Phylogenetic and diversity analyses revealed that leek yellow stripe virus population consists of three types: S, L, and N.

Phylogenetic and evolutionary analyses were performed on the P1 and CP genes of global isolates to clarify the phylogrouping of leek yellow stripe virus (LYSV, genus Potyvirus), a pathogen affecting Allium spp. worldwide, into different types based on genetic variation and host species. The constructed phylogenetic trees divided the isolates into three major groups: S, L, and N. Low nucleotide (nt) and amino acid (aa) percent identities among the three groups were observed on full ORF (75.4-99.0 and 79.1-99.0), P1 (59.1-98.3 and 36.8-98.3), and CP (76.6-100 and 75.7-100) coding regions. The dN/dS values of P1 and CP confirmed that both genes are under strong negative (purifying) selection pressure. Neutrality tests on Eastern Asian isolates suggested that the ancestors of current LYSV isolates evolved with garlic while they were in Asia before spreading to other world regions through garlic propagative materials. Genetic differentiation and gene flow analysis showed extremely frequent gene flow from S group to L and N groups, and these phylogroups differentiated from each other over time. Host differences, inconsistent serological test results, substantial nt and aa variation, and phylogenetic and diversity analyses in this study supported previous reports that LYSV can be separated into three major evolutionary lineages: S, L, and N types.

Occurrence of leek yellow stripe virus and onion yellow dwarf virus from edible Allium plants in the south Marmara region of Turkey.

Among edible Allium plants (leek, onion, and garlic), leek yellow stripe (LYSV) and onion yellow dwarf virus (OYDV) are the most common viruses worldwide. While the presence of these two viruses in Turkey has previously been confirmed, only a few studies on their prevalence and genetic diversity have been performed. The aim of this study, conducted in the southern Marmara region of Turkey (SMR), was to identify the presence and genetic diversity of these viruses. Samples were collected from 494 plants exhibiting virus and virus-like symptoms. Samples were tested for the relevant viruses by double-antibody sandwich enzyme-linked immunosorbent assay and reverse transcription polymerase chain reaction (DAS-ELISA and RT-PCR, respectively). Tests revealed the presence of OYDV in 95 samples and LYSV in 52, whereas 33 samples were observed to have a combined infection. To examine the genetic diversity, 10 isolates from each virus were chosen from the infected samples. Using RT-PCR, the complete coat protein (CP) gene for LYSV and a partial sequence region of the nuclear inclusion b + CP gene for OYDV were amplified, cloned, and sequenced from the selected isolates. The sequence data were compared with the isolates in GenBank; it was determined that SMR LYSV and OYDV isolates show similarities over 77% with world isolates at the nucleotide and amino acid levels. Phylogenetic analyses showed that the LYSV and OYDV isolates had some diversity with isolates from different parts of the world, and the host had an important role in the phylogenetic relationships, particularly for LYSV. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-03067-1.

The Timescale of Emergence and Spread of Turnip Mosaic Potyvirus.

Plant viruses have important global impacts on crops, and identifying their centre and date of emergence is important for planning control measures. Turnip mosaic virus (TuMV) is a member of the genus Potyvirus in the family Potyviridae and is a major worldwide pathogen of brassica crops. For two decades, we have collected TuMV isolates, mostly from brassicas, in Turkey and neighbouring countries. This region is thought to be the centre of emergence of this virus. We determined the genomic sequences of 179 of these isolates and used these to estimate the timescale of the spread of this virus. Our Bayesian coalescent analyses used synonymous sites from a total of 417 novel and published whole-genome sequences. We conclude that TuMV probably originated from a virus of wild orchids in Germany and, while adapting to wild and domestic brassicas, spread via Southern Europe to Asia Minor no more than 700 years ago. The population of basal-B group TuMVs in Asia Minor is older than all other populations of this virus, including a newly discovered population in Iran. The timescale of the spread of TuMV correlates well with the establishment of agriculture in these countries.

First Genome Sequence of Wild Onion Symptomless Virus, a Novel Member of Potyvirus in the Turnip Mosaic Virus Phylogenetic Group.

The nearly complete genome sequence of a new species of potyvirus was obtained from the symptomless wild onion (Allium sp.) in Turkey. This virus has less than 67% nucleotide sequence identities over the polyprotein to other known potyviruses. We propose the name wild onion symptomless virus for this novel potyvirus.

