Progress in this research is measured by the number of SCN populations that can be scored for HG type. Twenty soil samples with positive SCN will be identified in the surrounding areas of the field site with the new virulent type. Each of the 20 field SCN populations will be tested for HG type and classified according to the most current HG type system. The new virulent type is anticipated to occur in the same field location as that tested in 2015. New virulent SCN populations will likely be discovered in nearby fields or surrounding areas.
This data will demonstrate if the selection pressure has been great enough to change virulent types over the past 12 years since SCN was first reported in ND. This information has practical applications since the forms of SCN resistance used to manage this pathogen will depend on which virulent types of SCN occur in our area. Growers will have a better understanding of how virulence of SCN is changing in infested fields where resistant soybean are being grown.

Update:

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MONITORING VIRULENCE CHANGING OF SOYBEAN CYST NEMATODE IN NORTH DAKOTA

EXECUTIVE SUMMARY

NORTH DAKOTA SOYBEAN COUNCIL
June, 2017

Principal Investigator: Dr. Guiping Yan, Dept. Plant Pathology, NDSU
Co-investigators: Dr. Sam Markell, Dept. Plant Pathology, NDSU

Today soybean cyst nematode (SCN) is the most destructive pest of soybean in the world. This nematode has already spread to most soybean producing counties of North Dakota. Cultivar resistance is the primary management tactic used against this pathogen and PI 88788 is the major source of resistance which is widely used in ND. Thus it is important to monitor the virulence changing of SCN populations across the state, so that we are better equipped to recommend cultivars that are still resistant to SCN to farmers, thus preventing yield losses due to SCN.

Prior to 2015, there was no report of SCN field populations reproducing well on any of the major sources of resistance in ND. However, during the last funding cycle we reported one SCN field population from Cass County reproducing well on PI 88788, indicating a new virulent type of SCN may exist in ND. Thus the main objective of this study was to sample that location and nearby fields to confirm the new virulent type and determine its distribution in the surrounding areas.
The change in virulence of SCN can be characterized by using HG type testing Bioassay. HG refers to Heterodera glycines and the type indicates which sources of resistance, the particular SCN population is able to overcome. For example, HG type 1.2.3 refers to a strain of the nematode that is capable of reproducing on the sources of resistance: PI 54840, PI 88788 and PI90763. And so, that strain is not controlled by the resistance genes in those three sources of resistance.
A total of forty-one greenhouse HG type bioassays were performed to achieve the main goal of this study. Inoculated plants were grown in four replicates in a growth chamber for approximately 30 days at 27° C. Thirty-one of these SCN populations were assayed for HG types by growing the plants in naturally infested soil. In order to conduct the HG type bioassays on field samples with low numbers of eggs, inoculum was first increased. Then, HG type bioassays were performed on these populations by inoculating autoclaved river sand soil with 2,000 eggs for each plant. To confirm new HG type results, seven experiments were repeated.

Among the successful experiments, the most common HG types were HG 7 (frequency rate: 34%) and HG 2.5.7 (22%). Other HG types included HG 0 (19%), HG 5.7 (16%), HG 2.7 (6%) and HG 5 (3%). Through repetition of the experiments we confirmed the presence of HG 2.5.7 and HG 2.7. Thus we were able to validate that there are populations of soybean cyst nematode in North Dakota fields that reproduce well on the major source of resistance (PI88788) that has been widely used in ND. Knowledge of virulence types should influence the choice of populations and HG types used in resistance assays of new soybean cultivars and breeding lines.

This research is important to navigate the use of resistance sources for growers and the new resistance sources that should be introduced to North Dakota.