PLANT PATHOLOGY (100 Questions)
Fundamental Concepts
- The term “Pathogenicity” refers to:
a) Ability to cause disease
b) Severity of disease
c) Disease spread
d) Disease symptoms
Answer: a) Ability to cause disease
Explanation:Pathogenicity is the capacity of a pathogen to cause disease. Virulence refers to the degree of pathogenicity.
- “Monocyclic diseases” are those that:
a) Complete one life cycle per season
b) Have multiple cycles per season
c) Are perennial
d) Are seed-borne only
Answer: a) Complete one life cycle per season
Explanation:Monocyclic pathogens (e.g., soil-borne fungi like Fusarium) have single infection cycle/year. Polycyclic have multiple cycles (e.g., rusts, powdery mildews).
- The “Inoculum potential” concept was given by:
a) Garrett
b) Van der Plank
c) De Bary
d) Millardet
Answer: a) Garrett
Explanation:D. Garrett defined inoculum potential as “energy of growth of a pathogen available for infection”.
- “Hypersensitive response” in plants leads to:
a) Rapid cell death at infection site
b) Systemic infection
c) Tolerance
d) Susceptibility
Answer: a) Rapid cell death at infection site
Explanation:HR is programmed cell death around infection site, restricting pathogen spread. Key feature of gene-for-gene resistance.
- “Phytoalexins” are:
a) Antimicrobial compounds produced after infection
b) Pre-formed antimicrobial compounds
c) Plant hormones
d) Nutrient compounds
Answer: a) Antimicrobial compounds produced after infection
Explanation:Phytoalexins (e.g., pisatin, phaseollin) are synthesized de novo in response to pathogen attack, unlike phytoanticipins which are pre-formed.
Fungal Diseases
- “Green ear disease” of bajra is caused by:
a) Sclerospora graminicola
b) Ustilago maydis
c) Tolyposporium penicillariae
d) Claviceps fusiformis
Answer: a) Sclerospora graminicola
Explanation:Downy mildew of bajra causes transformation of floral parts into leafy structures (phyllody). Oomycete pathogen.
- The causal organism of “Red rot of sugarcane” is:
a) Colletotrichum falcatum
b) Xanthomonas axonopodis
c) Cercospora personata
d) Ustilago scitaminea
Answer: a) Colletotrichum falcatum
Explanation:Causes red lesions with white patches (called “cock’s eye” marks). Serious disease in subtropical India.
- “Late blight of potato” is caused by:
a) Phytophthora infestans
b) Alternaria solani
c) Phoma exigua
d) Fusarium oxysporum
Answer: a) Phytophthora infestans
Explanation:Oomycete pathogen causing Irish famine (1845-49). Produces sporangia on sporangiophores emerging from stomata.
- “Ergot of bajra” is caused by:
a) Claviceps fusiformis
b) Claviceps purpurea
c) Ustilago maydis
d) Tolyposporium penicillariae
Answer: a) Claviceps fusiformis
Explanation:Replaces grains with dark sclerotia containing alkaloids (ergotism). Different species infect different hosts.
- “Powdery mildew of mango” is caused by:
a) Oidium mangiferae
b) Colletotrichum gloeosporioides
c) Phytophthora palmivora
d) Cercospora mangiferae
Answer: a) Oidium mangiferae
Explanation:White powdery growth on inflorescence and fruits. Erysiphaceae family, obligate parasite.
Bacterial Diseases
- “Citrus canker” is caused by:
a) Xanthomonas axonopodiscitri
b) Xanthomonas campestris pv. citri
c) Pseudomonas syringae pv. citri
d) Erwinia amylovora
Answer: a) Xanthomonas axonopodis pv. citri
Explanation: Causes raised corky lesions on leaves, stems, fruits. Quarantine disease, eradication programs implemented.
- “Bacterial blight of rice” is caused by:
a) Xanthomonas oryzaeoryzae
b) Xanthomonas campestris pv. oryzae
c) Pseudomonas syringae
d) Erwinia chrysanthemi
Answer: a) Xanthomonas oryzae pv. oryzae
Explanation: Causes kresek (wilting) and leaf blight phases. Spread through rain splashes, infected seeds.
- “Fire blight of apple and pear” is caused by:
a) Erwinia amylovora
b) Pseudomonas syringae
c) Xanthomonas campestris
d) Agrobacterium tumefaciens
Answer: a) Erwinia amylovora
Explanation:Gram-negative bacterium causing shoot blight with “shepherd’s crook” symptom. Spread by insects, rain.
