Yellow Virus Research Articles

Economic viability of companion plants to lower the spread of virus yellows in sugar beets

Following EU’s decision to ban neonics, several alternative solutions have emerged from the dedicated French national research program initiated in 2020. Companion plants, such as barley or oats, sown at the same time as beets, proved to have a repellent effect and reduce aphids’ presence in sugar beet fields. This paper evaluates the economic viability of this particular solution and assesses how it reduces the risk of sugar beet infections by virus yellows. We show that although companion plants may be effective in repelling aphids, the strict economic impact associated with the reduction of aphids’ population is mainly negative under cost-benefit assumptions currently adopted. Our analysis is based on the incidence model developed by Qi et al. It factors in costs induced by the planting and destruction of companion plants at a [4-6] leaf stage and factors in a ”competition” effect between companion plants and beets. As a consequence of our analysis, we highlight the need to run further research work in two directions, (1) analyse the potential of additional benefits offered by the solution to complement its strict impact on the number of aphids in sugar beet fields and (2) analyse potential benefits offered by synergies and combinations of companion plants with other viable solutions used to mitigate the spread of virus yellows in sugar beets.

Revealing hidden viruses inducing similar yellowing symptoms or remaining asymptomatic in cucurbit crops

AbstractMixed viral infections occur frequently in plants, leading to diseases that can be difficult to diagnose, especially when an unknown virus is hidden behind expression of symptoms common to other viruses. We monitored aphid‐ and whitefly‐transmitted viruses in two cucurbit crops (melon and watermelon) for three consecutive seasons (2021–2023) across three production regions in Spain, focusing on the common yellowing and mosaic symptoms. A total of 984 symptomatic leaf samples from 246 field plots were tested for 10 frequently found cucurbit viruses. Cucurbit aphid‐borne yellows virus (CABYV) was the most prevalent virus infecting both cucurbit crops over the three seasons. Additionally, occurrence of watermelon mosaic virus (WMV) in samples with mosaic symptoms was significant. However, an important proportion of yellowing symptomatic samples tested negative for known viruses. Using a sequence‐independent approach, we identified a novel polerovirus, Pepo aphid‐borne yellows virus (PABYV), which was widespread, infecting both crops. Analysis of our long‐term cucurbit frozen‐sample collection revealed that PABYV had emerged in Spain in 2018, possibly unnoticed as its yellowing symptoms were similar to CABYV, with which it was frequently associated. Additionally, we found the cryptic Cucumis melo endornavirus (CmEV) in all tested melon samples from 2011 and, for the first time, in pumpkin. Genetic characterization of CABYV, PABYV and CmEV populations revealed a replacement of ancient CABYV isolates by contemporary ones, while PABYV and CmEV isolates were genetically homogenous among their populations. This study underlines the need for continuous surveillance and further investigation into common symptoms of mixed viral infections.

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.

Actuarial implications and modeling of virus yellows on sugar beet after the EU's ban on neonics and climate change

Following the EU's decision to ban neonics, this article investigates the impacts of virus yellows on sugar beet yields under the ban and under current and future climates. Using a model that factors in key variables such as sowing dates, phenological stages, first aphid flight and aphid abundance, simulations are performed using long-period climate datasets as inputs. Coupled with incidence and sugar yield loss assumptions, this model allows to reconstruct the impact of virus yellows on sugar beet yields using a so called ‘as if’ approach. By simulating the effects of viruses over a long period-of-time, as if neonics weren't used in the past, this methodology allows an accurate assessment of risks associated with virus yellows, as well as impact of future agro-ecological measures.The analysis provides in addition an actuarial rating for an insurance policy that compensates the losses triggered by those viruses.

Time point of virus yellows infection is crucial for yield losses in sugar beet, and co‐infection with beet mosaic virus is negligible under field conditions

