Beet Chlorosis Virus Research Articles

Interplay between a polerovirus and a closterovirus decreases aphid transmission of the polerovirus.

Multi-infection of plants by viruses is very common and can change drastically infection parameters such as virus accumulation, distribution, and vector transmission. Sugar beet is an important crop that is frequently co-infected by the polerovirus beet chlorosis virus (BChV) and the closterovirus beet yellows virus (BYV), both vectored by the green peach aphid (Myzus persicae). These phloem-limited viruses are acquired while aphids ingest phloem sap from infected plants. Here we found that co-infection decreased transmission of BChV by ~50% but had no impact on BYV transmission. The drastic reduction of BChV transmission was due to neither lower accumulation of BChV in co-infected plants nor reduced phloem sap ingestion by aphids from these plants. Using the signal amplification by exchange reaction fluorescent in situ hybridization technique on plants, we observed that 40% of the infected phloem cells were co-infected and that co-infection caused redistribution of BYV in these cells. The BYV accumulation pattern changed from distinct intracellular spherical inclusions in mono-infected cells to a diffuse form in co-infected cells. There, BYV co-localized with BChV throughout the cytoplasm, indicative of virus-virus interactions. We propose that BYV-BChV interactions could restrict BChV access to the sieve tubes and reduce its accessibility for aphids and present a model of how co-infection could alter BChV intracellular movement and/or phloem loading and reduce BChV transmission.IMPORTANCEMixed viral infections in plants are understudied yet can have significant influences on disease dynamics and virus transmission. We investigated how co-infection with two unrelated viruses, BChV and BYV, affects aphid transmission of the viruses in sugar beet plants. We show that co-infection reduced BChV transmission by about 50% without affecting BYV transmission, despite similar virus accumulation rates in co-infected and mono-infected plants. Follow-up experiments examined the localization and intracellular distribution of the viruses, leading to the discovery that co-infection caused a redistribution of BYV in the phloem vessels and altered its repartition pattern within plant cells, suggesting virus-virus interactions. In conclusion, the interplay between BChV and BYV affects the transmission of BChV but not BYV, possibly through direct or indirect virus-virus interactions at the cellular level. Understanding these interactions could be crucial for managing virus propagation in crops and preventing yield losses.

One-step TaqMan® RT-qPCR detection of sugar beet-infecting poleroviruses in Myzus persicae from yellow water pan traps opens up new possibilities for early risk assessment of virus yellows disease

Virus yellows disease (VY) is a major threat to sugar beet production in Europe. Beet chlorosis virus (BChV) and beet mild yellowing virus (BMYV) are of particular economic importance and are both persistently transmitted by the aphid vector Myzus persicae. As part of integrated pest management strategies, M. persicae influx into sugar beet fields is recorded weekly using yellow water pan traps. To date, only ELISA and RT-PCR assays have been described for BChV and BMYV detection in individual aphids.In this study, we describe for the first time two one-step TaqMan® RT-qPCR assays designed for the specific detection of BChV and BMYV in M. persicae after 7d incubation in water pan trap medium. Both viruses were reproducibly detected in individual aphids. After 7d incubation in trap medium, both viruses were reproducibly detected in individual aphids, as well as in one viruliferous aphid in a pool of 99 non-viruliferous aphids. Significant correlations can be shown between different mixing ratios of viruliferous to non-viruliferous aphids and Ct values of total RNA templates, allowing the percentage of viruliferous aphids in yellow water pan traps to be estimated using a standard curve.The described methodology provides a high sensitivity combined with a high sample throughput and can be used, after evaluation in the field, for practical monitoring, risk modelling and development of decision support systems for VY.

