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on May 17, 2023

This article was written by Jorge Luis Alonso G., an information consultant specializing
in the potato crop.

Scientists at the Inner Mongolia Agricultural University in China recently published a review in the journal Plants describing the advancement of antiviral strategies in potatoes through the engineering of both viral and plant-derived genes.

The article below is a summary of the information presented in this scientific paper.

1. Introduction

Potatoes, as a nutritious and staple food crop, have the potential to address food insecurity in developing countries. However, a major impediment to this aptitude is the prevalence of viral diseases in potato production, which result in the destruction of seed potatoes and often cause yield losses of 20–30%. Major viruses, including Potato virus Y (PVY), Potato leafroll virus (PLRV), and Potato virus X (PVX), cause various damaging symptoms such as leaf curling, necrosis, and stunted growth.

Complicating disease prevention, these viruses enter the plant through various vectors and use plant resources to replicate. Although virus-free seed potato technology can limit disease damage, some viruses are persistent and can re-infect during the growing season.

In addition, the hetero-tetraploid nature of the plant limits conventional breeding methods in developing antiviral potato varieties. On the positive side, advances in molecular biology and plant genetic engineering have opened the door to creating virus-resistant crops. Promising strategies have emerged, such as RNA interference (RNAi)-mediated resistance, which targets the viral coat proteins of the major potato viruses.

Eventually, genetically modified (GM) potatoes, including virus-resistant varieties, are now being introduced and commercialized in certain countries. This progress represents a major step forward in the fight against potato virus diseases.

2. Engineering Virus-Derived Viral Resistance in Potato

Researchers have developed genetically engineered virus-resistant plants, including potatoes, by using the coat protein (CP) gene of viruses such as tobacco mosaic virus (TMV), PVY, PVX, and PLRV. CP has several functions, including protection of the viral nucleic acid and regulation of the host range of infection. However, CP-mediated resistance is often limited, providing protection only against the CP donor virus or related strains and only at low viral doses. Additional complications in virus transmission can arise when the plant is transformed with the CP of an insect-borne virus.

To overcome these challenges, investigators are attempting to combine different viral CPs in the same plant or to incorporate coat protein genes with satellite RNA for a broader antiviral spectrum. An alternative approach involves replicase, an RNA polymerase encoded by viral genes. This enzyme synthesizes the positive and negative strands of viral RNA during replication. Although researchers have shown that replicase-mediated resistance is stronger than CP-mediated resistance, its specificity limits its use in the field due to the rapid mutation rate of plant RNA viruses.

In addition, antisense RNAs (asRNAs), which are complementary to messenger RNA (mRNA), have also been used for viral resistance. Although some success has been achieved in acquiring antiviral infection ability and protecting plants, antisense RNA-directed resistance is generally weak due to insufficient expression, which limits its practical application. However, there are still ways to improve the expression level of antisense RNA, which keeps this avenue open for exploration.

3. Engineering Virus-Resistant Plants Using Plant Endogenous Genes in Potato

Scientists are increasingly focusing on creating virus-resistant plants by using the plant’s own genes. They have discovered antiviral genes in both wild and cultivated potato species. These can be categorized into two distinct groups: extreme resistance (ER) genes and hypersensitive resistance (HR) genes. ER genes are known to resist many viruses and thwart viral reproduction in the early stages of infection. On the other hand, HR genes resist various virus species, triggering cell necrosis after a virus infection to limit its spread.

In potatoes, the Ry genes confer ER to all PVY strains, including the Rysto, Ryadg, and Rychc genes. Breeders have incorporated these into potato breeding programs and have identified Rysto as recognizing the central 149 amino acids of the PVY coat protein domain, suggesting its potential utility in engineering virus resistance.

The Y-1 gene is unique in its action as it induces cell death without preventing the systemic spread of PVY, thus hinting at its possible use in potato breeding. The G-Ry gene, a Y-1 homolog, has been detected to enhance resistance to PVY. Meanwhile, Ny genes, such as Ny-1 and Ny-2, have demonstrated HR against PVY in many potato cultivars. The Nytbr gene exhibits hypersensitivity to PVY, showing necrosis symptoms upon infection. Interestingly, scientists have identified the HCPro cistron of PVY as influencing necrotic reactions and resistance in plants carrying certain resistance genes.

