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TECHNICAL SESSION: Population diversity of plant pathogenic nematodes

Population density and virulence phenotypes of Heterodera glycines associated with soybean fields in Tennessee
Rufus Akinrinlola - University of Tennessee Knoxville. Heather Kelly- University of Tennessee

Soybean cyst nematode (SCN), Heterodera glycines is responsible for up to $1.5 billion loss each year in the United States, and SCN is a major soybean pest in Tennessee. The use of resistant cultivars is helpful in reducing losses caused by the nematode, however continuous use of resistant cultivars can initiate a selection pressure that can cause SCN population to reproduce on resistant soybean cultivars. This study was conducted with two objectives: (1) to determine SCN population density in soybean fields in Tennessee, and (2) to determine SCN ability to overcome resistance in the resistant soybean cultivars using the HG – Heterodera glycines – Type test. To do this, 116 soil samples were collected from soybean fields across 20 counties, and subsamples were processed for the presence and density of SCN. The density was determined by counting the number of eggs present in 100 cc of soil. Forty-seven percent of the samples were infested with SCN, 17, and 10 % had densities greater than 500 and 1000 eggs per 100 cc, respectively. The average and maximum SCN densities observed were 1,048 and 4,569 eggs per 100 cc soil, respectively. These results indicate that SCN occurs in high density in many of the fields tested. HG-type test is being conducted to determine the virulence phenotypes of the populations and will be presented. Growers are advised to take appropriate actions to avoid damage by this pathogen in fields where high densities were observed.