Aerial low‐altitude remote sensing and deep learning for in‐field disease incidence scoring of virus yellows in sugar beet

AbstractThis study investigates the potential of high‐resolution (<0.5 cm/pixel) aerial imagery and convolutional neural networks (CNNs) for disease incidence scoring in sugar beet, focusing on two important aphid‐transmitted viruses, beet mild yellowing virus (BMYV) and beet chlorosis virus (BChV). The development of tolerant sugar beet cultivars is imperative in the context of increased disease management concerns due to the ban on neonicotinoids in the European Union. However, traditional methods of disease phenotyping, which rely on visual assessment by human experts, are both time‐consuming and subjective. Therefore, this study assessed whether aerial multispectral and RGB images could be harnessed to perform automated disease ratings comparable to those performed by trained experts. To this end, two variety trials were conducted in 2021 and 2022. The 2021 dataset was used to train and validate a CNN model on five cultivars, while the 2022 dataset was used to test the model on two cultivars different from those used in 2021. Additionally, this study tests the use of transformed features instead of raw spectral bands to improve the generalization of CNN models. The results showed that the best CNN model was the one trained for BMYV on RGB images using transformed features instead of conventional raw bands. This model achieved a root mean square error score of 11.45% between the model and expert scores. These results indicate that while high‐resolution aerial imagery and CNNs hold great promise, a complete replacement of human expertise is not yet possible. This research contributes to an innovative approach to disease phenotyping, driving advances in sustainable agriculture and crop breeding.

Development of a one‐step multiplex reverse transcription‐polymerase chain reaction and Luminex xTAG assay for the simultaneous detection of yellowing viruses infecting sugar beet

AbstractYellowing viruses are an increasing threat to sugar beet cultivation, due to limitations on insecticide usage and climate change. Virus detection, monitoring and resistance breeding are key to secure high sugar beet yields in the future. For this research, a one‐step multiplex reverse transcription (mRT)‐PCR method was designed to detect simultaneously beet mild yellowing virus, beet chlorosis virus, beet yellows virus (BYV), beet mosaic virus and turnip yellows virus. The addition of Luminex xTAG array technology was used as a follow‐up method to increase assay specificity. The one‐step mRT‐PCR was evaluated on 22 field samples with single and mixed virus infections. The xTAG assay works as expected both in a simplex and multiplex setting, except that BYV detection needs optimization in the multiplex setting. In the future, the Luminex xTAG assay would be an excellent method for the detection of beet yellowing viruses due to its high specificity and the potential to increase the number of targets.

Recessive resistance against beet chlorosis virus is conferred by the eukaryotic translation initiation factor (iso)4E in Beta vulgaris.

Eukaryotic translation initiation factors (eIFs) are important for mRNA translation but also pivotal for plant-virus interaction. Most of these plant-virus interactions were found between plant eIFs and the viral protein genome-linked (VPg) of potyviruses. In case of lost interaction due to mutation or deletion of eIFs, the viral translation and subsequent replication within its host is negatively affected, resulting in a recessive resistance. Here we report the identification of the Beta vulgaris Bv-eIF(iso)4E as a susceptibility factor towards the VPg-carrying beet chlorosis virus (genus Polerovirus). Using yeast two-hybrid and bimolecular fluorescence complementation assays, the physical interaction between Bv-eIF(iso)4E and the putative BChV-VPg was detected, while the VPg of the closely related beet mild yellowing virus (BMYV) was found to interact with the two isoforms Bv-eIF4E and Bv-eIF(iso)4E. These VPg-eIF interactions within the polerovirus-beet pathosystem were demonstrated to be highly specific, as single mutations within the predicted cap-binding pocket of Bv-eIF(iso)4E resulted in a loss of interaction. To investigate the suitability of eIFs as a resistance resource against beet infecting poleroviruses, B.vulgaris plants were genome edited by CRISPR/Cas9 resulting in knockouts of different eIFs. Asimultaneous knockout of the identified BMYV-interaction partners Bv-eIF4E and Bv-eIF(iso)4E was not achieved, but Bv-eIF(iso)4EKO plants showed a significantly lowered BChV accumulation and decrease in infection rate from 100% to 28.86%, while no influence on BMYV accumulation was observed. Still, these observations support that eIFs are promising candidate genes for polerovirus resistance breeding in sugar beet.

