ivoire shed light to plant-to-plant viral transmission

Yam (Dioscorea spp.) is a major staple food whose production is hampered by viral diseases. However, the prevalence, diversity, transmission, and impact of yam-infecting viruses remain poorly documented. This study reports on the symptomatology, prevalence, and molecular diversity of eight viruses in 38 D. rotundata accessions from a germplasm collection and 206 F₁ hybrid progenies maintained in Côte d'Ivoire. Mean severity scores as assessed from leaf symptoms ranged from 2 to 4 in the germplasm collection and from 1 to 3 in F₁ hybrids, respectively. Dioscorea mosaic-associated virus (DMaV), potexviruses, and yam mosaic virus (YMV) were detected by PCR-based diagnosis tools in single and mixed infections in both the D. rotundata collection and F₁ progenies, whereas badnaviruses were detected only in the germplasm collection. In contrast, cucumber mosaic virus (CMV), yam macluraviruses, yam asymptomatic virus 1 (YaV1), and yam mild mosaic virus (YMMV) could not be detected. No correlation could be established between severity scores and indexing results. Phylogenetic analysis performed on partial viral sequences amplified from infected samples unveiled the presence of two putative novel viral species belonging to genera Badnavirus and Potexvirus and provided evidence for plant-to-plant transmission of YMV, DMaV, and yam potexviruses.

Molecular Viral Diagnosis and Sanitation of Yam Genetic Resources: Implications for Safe Yam Germplasm Exchange

Yam (Dioscorea spp.) is an important crop in tropical and subtropical regions. Many viruses have been recently identified in yam, hampering genetic conservation and safe international exchanges of yam germplasm. We report on the implementation of reliable and cost-effective PCR-based detection tools targeting eight different yam-infecting viruses. Viral indexing of the in vitro yam collection maintained by the Biological Resources Center for Tropical Plants (BRC-TP) in Guadeloupe (French West Indies) unveiled a high prevalence of potyviruses, badnaviruses, Dioscorea mosaic associated virus (DMaV) and yam asymptomatic virus 1 (YaV1) and a high level of coinfections. Infected yam accessions were subjected to a combination of thermotherapy and meristem culture. Sanitation levels were monitored using PCR-based and high-throughput sequencing-based diagnosis, confirming the efficacy and reliability of PCR-based detection tools. Sanitation rates were highly variable depending on viruses. Sixteen accessions were successfully sanitized, paving the way to safe yam germplasm exchanges and the implementation of clean seed production programs worldwide.

Rapid detection of potyviruses from crude plant extracts

Potyviruses (genus Potyvirus; family Potyviridae) are widely distributed and represent one of the most economically important genera of plant viruses. Therefore, their accurate detection is a key factor in developing efficient control strategies. However, this can sometimes be problematic particularly in plant species containing high amounts of polysaccharides and polyphenols such as yam (Dioscorea spp.). Here, we report the development of a reliable, rapid and cost-effective detection method for the two most important potyviruses infecting yam based on reverse transcription-recombinase polymerase amplification (RT-RPA). The developed method, named 'Direct RT-RPA', detects each target virus directly from plant leaf extracts prepared with a simple and inexpensive extraction method avoiding laborious extraction of high-quality RNA. Direct RT-RPA enables the detection of virus-positive samples in under 30 min at a single low operation temperature (37 °C) without the need for any expensive instrumentation. The Direct RT-RPA tests constitute robust, accurate, sensitive and quick methods for detection of potyviruses from recalcitrant plant species. The minimal sample preparation requirements and the possibility of storing RPA reagents without cold chain storage, allow Direct RT-RPA to be adopted in minimally equipped laboratories and with potential use in plant clinic laboratories and seed certification facilities worldwide.

Exploiting Genetic Information to Trace Plant Virus Dispersal in Landscapes

During the past decade, knowledge of pathogen life history has greatly benefited from the advent and development of molecular epidemiology. This branch of epidemiology uses information on pathogen variation at the molecular level to gain insights into a pathogen's niche and evolution and to characterize pathogen dispersal within and between host populations. Here, we review molecular epidemiology approaches that have been developed to trace plant virus dispersal in landscapes. In particular, we highlight how virus molecular epidemiology, nourished with powerful sequencing technologies, can provide novel insights at the crossroads between the blooming fields of landscape genetics, phylogeography, and evolutionary epidemiology. We present existing approaches and their limitations and contributions to the understanding of plant virus epidemiology.

