SOIL-MOISTURE CONTROL AND DIRECT SEEDING FOR BIOASSAY OF HETERODERA-GLYCINES ON SOYBEAN

Soil moisture control during evaluations of Heterodera glycines-Glycin e max interactions has not been reported routinely as a standardized p rocedure. A novel soil moisture replacement system was examined in con trolled environmental chambers for use in bioassays for female develop ment. The system is compact, lightweight, and has a contained reservoi r for moisture supply to multiple test units. Varied soil moisture tre atment levels were sustained at or near replacement rates over extende d periods of testing. Direct seeding of selected soybean cultivars con sistently resulted in 100% seed germination. Subsequent shoot and root growth was successfully restricted to accommodate the size of the sys tem with minimal shoot pruning. Numbers of mature H. glycines females extracted from the roots of susceptible soybean cultivars were consist ently high. Inoculum levels of either 500 or 1,000 eggs/plant routinel y resulted in numbers of females at more than 30% of the initial inocu lum. No evidence of nematode contamination of uninfested plants was fo und at any level of observation. Results demonstrate a potential for t he standardization of two additional variables in determining races an d for screening cultivars or lines for resistance to H. glycines.