Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 10, 1998
Publication Date: N/A
Interpretive Summary: The soybean cyst nematode is an important economic pest of soybean in the United States, causing approximately $350 million in yield reductions each year. The primary method of suppressing the nematode is planting resistant varieties. However, the nematode is genetically variable and, thus, has the ability to overcome the resistance of soybean after a variety is planted for several years. The objective of this study was to determine if rotating varieties with different sources of resistance or rotating a resistant variety with a nonhost crop and a susceptible variety was effective in limiting the nematode's ability to overcome resistance in soybean. Rotating soybean varieties with different sources of resistance over a 12-year period was not effective in maintaining efficacy of resistance, apparently because selection pressure for the nematode to overcome resistance in one variety was much stronger than the opposing selection pressure exerted by other varieties. Rotating a resistant variety with a nonhost crop and susceptible soybean doubled the time required for the nematode to overcome resistance. This information is important because a hypothesized control (rotation of varieties with different sources of resistance) measure was identified as ineffective. Value of rotations of resistant variety with nonhost crop and susceptible soybean in slowing the loss of resistance in soybean was also demonstrated. Greater soybean yield was obtained with such rotations, making the rotation important when the nonhost crop is an economically viable crop. Research to identify new sources of resistance to the nematode and to incorporate that resistance into productive varieties is needed to maintain effective control of this pest.
Technical Abstract: Twelve soybean (Glycine max) cropping sequences were compared for 12 years in a field originally infested with race 14 of the soybean cyst nematode (SCN), Heterodera glycines. Continuous soybean cropping sequences included susceptible Forrest, J82-21, and a Peking X Centennial breeding line; and moderately resistant Bedford and J81-116. Forrest treated with aldicarb or PCNB plus metalaxyl and breeding line JS83-236 followed by Cordell and Hartwig were additional continuous soybean sequences. Rotations included two sequences each of Bedford with J81-116 or J82-21, and Bedford with corn (Zea mays) and susceptible Essex soybean. Rotations of Bedford, corn, and Essex had 12-year mean yields significantly greater than continuous Bedford or Forrest. The female index (F1) was measured in the greenhouse on four bioassay plants grown in soil from field plots. The F1 of Bedford bioassay plant increased significantly over time for all field treatments involving Bedford. When J82-21 was the bioassay, F1 decreased significantly in treatments involving Bedford. There were no significant changes in F1 for any treatment when Forrest, J81-16, and Peking were used as bioassays. Use of rotations of soybean cultivars with different sources of resistance and rotations of resistant and susceptible cultivars with a nonhost crop were not successful practices to manage the nematode's ability to parasitize the resistant cultivar Bedford. However, rotation of resistant and susceptible cultivars with a nonhost crop produced greater mean yield and slowed the shift toward greater parasitism of the resistant cultivar sufficiently to warrant adoption of this practice.