Nightshade weeds (Solanum spp.) confirmed as hosts of the potato pathogens Meloidogyne fallax and Spongospora subterranea f. sp. subterranea

Hairy nightshade (Solanum physalifolium) and black nightshade (S. nigrum) are common weeds in cropping soils and potato crops (S. tuberosum) in New Zealand. Root galls were found on field-grown plants of hairy and black nightshade, and potato. Microscopic examination indicated that small galls (approx. 1 mm diameter) were caused by Meloidogyne fallax and larger galls (1–5 mm diameter) were caused by Spongospora subterranea f. sp. subterranea, and this was confirmed using species-specific PCR primers. Furthermore, infections caused by both pathogens were found simultaneously on individual specimens from all three hosts, and in a few cases, both pathogens occurred in the same individual gall. Mycelia of Rhizoctonia solani were also observed on galls and roots. Pathogenicity of M. fallax and Sp. subterranea f. sp. subterranea from field-grown nightshade plants was confirmed by inoculating glasshouse-grown tomato (Lycopersicon esculentum) and potato plants. This is the first record of M. fallax infecting S. physalifolium. Nightshade weeds are very likely to be important sources of M. fallax and Sp. subterranea f. sp. subterranea inoculum. Control of these weeds should be an important component of management of soilborne diseases in potato crops, to reduce pathogen inoculum and between-crop perennation.