- “Crown gall” disease is caused by:
a) Agrobacterium tumefaciens
b) Agrobacterium rhizogenes
c) Pseudomonas savastanoi
d) Ralstonia solanacearum
Answer: a) Agrobacterium tumefaciens
Explanation:Causes tumorous growths via Ti plasmid transfer. Used in genetic engineering as vector.
- “Brown rot of potato” is caused by:
a) Ralstonia solanacearum
b) Erwinia carotovora
c) Clavibacter michiganensis
d) Pseudomonas solanacearum
Answer: a) Ralstonia solanacearum
Explanation:Causes bacterial wilt with vascular browning. Formerly Pseudomonas solanacearum. Race 3 biovar 2 is quarantine pest.
Viral Diseases
- “Tungro disease of rice” is transmitted by:
a) Green leafhopper (Nephotettix virescens)
b) Brown plant hopper
c) Whitefly
d) Aphid
Answer: a) Green leafhopper (Nephotettix virescens)
Explanation:Caused by Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). Semi-persistent transmission.
- “Bunchy top of banana” is caused by:
a) Banana bunchy top virus
b) Banana streak virus
c) Cucumber mosaic virus
d) Tobacco mosaic virus
Answer: a) Banana bunchy top virus
Explanation:Nanavirus transmitted by banana aphid (Pentalonia nigronervosa). Causes stunting and bunchy appearance.
- “Leaf curl of tomato” is caused by:
a) Tomato leaf curl virus
b) Tomato spotted wilt virus
c) Tobacco mosaic virus
d) Potato virus Y
Answer: a) Tomato leaf curl virus
Explanation:Begomovirus transmitted by whitefly (Bemisia tabaci). Causes upward curling, vein clearing. - “Potato leaf roll” is caused by:
a) Potato leaf roll virus
b) Potato virus X
c) Potato virus Y
d) Potato virus S
Answer: a) Potato leaf roll virus
Explanation:Polerovirus transmitted by aphids (Myzus persicae) in persistent manner. Causes upward rolling of leaves.
- “Mosaic disease of sugarcane” is caused by:
a) Sugarcane mosaic virus
b) Fiji disease virus
c) Grassy shoot phytoplasma
d) Ratoon stunting bacterium
Answer: a) Sugarcane mosaic virus
Explanation:Potyvirus causing mosaic pattern on leaves. Transmitted by aphids and through setts.
Phytoplasma Diseases
- “Grassy shoot of sugarcane” is caused by:
a) Phytoplasma
b) Virus
c) Bacterium
d) Fungus
Answer: a) Phytoplasma
Explanation:Caused by Candidatus Phytoplasma causing proliferation of tillers giving grassy appearance.
- “Little leaf of brinjal” is caused by:
a) Phytoplasma
b) Virus
c) Mycoplasma
d) Bacterium
Answer: a) Phytoplasma
Explanation:Causes reduction in leaf size, proliferation of branches. Transmitted by leafhopper (Hishimonus phycitis).
- “Witches’ broom of legumes” is caused by:
a) Phytoplasma
b) Fungus
c) Nematode
d) Virus
Answer: a) Phytoplasma
Explanation:Causes excessive branching giving broom-like appearance. Affects pigeonpea, sesame, etc.
- 24. Phytoplasmas belong to class:
a) Mollicutes
b) Actinomycetes
c) Spiroplasmas
d) Mycobacteria
Answer: a) Mollicutes
Explanation:Cell wall-less bacteria, formerly called mycoplasma-like organisms (MLOs). Candidatus Phytoplasma genus.
- 25. Phytoplasmas are transmitted by:
a) Leafhoppers
b) Aphids
c) Whiteflies
d) All of above
Answer: a) Leafhoppers
Explanation:Primarily by phloem-feeding leafhoppers (Cicadellidae), planthoppers (Fulgoroidea), and psyllids.
Nematode Diseases
- “Root knot nematode” belongs to genus:
a) Meloidogyne
b) Heterodera
c) Pratylenchus
d) Radopholus
Answer: a) Meloidogyne
Explanation:Causes gall formation on roots. Important species: incognita, M. javanica, M. arenaria.
- 27. “Cyst nematode of potato” is:
a) Globodera rostochiensis
b) Heterodera avenae
c) Meloidogyne incognita
d) Pratylenchus penetrans
Answer: a) Globodera rostochiensis
Explanation:Golden nematode causing yield loss up to 80%. Forms cysts on roots. Quarantine pest
- “Citrus nematode” is:
a) Tylenchulus semipenetrans
b) Radopholus similis
c) Pratylenchus coffeae
d) Meloidogyne incognita
Answer: a) Tylenchulus semipenetrans
Explanation:Causes “slow decline” of citrus. Only anterior portion penetrates root, hence “semipenetrans”.