AbstractBeet chlorosis virus (BChV), beet mild yellowing virus (BMYV) and beet yellows virus (BYV) transmitted by Myzus persicae cause virus yellows (VY) disease in sugar beet. M. persicae also transmits beet mosaic virus (BtMV), which is often associated with VY. So far, field trials to determine the effect of infection time point on yield have used 100% inoculation density and little is known about the yield effect of BtMV in mixed infections with VY species under field conditions. Therefore, we conducted sugar beet field trials using a new inoculation protocol with densities of 3%–10% in combination with different infection time points; we also tested the effect of BtMV/VY species mixed infections on white sugar yield (WSY). We observed a wide range of WSY losses for BChV (3.6%–26.8%), BMYV (1.7%–22.0%) and BYV (3.7%–37.0%) depending on infection time point, with no further significant losses after BBCH Stages 18/19, 35 and 39, respectively. Both the time of infection and area under disease progress curve showed excellent correlation with WSY losses for all VY species. BtMV had no significant effect on WSY losses either as a single infection or in mixed infections with BChV or BYV compared to control or single infections of these viruses. However, BMYV/BtMV mixed infection showed significantly increased WSY loss (+13.6%) compared to single BMYV infection. Our results can be used to predict yield losses in practical fields and to develop economic control thresholds for decision support systems.

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.

Using spectral sensing in plant science

Digital cameras are widely used tools for plant monitoring in plant science today. Used to track plant growth or even visible symptoms, they are important tools for breeding and plant protection field trials. Nevertheless, its extension to measure the near infrared (NIR) region (700–1000 nm) includes great potential as plants show a higher light reflectance within this spectrum. Various applications have shown its use for disease detection, quantification, virus content estimation, and stress monitoring. As the next step is a comprehensive integration into agricultural routines, this study will show two use-cases with a high technological readiness level. One use-case shows a handheld multispectral sensor, which is used for manual measurements to detect and discriminate different virus types in sugar beet. In contrast, the second use-case shows a transfer to an UAV based disease quantification routine based on spectral imaging for Cercospora leaf spot. In addition, two prototypical workflows are shown for processing non-imaging and imaging spectral data in an agricultural setting. This study shows the state of the art in spectral sensing in the field for the two major sugar beet diseases – virus yellows and Cercospora leaf spot. Furthermore a future perspective for coming technological challenges regarding the integration of AI in sensors or robotic workflows is provided.

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.

Predicting the seasonal flight activity of Myzus persicae, the main aphid vector of Virus Yellows in sugar beet.

Virus Yellows (VY), a disease caused by several aphid-borne viruses, is a major threat to the global sugar beet production. Following the ban of neonicotinoid-based seed treatments against aphids in Europe, increased efforts are needed to monitor and forecast aphid population spread during the sugar beet growing season. In particular, predicting aphid flight seasonal activity could allow anticipation of the timing and intensity of crop colonisation and contribute to the proper implementation of management methods. Forecasts should be made early enough to assess risk, but can be updated as the season progresses to refine management. Based on a long-term suction-trap dataset gathered between 1978 and 2014, we built and evaluated a set of models to predict the flight activity features of the main VY vector, Myzus persicae, at any location in the French sugar beet production area (c. 4 × 105 ha). Flight onset dates, length of flight period and cumulative abundance of flying aphids were predicted using climatic and land-use predictors as well as geographical position. Our predictions outperformed current models published in the literature. The importance of the predictor variables varied according to the predicted flight feature but winter and early spring temperature always played a major role. Forecasts based on temperature were made more accurate by adding predictors related to aphid winter reservoirs. In addition, updating the model parameters to take advantage of new weather data acquired during the season improved the flight forecast. Our models can be used as a tool for the mitigation in sugar beet crops. © 2023 Society of Chemical Industry.

First report of Pepo aphid‐borne yellows virus on watermelon plants in Spain

First report of <i>Pepo aphid‐borne yellows virus</i> on watermelon plants in Spain

Neonicotinoid seed treatment on sugar beet in England: a qualitative analysis of the controversy, existing policy and viability of alternatives

In 2021, the United Kingdom Government granted the possibility of an emergency derogation for the use of the neonicotinoid seed treatment, thiamethoxam, on sugar beet in England. This was met with heavy criticism and controversy due to the body of evidence demonstrating toxicity of the insecticide to non-target species, particularly pollinators. However, many viewed this decision to be reasonable in this system, as sugar beet is a non-flowering crop, and derogations were only implemented if a set of conditions, including viral risk, were met. This research aims to understand the policy and the perspective of stakeholders in this debate, and identify key problems associated with thiamethoxam use on sugar beet. Semi-structured interviews combined with a modified policy analysis were used, incorporating framework analysis and comparative analysis. Political polarisation, whereby respondents felt that the debate had become anti-pesticide or pro-pesticide and lacked nuance, and the monopsony of British Sugar (a UK company that buys and processes sugar beet), were found to be the most prevalent issues currently impeding political progress and the enhancement of sustainable agriculture in this system. Virus forecasting was considered a successful strategy at the time of writing, although limitations to the model are also discussed. Non-chemical alternatives were found to be limited in this system due to the specificity of the pest system and the low threshold of virus yellows, while forecasting was considered to have the lowest net-environmental impact. Additional policy strategies to work alongside forecasting, such as public education and intergroup contact are also discussed. This study reflects a more general tug-of-war that often sets up a false dichotomy between food security and environmental sustainability. It highlights the importance of addressing the complexity of sustainable food production by opening up the discussion and taking a more nuanced and adaptive approach to policy.