As for resistance to PVX, it is mediated by the Rx1 gene, which causes a rapid termination of viral replication. A transcription factor that interacts with Rx1 mediates antiviral immunity, thereby enabling the Rx1 gene to confer ER to PVX.

One major and two minor quantitative trait loci (QTL) for resistance to potato leaf roll virus (PLRV), a potato disease, have been identified. The major QTL has mapped to potato chromosome XI. These identified genes associated with potato virus resistance can be used for antiviral breeding and for the development of potato varieties resistant to a single virus or many viruses. However, further research is needed to use these resistance genes and to discover new ones.

4. RNAi-Mediated Viral Resistance in Potato

RNA silencing, a common gene regulation mechanism in eukaryotes, plays a central role in protecting against viruses. This mechanism involves the interaction of small interfering RNAs (siRNAs), Dicer-like (DCL) endonucleases, and AGO family proteins. Specifically, DCL4 and DCL2 are responsible for generating siRNAs that mount a defense against RNA viruses. Further amplifying this system, RNA-dependent RNA polymerases (RDRs) convert aberrant single-stranded RNA into double-stranded RNA precursors of secondary siRNAs. This strategy is particularly promising for the development of virus-resistant transgenic plants.

In the specific context of viroid infection in plants, RNA silencing plays an important role. For example, replication of potato spindle tuber viroid in tomato plants induces resistance to RNA silencing, suggesting the critical role of secondary structures in resistance to RNAi.

The process of RNAi silencing can be manipulated to change miRNA sequences, creating artificial miRNAs (amiRNAs) that can target specific sequences. This ingenious approach has been used to engineer virus-resistant plants by creating resistant plants by creating amiRNAs that can actively fight viral infections.

In nature, however, viruses often encode silencing suppressors to counteract host RNAi-based defenses. To improve viral resistance, research is focused on enhancing RNAi activity by increasing the efficiency of AGO proteins and modifying siRNAs.

Despite extensive studies on RNA silencing as a strategy in plant antiviral protection, the beneficial effect of RNA silencing in viral infection remains somewhat puzzling. In particular, the mechanism by which some components of RNA silencing systems contribute to viral infection is not well understood. A deeper understanding of this could open up new opportunities for engineering viral resistance in various crops, such as potato.

5. CRISPR/Cas9-Mediated Viral Resistance in Potato

CRISPR/Cas, a system created to provide immune protection against invading nucleic acids in bacteria, has been repurposed for efficient genome engineering and the development of antiviral immunity in plants. This was amply demonstrated by the ability of CRISPR/Cas systems to effectively control Beet Severe Curly Top Virus (BSCTV) in N. benthamiana and A. thaliana. In addition, the CRISPR/Cas9 system has been ingeniously used to mutate susceptibility genes in rice and tobacco to confer resistance to Rice Tungro Spherical Virus (RTSV) and Potato Virus Y (PVY), respectively.

Besides these applications, the CRISPR/LshCas13a system was used in potato crops to generate resistance to Potato Virus Y, further demonstrating the potential of CRISPR technology in crop protection. Taken together, these studies underscore the significant capacity of CRISPR/Cas9 to control plant RNA viruses in major crops such as potato.

6. Future Prospects and Conclusions

As the battle against genetically complex virus strains in potato varieties escalates, researchers are moving to strengthen virus resistance. They are gearing up for a multi-pronged strategy.

First and foremost, they aim to disrupt the virus-host interaction by editing the potato genome. Using the available potato genome sequences, their goal is to construct an effective shield to protect potato plants from viral invasion. In this regard, they’ve identified CRISPR editing technology as a possible powerhouse in the fight against plant virus infections, a tool that could outperform RNAi.