Molecular variability and genetic structure of the population of Onion yellow dwarf virus infecting garlic in Iran

Onion yellow dwarf virus (OYDV) is one of the most important viral diseases of garlic crops worldwide. This study surveyed the occurrence of OYDV in 26 garlic ecotypes collected from different regions in Iran during 2008-2009. Using an electron microscope, we detected filamentous particles with about 700-800 nm in length and 12 nm in width in five samples. These features are typical of the genus Potyvirus. The coat protein (CP) gene from 26 samples was PCR amplified, cloned, sequenced, and compared with the sequences available in GenBank. Phylogenetic analysis using 235 deduced amino acids of the CP gene showed that virus isolates fell into two groups, group A and group B. Members of group A were divided into two subgroups: A-I and A-II. The subgroup A-I appears to be a new subgroup comprising 17 Iranian isolates. The identity levels among the amino acid of 26 Iranian isolates ranged between 90 and 100%. The results indicated that the genetic diversity found in Iran is due to local OYDV populations rather than introduction from other geographical regions. This study is the first report about the molecular structure and geographically diverse range of OYDV populations in this country.

Evidence of diploidy in the wild Amerindian yam, a putative progenitor of the endangered species Dioscorea trifida (Dioscoreaceae)

The fundamental question about Dioscorea trifida (Dioscoreaceae), the most important Amerindian yam, that remains unresolved concerns its evolutionary origin, since no wild relative has been reported. In this paper we report the existence of D. trifida’s wild relative for the first time. The diploidy of wild D. trifida (2n = 40) is clearly demonstrated by flow cytometry, chromosome counts, and microsatellite pattern analysis, whereas the cultivated form was previously shown to be autotetraploid (2n = 80). In the coastal region where the wild and cultivated forms are sympatric, tetraploid and triploid cytotypes coexist within the same populations. In the sites where the wild and cultivated forms are allopatric, the wild diploid cytotype predominates. AFLP (amplified fragment length polymorphism) analyses gave an initial idea of the position of the wild forms in relation to the cultivated forms. All the wild and cultivated types form a monophyletic group structured into two major subgroups corresponding to the tetraploid cytotype of the cultivated form and the diploid cytotype of the wild form. The triploid cytotypes of the wild form are in an intermediary position. Wild accessions are grouped on the basis of their geographic origin. The data presented in this paper are significant for the effective breeding and conservation of D. trifida and to assess its genetic diversity and population structure for the general understanding of the evolution and domestication of the species.

Dilemmas caused by endogenous pararetroviruses regarding the taxonomy and diagnosis of yam (Dioscorea spp.) badnaviruses: analyses to support safe germplasm movement

The discovery of endogenous pararetroviral sequences (EPRVs) has had a deep impact on the approaches needed for diagnosis, taxonomy, safe movement of germplasm and management of diseases caused by pararetroviruses. In this article, we illustrate this through the example of yam (Dioscorea spp.) badnaviruses. To enable progress, it is first necessary to clarify the taxonomical status of yam badnavirus sequences. Phylogeny and pairwise sequence comparison of 121 yam partial reverse transcriptase sequences provided strong support for the identification of 12 yam badnavirus species, of which ten have not been previously named. Virus prevalence data were obtained, and they support the presence of EPRVs in D. rotundata, but not in D. praehensilis, D. abyssinica, D. alata or D. trifida. Five yam badnavirus species characterised by a wide host range seem to be of African origin. Seven other yam badnavirus species with a limited host range are probably of Asian-Pacific origin. Recombination under natural circumstances appears to be rare. Average values of nucleotide intra-species genetic distances are comparable to data obtained for other RNA and DNA virus families. The dispersion scenarios proposed here, combined with the fact that host-switching events appear common for some yam badnaviruses, suggest that the risks linked to introduction via international plant material exchanges are high.

