EFFECT OF CROP-ROTATION ON SOIL POPULATION-DENSITIES OF FUSARIUM-SOLANI AND HETERODERA-GLYCINES AND ON THE DEVELOPMENT OF SUDDEN-DEATH SYNDROME OF SOYBEAN

The effect of crop rotation on the development of sudden death syndrom e (SDS) of soybean and on the soil population densities of Fusarium so lani and the soybean cyst nematode (Heterodera glycines) was observed for four years in a field naturally infested with both pathogens. In 1 989 all plots were planted to a soybean cultivar susceptible to both p athogens (cv. Lee 74). In 1990 and 1991, the plots were planted to one of the following crops: soybean cv. Lee 74, soybean cv. Hartz 6130 (r esistant to both pathogens), sorghum, fescue, or wheat (not double-cro pped). In 1992 all plots were planted to soybean cv. Lee 74. The param eters measured to determine rotation effects were severity of SDS over the season, the soil population densities of both pathogens, soybean yields and soybean seed weights. Rotation to any crop except soybean s ignificantly reduced the H. glycines population densities in 1990 and 1991. In 1991, the H. glycines population densities began to rise in t he nematode-resistant soybean treatment, but were lower than those in the susceptible soybean treatment. Averaged over all years, the F. sol ani population densities were significantly lower when sorghum or whea t were grown than when soybean or fescue were grown. Considering the w hole season, the F. solani population densities were generally the hig hest at harvest. Negative correlations between SDS and yield were sign ificant, as were positive correlations between SDS and population dens ities of F. solani. In 1992, SDS was very low in all treatments, but y ields were highest in plots planted to non-soybean crops and lowest in plots planted to the susceptible soybean. (C) 1997 Elsevier Science L td.