Second, they are embarking on a mission to discover resistance genes that are key to antiviral response. This discovery could provide a significant boost to potato breeding efforts. Once identified, these genes will be introduced into potato plants through genetic transformation.

Third, they are formulating plans to harness the power of inducible responses in naturally virus-resistant plants. Because these plant defenses have broad-spectrum capabilities, their goal is to identify viral components that activate plant immune mechanisms. This promising area of study could reveal resistance genes that control these protective mechanisms. This, in turn, would pave the way for the development of strategies to engineer the broad-spectrum components of natural defenses.

Fourth, armed with an increasing understanding of the molecular functions of viral proteins, they plan to manipulate these proteins to create cross-protection against further viral infection in potato plants.

Finally, they see the transgenic expression of antiviral proteins of non-plant origin, including antibodies, as a promising frontier in the search for increased resistance to specific potato viruses. This approach underscores the relentless pursuit of new strategies to strengthen potatoes against viral threats.

Source: Liu, J., Yue, J., Wang, H., Xie, L., Zhao, Y., Zhao, M., & Zhou, H. (2023). Strategies for Engineering Virus Resistance in Potato. Plants, 12(9), 1736. https://doi.org/10.3390/plants12091736
Photo: Potato leafroll virus causes stunted plants. Credit Government of Western Australia

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Solomon Duah

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Farmers in Ghana prepare and use neem seed-based biopesticide

CABI collaborates with entomologist in Ghana to train vegetable farmers in the local preparation of neem seed-based biopesticides.

In collaboration with Professor Ken Owae Fening, an entomologist from the University of Ghana, PlantwisePlus has trained 44 vegetable farmers in the local preparation of neem-based biopesticides for pest control in vegetable production.

The training took place in March with 38 males and 6 female farmers engaged in vegetable production in the Anloga district of the Volta Region. It forms part of strategic objectives of the CABI PlantwisePlus programme to develop capacity and systems for, and also promote the increased production and use of, safer locally available and affordable low-risk plant protection products. Therefore, replacing the use of the highly hazardous chemicals for pest control in crop production.

Through this, the programme seeks to enhance knowledge and uptake of climate adaptive, environmentally-friendly and low-tech agricultural technologies. These can provide low-risk solutions for managing devastating crop pests.

Why use neem seed?

The initiative to use neem seed extracts for pest control comes on the back of research and trials done by the University of Ghana which proved that neem seed extract is effective for controlling the Diamond Back Moth (DBM) in cabbage. The research showed that the active ingredient in neem (Azadirachtin) is much more concentrated in the neem seeds. Therefore, training farmers to prepare and use extracts from the neem seeds can be an effective way of increasing access to safer and affordable homemade biopesticides. This will reduce overreliance on the more hazardous chemical pest control options.

Unlike the conventional pesticides, neem exhibits different modes of action. For example, serving as antifeedant or feed deterrent, repellent, growth arrestant, among others. This makes the extract effective for controlling a range of pest infestations in the field.

Preparing the neem seed extract

The training focused on equipping the farmers with the specific skills required to undertake each step of the preparation process. This included harvesting/collection and de-pulping of mature fruits to obtain seeds. And appropriate methods of drying and storing them.

The farmers also learned about the manual pounding of dried neem seeds to obtain a fine paste, from which the extract is finally obtained. The extract is mixed with water and strained to obtain the solution used for in spraying fields.

Increasing the uptake of lower-risk plant protection products

It is expected that the training will stimulate the interest of farmers in adopting proven low-cost, low-tech, locally available and safer pest control products. This will in turn help to reduce the health, environmental and food safety hazards associated with the overuse of chemical pesticides.

The farmers are likely to actively share the knowledge they acquired from the training with other farmers in their network. Thereby, helping to reach more farmers with the technology.

A post-training follow-up has shown that some of the trained farmers have already started harvesting matured neem fruits which are currently in season. They have de-pulped the fruit to obtain the seeds for storage. These seeds will later be processed and used in the new cropping season.

Going forward, the PlantwisePlus programme aims to develop a training manual on the collection, preparation and application of neem seed extract to support further trainings in other districts and regions.    

