Soybean Varieties with non-88788 SCN Resistance Adapted to Minnesota

Aaron Lorenz¹, Senyu Chen², Seth Naeve^1,3 and Bruce Potter<sup>3

1</sup>Department of Agronomy and Plant Genetics, ²Department of Plant Pathology, ³University of Minnesota Extension

The most common source of SCN resistance in commercial soybean varieties adapted to Minnesota is PI 88788. Over 90% of the varieties entered into the 2022 UMN Variety trials carried this single source of SCN resistance. The PI 88788 resistance source provides good resistance to some races of SCN. Over time, however, the overuse of this resistance source has led to shifts in SCN populations to those able to overcome PI88788 resistance. There has been increased interest in alternative sources of SCN resistance such as Peking and PI 89772. The commercial availability of these varieties adapted to Minnesota has gradually increased in recent years. However, little independent information is available on their actual resistance to SCN races known to overcome the PI 88788 source.

Study methods

Starting in the spring of 2021, we have annually solicited seed of commercial varieties advertised to carry a non-88788 source of resistance and tested submissions for resistance to Race 1 (HG Type 2.5.7) using a greenhouse bioassay with five replicates. Each container (one plant) was inoculated with 4000 SCN eggs. After 30 days a Female Index (FI) was calculated for each entry using Williams 82 as the susceptible check. The FI was calculated with the following formula: 

FI = (# of cysts on entry/# of cysts on Williams 82) x100

If the FI was <10%, an entry was considered resistant (R). If the FI was 10 – 30%, it was considered moderately resistant (MR). If the FI was 30-60%, it was considered moderately susceptible (MS), and greater than 60% susceptible (S).

Results

The following table includes only those varieties that exhibited resistance or moderate resistance to Race 1 in our test. A specific variety may not be listed because either the seed provider did not consent to testing, or it did not exhibit resistance. Resistance to SCN is a product of large-effect single genes donated by certain resistance sources, in addition to many small-effects genes that may or may not be present in the variety, making resistance a complex genetic phenomenon. A variety with a resistance source in its ancestry does not necessarily make it completely resistant, and thus results from bioassays such as this one are helpful to ensure resistance is present. These results will assist producers in selecting varieties with independently verified resistance. If you are a seed provider and want your varieties to appear in this table, please inquire with Aaron Lorenz (lore0149@umn.edu).

Table 1. Soybean varieties in trial that exhibited resistance or moderate resistance to SCN Race 1.

* Control varieties Peking and PI 88788 are two sources of SCN resistance, which were included in SCN race determination. The Female Indexes on these two varieties indicate that the SCN population can overcome the resistance in the varieties derived from PI 88788 but not the varieties with good level of Peking resistance. Seed is not available for these non-commercial varieties.