Q.60. Select the CORRECT combination by matching the disease, causal organism and the affected
plant.
Disease
P. Stem rust
Q. Wart disease
R. Tikka/leaf spot
S. Downey mildew
Causal organism
i. Cercospora personata
ii. Plasmopara viticola
iii. Synchytrium endobioticum
iv. Puccinia graminis
Affected plant
1. Wheat
2. Ground nut
3. Potato
4. Grape
5. Apple
6. Rice
(A) P-iv-1, Q-iii-3, R-i-2, S-ii-4
(B) P-ii-1, Q-i-6, R-iv-4, S-iii-2
(C) P-iii-1, Q-iv-3, R-i-5, S-ii-4
(D) P-iv-1, Q-ii-3, R-iii-2, S-i-5
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Understanding Plant Pathology MCQs: Disease, Causal Organism, and Host Matching
Plant diseases devastate crops worldwide, and exams in agriculture, botany, and plant pathology often test your ability to match diseases with their causal organisms and affected plants. This guide solves a key multiple-choice question (MCQ) on stem rust, wart disease, tikka/leaf spot, and downy mildew. We’ll break down each option, highlight the correct answer (Option A), and explain why others fail—perfect for competitive exams like ICAR, BSc Agriculture, or UPSC.
The Question Breakdown
Match the disease, causal organism, and affected plant:
| Disease | Causal Organism Options | Affected Plant Options |
|---|---|---|
| P. Stem rust | i. Cercospora personata ii. Plasmopara viticola iii. Synchytrium endobioticum iv. Puccinia graminis |
1. Wheat 2. Groundnut 3. Potato 4. Grape 5. Apple 6. Rice |
| Q. Wart disease | (same as above) | (same as above) |
| R. Tikka/leaf spot | (same as above) | (same as above) |
| S. Downy mildew | (same as above) | (same as above) |
Options:
(A) P-iv-1, Q-iii-3, R-i-2, S-ii-4
(B) P-ii-1, Q-i-6, R-iv-4, S-iii-2
(C) P-iii-1, Q-iv-3, R-i-5, S-ii-4
(D) P-iv-1, Q-ii-3, R-iii-2, S-i-5
Correct Answer: Option (A) – P-iv-1, Q-iii-3, R-i-2, S-ii-4
This matching is spot-on based on standard plant pathology facts:
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P. Stem rust → iv. Puccinia graminis → 1. Wheat: Puccinia graminis (a basidiomycete fungus) causes black stem rust, a major wheat disease leading to elongated pustules on stems. It triggered the 1953 Bengal Famine.
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Q. Wart disease → iii. Synchytrium endobioticum → 3. Potato: Synchytrium endobioticum (a chytridiomycete) forms warty galls on potato tubers, making them unmarketable. It’s a quarantine pathogen in many countries.
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R. Tikka/leaf spot → i. Cercospora personata → 2. Groundnut: Cercospora personata (an ascomycete) creates dark leaf spots (“tikka” in India) on groundnut (peanut), reducing photosynthesis and yield.
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S. Downy mildew → ii. Plasmopara viticola → 4. Grape: Plasmopara viticola (an oomycete) produces white, downy growth on grapevine undersides, causing the devastating “grape downy mildew” epidemic of the 19th century.
These pairings align with textbooks like Plant Pathology by G.N. Agrios and ICAR references.
Why Other Options Are Incorrect: Step-by-Step Analysis
Each wrong option swaps at least one key match, testing your precision. Here’s the breakdown:
Option (B): P-ii-1, Q-i-6, R-iv-4, S-iii-2
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P-ii-1: Plasmopara viticola (downy mildew) on wheat? No—it’s grape-specific.
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Q-i-6: Cercospora personata (tikka) on rice? Wrong—tikka hits groundnut.
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R-iv-4: Puccinia graminis (stem rust) on grape? Incorrect—rust targets cereals.
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S-iii-2: Synchytrium endobioticum (wart) on groundnut? No—it’s potato-exclusive.
Fully mismatched—eliminate.
Option (C): P-iii-1, Q-iv-3, R-i-5, S-ii-4
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P-iii-1: Synchytrium endobioticum (wart) on wheat? No—wart is potato-only.
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Q-iv-3: Puccinia graminis (stem rust) on potato? Wrong—rust affects grasses.
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R-i-5: Cercospora personata (tikka) on apple? Incorrect—groundnut host.
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S-ii-4: Downy mildew on grape—this one is correct, but others fail.
Three errors—invalid.
Option (D): P-iv-1, Q-ii-3, R-iii-2, S-i-5
-
P-iv-1: Stem rust on wheat—correct.
-
Q-ii-3: Plasmopara viticola (downy mildew) on potato? No—it’s grape.
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R-iii-2: Synchytrium endobioticum (wart) on groundnut? Wrong—potato.
-
S-i-5: Cercospora personata (tikka) on apple? No—groundnut.
Two correct, but swaps doom it.
Quick Reference Table for Plant Diseases Matching
| Disease | Causal Organism | Affected Plant | Key Symptom |
|---|---|---|---|
| Stem rust | Puccinia graminis (iv) | Wheat (1) | Black pustules on stems |
| Wart disease | Synchytrium endobioticum (iii) | Potato (3) | Warty galls on tubers |
| Tikka/leaf spot | Cercospora personata (i) | Groundnut (2) | Dark spots on leaves |
| Downy mildew | Plasmopara viticola (ii) | Grape (4) | White fuzz on leaf undersides |
Exam Tips for Plant Pathology MCQs
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Memorize fungal classes: Basidiomycetes (rusts like Puccinia), Oomycetes (downy mildews), Chytrids (warts).
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Link symptoms to hosts: Rusts on cereals, leaf spots on legumes, mildews on vines.
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Practice with real outbreaks—e.g., stem rust’s global impact on wheat.