Efficacy of neonicotinoid and non-neonicotinoid treatments on virus yellows and sugar beet yields

Myzus persicae (Sulzer), commonly known as the green peach aphid, plays a pivotal role in transmitting a range of yellowing viruses, including beet yellows virus, beet mild yellowing virus, beet chlorosis virus, and beet mosaic virus, to sugar beet plants (Beta vulgaris L.). Because of their environmental impacts, three neonicotinoid-based products (imidacloprid, thiamethoxam thiamethoxam, and clothianidine) have faced recent bans in multiple countries and there is thus an increasing need to explore alternative and effective methods for aphid control.In this study, we assess the efficacy of seven conventional aphicides, one neonicotinoid seed treatment, two foliar-applied neonicotinoids, and four companion plants in mitigating the propagation of virus yellows and increasing sugar beet yields. Our analysis is based on data obtained from 64 trials conducted from 2018 to 2022 2023 in France, Belgium, and the Netherlands. These trials were analyzed using linear mixed-effect models in order to estimate the efficacy of neonicotinoid and non-neonicotinoid treatments on the virus yellows and the sugar-beet yields.Our results revealed that the neonicotinoid seed treatment thiamethoxam exhibited strong efficacy in both reducing virus yellows and enhancing yields compared to alternative treatments. However, the most effective treatment for reducing virus yellows was a composite treatment combining barley companion plant, spirotetramat, and flonicamid, which led to an 87.0% reduction in virus yellows incidence compared to the untreated control group [95% confidence interval = (73.3; 93.6)]. In terms of sugar beet yields, spirotetramat at a dosage of 0.75 l/ha proved to be the most effective treatment, resulting in a 15.7% increase in yields compared to the untreated group [95% confidence interval = (9.1; 22.6)]. While companion plants were able to reduce virus yellows, they did not significantly increase yields compared to the untreated treatment. This outcome may be attributed to the competitive interactions between companion plants and sugar beets, in the context of dry seasons. Furthermore, our analysis indicated that the impact of spirotetramat, sulfoxaflor, flonicamid and thiamethoxam on yields tended to increase with higher aphid pressures.

First Report of Beet Yellows Virus Causing Virus Yellows in Sugar Beet in Serbia.

Several viruses have been described to infect sugar beet (Beta vulgaris var. saccharifera L.), but virus yellows disease is one of the most important diseases in many sugar beet growing areas. It is caused by four viruses either in single or mixed infection, including the poleroviruses beet western yellows virus (BWYV), beet mild yellowing virus (BMYV), and beet chlorosis virus (BChV), and a closterovirus beet yellows virus (BYV) (Stevens et al. 2005; Hossain et al. 2021). In August 2019, five samples of sugar beet plants showing yellowing on interveinal leaf tissue were collected in a sugar beet crop in the Novi Sad locality (Vojvodina Province, Serbia). Double-antibody sandwich (DAS)-ELISA commercial antisera (DSMZ, Braunschweig, Germany) were used to test the collected samples for the presence of the most common sugar beet viruses: beet necrotic yellow vein virus (BNYVV), BWYV, BMYV, BChV, and BYV. Commercial positive and negative controls were included in each ELISA test. BYV was serologically detected in all sugar beet samples, but no other viruses tested were found. The presence of BYV in sugar beet plants was further confirmed by conventional reverse transcription (RT)-PCR. Total RNAs were extracted using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany), according to the manufacturer's instructions, and used as template in the RT-PCR. Total RNAs extracted from healthy sugar beet leaves and molecular-grade water were included as negative controls in the RT-PCR analysis. RT-PCR confirmed the presence of BYV in all naturally infected plants using four sets of specific primers (Kundu and Ryšánek 2004), whereas no amplification products were obtained in the negative controls. The RT-PCR products derived from isolate 209-19 were purified and directly sequenced in both directions using the same primer pairs as in RT-PCR (accession numbers OQ686792 to OQ686794). Multiple sequence alignment of the L-Pro and N-terminal part of the MET genes showed that the Serbian BYV isolate had the highest nucleotide identity (99.01% and 100%, respectively) with several BYV isolates in GenBank originating from different parts of the world. Sequence analysis of the HSP70 gene showed the highest similarity (99.79%) with the BYV-Cro-L isolate found in Croatia. In a semi-persistent type of transmission test, aphids (Myzus persicae Sulzer) were allowed to feed on BYV-infected leaves of an ELISA-positive sample (209-19) for 48 hours, and then the aphids were transferred to five plants each of Spinacia oleracea cv. Matador and B. vulgaris ssp. vulgaris cv. Eduarda for a three-day inoculation access period. All test plants were successfully infected and exhibited symptoms in the form of interveinal yellowing up to three weeks postinoculation. RT-PCR confirmed the presence of BYV in all inoculated plants. A study by Nikolić (1951) suggested a possible presence of BYV based on symptoms observed on sugar beet plants in fields, but to our knowledge this is the first report of BYV in sugar beet in Serbia. As sugar beet is one of the most important industrial crops in Serbia, the presence of BYV could lead to significant losses, considering that aphid vectors are widespread under Serbian environmental conditions. The discovery of BYV on sugar beet should prompt a more detailed survey and subsequent testing of susceptible hosts to determine the distribution and incidence of BYV in Serbia.

