Short communicationInteractions between some plant-parasitic nematodes and Rhizoctonia solani in potato fields

- Severity of stem canker was higher in the centre of patches of stunted plants.
- No difference in the number of nematodes within the patches.
- Spatial correlation between R. solani and stubby-root and potato cyst nematodes.

The pathogenic fungus Rhizoctonia solani causes major economic losses for potato producers in Sweden. Producers, as well as extension officers, have reported possible increases in severity of R. solani when free-living plant-parasitic nematodes are present and active. The aim of this study was to investigate possible interactions and spatial correlations between root-lesion nematodes (Pratylenchus spp.), stubby-root nematodes (Trichodoridae) and the severity of stem canker caused by the fungus R. solani under field conditions. Nematodes in the genus Globodera were also included after finding high numbers of these potato cyst nematode juveniles in the samples. Soil samples were taken in eight potato fields, located in the middle part of Sweden, with observed outbreaks of soil-borne stem canker caused by R. solani. Grading of stem canker and soil collections for nematode extraction were performed along transects starting from the centre of field patches with observed stem canker. There was no difference in the number of nematodes within the patches for any of the investigated nematode taxa, but the severity of stem canker was higher on plants graded in the centre of the patches compared to those graded in the margins. In addition, there was a spatial correlation between R. solani and stubby-root nematodes as well as potato cyst nematodes, but not for root-lesion nematodes. These results show that there is an interaction between plant-parasitic nematodes and R. solani in the field and this knowledge is of importance for future decisions of appropriate management methods.