The promiscuous evolutionary history of the family Bromoviridae

Recombination and segment reassortment are important contributors to the standing genetic variation of RNA viruses and are often involved in the genesis of new, emerging viruses. This study explored the role played by these two processes in the evolutionary radiation of the plant virus family Bromoviridae. The evolutionary history of this family has been explored previously using standard molecular phylogenetic methods, but incongruences have been found among the trees inferred from different gene sequences. This would not be surprising if RNA exchange was a common event, as it is well known that recombination and reassortment of genomes are poorly described by standard phylogenetic methods. In an attempt to reconcile these discrepancies, this study first explored the extent of segment reassortment and found that it was common at the origin of the bromoviruses and cucumoviruses and at least at the origin of alfalfa mosaic virus, American plum line pattern virus and citrus leaf rugose virus. Secondly, recombination analyses were performed on each of the three genomic RNAs and it was found that recombination was very common in members of the genera Bromovirus, Cucumovirus and Ilarvirus. Several cases of recombination involving species from different genera were also identified. Finally, a phylogenetic network was constructed reflecting these genetic exchanges. The network confirmed the taxonomic status of the different genera within the family, despite the phylogenetic noise introduced by genetic exchange.

Taxonomy, molecular phylogeny and evolution of plant reverse transcribing viruses (family Caulimoviridae) inferred from full-length genome and reverse transcriptase sequences

This study constitutes the first evaluation and application of quantitative taxonomy to the family Caulimoviridae and the first in-depth phylogenetic study of the family Caulimoviridae that integrates the common origin between LTR retrotransposons and caulimoviruses. The phylogenetic trees and PASC analyses derived from the full genome and from the corresponding partial RT concurred, providing strong support for the current genus classification based mainly on genome organisation and use of partial RT sequence as a molecular marker. The PASC distributions obtained are multimodal, making it possible to distinguish between genus, species and strain. The taxonomy of badnaviruses infecting banana (Musa spp.) was clarified, and the consequence of endogenous badnaviruses on the genetic diversity and evolution of caulimoviruses is discussed. The use of LTR retrotransposons as outgroups reveals a structured bipolar topology separating the genus Badnavirus from the other genera. Badnaviruses appear to be the most recent genus, with the genus Tungrovirus in an intermediary position. This structuring intersects the one established by genomic and biological properties and allows us to make a correlation between phylogeny and biogeography. The variability shown between members of the family Caulimoviridae is in a similar range to that reported within other DNA and RNA plant virus families.

Yams (Dioscorea spp.) from the South Pacific Islands contain many novel badnaviruses: implications for international movement of yam germplasm

Yam (Dioscorea spp.) samples (n = 690) from seven South Pacific Islands were screened for badnavirus infection by ELISA using two antisera to African badnaviruses. Positive readings were obtained for 26.4-34.6% of samples representing both known (D. bulbifera, D. nummularia and D. pentaphylla) and unreported host species (D. alata, D. esculenta, D. rotundata and D. trifida) in this region. Total DNAs were extracted from 25 ELISA-positive plants and 4 ELISA-negative controls and subjected to PCR amplification with badnavirus-specific primers targeting the reverse transcriptase (RT)-RNaseH genes. All 29 samples yielded the expected size PCR-product for badnaviruses, which were cloned and sequenced. Phylogenetic analyses of the resulting 45 partial (500-527 bp) RT-RNaseH sequences revealed 11 new sequence groups with <79% nucleotide identity to each other or any EMBL sequence. Three sequences (two groups) were highly divergent to the other nine new South Pacific yam badnavirus groups (47.9-57.2% identity) and probably represent either new Caulimoviridae genera or endogenous pararetrovirus sequences. Some sequence groups appeared specific to particular Dioscorea host species. Four 99.9% identical RT-RNaseH sequences possessing nine amino acid deletions from D. esculenta from three islands represent a putative integrated sequence group. The distribution of sequence groups across the islands indicates that badnaviruses have spread extensively between islands and continents through infected germplasm.

Molecular variability of sweet potato feathery mottle virus and other potyviruses infecting sweet potato in Peru

Several potyviruses are found infecting sweet potato (Ipomoea batatas) in Peru, of which sweet potato feathery mottle virus (SPFMV, genus Potyvirus) is the most common. However, sequence data for these viruses are not available from Peru. In this study, the 3'-terminal approximately 1,800 nucleotide sequences of 17 potyvirus samples collected from the six main sweet potato-producing areas of Peru over the past 20 years were determined and analyzed. Results of sequence comparisons and phylogenetic analysis showed that three of the four recognized SPFMV strain groups, including the East African strain, are established in Peru as well as two other potyviruses: sweet potato virus G (SPVG) and sweet potato virus 2 (SPV2). The analysis further revealed that SPFMV, SPVG and SPV2 are related and form an Ipomoea-specific phylogenetic lineage within the genus Potyvirus and identified for the first time recombination events between viruses from different strain groups of SPFMV.

