Question

Late blight of potato is caused by

• A. Phytophthora infestans
• B. Alternaria solani
• C. Erwinia carotovora
• D. Pythium aphanidermatum

Hint:

Phytophthora infestans is an oomycete, not a true fungus. It has cellulose in its cell walls instead of chitin and produces biflagellate zoospores. This taxonomic distinction is a common topic in plant pathology exams.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Late blight of potato is one of the most historically significant plant diseases. It was responsible for the Irish Potato Famine in the 1840s, which led to mass starvation and migration.

Step 2: Detailed Explanation:
Let us identify the causal organisms and the diseases they cause in potato:
- Option (A) Phytophthora infestans: An oomycete (water mold) pathogen that causes late blight of potato and tomato. It produces pale green to dark water-soaked lesions on leaves and causes destructive tuber rot, leading to total crop failure under cool, humid conditions.
- Option (B) Alternaria solani: A deuteromycete fungus that causes early blight of potato, characterized by dark brown, concentric necrotic spots on older leaves (target-board effect).
- Option (C) Erwinia carotovora: A Gram-negative plant pathogenic bacterium that causes bacterial soft rot of tubers and blackleg of potato stems.
- Option (D) Pythium aphanidermatum: An oomycete pathogen that causes damping-off in nurseries and leak disease of potato tubers during harvest and transit.

Step 3: Final Answer:
Late blight of potato is caused by the oomycete pathogen Phytophthora infestans.
Therefore, the correct option is (A).