Explanation:

The correct option is (C) Phytophthora infestans. This oomycete (water mold) is the specific pathogen responsible for late blight of potato and famously caused the devastating Great Irish Famine in the 1840s due to widespread crop destruction. Option (A) Plasmopara viticola causes downy mildew of grapes, not potato blight. Option (B) Helminthosporum oryzae (now *Bipolaris oryzae*) causes brown spot disease of rice and was linked to the Bengal Famine, not the Irish Famine. Option (D) 'Hemilia vesterfricala' is likely a misspelling of *Hemileia vastatrix*, which causes coffee rust, unrelated to potato blight.