Cropping Sequence Effects on Soybean and Heterodera glycines. Lawrence D. Young, Agricultural Research Service, U.S. Department of Agriculture, 605 Airways Boulevard, Jackson, TN 38301. E. E. Hartwig, USDA-ARS, P.O. Box 196, Stoneville, MS 38776. Plant Dis. 76:78-81. Accepted for publication 24 July 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/PD-76-0078.

Nine soybean (Glycine max) cropping sequences were compared for 11 yr in a field infested with the soybean cyst nematode (SCN), Heterodera glycines. Continuous cropping sequences included six soybean lines resistant to race 3 (Bedford, Forrest, Nathan, Peking, D72-8927, and D75-10710) with varying levels of resistance to race 4 and a 70:30 Bedford/Forrest (susceptible to this SCN population) blend. Two rotations, Bedford with corn (Zea mays) and Bedford with susceptible Forrest and Essex, were the other treatments. The most notable effect of continuous cropping of resistant soybean was the increased reproduction of the SCN population on resistant Bedford relative to reproduction on susceptible Essex. The increase in the ability to reproduce on Bedford was less in the continuously planted blend treatment and rotation of Bedford with Forrest and Essex than with continuously planted Bedford. Yield of continuously cropped resistant Bedford was significantly less than that of Bedford in rotation with corn in only one of two treatments with this rotation when compared over the 11-yr period. Yield of Bedford in rotation with Forrest and Essex was not greater than that of continuously cropped Bedford. In most years, continuously cropped Bedford had higher yield than continuously cropped Forrest. Cyst population density did not increase over time in plots of continuously grown Bedford, which may explain the lack of yield suppression.