Milder autumns may increase risk for infection of crops with turnip yellows virus.

Climate change has increased the risk for infection of crops with insect-transmitted viruses. Mild autumns provide prolonged active periods to insects, which may spread viruses to winter crops. In autumn 2018, green peach aphids (Myzus persicae) were found in suction traps in southern Sweden that presented infection risk for winter oilseed rape (OSR; Brassica napus) with turnip yellows virus (TuYV). A survey was carried out in spring 2019 with random leaf samples from 46 OSR fields in southern and central Sweden using DAS-ELISA resulting in TuYV being detected in all fields except one. In the counties of Skåne, Kalmar and Östergötland, the average incidence of TuYV-infected plants was 75% and the incidence reached 100% for nine fields. Sequence analyses of the coat protein gene revealed a close relationship between TuYV isolates from Sweden and other parts of the world. High-throughput sequencing for one of the OSR samples confirmed the presence of TuYV and revealed co-infection with TuYV-associated RNAs. Molecular analyses of seven sugar beet (Beta vulgaris) plants with yellowing, collected in 2019, revealed that two of them were infected by TuYV together with two other poleroviruses: beet mild yellowing virus and beet chlorosis virus. The presence of TuYV in sugar beet suggests a spillover from other hosts. Poleroviruses are prone to recombination, and mixed infection with three poleroviruses in the same plant poses a risk for the emergence of new polerovirus genotypes.

Assessment of non-neonicotinoid treatments against aphids on sugar beets

Aphids can cause significant damage to sugar beet crops. Myzus persicae (Sulzer) (Hempitera: Aphididae), also called green peach aphid, is responsible for transmitting yellows (i.e., beet yellows virus, beet mild yellowing virus, beet chlorosis virus, and beet mosaic virus) to sugar beet (Beta vulgaris Linné) that can substantially decrease crop yields and cause significant economic losses.In a context of increasing awareness of environmental health, products containing neonicotinoids were recently banned in several countries, making it necessary to identify new effective means of aphid control. Our study aims to assess the effectiveness of six non-neonicotinoid conventional synthetic insecticides and five biopesticides in reducing the number of aphids on sugar beets. We used data from 35 trials (site-years) managed over five years (from 2018 to 2022) located in France's main sugar beet-producing regions. We fitted a mixed-effect model able to take the variability of treatment effect across site-years into account. The most effective conventional synthetic insecticides were spirotetramat and flonicamid, with a reduction in aphid numbers (compared to the untreated control) of up to 85.6% [95% confidence interval = (80.5; 89.4)] and 79.9% [95% confidence interval = (72.9; 85.2)], respectively, 14 days after their applications at registered rates when combined with oil-based adjuvant. Biopesticides were much less effective, with the best biopesticide (Lecanicillium muscarium R. Zare & W. Gams Ve6) leading to only 40.7% [95% confidence interval = (16.6; 57.9)] reduction in aphid numbers, 14 days after its application, with great uncertainty due to the limited number of trials available for this product. Our results reveal that the most effective alternative treatments to neonicotinoids could reduce aphid abundance by more than 70% in most cases.

Virus Yellows and Syndrome "Basses Richesses" in Western Switzerland: A Dramatic 2020 Season Calls for Urgent Control Measures.

