Tuesday, August 7, 2007 - 2:30 PM

OOS 16-4: Soil suppressiveness against soil-borne disease complexes including plant-parasitic nematodes

Andreas Westphal, Lijuan Xing, Alison Seyb, and Tony Vyn. Purdue University

A number of soils that suppress diseases caused by prokaryotes, oomycetes, basidiomycetes, hyphomycetes and plant-parasitic nematodes has been described. In these suppressive soils, pathogens are present together with their susceptible host but cause less disease and damage than in conducive soils. Typically, soils have been studied for suppressiveness against single pathogen species or species of the same kingdom. Sudden death syndrome (SDS) of soybean is a soil-borne disease complex of Fusarium solani f. sp. glycines and Heterodera glycines and causes large yield losses in many soybean production areas. A series of infestation trials was conducted with F. solani f. sp. glycines and natural or artificial infestations with H. glycines in soybean monoculture under no-tillage conditions. More severe foliar SDS symptoms were detected in originally fumigated plots than in non-treated plots, beginning to some extent in the second year after infestation and in the majority of the trials in the third year. During this monitoring period, cyst population densities of H. glycines at harvest were higher in the preseason-fumigated plots than in the non-treated plots in most trials. In these trials, non-treated soil had become suppressive to H. glycines in most trials and against both pathogens in at least three of the five trials. These data suggest that natural disease-suppressiveness exists not only to single organisms but also to disease complexes.