VIEW ARTICLE

Ecology and Epidemiology

Development of Sudden Death Syndrome of Soybean in Relation to Soil Temperature and Soil Water Matric Potential. H. Scherm, Department of Plant Pathology, Iowa State University, Ames 50011; X. B. Yang, Department of Plant Pathology, Iowa State University, Ames 50011. Phytopathology 86:642-649. Accepted for publication 26 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-642.

Sudden death syndrome, caused by strains of Fusarium solani, has been recognized as an important disease of soybean (Glycine max) in the southern United States for more than 20 years, but has only recently become more prevalent and severe in northern soybean production areas. Little is known about environmental factors that influence root infection and above-ground symptom expression in this pathosystem. We established quantitative relationships between soil temperature, the matric component of soil water potential (ψ_m), and disease development in controlled conditions. Soil temperature in the range of 15 to 30ēC was manipulated in pots equipped with heating tapes, and soil moisture was manipulated by withholding irrigation water until ψ_m reached threshold values of –0.003, –0.02, –0.05, –0.1, –0.2, –0.4, or –0.8 MPa; when ψ_m for a given moisture treatment had reached its threshold, the pots belonging to this treatment were watered until the soil was saturated. The most important results were that i) soil temperature differentially influenced the development of root symptoms and foliar symptoms, with the former being most severe at low temperatures (15ēC) and the latter being most severe at intermediate temperatures (22 to 24ēC); ii) the severity of foliar symptoms decreased rapidly with decreasing soil moisture and was negatively correlated with the number of days the average ψ_m was lower than –0.01 MPa; and iii) there was no close correlation between root disease severity and foliar disease severity. The relationships between ψ_m and disease derived in controlled conditions were confirmed in a field irrigation trial. The information provided here, when used together with long-term temperature data and regional soil moisture maps, should be valuable in assessing the risk that sudden death syndrome will continue to expand into previously unaffected production areas.