Massive outbreaks of virus yellows (VY) and syndrome “basses richesses” (SBR) are thought to be responsible for the major loss of sugar beet yields in 2020 in western cantons of Switzerland. Typical yellowing symptoms were visible during field inspections, and control measures were reportedly ineffective or even absent. Both diseases induce yellowing but have distinct etiologies; while VY is caused by aphid-transmitted RNA viruses, SBR is caused by the cixiid-transmitted γ-proteobacterium Candidatus Arsenophonus phytopathogenicus. To clarify the situation, samples from diseased plants across the country were screened for the causal agents of VY and SBR at the end of the season. Beet yellows virus (BYV) and Beet chlorosis virus (BChV) showed high incidence nationwide, and were frequently found together in SBR-infected fields in the West. Beet mild yellowing virus (BMYV) was detected in two sites in the West, while there was no detection of Beet western yellows virus or Beet mosaic virus. The nucleotide diversity of the detected viruses was then investigated using classic and high-throughput sequencing. For both diseases, outbreaks were analyzed in light of monitoring of the respective vectors, and symptoms were reproduced in greenhouse conditions by means of insect-mediated inoculations. Novel quantification tools were designed for BYV, BChV and Ca. A. phytopathogenicus, leading to the identification of specific tissues tropism for these pathogens.

Beet chlorosis virus

This datasheet on Beet chlorosis virus covers Identity, Distribution, Hosts/Species Affected, Vectors & Intermediate Hosts, Further Information.

Virus Yellows in sugar beet – possibilities to achieve virus resistance

Virus yellows in sugar beet is caused by different virus species. Monitoring has shown that Beet yellows virus (BYV), Beet mild yellowing virus (BMYV), Beet chlorosis virus (BChV) are common and widespread, while Beet mosaic virus (BtMV) is less prevalent. The green peach aphid (Myzus persicae) is considered the main vector of these viruses. Sugar beet varieties with resistance or tolerance traits are currently not available to practical growers, therefore it is imperative to support breeding efforts with improved strategies to achieve virus resistance. For this purpose, a field test was established in which yield differences between susceptible and tolerant varieties can be generated by a 3% inoculation with BMYV-carrying aphids. A greenhouse bioassay has also been developed to distinguish susceptible and tolerant genotypes following BYV infection. Both assays pave the way for future use of natural resources such as wild forms and other breeding material to screen for virus resistance. In addition, molecular biology approaches are used to identify plant susceptibility factors of the plant-virus interaction, which will be knocked out via modern precision breeding methods to generate recessive virus resistance. Consequently, genotypes with naturally occurring mutations in the appropriate factors can be used for crossbreeding processes into elite breeding material.

New insights into virus yellows distribution in Europe and effects of beet yellows virus, beet mild yellowing virus, and beet chlorosis virus on sugar beet yield following field inoculation

AbstractBeet yellows virus (BYV), beet mild yellowing virus (BMYV), beet chlorosis virus (BChV), and beet mosaic virus (BtMV) cause virus yellows (VY) disease in sugar beet. The main virus vector is the aphid Myzus persicae. Due to efficient vector control by neonicotinoid seed treatment over the last decades, there is no current knowledge regarding virus species distribution. Therefore, Europe‐wide virus monitoring was carried out from 2017 to 2019, where neonicotinoids were banned in 2019. The monitoring showed that closterovirus BYV is currently widely spread in northern Europe. The poleroviruses BMYV and BChV were most frequently detected in the northern and western regions. The potyvirus BtMV was only sporadically detected. To study virus infestation and influence on yield, viruses were transmitted to sugar beet plants using viruliferous M. persicae in quadruplicate field plots with 10% inoculation density simulating natural infection. A plant‐to‐plant virus spread was observed within 4 weeks. A nearly complete infection of all plants was observed in all treatments at harvest. In accordance with these findings, a significant yield reduction was caused by BMYV and BChV (−23% and −24%) and only a moderate reduction in yield was observed for BYV (−10%). This study showed that inoculation at low densities mimics natural infection, and quick spreading induced representative yield effects. Within the background of a post‐neonicotinoid era, this provides the basis to screen sugar beet genotypes for the selection of virus tolerance/resistance and to test the effectiveness of insecticides for the control of M. persicae with a manageable workload.

