VI. Research plan and approaches
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 transfer), 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
4
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
5
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