- “Burrowing nematode” affecting banana is:
a) Radopholus similis
b) Pratylenchus coffeae
c) Meloidogyne incognita
d) Heterodera oryzae
Answer: a) Radopholus similis
Explanation:Causes toppling disease of banana by burrowing in roots and rhizome. Also affects black pepper.
- “Seed gall nematode of wheat” is:
a) Anguina tritici
b) Heterodera avenae
c) Meloidogyne naasi
d) Pratylenchus thornei
Answer: a) Anguina tritici
Explanation:Causes “ear cockle” disease, replacing grains with galls. Associated with Clavibacter causing tundu disease.
Disease Diagnosis
- “Koch’s postulates” were proposed in:
a) 1884
b) 1890
c) 1905
d) 1910
Answer: a) 1884
Explanation:Robert Koch established criteria to prove pathogen-disease relationship: isolation, inoculation, re-isolation.
- ELISA test is used for detection of:
a) Viruses
b) Bacteria
c) Fungi
d) All pathogens
Answer: d) All pathogens
Explanation:Enzyme-Linked Immunosorbent Assay detects antigens/antibodies. DAS-ELISA common for viruses.
- 33. “PCR technique” amplifies:
a) DNA
b) RNA
c) Proteins
d) Carbohydrates
Answer: a) DNA
Explanation:Polymerase Chain Reaction amplifies specific DNA sequences. RT-PCR for RNA viruses.
- 34. “Selective media” for Erwiniacontains:
a) Crystal violet
b) Cycloheximide
c) Streptomycin
d) All of above
Answer: a) Crystal violet
Explanation: Crystal violet pectate (CVP) medium selective for soft rot erwinias.
- 35. “Thermotherapy” is used for eliminating:
a) Viruses from planting material
b) Fungal spores
c) Bacterial cells
d) Nematodes
Answer: a) Viruses from planting material
Explanation:Heat treatment (37-40°C for weeks) eliminates viruses from meristems for virus-free planting material.
Disease Cycles
- “Primary inoculum” originates from:
a) Overwintering/oversummering sources
b) Current season infections
c) Alternate hosts
d) All of above
Answer: d) All of above
Explanation:Inoculum that initiates first infections: infected seeds, soil, plant debris, alternate hosts, volunteer plants.
- “Secondary spread” occurs through:
a) Wind
b) Water
c) Insects
d) All of above
Answer: d) All of above
Explanation:Spread from primary infections to cause new infections within same season.
- 38. “Oospores” function as:
a) Resting spores
b) Vegetative spores
c) Sexual spores
d) Both a and c
Answer: d) Both a and c
Explanation:Thick-walled sexual spores of oomycetes that survive adverse conditions (resting) and cause primary infections.
- 39. “Uredospores” are:
a) Repeating spores of rusts
b) Resting spores
c) Sexual spores
d) Vegetative spores
Answer: a) Repeating spores of rusts
Explanation:Binucleate, dikaryotic spores produced in uredia, responsible for secondary spread (summer spores).
- 40. “Chlamydospores” are:
a) Thick-walled resting spores
b) Thin-walled spores
c) Sexual spores
d) Motile spores
Answer: a) Thick-walled resting spores
Explanation:Formed by thickening of hyphal cells (e.g., Fusarium, Phytophthora) for survival.
Host-Pathogen Interaction
- “Gene-for-gene hypothesis” was proposed by:
a) Flor
b) Vanderplank
c) Stakman
d) De Bary
Answer: a) Flor
Explanation:H. Flor (1942) working on flax rust: for each resistance gene in host, corresponding avirulence gene in pathogen.
- 42. “Vertical resistance” is also called:
a) Race-specific resistance
b) Race-non-specific resistance
c) Durable resistance
d) Field resistance
Answer: a) Race-specific resistance
Explanation:Effective against specific races, governed by major genes, shows hypersensitive response.
- 43. “Horizontal resistance” is:
a) Polygenic
b) Durable
c) Race-non-specific
d) All of above
Answer: d) All of above
Explanation:Partial resistance against all races, polygenic inheritance, more durable.
- 44. “Elicitors” are:
a) Molecules triggering defense responses
b) Toxins produced by pathogens
c) Plant hormones
d) Nutrients
Answer: a) Molecules triggering defense responses
Explanation:Pathogen-derived (PAMPs) or host-derived (DAMPs) molecules that activate plant immunity.
- 45. “Systemic acquired resistance” involves:
a) Salicylic acid pathway
b) Jasmonic acid pathway
c) Ethylene pathway
d) All of above
Answer: a) Salicylic acid pathway
Explanation:SAR provides broad-spectrum resistance throughout plant after local infection. Mediated by SA, involves PR proteins.
