Ohio

Determination of Yield Loss Caused by Soybean Cyst nematode (Heterodera glycines), SCN, on SCN-resistant and SCN-susceptible Soybeans Using the Adjacent Strip Comparison Method

Principal Investigator:

R. Mac Riedel, Plant Pathology Dept.

Cooperators:

Ohio State University Extension

J. Bruce Eisley, Research Associate, Entomology Dept.
Jim R. Jasinski, Ext. Agent, Southwest District Office
Greg Meyer, Ext. Agent, Warren County
Curtis E. Young, Ext. Agent, Northwest District Office

Thanks to Tom Doerge, Troy Putnam, Sandy Thomas and Dennis Wickham from Pioneer Hi-Bred International, Inc. for their support of this project.

Problem and Objectives:

Problem:

Data from small plot research at Ohio State and elsewhere in the North-centeral United States indicate that soybean cyst nematode (SCN) is a major pest of soybeans causing overall losses of 8 to 10 percent of bean yield. This type of research in heavily infested problem soils indicates that losses can be 30 to 50 percent of yield. These data presented in tabular form or verbally at schools have had minimal impact on grower appreciation of the importance of SCN as well as little impact on grower implementation of prime control methods such as crop rotation and use of SCN-resistant varieties. Large field trials managed by growers on grower land would provide the type of data likely to be trusted by soybean growers in Ohio. Strip plots alternating SCN-susceptible and SCN-resistant varieties would provide comparisons needed to convince growers of the value of genetic resistance in the control of SCN.

Objectives:

1. Establish alternate strip trials of SCN-susceptible and SCN-resistant soybeans in light soil.
2. Correlate SCN populations and soybean yield.
3. Produce yield loss maps.

Methods and Materials

A site in Wood County had been sampled for 4 years previous to initiation of these tests. The SCN population was well documented in this field on the basis of twice yearly sampling of 7 360 X 360 ft grids (approximately 3 acre plots). Populations spread in this field was ideal for this work, being generally high on the south and west edge of the field and lower in the northwest quadrant. Each of these grids were split into 4, 180 X 180 ft grid for this research. Soil in the area was mixture of Spinks and Ottakee sandy loam soil.

A grid system (180 X 180) was established in the spring of 1999 using Global Position System (GPS) technology. The corners of the grid were located using a backpack Satlock® differentially corrected global positioning statellite receiver.

The grids were sampled for soybean cyst nematode populations before planting in 1999, mid- season and after harvest. Soil cores were taken with a 1 X 8 in probe to six inches depth on 30 ft centers in each grid. Soil samples were not take within 15ft of the grid borders. Approximately 20 cores were collected per grid, the combined cores thoroughly mixed by hand and 500 cc aliquot of this mixed sample was used for laboratory analysis.

In the laboratory 200 cc of the 500 cc mixed field sample were washed through a 20 mesh sieve to remove large stones and plant trash, and then through a 60 mesh sieve to remove nematode cysts. Cysts collected on the 60 mesh sieve were crushed in a Ten-Broeck tissue homogenizer to liberate eggs from the cysts. Eggs in this solution were collected on a 500 mesh sieve, stained with hot 5% acid fuchsin dye and counted at 40X. This is a standard method used by university labs throughout the Midwest.

PI 88788 SCN-resistant and SCN-susceptible soybean varieties were planted in alternating strips in widths (20 feet) that corresponded to the harvester width.

The Satlock® receiver was mounted on the farmers combine and attached to an Ag Leader® PF3000 yield monitor on the combine. The yields from the field were stored on a flash card in the yield monitor and then transferred to a desktop computer so that yield maps could be created for resistant soybeans (see Figure) and susceptible soybeans (see Figure).

Results & Discussion

Nematode populations characteristically vary widely even in uniform soil types. The preplant counts varied between 0 (none detectable) and 9,000 eggs/200 cc soil in the grids (see figure). At harvest populations were 0 to 21,000 eggs/200cc soil (see figure). The fit between SCN populations and soybean yield was excellent. The alternating strips of resistant and susceptible beans were clearly seen on the overall yield map for the field (see figure). Generally, the work indicated that susceptible beans out yielded resistant beans by as much as 5 to 10 bu/A when soil populations were below 200 eggs/200 cc of soil. When populations were between approximately 2000 to 6-8,000 eggs/200 cc of soil, the resistant varieties had a 5 to 10 bu/A advantage over susceptible varieties. Above 10,000 the resistant varieties had a greater than 10 bu/a advantage (see Figure).

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