Unraveling the spatial distribution and association between Spongospora subterranea f. sp. subterranea and Potato Mop-Top Virus in potato fields (P-36)

Spongospora subterranea f. sp. subterranea (Sss) causes powdery scab of potatoes and vectors potato mop-top virus (PMTV). Sss and potentially PMTV are spread with seed-tubers and soil. Research addressing the spatial distribution of PMTV-carrying and PMTV-free Sss in commercial potato fields is limited. The objective of this study was to map the quantity of both pathogens across a potato farm and determine if spatial distribution patterns can be established using multiple geospatial analyses. The concentrations of Sss and PMTV were quantified in soil samples collected from 31 potato fields on a single farm from 2022 to 2025. Soil samples were collected in rotational cropping years. Optimized Hot Spot Analysis, Gaussian process regression, and Kernel density estimation analyses were performed to establish spatial distribution patterns between the number of Sss sporosori and PMTV gene copies determined using qPCR and ddPCR, respectively. Linear regression was performed to identify associations between these pathogens. Across the 31 fields, spatial clustering patterns were present for both Sss and PMTV. However, based on confidence intervals, statistical associations were not detected between quantities of Sss and PMTV across all fields tested on this farm, or within single fields. PMTV was detected in fields with low levels of sporosori, potentially indicating recent and co-introduction of these two pathogens. In other fields, high levels of Sss were observed with no PMTV, potentially indicating a more distant introduction of the powdery scab pathogen, without co- or subsequent PMTV introduction. Farm-level maps indicate that these pathogens could have spread with soil to nearby fields via farm equipment, or may have been wind-blown. More isolated detections may have resulted from Sss and PMTV-infected seed tubers planted in those fields.