UPSC Prelims 2018 Q99: Environment & Ecology – Sustainable Agriculture & Forestry
- (a) 1 and 3 only
- (b) 3 and 4 only
- (c) 1, 2 and 4 only
- (d) 1, 2, 3 and 4
Answer: (d) 1, 2, 3 and 4
Explanation
Plant Disease Spread - Mechanisms
Plant pathogens (bacteria, viruses, fungi, nematodes) spread through multiple vectors:
| Vector | Spreads plant diseases? | Detail |
|---|---|---|
| 1. Birds | YES | Birds carry seeds, pathogens, insect vectors on plumage/feet; e.g., avian spread of citrus canker, fire blight bacteria, and viruses like Cherry Leaf Roll. |
| 2. Dust blowing | YES | Dust storms carry fungal spores, bacterial cells, and even viruses across long distances (e.g., wheat rust spores across continents). |
| 3. Rain | YES | Rain splash disperses fungal spores and bacteria vertically and horizontally within crops - very effective for foliar disease spread. |
| 4. Wind blowing | YES | Wind is the classic long-distance disperser of fungal spores (wheat rust, coffee rust, potato late blight spores travel hundreds of km via wind). |
All four are established plant disease transmission vectors.
Answer: (d) 1, 2, 3 and 4.
Why each option is right or wrong
- (a) Incorrect. Dust blowing (2) and wind blowing (4) are also major spore/pathogen dispersers.
- (b) Incorrect. Birds (1) and dust (2) also spread plant diseases.
- (c) Incorrect. Rain (3) is also a major disease-spread vector via splash dispersal.
- (d) CORRECT. All four - birds, dust, rain, wind - can spread plant diseases through various mechanisms.
Key point
Plant disease dispersal: Wind (long-distance spores - rusts, blights), Rain (splash dispersal within canopy), Insects (vectors for viruses/bacteria), Birds (mechanical carry), Dust (long-distance airborne spores), Water flow, Human/machinery, Seed material.
Remember
Plant diseases spread through multiple vectors: birds (carrying pathogens on plumage/feet), dust blowing (carrying spores over long distances), rain (splash dispersal within canopy), and wind blowing (the classic long-distance spore disperser - wheat rust, coffee rust travel hundreds of km via wind). All four modes are established plant disease transmission mechanisms.
Common mistakes
- Assuming disease spread is only through insects - insects are important but wind, water, birds, dust are equally significant.
- Underestimating wind dispersal - wheat rust spores have crossed oceans (Puccinia striiformis pandemic spread).
- Missing rain splash - very effective for local canopy disease spread within farms.
Exam tip
Plant disease spread mechanisms: Autonomous (movement of the pathogen itself), abiotic (wind, water, rain, dust), biotic (insects, birds, mammals, humans, machinery), seed-borne, soil-borne, tuber/planting-material-borne.
Sources
- George N. Agrios — Plant Pathology (Academic Press)
- FAO - Plant Health and Pest Management Guidelines