About CABI PlantwisePlus

The CABI-led worldwide programme – PlantwisePlus – seeks to help smallholder farmers produce more and high-quality food. Over a period of ten years (2020 – 2030), the programme will help the ministries of agriculture and other relevant state agencies of focus countries to predict, prepare and prevent a range of plant health issues which put food security and livelihoods at risk.

PlantwisePlus aims to accelerate the availability and use of nature-positive and low-risk plant protection products to reduce reliance on high-risk farm inputs and contribute to consumer demand for safer, higher quality and locally produced food.

The programme is also working to provide digital advisory tools to boost sustainable agriculture and improve the capacity of public and private actors offering support to smallholder farmers to diagnose crop health problems – and recommend sustainable management practices.”

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Read more

CABI Compendium datasheet: Azadirachta indica (neem tree)

Selecting the right biopesticide or biocontrol product for your needs

Neem-based biopesticides ‘as good as’ insecticides to fight Fall armyworm

5 advantages of biocontrol compared to chemical pest control

Conserving biodiversity: biocontrol for sustainable agriculture

Local biopesticide production hubs and the empowerment of rural women in Tamil Nadu, India

Images provided by the author

Ghana, biopesticides, neem

May 26, 2023

Solomon Duah

1 comment

lholder farmers to diagnose crop health problems – and recommend sustainable management practices.”

---

Read more

CABI Compendium datasheet: Azadirachta indica (neem tree)

Selecting the right biopesticide or biocontrol product for your needs

Neem-based biopesticides ‘as good as’ insecticides to fight Fall armyworm

5 advantages of biocontrol compared to chemical pest control

Conserving biodiversity: biocontrol for sustainable agriculture

Local biopesticide production hubs and the empowerment of rural women in Tamil Nadu, India

Images provided by the author

Ghana, biopesticides, neem

Entomology Today 2 weeks ago Leave a Comment

Detecting pest insects across large areas means placing vast numbers of traps, with associated costs to set them up and check them regularly. Grid patterns have been the traditional choice, but a new study shows trap-placement patterns using parallel lines could be just as effective with much lower servicing requirements. Such large-scale trapping is used in detection of pests such as the spongy moth (Lymantria dispar), and the study of trap patterns used trapping data from spongy moth detection efforts in North Carolina and Ohio in 2021 to evaluate various trapping simulations. (Photo by Susan Ellis, Bugwood.org)

By John P. Roche, Ph.D.

Sampling for the presence of insect pests has traditionally used traps laid out in grid patterns. While effective, they are labor intensive to set up and monitor and thus a costly way to sample. In a new study, however, researchers at the U.S. Department of Agriculture and North Carolina State University show that alternative trap-layout designs can match grid patterns in effectively detecting pest insects with lower servicing requirements.

Because of the expense that would be involved with testing trap-layout designs in the field, the researchers used simulations with a computer model called TrapGrid. Barney Caton, Ph.D., of the USDA Animal & Plant Health Inspection Service; Hui Fang, Ph.D., and Godshen Pallipparambil, Ph.D., of the Center for Integrated Pest Management at NC State; and Nicholas Manoukis, Ph.D., of the USDA Agricultural Research Service published their findings in April in the Journal of Economic Entomology.

TrapGrid can simulate the detection of insect pests by traps arranged in different patterns in a simulated landscape. In their simulations, the research team compared the performance of traditional grid patterns with alternative designs based on transects that they called “trap-sect” designs. Building on earlier work the researchers have conducted in trap-layout models, the team’s hypothesis was that trap-sect designs would detect pests as effectively as traditional grids but with much greater efficiency.

The alternative trap-layout designs tested were crossed lines, parallel lines, and spoked patterns. (See Figure 2.) In their simulations, Caton and colleagues measured the average probability of detection of a pest and the distance traveled to service the traps. Good sampling designs would have a high probability of detecting a pest and low servicing distances.

