Objective 1. Characterization of virulence phenotypes of SCN inbred populations.
A total of 232 inbred lines of the soybean cyst nematodes were selected from the about 100 SCN field populations that were ‘randomly’ collected across Minnesota soybean growing counties in 2013. To develop an inbred line, a single cyst was transferred to a soybean plant. After 45 days, when the first generation of females (cysts) developed, a single cyst was transferred to a new soybean plant. Each of the cysts and females were developed from fertilization of the siblings within the same parent cyst. After a number of transfers (8 to 24 transfers), the SCN lines are relatively homogenous in genetics. The 232 inbred lines can represent diversity of SCN in Minnesota. The virulence of the SCN inbred lines will be tested on the SCN-resistant soybean lines that are used or potentially used for breeding SCN-resistance in the University of Minnesota breeding program, including PI 88788, Peking, PI 437654, PI 567516C, PI 438489B, and a line that has novel SCN resistance QTL as discovered in a previous project. The test will be similar to the HG Type test, but the soybean lines included will be different.

Briefly, soybean will be planted in 100-ml cone-tainers in the greenhouse and inoculated with 3000 SCN eggs. Each line will be planted to six plants in six separate cone-tainers. After 35 days, the cysts will be collected from each cone-tainer, and counted. Female Index (FI) will be calculated for each plant: FI = the female number on the test line × 100 / the female number on the standard SCN-susceptible soybean line Williams 82. The FI is used for evaluation of the virulence of SCN to a soybean the line.

Objective 2. Study of variations of SCN morphology and detection of white soybean cyst nematode.
To detect white soybean cyst nematode (H. sojae), morphological characterization and DNA sequencing will be carried out. For morphological studies, SCN female, male, and juvenile specimen will be prepared. Key morphological traits will be measured and described. The morphological traits will be used to detect WSCN or confirm these inbred lines are SCN. In addition, the morphological traits can also be used to study the morphological diversity of SCN. For detecting WSCN, the morphological traits may not sufficient to accurately identify WSCN. DNA sequencing is necessary to accurately distinguish WSCN and SCN. Genomic DNA will be isolated from each inbred line.

Specific DNA primers (e.g., D2A, D3B, and TW81) will be used to amplify DNA with PCR. The amplified DNA will be sequenced in the University of Minnesota Genomic Center. The DNA sequence data will be used to compare the published DNA sequence data of SCN, WSCN and other cyst nematodes, and determine any of the inbred lines is WSCN and confirm they are SCN.

Objective 3. Determine the effect of sequences of SCN-resistance sources on SCN population densities and virulence phenotypes.
In previous studies, we have demonstrated that the use of the SCN-resistant cultivars resulted in SCN populations that are able to break the resistance of existing cultivars in Minnesota. The SCN resistance in most current commercial cultivars is from PI 88788, only a few from Peking. The selection pressure of SCN-resistance on SCN populations may differ in different sources of resistance. We have initiated long-term field experiments to determine how the cultivars from the three sources of resistance PI 88788, Peking, and PI 437654 affect the reproductive ability of SCN over time. Based on the data of HG Type analysis of the populations collected in 2007, 2008, 2009, 2010, 2012, and 2014 from a field experiment in Waseca, SCN population selected by the cultivar with PI 88788 source of resistance can only overcome the resistance of PI 88788 not the other two, and Peking-derived cultivar selected SCN populations can only overcome the resistance in Peking. In contrast, PI437654-derived cultivar selected SCN populations that could overcome both Peking and PI 88788 sources of resistance.

In this proposal, funding is requested for the field experiment initiated in 2008 in Lamberton to study how the rotations of different resistance sources affect the dynamics of SCN population densities and their virulence phenotype. The initial population was race 1 (HG Type 2.5.7), which is virulent to cultivars carrying the PI 88788 resistance. The main aim of the experiment is to determine whether any cultivar sequence can change the population from virulent to avirulent or change to other HG Types so that the PI 88788-source and/or Peking-source cultivars can be used. We will determine if there is any fitness cost for SCN virulence and if rotation with SCN-susceptible cultivars can select avirulent phenotypes and be helpful in managing problematic HG Types. The treatments include different combinations of the four cultivars Pioneer 92B13 (susceptible), Latham EX547 RR N (PI 88788 resistance), Pioneer 91M90 (Peking resistance), and Latham AR5084 (PI 437654 resistance). This is a long-term study (Table 1) and the data from the site will serve as a model to predict trend of race shift.

Nematode population densities were/will be determined at planting and harvest. The HG Types of populations collected from different crop sequences from the site in the spring of 2008, 2011, 2013, and 2017 have been determined on the source of resistance PI 887888, Peking, and PI 437654 with Lee74 or William 82 as susceptible soybean control, and the experiment has been set up to determine the HG Types of SCN populations in the samples collected in September of 2020. In this proposal, funding is requested for the maintaining the plots and determining SCN population densities at planting and harvest in 2021.

V. Deliverables and Utility of the Information
• This project will develop knowledge of diversity SCN virulence (HG Types) in Minnesota, and the knowledge will be used to strategically deploy effective type of resistance in soybean cultivars.
• This project will determine if white soybean cyst nematode, another important cyst nematode on soybean, occurs in Minnesota.
• The study will result in a better understanding of basic biology of the soybean cyst nematode.
• The information developed from this project will be used in extension education such as Agronomy Field Tour, Open House at the University of Minnesota Southern Research and Outreach Center, and MN Ag Expo.
• The research will be published in scientific journal for a broader dissemination

Update:

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The soybean cyst nematode (SCN, Heterodera glycines) is the most destructive pathogen of soybean and widely spread in Minnesota and most soybean-growing regions throughout the world. Recently, a new cyst nematode species, Heterodera sojae, also known as ‘white soybean cyst nematode’ (WSCN) as a common name, was found in Korea and China. Soybean cyst nematode has big variations in morphology and virulence phenotypes (ability of reproduction on different soybean germplasm lines). In this project, we are studying diversity of the SCN and detecting WSCN in Minnesota. Specifically, we plan to phenotype 178 inbred lines of cyst nematodes for their virulence phenotypes on the SCN-resistant source germplasm lines Pickett, Peking, PI 88788, PI 90763, PI 834489B, and PI 567516C. We study variations in SCN morphology and determine if WSCN occurs in Minnesota or not. So far, 86 SCN lines have been phenotyped for their virulence on the eight soybean lines and additional 92 SCN lines on PI 88788 and Peking. Genomic DNA of the 177 lines has been extracted, and the genomes sequenced.
In an on-going field experiment, the impact of rotation of soybean cultivars with different sources of resistance on SCN virulence is studied. The experiment was established in 2008. SCN population densities were determined at planting and harvest every year. Virulence phenotypes of SCN were determined in 2008, 2011, 2013, 2017, 2020, and 2022.