Host–pathogen interaction between Phytophthora infestans and Solanum nigrum, S. villosum, and S. scabrum

Potato and tomato are the two major hosts for Phytophthora infestans causing late blight. The susceptibility of leaves and whole plants of Solanum nigrum, S. villosum, and S. scabrum to infection by P. infestans was tested under laboratory conditions. Out of 39 plants representing 38 different S. nigrum accessions, 16 were highly resistant (seven accessions did not show any symptoms of infection, nine were highly resistant showing necrotic lesions in the place of infection), and 23 plants of S. nigrum were colonized by, at least, 1 of the 2 isolates of P. infestans (17 accessions were infected with two P. infestans isolates, and 6 accessions showed different reactions depending on the isolate used for inoculation). Three accessions of S. villosum, and one accession of S. scabrum were tested and did not show any symptoms of infection. The majority of S. nigrum accessions infected by P. infestans in a detached leaf assay were also infected in the whole plant assay. The reaction of field- and greenhouse-grown plants to inoculation with P. infestans in detached leaf assays was similar, but in some cases leaves from field-grown plants reacted as resistant in comparison with the leaves from greenhouse-grown plants, which were susceptible.