The researchers found that many of the alternative trap-layout designs provided pest detection that was similar to that provided by full grids. Of the alternative layouts, parallel-line designs showed the greatest probability of detection, followed by spoke designs, and then crossed-line designs. With parallel-line designs, the probability of detection increased incrementally with each additional line that was added, from two lines to seven lines, as would be expected.

Full grids had the longest servicing distance, followed by spokes and crossed lines (75 percent shorter), followed by parallel lines (66–89 percent shorter). Overall, in terms of detectability and efficiency combined, the best designs were four to seven parallel lines, followed by spoked lines.

A study of pest-insect trap-layout designs using the TrapGrid computer simulation, compared traditional grid patterns (A and B) with several alternate designs: four crossed lines (C), eight spokes with an untrapped hub (D), two parallel lines (E), four parallel lines (not pictured), five parallel lines (F), six parallel lines (G), and four parallel lines in a modified alignment (H). All designs used 250 traps, indicated by blue diamonds. Establishment positions of pests are indicated with red circles. (Image originally published in Caton et al 2023, Journal of Economic Entomology)

It makes sense that the alternative designs such as parallel lines and spoked lines were more efficient—with the shorter servicing distances of these designs, efficiency increases. But why was pest detectability in the parallel-line and spoked-line designs similar to the detectability in the full grid?

“This similarity is dependent on many things,” Manoukis says, “like the attractiveness of the traps.” With attractive traps, pests will be drawn to traps even if they are not in a full grid pattern. In addition, in the comparisons in these simulations, pest outbreaks occurred randomly in space, which might help them be detected by the alternative designs, making detectability more similar to that in the full grid.

To approximate how alternative sampling designs might work in the field, the investigators overlaid alternative designs onto actual trapping data for two pest moth species, the European grapevine moth (Lobesia botrana) in California in 2010 and the spongy moth (Lymantria dispar) in North Carolina and Ohio in 2021. In the overlay of a four-parallel-line trap design on European grapevine moth data from California, the service distance was reduced by 43 percent. In the overlay of a crossed-lines trap design on spongy moth data in North Carolina and Ohio, the service distance was reduced by 35 percent and 47 percent, respectively.

“Aligning traps in this way is a new idea,” Caton says, “but it makes sense to improve efficiency. Survey managers already have to place traps in the field; this method just has them being placed in different shapes. The basic process is unchanged.”

Barney Caton, Ph.D. (left), of the USDA Animal & Plant Health Inspection Service; Hui Fang, Ph.D. (second from left), and Godshen Pallipparambil, Ph.D. (right), of the Center for Integrated Pest Management at NC State; and Nicholas Manoukis, Ph.D. (second from right), of the USDA Agricultural Research Service tested the probability of detection and the servicing distance of several alternative trap-layout designs for pest-insect sampling and compared the results to a traditional square grid design. They found that parallel-line and spoked-line trap designs offered good detection with significantly improved servicing efficiency. (Photo courtesy of USDA)

The investigators conclude that alternative trapping designs would reduce sampling costs considerably. But there are hurdles to overcome to implement these new designs. “The ‘tried and true’ methods often have some inertia behind them,” Caton says. “So, a new approach is almost always difficult to implement. But cost-cutting is usually a significant motivator, so our hope is that managers will adopt the trap-sect approach on that basis.”

The parallel-line and spoked-line sampling patterns worked well in the simulations in the study. Pest managers could refine these strategies even more by using an adaptive approach where surveyors add traps as pests are detected. This would permit pest detection with even greater efficiency. In future research, Caton and colleagues plan to investigate dynamic strategies of sampling that adapt over time.

“The TrapGrid model really made this research possible,” Caton says. “In the field it would be very time-consuming and costly to evaluate different designs. While some field validation is likely still needed, the results were strong enough that, given the good track record of the model, we are confident that the new sampling designs should work well.”

This investigation was the first test of alternative trap placement patterns for area-wide delimitation trapping in 40 years. Additional studies, including looking at dynamic sampling strategies, should further refine this promising approach.

Read More

“Transect-based trapping for area-wide delimitation of insects”

Journal of Economic Entomology