Effects of Soil Conditions on Root Rot of Soybean Caused by Fusarium graminearum

Fusarium graminearum is an important soybean pathogen that causes seedling disease, root rot, and pre- and postemergence damping-off. However, effects of soil conditions on the disease are not well understood. The objective of this greenhouse study was to determine the impacts of soil texture, pH, and soil moisture on seedling root rot symptoms and detrimental effects on seedling development caused by F. graminearum. F. graminearum-infested millet was added (10%, vol/vol) to soil with four different textures (sand, loamy sand, sandy loam, and loam). Soil moisture was maintained at saturation, field capacity or permanent wilting point at soil pH levels of 6 or 8. Seedlings were evaluated 4 weeks after planting for root rot, root length, root and shoot dry weights, leaf area, and F. graminearum colonization (by qPCR). There was a significant interaction between soil moisture and soil texture for root rot assessed visually (P < 0.0001). Highest severity (67%) and amount of F. graminearum DNA were observed at pH 6 and permanent wilting point in sandy loam soils. Pot saturation resulted in the lowest levels of disease in sandy loam and loam soils (11.6 and 10.8%, respectively). Reductions in seedling growth parameters, including root length, foliar area, shoot and root dry weights, and root tips, relative to the noninfested control, were significantly greater in sandy loam soils. In contrast, there were no significant growth reductions in sand. This study showed that levels of root rot increased under moisture-limiting conditions, producing detrimental effects on plant development.