(A)
P-1
Q-5
R-2
S-4

(B)
P-4
Q-3
R-2
S-1

(C)
P-6
Q-2
R-4
S-1

(D)
P-5
Q-3
R-2
S-4

Correct Answer

✅ Option (B)

Detailed Explanation

Correct identification of plant diseases and their causal agents is a core topic in plant pathology and is frequently tested in competitive exams.

P. False smut of rice → Ustilaginoidea virens (4)

• False smut of rice is a fungal disease.

• Caused by Ustilaginoidea virens, which converts rice grains into greenish smut balls.

• ✔ Correct match: P-4

Q. Ring rot of potato → Corynebacterium sepedonicum (3)

• Ring rot of potato is a bacterial disease.

• Caused by Corynebacterium sepedonicum (also known as Clavibacter michiganensis subsp. sepedonicus).

• ✔ Correct match: Q-3

R. Red rot of sugarcane → Colletotrichum falcatum (2)

• Red rot is a major fungal disease of sugarcane.

• The causal organism is Colletotrichum falcatum.

• ✔ Correct match: R-2

S. Downy mildew of grape → Plasmopara viticola (1)

• Downy mildew of grape is caused by an oomycete.

• The pathogen responsible is Plasmopara viticola.

• ✔ Correct match: S-1

Why Option (B) Is Correct

Option (B) correctly matches all four diseases with their authentic and well-established causal organisms.
All other options contain one or more incorrect disease–pathogen pairings.

Why Other Options Are Incorrect (Quick Check)

• Option (A): False smut and downy mildew are wrongly matched

• Option (C): Ring rot and false smut are incorrectly assigned

• Option (D): Fire blight pathogen is wrongly linked to false smut

Quick Exam Memory Tips

• False smut of rice → Ustilaginoidea virens

• Ring rot of potato → Corynebacterium sepedonicum

• Red rot of sugarcane → Colletotrichum falcatum

• Downy mildew of grape → Plasmopara viticola

Exam Relevance

🔹 Frequently asked in CSIR-NET Life Sciences
🔹 Important for plant pathology & agricultural sciences
🔹 High-yield match-the-following MCQs