FRACTIONAL ORDER GEMINIVIRUS IMPRESSION IN CAPSICUM ANNUUM MODEL WITH MITTAG-LEFFLER KERNAL

In the cultivation of Capsicum annuum (C. annuum), the major obstacles are triggered by the Yellow virus (Gemini virus). The virus is spread through insects, namely Bemisia tabaci (B. tabaci). To reduce the spreading of the virus in C. annuum, the entomopathogenic fungi (Verticillium lecanii) are used. We have analyzed the fractional-order model of chili plants with Atangana–Baleanu derivative (AB-derivative). Also, we calculate the numerical values to illustrate the results.

Quantifying inherent predictability and spatial synchrony in the aphid vector Myzus persicae: field-scale patterns of abundance and regional forecasting error in the UK.

Sugar beet is threatened by virus yellows, a disease complex vectored by aphids that reduces sugar content. We present an analysis of Myzus persicae population dynamics with and without neonicotinoid seed treatment. We use 6 years' yellow water trap and field-collected aphid data and two decades of 12.2m suction-trap aphid migration data. We investigate both spatial synchrony and forecasting error to understand the structure and spatial scale of field counts and why forecasting aphid migrants lacks accuracy. Our aim is to derive statistical parameters to inform regionwide pest management strategies. Spatial synchrony, indicating the coincident change in counts across the region over time, is rarely present and is best described as stochastic. Uniquely, early season field populations in 2019 did show spatial synchrony to 90 km compared to the overall average weekly correlation length of 23 km. However, 70% of the time series were spatially heterogenous, indicating patchy between-field dynamics. Field counts lacked the same seasonal trend and did not peak in the same week. Forecasts tended to under-predict mid-season log10 counts. A strongly negative correlation between forecasting error and the proportion of zeros was shown. Field populations are unpredictable and stochastic, regardless of neonicotinoid seed treatment. This outcome presents a problem for decision-support that cannot usefully provide a single regionwide solution. Weighted permutation entropy inferred that M. persicae 12.2m suction-trap time series had moderate to low intrinsic predictability. Early warning using a migration model tended to predict counts at lower levels than observed. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Biochemical alterations in soybean (Glycine max) infected with Mungbean yellow mosaic India virus in Lalitpur dist., Bundelkhand region of India

The yellow mosaic symptoms on soybean (Glycine max) were observed at various sites in the Bundelkhand region of India and infection of begomovirus was detected through PCR. The begomovirus isolates were identified as Mungbean yellow mosaic India virus (MYMIV). MYMIV infection in soybean results in the production of reactive oxygen species to activate defense mechanisms at different levels to overcome the damage caused in the severely infected crops. The biomarkers of stress in plants such as, hydrogen peroxide (H2O2), catalase (CAT), Superoxide dismutase (SOD), Ascorbate peroxidase (APX) contents studies also suggested elevation in stress-related enzymes and also a significant reduction in sugar, chlorophyll, and protein contents have been observed. Previously alteration in biochemical due biotic and abiotic stresses have been reported in different varieties of legumes, but biochemical alterations in soybean infected by MYMIV are being reported for the first time from the Bundelkhand region of India.

