Solution

Phytophthora infestans is an oomycete that causes the serious potato disease known as late blight or potato blight. Late blight was a major culprit in the 1840s European, the 1845 Irish and 1846 Highland potato famines. The organism can also infect tomatoes and some other members of the Solanaceae.
At first, the spots are gray-green and water-soaked, but they soon enlarge and turn dark brown and firm, with a rough surface. Solanum demissum is an interesting species for the improvement of cultivated potatoes because it has resistance traits to diseases, especially to late blight of potato (Phytophthora infestans), to pests and abiotic factors such as cold. This species can be crossed with the cultivated potato, despite the level of ploidy different and has been widely used to introduce mildew resistance genes in many cultivars since the beginning of the twentieth century.
With regard to the mildew was identified at least 11 resistance genes to specific breeds mildew (R1 to R11). Most current potato cultivars have at least one resistance gene from Solanum demissum.
However, these genes have all been circumvented by new mildew strains. Solanum tuberosum, Solanum acaule and Solanum stolniferum does not have natural resistance to late blight.
Therefore, the correct answer is option C.