Soil Moisture Control and Direct Seeding for Bioassay of Heterodera glycines on Soybean.

Soil moisture control during evaluations of Heterodera glycines-Glycine max interactions has not been reported routinely as a standardized procedure. A novel soil moisture replacement system was examined in controlled environmental chambers for use in bioassays for female development. The system is compact, lightweight, and has a contained reservoir for moisture supply to multiple test units. Varied soil moisture treatment levels were sustained at or near replacement rates over extended periods of testing. Direct seeding of selected soybean cultivars consistently resulted in 100% seed germination. Subsequent shoot and root growth was successfully restricted to accommodate the size of the system with minimal shoot pruning. Numbers of mature H. glycines females extracted from the roots of susceptible soybean cultivars were consistently high. Inoculum levels of either 500 or 1,000 eggs/plant routinely resulted in numbers of females at more than 30% of the initial inoculum. No evidence of nematode contamination of uninfested plants was found at any level of observation. Results demonstrate a potential for the standardization of two additional variables in determining races and for screening cultivars or lines for resistance to H. glycines.