Project Details:

Quantification of viral suppression in SCN populations: Nematode virus impact on SCN reproduction and egg viability

Parent Project: This is the first year of this project.
Checkoff Organization:North Central Soybean Research Program
Organization Project Code:
Project Year:2015
Lead Principal Investigator:Gregory Tylka (Iowa State University)
Co-Principal Investigators:
Kaustubh Bhalerao ((not specified))
Sadia Bekal (University of Illinois-Carbondale)
Keywords: Biological Control, Soybean Cyst Nematode

Contributing Organizations

Funding Institutions

Information and Results

Click a section heading to display its contents.

Project Summary

Heterodera glycines, better known as the soybean cyst nematode (SCN), is the most damaging pathogen of soybean in the North Central Region of the USA. This nematode is particularly problematic because viable eggs can persist in the soil for years, making this disease difficult to manage. A control strategy that would limit SCN egg hatch would be the most effective way to disrupt a critical point in the nematodes' life cycle. Commonly used nematicides do not kill nematode eggs, but newly discovered SCN viruses reproduce in nematode eggs and lower their viability. The goal of this project is to quantify the extent of damage SCN viruses inflict on the nematode in laboratory and field SCN populations, with the goal that these viruses may be deployed as self-replicating SCN-specific biological pesticides.

Project Objectives

1. Test fields in Iowa to quantify the damage to SCN caused by viruses.
2. Collect quantitative laboratory data on which viruses cause the most damage to SCN.

Project Deliverables

Our main goal is to quantify the damage that viruses cause on SCN. We will quantify the damage to SCN in both the field and in laboratory experiments. For the field phase of the project, the first goal will be to identify and locate virus-infected SCN populations. The next step will be to assess the extent of damage to SCN reproduction caused by the viruses. In the laboratory studies, we will utilize inbred SCN populations with differing levels of the viruses or no virus at all. These studies will be ongoing throughout the first year and should establish the level of damage to egg hatch rates and nematode mobility.

Progress of Work

From March through September 2014, we have initiated the project and begun to collect data. More specifically, we have:
• Established, maintained, and harvested nine field experiments located throughout Iowa;
• Collected soil samples at the time of planting and again at harvest from plots in all nine experiments that were planted with susceptible soybean varieties and with resistant varieties with PI 88788 and Peking resistance;
• Extracted SCN cysts and eggs from soil samples collected at the time of planting and attempted to use two methods of SCN virus detection: detection of viruses from stained SCN eggs and detection of viruses from isolated SCN cysts; and
• Determined that stained eggs, while useful for counting, proved difficult as material from which to obtain pure RNA for virus detection; at the moment, virus testing works best on isolated cysts that are free of soil and root debris.

Soil samples were collected from replicated plots in 9 experiments conducted in SCN-infested fields throughout Iowa in the spring and fall of 2014. The plots had either susceptible or SCN-resistant soybean varieties grown in them. Some resistant varieties had the PI 88788 source of resistance and some had the Peking source of resistance.

SCN cysts were extracted from the soil samples and tested for the presence of SCN viruses. All five known SCN viruses were detected in SCN cysts: SCN Tenuivirus (ScTV), SCN Nyavirus (ScNV), SCN Rhabdovirus (ScRV), SCN Phlebovirus (ScPV), and SCN virus 5 (SbCNV-5).

Not all SCN cysts contained eggs infected with all the viruses, and virus frequency varied greatly from field experiment location to location. The highest incidence of virus detection in the SCN populations was in three experiments located across northern Iowa and the experiment in east central Iowa.

The viruses were detected more frequently in eggs from SCN cysts extracted from fall samples than from eggs from cysts extracted from soil samples collected at the time of spring planting, indicating that the viruses may be replicating and increasing in levels in the SCN populations throughout the growing season.

High virus levels were observed in SCN populations that decreased in numbers throughout the growing season on a susceptible soybean variety, supporting our hypothesis that damage to SCN populations would increase as virus level increased.

The effects of virus infection on hatching of SCN eggs were variable; more than half of the virus-containing populations of SCN eggs hatched poorly.

Results of laboratory experiments conducted with virus-infected nematodes revealed that the SbCNV-5 virus significantly increased movement of SCN second-stage juveniles. This was an unexpected result.

Potential impact: If SCN egg hatching and population densities are suppressed consistently by viruses in the field, these viruses may represent a new SCN management strategy.

Brief Statement of Plans & Next Steps
The data obtained to date indicate that viruses are common in field populations of SCN and that high virus levels may cause population densities of SCN to decrease dramatically. Future work will determine virus levels that cause SCN population decline and focus on field and greenhouse data collection to determine which viruses are most suppressive to SCN.

Final Project Results

Benefit to Soybean Farmers

Performance Metrics

Project Years