Effects of Spore Density and Interaction With Heterodera glycines on Soybean Root Rot Caused by Fusarium solani and F. tricinctum

Abstract

Fusarium root rot, caused by Fusarium solani and F. tricinctum, is a major soybean disease in the North Central United States. This study investigated the effects of the macroconidia density and the additive effects of soybean cyst nematode (SCN), Heterodera glycines, on the severity of Fusarium root rot. To determine the effect of spore density on severity, experiments were conducted in La Prairie silt loam soil in a greenhouse using conidial suspensions ranging from 101 to 106 macroconidia/ml soil. Root discoloration and lesion lengths on taproots increased as spore numbers increased, with significant effects of spore densities starting at 104 and 105 macroconidia/ml soil for F. solani and F. tricinctum, respectively. A nonlinear sigmoid model was fitted to root discoloration against density, whereas a linear regression model was fitted to root lesion length against density. The interaction between the nematode at different egg densities with the two Fusarium spp. at 105 macroconidia/ml soil was investigated. In the greenhouse, root discoloration and lesion length were significantly greater in plants inoculated with Fusarium spp. and H. glycines at 10 eggs/ml soil or greater, compared with Fusarium spp. alone. In field trials, coinfestation of soil with the two Fusarium spp. and H. glycines significantly increased root rot severity at an egg density of 16.7 eggs/ml soil. The results indicated that the presence of SCN can increase severity of root rot caused by F. solani and F. tricinctum and egg density in the soil is an important factor in the interaction.