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Research Objectives: Determine if severity of Fusarium and Rhizoctonia roots rots are increased under low to moderate levels of soil salinity.

Soil salinity is a serious problem in some areas of soybean production. A series of experiments under greenhouse conditions were conducted using the root rot fungi Fusarium solani , F. tricinctum and Rhizoctonia solani to determine if low levels of soil salinity might increase root rot damage to soybean plants. Since we know that salinity has a great effect on growth of soybean, the most likely interaction between soil salinity and roots rots would be at low levels of salinity where plants would grow under field conditions. Our experiments tested soil salinity levels of EC 1 and EC 2 compared to EC 0 (EC= electrical conductivity, a measurement of soil salinity), at several different levels of inoculum of these root rot fungi. The fungi were grown on sterilized wheat seeds then those infested seeds were mixed into the soil. The plants were grown for three weeks then root rot lesions, plant height, root weight and total plant weight were measured. The soil salinity was adjusted to EC 1 and 2 using sodium sulfate and magnesium sulfate. Salinity levels were maintained by careful adjustment of water loss from the soil.

The results of the experiments indicated there was no major evidence that soil salinity would in general increase root rot of soybean in the seedling stage. Indeed, the evidence indicated that soil salinity between EC 1 and EC 2 had a major negative effect on growth of soybean in these experiments and the effects of the root rot pathogens were either less important to plant growth under soil salinity or the activity of the root rot fungi were generally suppressed by soil salinity. There were few indications of significant interactions between the root rot fungi and soil salinity, but these interactions appeared to be less important than the overall effect of soil salinity on the growth of soybean. It is important to point out that the EC 1 and EC 2 levels in these experiments were very uniform throughout the soil whereas under field conditions such uniform salinity would be less likely and plants in the field would be growing in soil with more variation in EC levels. These experiments are further evidence of the major effects of soil salinity on the growth of soybean and the need to manage this soil condition.

Root systems of three plants all inoculated with the same amount of Fusarium, but growing at different soil salinity levels. The plant on the right growing at EC 2 has a 43% reduction in root mass compared to the plant growing in the soil with no salinity (EC 0). The plant at EC 1 also has a reduced root mass.