Molecular characterization of a novel Conyza canadensis-infecting begomovirus in China

A novel monopartite begomovirus was found in naturally infected Conyza canadensis plants exhibiting typical begomovirus-induced yellow vein symptoms in Yunnan Province of China. Analysis of two obtained full-length viral genome sequences showed that they shared 99.8% nucleotide (nt) sequence similarity, and both consisted of 2733 nts (GenBank accession no. OK120264 and OK120266, respectively). Further analysis showed that these two sequences shared the highest nt sequence similarity (78.9%) with tomato yellow leaf curl Vietnam virus (TYLCVV) (EU189150). In the assayed C. canadensis plants, a betasatellite of 1,341 nts (Accession no. OK120265 and OK120267, respectively) was also found, and it shared 98.1% sequence similarity with malvastrum yellow vein betasatellite (MaYVB) (JX679254). Based on the current classification criteria for begomoviruses, we consider that the two obtained viral isolates are a novel begomovirus, and named it as conyza yellow vein virus (CoYVV). Our further analysis result showed that CoYVV is likely originated from a recombination event between tomato yellow leaf curl Yunnan virus (TYLCYnV) and tomato yellow leaf curl China virus (TYLCCNV). To investigate the effect of CoYVV infection in plant, we constructed two infectious clones (i.e., pCoYVV and pMaYVB), and inoculated them individually or together to Nicotiana benthamiana plants through agro-infiltration. The result showed that the plants co-inoculated with CoYVV and MaYVB developed yellow vein and downward leaf-curling symptoms, whereas the plants inoculated with CoYVV alone showed no clear virus-like symptoms. Virus infection in the inoculated N. benthamiana plants was confirmed through polymerase chain reaction (PCR). The result of quantitative PCR (qPCR) showed that in the presence of MaYVB, the accumulation level of CoYVV DNA was significantly increased compared to that in the plants infected with CoYVV alone.

Barley yellow dwarf virus em trigo no Brasil

The history of the barley yellow dwarf virus (BYDV) in Brazil began to be officially reported in 1968 when symptoms of yellowing in wheat were atributed to this ecological agent. The exact date of introductio of the virus in Brazil is unknown, but plants with symptoms similar to those caused by the virus and the aphid vectors had already been reported decades before the official diagnosis. After the identification of BYDV in Rio Grande do Sul, the virus was also found in other wheat regions in Santa Catarina, Paraná, São Paulo, Mato Grosso do Sul, Distrito Federal and Minas Gerais. This history will be explored from two points of view. First, considering the description of the variability of the viral population according to the detection and diagnosis methods and technologies available at each at me, and second, analyzing the impacts of changes in the Brazilian agricultural landscape and management practices on viral epidemiology

Differential Symptom Development and Viral RNA Loads in 10 Nicotiana benthamiana Accessions Infected with the Tobamovirus Yellow Tailflower Mild Mottle Virus.

Yellow tailflower mild mottle virus (YTMMV, genus Tobamovirus) was identified from wild plants of solanaceous species in Australia. Nicotiana benthamiana is a species indigenous to the arid north of Australia. N. benthamiana accession RA-4 (the lab type), which has a mutant, functionally defective, RNA-dependent RNA polymerase 1 (Rdr1) gene (Nb-Rdr1m), has played a significant role in plant virology, but little study has been done regarding responses to virus infection by other accessions of N. benthamiana. All wild-collected N. benthamiana accessions used in this study harbored wild-type Rdr1 genes (Nb-Rdr1). We compared symptoms of YTMMV infection and viral RNA load on RA-4 and nine wild-collected accessions of N. benthamiana from mainland Western Australia, an island, and the Northern Territory. After inoculation with YTMMV, RA-4 plants responded with systemic hypersensitivity and all individuals were dead 35 days postinoculation (dpi). Plants of wild-collected accessions exhibited a range of symptoms, from mild to severe, and some, but not all, died in the same period. Quantitative reverse transcription PCR revealed that the Rdr1 mutation was not a predictor of viral RNA load or symptom severity. For example, wild-collected A019412 plants carried more than twice the viral RNA load of RA-4 plants, but symptom expression was moderate. For plants of most accessions, viral RNA load did not increase after 10 dpi. The exception was plants of accession Barrow-1, in which viral RNA load was low until 15 dpi, after which it increased more than 29-fold. This study revealed differential responses by N. benthamiana accessions to infection by an isolate of YTMMV. The Rdr1 gene, whether mutant or wild-type, did not appear to influence viral RNA load or disease expression. Genetic diversity of the 10 N. benthamiana accessions in some cases reflected geographical location, but in other accessions this was not so.

Complete genomic characterization of a reassortment isolate of Sophora yellow stunt virus from Sophora alopecuroides in China

Complete genomic characterization of a reassortment isolate of Sophora yellow stunt virus from Sophora alopecuroides in China