Effects of Soil Type, Temperature, and Moisture on Development of Fusarium Root Rot of Soybean by (FSSC 11) and .

FSSC 11 and are important root rot pathogens of soybean in North Dakota. The roles of soil type, temperature, and moisture in disease development by both species are poorly documented. To assess the effect of soil type on disease, three types of soil (Glyndon sandy loam, La Prairie silt loam, and Fargo clay) that represent soils of the soybean production region in the Red River Valley were examined in greenhouse, microplot, and growth chamber studies. Disease incidence and lesion length on roots were evaluated at growth stages V3 and R6. Soil type significantly affected disease development, with higher severity in the lighter soils of Glyndon sandy loam and La Prairie silt loam compared with Fargo clay. Soil type also interacted with species, in which the maximum severity was observed in Glyndon sandy loam for , and in La Prairie silt loam for . In addition, the cumulative effects of soil type, temperature, and soil moisture were tested in a growth chamber. Emergence and disease on seedlings were evaluated at growth stage V3. Significant reductions in emergence occurred at 10°C in treatments with and , but there was no significant difference among the three soils. Infection was visible at temperatures of 10 to 20°C for and 15 to 20°C for caused the greatest infection at 20°C in Glyndon sandy loam, while it was at 15°C in La Prairie silt loam for . The isolates of the two species caused root rot in soil moisture ranging from 20 to 100% water holding capacity (WHC). The greatest reduction in emergence caused by the spp. was observed at 80% WHC in silt loam and clay soils and 40% WHC in sandy loam soil, when compared with the same WHC in noninfested soils. Ranges of soil moisture causing infection were negatively correlated with temperature. At the lower temperature there was a broader range of soil moistures resulting in infection compared with higher temperatures. At 18°C, most infection occurred at soil moistures of 20 to 80% WHC, while it was 40 to 80% WHC at 28°C. Disease caused by was favored by a temperature of 18°C with high soil moisture (60 to 80% WHC) or 28°C with low soil moisture (20 to 40% WHC), while was favored by cooler temperature and lower soil moisture.