Long-Term Agricultural Research- Plant Diseases.

Plant disease epidemiology involves the study of pathogen movement over time and space. Foliar airborne pathogens such as rusts can spread across a large region over a short period of time within a season. These pathogens have short generation times and can be spread long distances by wind and rain. But soilborne pathogens that infect plant roots spread more slowly in the soil, and may take many years to move within a field or between fields.  Long term studies are needed to model or describe their spread.  Spatial analysis studies were conducted at the Cook Agronomy Farm in Pullman WA to determine the distribution of soilborne pathogens and identify those factors that impact these organisms. This no-till farm of over 90 acres was initiated in 1998, and contains a wealth of georeferenced information on soil edaphic factors, N, C, environmental factors, pathogens, and weeds. Long-term agriculture research has also been indispensable in the study of suppressive soils. These are soils where the pathogen is present, the host is susceptible, but the disease is held in check by a microbial community that has developed to suppress the disease. Typically, the disease develops the first few years after a susceptible host is planted, then declines as the soil becomes suppressive. Examples include decline of take-all of wheat and suppression to Rhizoctonia bare patch of wheat, first discovered in North America in a long-term cropping systems experiment near Ritzville, WA. With the advent of next-generation sequencing methods, we can describe in fine detail the microbial communities in the soil. Using long-term sites with cropping practices such as no-till or long-term herbicide application of glyphosate, we can study the effects on bacterial and fungal communities in wheat soils. Shifts in these microbial communities may play a role in the dynamics of soilborne pathogens such as Rhizoctonia.