Temporal analysis of reassortment and molecular evolution of Cucumber mosaic virus: Extra clues from its segmented genome.

Cucumber mosaic virus (CMV) is a damaging pathogen of over 200 mono- and dicotyledonous crop species worldwide. It has the broadest known host range of any virus, but the timescale of its evolution is unknown. To investigate the evolutionary history of this virus, we obtained the genomic sequences of 40 CMV isolates from brassicas sampled in Iran, Turkey and Japan, and combined them with published sequences. Our synonymous ('silent') site analyses revealed that the present CMV population is the progeny of a single ancestor existing 1550-2600 years ago, but that the population mostly radiated 295-545 years ago. We found that the major CMV lineages are not phylogeographically confined, but that recombination and reassortment is restricted to local populations and that no reassortant lineage is more than 251 years old. Our results highlight the different evolutionary patterns seen among viral pathogens of brassica crops across the world.

The temporal evolution and global spread of Cauliflower mosaic virus, a plant pararetrovirus.

Cauliflower mosaic virus (CaMV) is a plant pararetrovirus with a double-stranded DNA genome. It is the type member of the genus Caulimovirus in the family Caulimoviridae. CaMV is transmitted by sap inoculation and in nature by aphids in a semi-persistent manner. To investigate the patterns and timescale of CaMV migration and evolution, we sequenced and analyzed the genomes of 67 isolates of CaMV collected mostly in Greece, Iran, Turkey, and Japan together with nine published sequences. We identified the open-reading frames (ORFs) in the genomes and inferred their phylogeny. After removing recombinant sequences, we estimated the substitution rates, divergence times, and phylogeographic patterns of the virus populations. We found that recombination has been a common feature of CaMV evolution, and that ORFs I-V have a different evolutionary history from ORF VI. The ORFs have evolved at rates between 1.71 and 5.81×10(-4) substitutions/site/year, similar to those of viruses with RNA or ssDNA genomes. We found four geographically confined lineages. CaMV probably spread from a single population to other parts of the world around 400-500 years ago, and is now widely distributed among Eurasian countries. Our results revealed evidence of frequent gene flow between populations in Turkey and those of its neighboring countries, with similar patterns observed for Japan and the USA. Our study represents the first report on the spatial and temporal spread of a plant pararetrovirus.

The First Identified Citrus tristeza virus Isolate of Turkey Contains a Mixture of Mild and Severe Strains.

The presence of Citrus tristeza virus (CTV) has previously been reported in citrus growing regions of Turkey. All serologically and biologically characterized isolates including Igdir, which was the first identified CTV isolates from Turkey, were considered mild isolates. In this study, molecular characteristics of the Igdir isolate were determined by different methods. Analysis of the Igdir isolate by western blot and BD-RT-PCR assays showed the presence of MCA13 epitope, predominantly found in severe isolates, in the Igdir isolate revealing that it contains a severe component. For further characterization, the coat protein (CP) and the RNA-dependent RNA polymerase (RdRp) genes representing the 3' and 5' half of CTV genome, respectively, were amplified from dsRNA by RT-PCR. Both genes were cloned separately and two clones for each gene were sequenced. Comparisons of nucleotide and deduced amino acid sequences showed that while two CP gene sequences were identical, two RdRp clones showed only 90% and 91% sequence identity in their nucleotide and amino acid sequences, respectively, suggesting a mixed infection with different strains. Phylogenetic analyses of the CP and RdRp genes of Igdir isolate with previously characterized CTV isolates from different citrus growing regions showed that the CP gene was clustered with NZRB-TH30, a resistance breaking isolate from New Zealand, clearly showing the presence of severe component. Furthermore, two different clones of the RdRp gene were clustered separately with different CTV isolates with a diverse biological activity. While the RdRp-1 was clustered with T30 and T385, two well-characterized mild isolates from Florida and Spain, respectively, the RdRp-2 was most closely related to NZRB-G90 and NZRB-TH30, two well-characterized resistance breaking and stem pitting (SP) isolates from New Zealand confirming the mixed infection. These results clearly demonstrated that the Igdir isolate, which was previously described as biologically a mild isolate, actually contains a mixture of mild and severe strains.