Host range and molecular analysis of Beet leaf yellowing virus, Beet western yellows virus‐JP and Brassica yellows virus in Japan

Beet western yellows virus (BWYV; genus Polerovirus, family Luteoviridae) is one of the most important viruses causing yellowing disease of many field and vegetable crops. This study isolated different poleroviruses from sugar beet, spinach, radish and brassica in Japan, and identified them as BWYV‐JP, Beet leaf yellowing virus (BLYV), Brassica yellows virus (BrYV) and BrYV‐R (radish strain) based on host range and molecular analysis. Among over 100 plant species from 19 families inoculated with the vector Myzus persicae, about half of the species in 13 families were infected with some of these viruses. BLYV shared a similar host range to Beet mild yellowing virus (BMYV). These had a much more limited host range than BWYV‐JP, which resembled BWYV‐USA. The host range of BrYV was similar to that of Turnip yellows virus (TuYV). Phylogenetic analyses at the 5′ portion (replication‐related gene) of the genome showed that BLYV, BMYV, BWYV (‐JP and ‐USA) and Cucurbit aphid‐borne yellows virus (CABYV) formed one large group, whereas BrYV and TuYV were grouped together. BLYV and BWYV were most closely related to each other, and were more closely related to CABYV than to BMYV. However, at the 3′ end (coat protein gene), BLYV and BWYV‐JP formed a distinct group, separated from the BrYV group, which in turn was more closely related to BWYV‐USA, BMYV, TuYV and Beet chlorosis virus, a group originating from outside Asia. Thus, this study presents host range differences and phylogeographical relationships of BWYV‐like poleroviruses that are distributed worldwide.

Molecular characterization of a new recombinant brassica yellows virus infecting tobacco in China.

Brassica yellows virus (BrYV), prevalently distributed throughout mainland China and South Korea while triggering serious diseases in cruciferous crops, is proposed to be a new species in the genus Polerovirus within the family Luteoviridae. There are three distinct genotypes (BrYV-A, BrYV-B and BrYV-C) reported in cabbage and radish. Here, we describe a new BrYV isolate infecting tobacco plants in the field, which was named BrYV-NtabQJ. The complete genome sequence of BrYV-NtabQJ is 5741 nt in length, and 89% of the sequence shares higher sequence identities (about 90%) with different BrYV isolates. However, it possesses a quite divergent region within ORF5, which is more close to Beet western yellows virus (BWYV), Beet mild yellowing virus (BMYV) and Beet chlorosis virus (BChV). A significant recombination event was then detected among BrYV-NtabQJ, BrYV-B Beijng isolate (BrYV-BBJ) and BWYV Leonurus sibiricus isolate (BWYV-LS). It is proposed that BrYV-NtabQJ might be an interspecific recombinant between BrYV-BBJ and BWYV-LS, and the recombination might result in the successful aphid transmission of BrYV from cruciferous crops to tobacco. And it also poses new challenges for BrYV diagnosis and the vegetable production.

Production of a Beet chlorosis virus full-length cDNA clone by means of Gibson assembly and analysis of biological properties.

Beet chlorosis virus (genus Polerovirus, family Luteoviridae), which is persistently transmitted by the aphid Myzus persicae, is part of virus yellows in sugar beet and causes interveinal yellowing as well as significant yield loss in Beta vulgaris. To allow reverse genetic studies and replace vector transmission, an infectious cDNA clone under cauliflower mosaic virus 35S control in a binary vector for agrobacterium-mediated infection was constructed using Gibson assembly. Following agroinoculation, the BChV full-length clone was able to induce a systemic infection of the cultivated B. vulgaris. The engineered virus was successfully aphid-transmitted when acquired from infected B. vulgaris and displayed the same host plant spectrum as wild-type virus. This new polerovirus infectious clone is a valuable tool to identify the viral determinants involved in host range and study BChV protein function, and can be used to screen sugar beet for BChV resistance.

Distribution of some aphid-borne viruses infecting sugar beet in Turkey

Surveys were conducted in sugar beet (Beta vulgaris L.) growing areas, which cover 52% of Turkey’s sugar beet production. Sugar beet leaves showing virus-like symptoms such as chlorosis, mosaic and chlorotic spots, were collected from 291 different fields located in ten different provinces in northern and central parts of Turkey in 2011. Beet leaf samples were tested by ELISA for Beet yellowing virus (BYV), Beet mosaic virus (BtMV) and beet-related Poleroviruses [Beet mild yellowing virus (BMYV) and Beet chlorosis virus (BChV)]. Based on the ELISA tests, 58.4% of the samples collected from sugar beet fields gave positive reactions for the viruses tested. None of the samples were found to be infected in Kastamonu and Krkkale provinces. Beet-related Poleroviruses (BMYV and BChV) were the most common viruses obtained from 38.5% of the samples followed by BYV and BtMV with 29.6% and 12.7% respectively. The incidences of single virus infection were 11.3% for BYV and 5.5% for BtMV. Mixed virus infections occurred in 20.3% of the sugar beet samples. Out of four groups of symptoms, chlorosis was the most common symptom (72.9%) followed by mosaic (15.3%), chlorosis+mosaic (7.1%) and chlorotic spots (4.7%) in the surveyed areas.

