Simultaneous detection of papaya ringspot virus, papaya leaf distortion mosaic virus, and papaya mosaic virus by multiplex real-time reverse transcription PCR

Occurrence, Distribution, and Management of Aphid-Transmitted Viruses in Cucurbits in Spain

The effectiveness of pest and disease management in crops relies on knowledge about their presence and distribution in crop-producing areas. Aphids and whiteflies are among the main threats to vegetable crops since these hemipterans feed on plants, causing severe damage, and are also able to transmit a large number of devastating plant viral diseases. In particular, the widespread occurrence of aphid-transmitted viruses in cucurbit crops, along with the lack of effective control measures, makes surveillance programs and virus epidemiology necessary for providing sound advice and further integration into the management strategies that can ensure sustainable food production. This review describes the current presence and distribution of aphid-transmitted viruses in cucurbits in Spain, providing valuable epidemiological information, including symptom expressions of virus-infected plants for further surveillance and viral detection. We also provide an overview of the current measures for virus infection prevention and control strategies in cucurbits and indicate the need for further research and innovative strategies against aphid pests and their associated viral diseases.

Detection of Cucumber green mottle mosaic virus in low-concentration virus-infected seeds by improved one-step pre-amplification RT-qPCR

BACKGROUND

Seeds were an important medium for long-distance transmission of plant viruses. Therefore, appropriate, more sensitive methods for detecting low concentrations of virus-infected in seeds were crucial to ensure the quality of seed lots. In this study, we have developed a one-step pre-amplification reverse transcription quantitative PCR (RT-qPCR) assay based on the TaqMan technology to detect Cucumber green mottle mosaic virus (CGMMV) in zucchini seeds.

RESULT

Seed powder samples with simulated CGMMV-infected at a low concentration were prepared (the mass ratio 1:900 and 1:1000), and their uniformity were verified using one-step pre-amplification RT-qPCR. We used one-step pre-amplification RT-qPCR to detect CGMMV in low-concentration virus-infected seeds and compared this method with universal RT-qPCR and double antibody sandwich-enzyme-linked immunosorbent (DAS-ELISA) assay, the main methods used for virus detection in seeds. The minimum limit of detection (LOD) of the improved one-step pre-amplification RT-qPCR assays for simulated CGMMV-infected seeds in large lots seeds samples were 0.1%.

CONCLUSIONS

One-step pre-amplification RT-qPCR assays could reliably and stably detected a single CGMMV-infected seed in 1000 seeds and demonstrated a higher detection sensitivity than universal RT-qPCR (infected seeds versus healthy seeds 1:900) and DAS-ELISA assay (infected seeds versus healthy seeds 1:500). Our improved one-step pre-amplification RT-qPCR assay have proved to be very suitable for the analysis of large seed lots.

One-step real-time multiplex reverse transcription-polymerase chain reaction assay with melt curve analysis for detection of potato leafroll virus, potato virus S, potato virus X, and potato virus Y

Background

Certification of seed potato as free of viruses is essential for stable potato production. Among more than 30 virus species infecting potato, potato leafroll virus (PLRV), potato virus S (PVS), potato virus X (PVX), and potato virus Y (PVY) predominate worldwide and should be the targets of a high-throughput detection protocol for seed potato quarantine.

Results

We developed an assay based on one-step real-time multiplex reverse transcription-polymerase chain reaction (mRT-PCR) with melt curve analysis for the four viruses and one internal control, potato elongation factor 1 alpha gene (EF1α). Virus-specific primers were derived from conserved regions among randomly selected representatives considering viral genomic diversity. Our assay simultaneously detected representative Japanese isolates of PLRV, O lineage of PVS, PVX, and NTN strain of PVY. The variability of melting temperature (Tm) values for each virus was confirmed using Japanese isolates, and virus species could be identified by the values of 87.6 for PLRV, 85.9 for PVX, 82.2 (Ordinary lineage) to 83.1 (Andean lineage) for PVS, and 79.4 (NA-N strain) to 80.5 (O strain and NTN strain) for PVY on average. The reliability of calculation was validated by comparing the calculated Tm values and measured Tm values and the values had a strong linear correlation (correlation of determination: R² = 0.9875). Based on the calculated Tm values, representative non-Japanese isolates could also be identified by our assay. For removing false positives, two criteria were set for the evaluation of result; successful amplification was considered as 30.0 ≥ threshold cycle value, and the virus-specific peak higher than the EF1α-specific peak was considered as positive. According to these criteria, our assay could detect PLRV and PVS from 100-fold dilution of potato leaf homogenate and PVX and PVY from 1000-fold in a model assay.

