Soil spatial distribution in a smut fungus-annual grass interaction: Exploring patterns to understand disease dynamics at plot scale

Infection of large crabgrass by loose smut occurs in the first centimetres of the soil profile. To understand the spatial-temporal disease dynamics, we try to find out the importance of the spatial distribution of spores and seeds in a field. Two soil sampling strategies were carried out after doing soil tillage, and propagules were counted; in the following season the level of disease was assessed. There was spatial autocorrelation in the case of the spores, but not in that of the seeds. Spores were arranged in a single patch. A significant relationship was found between the density of spores and the percentage of diseased host plants in the next season. Both variables displayed a spatial structure based on multiple regression. The role that the different zones of the field, varying in spore abundance, may play in the coexistence of both partners is discussed in the light of the results.