Lack of Predictable Race Shift in Heterodera glycines-Infested Field Plots

Area of Science:

• Plant Pathology
• Agronomy
• Nematology

Background:

• Soybean cyst nematode (SCN), Heterodera glycines, is a major soybean pest.
• Understanding SCN race dynamics is crucial for effective resistance management.
• Previous studies have indicated potential shifts in SCN populations.

Purpose of the Study:

• To investigate Heterodera glycines race shifts in field populations.
• To evaluate the impact of soybean cultivar resistance and sampling time on SCN race designations.
• To determine the influence of temperature on SCN race identification.

Main Methods:

• Field experiments were conducted at three Missouri locations using paired plots rotated with corn.
• Soybean cultivars with different SCN resistance sources (Peking, PI 88788, PI 437654) were planted.
• Soil samples were collected seasonally, and SCN race tests were performed under varying temperature regimes.

Main Results:

• SCN race shifts were not predictable based on the resistance source of the planted soybean cultivar.
• Variability in female indices (FI) was observed due to fluctuations in female nematode numbers.
• Race designations were significantly influenced by sampling time and the temperature used during race testing.

Conclusions:

• The inherent variability of Heterodera glycines populations in both field and laboratory settings complicates accurate race identification.
• Current race test results may have diminished value for making reliable soybean cultivar recommendations due to population unpredictability.
• Further research is needed to develop more robust methods for assessing SCN virulence and guiding resistance deployment.