Genome sequence of a recombinant brassica yellows virus infecting Chinese cabbage.

RNA from a Chinese cabbage plant (Brassica campestris ssp. pekinensis) showing leaf malformation and mottling was labeled and hybridized to a DNA chip capable of detecting plant viruses and viroids. Probes specific for beet mild yellowing virus (BMYV) and beet western yellows virus (BWYV) yielded positive results, suggesting that the plant was infected by a polerovirus. Primers designed from the sequences of the positive probes were used to amplify and sequence one portion of the viral genome. This sequence showed a 90% or greater identity to several poleroviruses, including BMYV, BWYV, beet chlorosis virus (BChV) and turnip yellows virus (TuYV). The complete genome sequence of the Chinese cabbage-infecting polerovirus consisted of 5,666 nt and was most closely related to brassica yellows virus (BrYV; 94% identity). The virus was named BrYV-Cheongsong (BrYV-CS). However, ORF3, ORF4 and the 5' half of ORF5 of BrYV-CS were more closely related to those of TuYV, BWYV, BChV and BMYV than to those of BrYV. Interestingly, a recombination event (positions 3531-4819 in BrYV-CS) was detected when this sequence was aligned with those of BrYV and TuYV. This region showed the highest sequence identity to that of TuYV (94% identity) and had greater than 93% identity to those of BWYV, BChV and BMYV, but it shared only 81% identity with that of BrYV. Taken together, the genomes of BrYV-CS and BrYV are closely related. However, the structural genes in the 3' half of the genome of BrYV-CS are more closely related to those of other poleroviruses.

Phylogenetic relationships and the occurrence of interspecific recombination between beet chlorosis virus (BChV) and Beet mild yellowing virus (BMYV).

Samples containing two viruses belonging to the genus Polerovirus, beet chlorosis virus (BChV) and beet mild yellowing virus (BMYV), were collected from French and Polish sugar beet fields. The molecular properties of 24 isolates of BChV and BMYV were investigated, and their genetic diversity was examined in the coat protein (CP)- and P0-encoding genes. For the first time, we have demonstrated that beet polerovirus populations include recombinants between BChV and BMYV containing breakpoints within the CP gene. Moreover, a partial correlation between geographic origin and phylogenetic clustering was observed for BMYV isolates.

Detection and discrimination of members of the family Luteoviridae by real-time PCR and SYBR ® GreenER™ melting curve analysis

This study investigated the suitability of a two step real-time RT-PCR melting curve analysis as a tool for the detection and discrimination of nine species in the plant virus family Luteoviridae, being Soybean dwarf virus [SbDV], Bean leafroll virus [BLRV], Beet chlorosis virus [BChV], Beet mild yellowing virus [BMYV], Beet western yellows virus [BWYV], Cereal yellow dwarf virus-RPV [CYDV-RPV], Cucurbit aphid-borne yellows virus [CABYV], Potato leafroll virus [PLRV] and Turnip yellows virus [TuYV]. Melting temperature and shape of the melting peak were analysed for 68 bp and 148 bp coat protein gene amplicons using SYBR ® GreenER™ fluorescent dye. Specific melting peaks with unique melting temperature were observed for the various species of the family Luteoviridae using the 68 bp amplicon, but not with the 148 bp amplicon. Due to the high variability of sequences for some members of this family, different melting temperatures were also observed between different isolates of the species CYDV-RPV and TuYV. Nevertheless, discrimination between species was achieved for SbDV, BLRV, BChV, BMYV, CABYV and either PLRV or BWYV. Melting curve analysis, in this study, is a faster and more discriminatory alternative to gel electrophoresis of end-point PCR products for the detection of Luteoviridae infection.