LAUSR

Fusarium solani FSSC 11 and F. tricinctum 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) which represent soils of the soybean production region in the Red River Valley were examined in greenhouse and field 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 to Fargo clay. Soil type also interacted with Fusarium species, in which the maximum severity was observed in Glyndon sandy loam for F. solani, and in La Prairie silt loam for F. tricinctum. The cumulative effects of soil type, temperature and soil moisture were tested in a growth chamber. Emergence and disease on seedling were evaluated at growth stage V3. Significant reductions in emergence occurred at 10°C in treatments with F. solani and F. tricinctum, but there was no significant difference among the three soils. Infection was visible at temperatures of 10-20°C for F. solani and15-20°C for F. tricinctum. Fusarium solani caused the greatest infection at 20°C in Glyndon sandy loam, while it was at 15°C in La Prairie silt loam for F. tricinctum. The two Fusarium species were able to cause root rot in soil moisture ranging from 20% to 100% water holding capacity (WHC). The greatest reduction of emergence caused by the Fusarium spp. was observed at 80% WHC in silt loam and clay soils and 40% WHC in sandy loam soil, when compared to the same WHC in the non-infested 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 to higher temperatures. At 18oC, most infection occurred at soil moistures of 20-80% WHC, while it was 40-80% WHC at 28oC. Disease caused by F. solani was favored by low temperature (18oC) with high soil moisture (60-80% WHC) or high temperature (28oC) with low soil moisture (20-40% WHC) while F. tricinctum was favored by cooler temperature and lower soil moisture.