Q40. Which pathogen produces cedar–apple rust?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Hemileia vastatrix
(B) Melampsora lini
(C) Uromyces appendiculatus
(D) Gymnosporangium juniperi-virginianae
Answer: (D) Gymnosporangium juniperi-virginianae
Explanation: Gymnosporangium juniperi-virginianae alternates between junipers or cedars and apple-family hosts. Its life cycle produces conspicuous galls and orange spore structures. Removing nearby alternative hosts may sometimes reduce infection pressure in managed orchards.
Q39. The drooping of leaves and shoots because of lost turgidity is described as what symptom?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Rust
(B) Smut
(C) Wilting
(D) Powdery mildew
Answer: (C) Wilting
Explanation: Wilting results when water uptake or movement fails to match transpiration. It can occur through drought or pathogens that damage roots or block vascular tissues. Rust and smut instead denote characteristic groups of fungal diseases.
Q38. Which organism causes late blight of tomato?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Phytophthora cactorum
(B) Phytophthora cambivora
(C) Phytophthora infestans
(D) Phytophthora citrophthora
Answer: (C) Phytophthora infestans
Explanation: Phytophthora infestans, an oomycete, causes devastating late blight of both potato and tomato. Cool, moist conditions permit fast lesion expansion and spore production. The organism is fungus-like but belongs to a distinct evolutionary lineage.
Q37. Downy mildew of grapevine is associated with which pathogen?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Plasmopara halstedii
(B) Plasmopara viticola
(C) Peronospora destructor
(D) Peronospora effusa
Answer: (B) Plasmopara viticola
Explanation: Plasmopara viticola is the causal oomycete of grape downy mildew. Pale oily patches may appear on leaf surfaces, with white sporulation beneath in humid weather. Canopy aeration and timely protection help limit disease spread.
Q36. Powdery-mildew pathogens generally obtain nutrients from living host tissue and are classified as:
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Obligate biotrophs
(B) Facultative parasites only
(C) Obligate saprophytes
(D) Free-living decomposers
Answer: (A) Obligate biotrophs
Explanation: Most powdery mildew fungi are obligate biotrophs, maintaining associations with living host cells through specialised feeding structures. Their superficial whitish colonies can interfere with photosynthesis. Because they require living hosts, routine cultivation on artificial media is difficult.
Q35. Which fungus was classically identified as the cause of yellow Sigatoka disease of banana?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Mycosphaerella fragariae
(B) Mycosphaerella musicola
(C) Mycosphaerella citri
(D) Magnaporthe oryzae
Answer: (B) Mycosphaerella musicola
Explanation: Yellow Sigatoka is associated with Mycosphaerella musicola, currently also referred to by its Pseudocercospora musae asexual name. Leaf streaks develop into necrotic patches, reducing effective leaf area and potentially damaging bunch development.
Q34. Whip smut of sugarcane is caused by which fungus?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Sporisorium scitamineum (formerly Ustilago scitaminea)
(B) Ustilago nuda
(C) Ustilago maydis
(D) Ustilago hordei
Answer: (A) Sporisorium scitamineum (formerly Ustilago scitaminea)
Explanation: Sugarcane smut produces a long black whip-like structure from infected shoots. The accepted pathogen name is Sporisorium scitamineum, historically Ustilago scitaminea. Planting clean seed cane and resistant varieties are major management measures.
Q33. Who demonstrated the need for alternate hosts in the life cycle of wheat stem rust?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Anton de Bary
(B) Eriksson
(C) Stakman
(D) Craigie
Answer: (A) Anton de Bary
Explanation: Anton de Bary demonstrated the host alternation of the stem-rust fungus between wheat and barberry. The fungus forms different spore stages on these hosts. This discovery clarified complex fungal life cycles and influenced rust management.
Q32. In the classical life cycle of wheat stem rust, which spore stage is designated stage zero (0)?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Basidial
(B) Uredinial
(C) Telial
(D) Pycnial or spermogonial
Answer: (D) Pycnial or spermogonial
Explanation: In the five-stage rust notation, stage 0 is the pycnial or spermogonial stage, generally produced on the alternate host. Stages I to IV are aecial, uredinial, telial and basidial, respectively, although not every rust has all stages.
Q31. Which subviral plant pathogen consists of a small circular RNA molecule without a protein coat?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Virus
(B) Viroid
(C) Bacteriophage
(D) Phytoplasma
Answer: (B) Viroid
Explanation: Viroids are tiny infectious circular RNA molecules that lack a protective protein capsid. They replicate using host cellular machinery and are known primarily as plant pathogens. Their extremely small genomes distinguish them from ordinary plant viruses.
