Final answer:
The pathogen Phytophthora infestans originated in Central America, and optimal conditions for its spread are cool and moist environments. Potato and tomato are its primary hosts.
Step-by-step explanation:
The center of origin for the pathogen Phytophthora infestans, which causes late blight in plants like the potato (Solanum tuberosum) and tomato (Solanum lycopersicon), lies outside the native range of these host plants. This pathogen is thought to have originated in Central America and later 'jumped' hosts when potatoes spread from South America into this region. Additionally, the optimal environment for the outbreak of this disease is characterized by cool and moist conditions which favor the growth, reproduction, and spread of the pathogen.