Q20. The blackheart disorder of stored potato tubers is most directly associated with:
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Excessive sunlight
(B) Frost alone
(C) High calcium
(D) Insufficient oxygen
Answer: (D) Insufficient oxygen
Explanation: Blackheart develops when potato tuber tissues experience low oxygen availability, particularly during poorly ventilated storage or transport. Internal cells die and darken, often before outward symptoms are apparent. It is a physiological disorder, not an infection.
Q19. A plant disease whose epidemic development extends over more than one growing season is called:
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Polyetic
(B) Monocyclic
(C) Polycyclic
(D) Acyclic
Answer: (A) Polyetic
Explanation: Polyetic epidemics develop over several years or growing seasons, often involving perennial hosts or persistent pathogens. Monocyclic epidemics have one primary infection cycle per season, while polycyclic epidemics generate repeated secondary infections within a season.
Q18. Tundu disease of wheat is associated with a bacterium together with which nematode?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Anguina tritici
(B) Meloidogyne graminicola
(C) Heterodera avenae
(D) Ditylenchus angustus
Answer: (A) Anguina tritici
Explanation: Tundu, or yellow ear rot of wheat, involves Rathayibacter tritici in association with the seed-gall nematode Anguina tritici. The nematode assists bacterial dissemination. This mixed disease must be distinguished from nematode-only ear cockle.
Q17. Khaira disease of rice is associated with deficiency of which mineral nutrient?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Nitrogen
(B) Zinc
(C) Potassium
(D) Phosphorus
Answer: (B) Zinc
Explanation: Zinc deficiency causes Khaira disease in rice, producing rusty-brown spots, stunting and poor tillering. Unlike infectious blights, it is a nutritional disorder. Appropriate zinc fertilisation and correction of soil conditions can prevent or alleviate symptoms.
Q16. Peach leaf curl is produced by which broad category of pathogen?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Virus
(B) Bacterium
(C) Fungus
(D) Phytoplasma
Answer: (C) Fungus
Explanation: Peach leaf curl is caused by the fungus Taphrina deformans. Young leaves become thickened, puckered and discoloured. The fungus overwinters on plant surfaces, so preventive treatment during dormancy is more effective than treatment after symptoms appear.
Q15. The severe wilting syndrome known as the “kresek” phase occurs in which crop disease?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Potato late blight
(B) Cotton black arm
(C) Rice bacterial leaf blight
(D) Banana Moko disease
Answer: (C) Rice bacterial leaf blight
Explanation: Kresek is the early systemic form of bacterial leaf blight of rice, caused by Xanthomonas oryzae pv. oryzae. Infected seedlings or young plants may wilt and die rapidly, whereas older plants show characteristic blighted leaf margins.
Q14. Tungro disease of rice is caused by which kind of agent?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Bacterium
(B) Fungus
(C) Viruses
(D) Phytoplasma
Answer: (C) Viruses
Explanation: Rice tungro results from infection by two viruses, rice tungro bacilliform virus and rice tungro spherical virus. Green leafhoppers transmit them. Infected plants are stunted, with orange-yellow leaves and reduced grain yield.
Q13. Which crop disease is transmitted by an eriophyid mite?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Brinjal little leaf
(B) Banana bunchy top
(C) Pigeonpea sterility mosaic
(D) Citrus greening
Answer: (C) Pigeonpea sterility mosaic
Explanation: Sterility mosaic disease of pigeonpea is associated with emaraviruses carried by the eriophyid mite Aceria cajani. Diseased plants show excessive vegetative growth, mosaic-like leaves and reduced flower formation, making mite management and resistant cultivars important.
Q12. A bacterial streaming or ooze test is mainly used when diagnosing infections caused by:
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Bacteria
(B) Viruses
(C) Nematodes
(D) Fungi
Answer: (A) Bacteria
Explanation: Cut plant tissue containing bacterial populations may release cloudy strands into clean water. This bacterial streaming provides a useful field clue for some vascular and soft-rot infections, although laboratory tests are needed for exact identification.
Q11. Which fungicide has been especially associated with control of oomycete downy mildews?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Chlorothalonil
(B) Carboxin
(C) Metalaxyl
(D) Thiram
Answer: (C) Metalaxyl
Explanation: Metalaxyl targets susceptible oomycetes, including many downy mildew pathogens, and moves within treated plants. Resistant pathogen populations can arise, so it should be used according to current local labels within resistance-management programmes.