Conclusion

This new high-throughput detection protocol using one-step real-time mRT-PCR was sensitive enough to detect viruses in a 100-fold dilution of singly-virus contaminated homogenate in a model assay. This protocol can detect the four viruses in one assay and yield faster results for a vast number of samples, and greatly save the labor for seed potato quarantine and field surveys.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01591-3.

Targeted Genome Sequencing (TG-Seq) Approaches to Detect Plant Viruses

Globally, high-throughput sequencing (HTS) has been used for virus detection in germplasm certification programs. However, sequencing costs have impeded its implementation as a routine diagnostic certification tool. In this study, the targeted genome sequencing (TG-Seq) approach was developed to simultaneously detect multiple (four) viral species of; Pea early browning virus (PEBV), Cucumber mosaic virus (CMV), Bean yellow mosaic virus (BYMV) and Pea seedborne mosaic virus (PSbMV). TG-Seq detected all the expected viral amplicons within multiplex PCR (mPCR) reactions. In contrast, the expected PCR amplicons were not detected by gel electrophoresis (GE). For example, for CMV, GE only detected RNA1 and RNA2 while TG-Seq detected all the three RNA components of CMV. In an mPCR to amplify all four viruses, TG-Seq readily detected each virus with more than 732,277 sequence reads mapping to each amplicon. In addition, TG-Seq also detected all four amplicons within a 10-8 serial dilution that were not detectable by GE. Our current findings reveal that the TG-Seq approach offers significant potential and is a highly sensitive targeted approach for detecting multiple plant viruses within a given biological sample. This is the first study describing direct HTS of plant virus mPCR products. These findings have major implications for grain germplasm healthy certification programs and biosecurity management in relation to pathogen entry into Australia and elsewhere.

A Double Mutation in the Conserved Motifs of the Helper Component Protease of Papaya Leaf Distortion Mosaic Virus for the Generation of a Cross-Protective Attenuated Strain

Potyviral helper component protease (HC-Pro), as a major determinant of symptom expression in susceptible plants, is a likely target candidate in the production of attenuated strains for cross-protection. In this study, single or double mutations of Lys (K) to Glu (E) in the Lys-Ile-Thr-Cys motif and Arg (R) to Ile (I) in the Phe-Arg-Asn-Lys motif of the HC-Pro from the severe papaya leaf distortion mosaic virus strain DF (PLDMV-DF) reduced symptom expression and virus accumulation in infected papaya (Carica papaya) plants. The papaya plants infected with the attenuated double mutant of PLDMV-EI presented as symptomless. PLDMV-EI provided effective protection against PLDMV-DF infection in three papaya cultivars and had no effect on plant growth and development. Our result showed that PLDMV-EI is a promising mild strain for the practical use of cross-protection in the field.

Recent Advances on the Multiplex Molecular Detection of Plant Viruses and Viroids

Plant viruses are still one of the main contributors to economic losses in agriculture. It has been estimated that plant viruses can cause as much as 50 billion euros loss worldwide, per year. This situation may be worsened by recent climate change events and the associated changes in disease epidemiology. Reliable and early detection methods are still one of the main and most effective actions to develop control strategies for plant viral diseases. During the last years, considerable progress has been made to develop tools with high specificity and low detection limits for use in the detection of these plant pathogens. Time and cost reductions have been some of the main objectives pursued during the last few years as these increase their feasibility for routine use. Among other strategies, these objectives can be achieved by the simultaneous detection and (or) identification of several viruses in a single assay. Nucleic acid-based detection techniques are especially suitable for this purpose. Polyvalent detection has allowed the detection of multiple plant viruses at the genus level. Multiplexing RT polymerase chain reaction (PCR) has been optimized for the simultaneous detection of more than 10 plant viruses/viroids. In this short review, we provide an update on the progress made during the last decade on techniques such as multiplex PCR, polyvalent PCR, non-isotopic molecular hybridization techniques, real-time PCR, and array technologies to allow simultaneous detection of multiple plant viruses. Also, the potential and benefits of the powerful new technique of deep sequencing/next-generation sequencing are described.