Population Dynamics of Wheat Root Pathogens Under Different Tillage Systems in Northeast Oregon

No-till or direct seeding can be described as seeding directly into the crop stubble from the previous season without use of tillage. A reduction in tillage can result in many benefits, including increased soil organic matter, increased water holding capacity, and reduced fuel costs. However, the effect of no-till and reduced tillage on crop root disease profiles is poorly understood. To study the effect of tillage on disease dynamics, soil samples were collected from commercial wheat fields representing a wide range of tillage strategies in fall 2016 and fall 2017. Because precipitation might affect soilborne diseases, wheat fields located across a diverse gradient of precipitation zones of the dryland Pacific Northwest were selected. Fusarium spp., Pythium spp., and Rhizoctonia spp. were quantified from soil samples using soil dilution plating and quantitative PCR (qPCR) assays. Results of dilution plating showed that the colony counts of Fusarium, Pythium, and Rhizoctonia at the genus level were negatively associated with tillage. However, the same patterns were not observed when specific causal agents of Fusarium, Pythium, and Rhizoctonia that are known to be pathogenic on wheat were quantified with qPCR. Furthermore, precipitation affected the population density of some fungal pathogens (F. culmorum, P. ultimum, and R. solani AG 8). Within the scope of inference of this study, results of this study indicate that the benefits of adopting reduced tillage likely outweigh potential risk for increased root disease.