Molecular characterization of two Chinese isolates of Beet mosaic virus

The complete genomic sequences of Beet mosaic virus Xinjiang (BtMV-XJ) and Inner Mongolia (BtMV-IM) isolates from China were determined and compared with US and German isolates, reported previously. Results showed that viral genome of the two isolates both comprise 9,591 nucleotides, and contain the large single open reading frame (ORF) encoding a single polyprotein of 3,085 amino acid residues, from which ten putative functional proteins may be produced by autolytic cleavage processing as the US (BtMV-Wa) and German (BtMV-G) isolates. Sequence comparisons showed that BtMV-XJ shared 89.8% and 98.3% overall nucleotide identity with BtMV-Wa and BtMV-G isolates, and BtMV-IM exhibited the overall identities of 91.6% and 93.8% with BtMV-Wa and BtMV-G, respectively. Further, analyses revealed that BtMV-XJ shared higher identities in almost every region to BtMV-G than to BtMV-Wa both at the nucleotide and the amino acid levels. While BtMV-IM in the regions (6,666-7,671 and 7,672-9,591) showed highest homology with BtMV-XJ and BtMV-G, especially, after nt 7,672 with similarity up to 99.2% with BtMV-G; the region (2,331-4,083) showed highest identity (98.0% nt identity) with BtMV-Wa. That suggested BtMV-XJ had a more close relationship to BtMV-G, while BtMV-IM was more likely to be a natural recombination virus. In addition, phylogenetic analysis of the available BtMV CP sequences showed that BtMV isolates fell into two distinct groups: Euroasia group (Europe and China) and America group (USA). To the best of our knowledge, this study reported the complete sequences of two BtMV isolates from Asia for the first time.

No recombination detected in artificial potyvirus mixed infections and between potyvirus derived transgenes and heterologous challenging potyviruses

Risk-assessment studies of virus-resistant transgenic plants (VRTPs) focussing on recombination of a plant virus with a transgenic sequence of a different virus should include a comparison of recombination frequencies between viruses in double-infected non-transgenic plants with those observed in singly infected transgenic plants to estimate recombination incidence in VRTPs. In this study, the occurrence of recombination events was investigated in non-transgenic plants double-infected with two different potyviruses, as well as in potyviral genomes in singly infected transgenic plants expressing potyvirus sequences. Different potyviruses, namely Potato virus A (PVA), Tobacco vein mottling virus (TVMV), two strains of Potato virus Y (PVY-O, PVY-H) and two strains of Plum pox virus (PPV-NAT, PPV-SK68), were used in three combinations for double infection of a common host. Furthermore, transgenic plants expressing either potyviral coat protein (CP), helicase (CI) or polymerase (NIb) coding sequences (PPV-NAT-CP, PVY-CI, PVY-NIb) were singly-infected with a heterologous potyvirus, which was not targeted by the respective transgenic resistance. To identify recombinant potyviral sequences, a sensitive RT-PCR was developed to detect up to one recombinant molecule out of 10(6) parental molecules. In 304 mixed infected non-transgenic plants, 92 mixed and 164 single infected transgenic plants screened for recombinant sequences no recombinant potyviral sequence was found. These results indicate that recombination events between different potyviruses in mixed infections and between a potyvirus infecting a potyvirus-resistant transgenic plant are likely to be very infrequent.

Microsatellite segregation analysis and cytogenetic evidence for tetrasomic inheritance in the American yam Dioscorea trifida and a new basic chromosome number in the Dioscoreae

Despite the economic and cultural importance of the indigenous "Amerindian" yam Dioscorea trifida, very little is known about their origin, phylogeny, diversity and genetics. Consequently, conventional breeding efforts for the selection of D. trifida genotypes resistant to potyviruses which are directly involved in the regression of this species have been seriously limited. Our objective of this paper is to contribute to the clarification of the cytogenetic status, i.e., inheritance and chromosome number. Our results provide genetic evidence supporting tetrasomic behaviour of the genome of D. trifida based on chromosomal segregation pattern analysis using eight SSRs markers in three different crosses. This is the first reliable evidence of an autopolyploid species in the genus Dioscorea. The second major result in this study is the revealing of a new base chromosome number in the botanical section Macrogynodium to which D. trifida belongs. To date, our assumptions about the ploidy level of yams are based on the observations that the basic chromosome number is 10 or 9, and D. trifida was described as octoploid. The chromosome number of D. trifida accessions was also assessed using somatic chromosomic count techniques. Flow cytometry did not show significant variation of 2C DNA content among 80 accessions indicating homogeneity of the ploidy level of the cultivated D. trifida. This suggests that autotetraploidy is well established as well as the rule for the cultivated pool of D. trifida, even if the direct diploid ancestor remains to be identified. The data presented in this paper are significant and important for the effective breeding and conservation of the species and for elucidating the phylogeny and the origins of the yam and the evolution of the genus Dioscorea.

A phylogenetic survey of recombination frequency in plant RNA viruses

The severe economic consequences of emerging plant viruses highlights the importance of studies of plant virus evolution. One question of particular relevance is the extent to which the genomes of plant viruses are shaped by recombination. To this end we conducted a phylogenetic survey of recombination frequency in a wide range of positive-sense RNA plant viruses, utilizing 975 capsid gene sequences and 157 complete genome sequences. In total, 12 of the 36 RNA virus species analyzed showed evidence for recombination, comprising 17% of the capsid gene sequence alignments and 44% of the genome sequence alignments. Given the conservative nature of our analysis, we propose that recombination is a relatively common process in some plant RNA viruses, most notably the potyviruses.

Role of recombination in evolution of enteroviruses

Enteroviruses, members of the Picornaviridae family, comprise a large (over 70 serotypes) group of viruses that are ubiquitous in nature, infect different species and cause a wide range of diseases. Human enteroviruses were recently classified into five species, human enterovirus A-D and poliovirus. Recombination has long been known to be an important property of poliovirus genetics. Recently, several publications demonstrated that recombination is extremely frequent also in non-polio enteroviruses, and allows independent evolution of enterovirus genome fragments even on a microevolutionary scale. Prototype enterovirus strains were shown to have complex phylogenetic relations, and almost all modern enterovirus isolates turned out to be recombinants compared with the prototype strains. Recombination takes place strictly between members of the same species, and usually spares the capsid-encoding genome region. Therefore, it can be concluded that the enterovirus species exist as a worldwide reservoir of genetic material comprising a limited quantity of capsid gene sets defining a finite number of serotypes and a range of non-structural genes that recombine frequently to produce new virus variants. This new model of enterovirus genetics helps to explain the failure of previous attempts to connect serotype and disease profile in non-polio enteroviruses, and seriously questions existing typing approaches that are based solely on the capsid-encoding genome region. It remains to be determined what role recombination plays in the emergence of new enterovirus variants and in the macroevolution of animal enteroviruses and viruses of the picorna-like supergroup.

Geographically and temporally distant natural recombinant isolates of Plum pox virus (PPV) are genetically very similar and form a unique PPV subgroup

Natural recombinant Plum pox virus (PPV) isolates were detected in Albania, Bulgaria, Czech Republic, Germany, Hungary and Slovakia. Despite different geographical origins and dates of isolation, all the recombinant isolates were closely related at the molecular level and shared the same recombination breakpoint as well as a typical signature in their N-terminal coat protein sequence, suggesting a common origin. Biological assays with four recombinant isolates demonstrated their capacity to be aphid-transmitted to various Prunus hosts. One of these isolates had a threonine-to-isoleucine mutation in the conserved PTK motif of its HC-Pro and showed a drastically decreased, although not abolished, aphid transmissibility. The complete genome sequence of one of the recombinant isolates, BOR-3, was determined, as well as some partial sequences in the HC-Pro and P3 genes for additional natural recombinant isolates. Analysis of the phylogenetic relationships between the recombinant isolates and other sequenced PPV isolates confirmed that the recombinant isolates form a phylogenetically homogeneous lineage. In addition, this analysis revealed an ancient recombination event between the PPV-D and M subgroups, with a recombination breakpoint located in the P3 gene. Taken together, these results indicate that recombinant isolates represent an evolutionarily successful, homogeneous group of isolates with a common history and unique founding recombination event. The name PPV-Rec is proposed for this coherent ensemble of isolates.