Epidemiology
- “Compound interest disease” model describes:
a) Polycyclic diseases
b) Monocyclic diseases
c) Perennial diseases
d) Soil-borne diseases
Answer: a) Polycyclic diseases
Explanation:Vanderplank’s model: disease increases exponentially like compound interest (multiple infection cycles).
- “Apparent infection rate (r)” is calculated from:
a) Logistic model
b) Exponential model
c) Monomolecular model
d) All models
Answer: a) Logistic model
Explanation:r = (1/t) × ln[x/(1-x)] where x = disease intensity at time t.
- 48. “Latent period” is the time between:
a) Infection and sporulation
b) Spore landing and infection
c) Symptom appearance and sporulation
d) Inoculation and symptom
Answer: a) Infection and sporulation
Explanation:Critical epidemiological parameter: shorter latent period means faster epidemic development.
- 49. “Critical point model” for disease forecasting uses:
a) Single observation
b) Multiple observations
c) Continuous monitoring
d) Historical data only
Answer: a) Single observation
Explanation:Decision based on disease level at critical growth stage (e.g., blast at tillering in rice).
- 50. “AUDPC” stands for:
a) Area Under Disease Progress Curve
b) Area Under Disease Pressure Curve
c) Average Universal Disease Progress Constant
d) Agricultural Unit Disease Protection Coefficient
Answer: a) Area Under Disease Progress Curve
Explanation:Measures total disease intensity over time: AUDPC = Σ[(yi + yi+1)/2] × (ti+1 – ti).
Disease Management
- “Quarantine” regulations in India are under:
a) Destructive Insects and Pests Act, 1914
b) Plant Quarantine Order, 2003
c) Both a and b
d) None
Answer: c) Both a and b
Explanation:DIP Act 1914 and PQ Order 2003 regulate import/export to prevent exotic pest introduction.
- “Roguing” is effective for diseases that are:
a) Systemic
b) Seed-borne
c) Soil-borne
d) Air-borne
Answer: a) Systemic
Explanation:Removing infected plants reduces inoculum source for viruses, phytoplasmas, etc.
- 53. “Hot water treatment” of seeds is at:
a) 50-55°C for 30 min
b) 60-65°C for 10 min
c) 70-75°C for 5 min
d) 80-85°C for 1 min
Answer: a) 50-55°C for 30 min
Explanation:For loose smut of wheat: 54°C for 10 min. Kills internally seed-borne pathogens without damaging seed.
- “Solarization” involves covering soil with:
a) Clear plastic
b) Black plastic
c) Organic mulch
d) Sand
Answer: a) Clear plastic
Explanation:Traps solar heat, raising soil temperature to 45-55°C, killing pathogens, weeds, nematodes.
- 55″Bio-priming” involves:
a) Seed treatment with biocontrol agents
b) Hot water treatment
c) Chemical treatment
d) Radiation treatment
Answer: a) Seed treatment with biocontrol agents
Explanation:Seeds coated with biocontrol agents (Trichoderma, Pseudomonas) during hydration process.
Chemical Control
- “Bordeaux mixture” contains:
a) Copper sulfate + lime
b) Copper oxychloride
c) Copper hydroxide
d) Copper carbonate
Answer: a) Copper sulfate + lime
Explanation:Invented by Millardet (1885) against downy mildew of grape. 4:4:50 ratio (CuSO₄:lime:water).
- “Systemic fungicides” move in:
a) Xylem
b) Phloem
c) Both
d) Neither
Answer: a) Xylem
Explanation:Most systemic fungicides (benzimidazoles, triazoles) move upward in xylem (apoplastic). Few are phloem-mobile.
- “Contact fungicides” are effective against:
a) Surface pathogens
b) Systemic pathogens
c) Vascular pathogens
d) All
Answer: a) Surface pathogens
Explanation:Protectants (mancozeb, chlorothalonil) remain on surface, no curative action.
- 59″Fungicide resistance” develops fastest in:
a) Systemic fungicides
b) Contact fungicides
c) Multisite inhibitors
d) All equally
Answer: a) Systemic fungicides
Explanation:Single-site inhibitors (systemics) prone to resistance. Multisite inhibitors (contacts) less prone.
- “FRAC” code on fungicides indicates:
a) Mode of action group
b) Toxicity level
c) Solubility
d) Persistence
Answer: a) Mode of action group
Explanation:Fungicide Resistance Action Committee codes help in resistance management by rotating different groups.
Biological Control
- “Trichoderma viride” controls diseases by:
a) Mycoparasitism
b) Competition
c) Antibiosis
d) All of above
Answer: d) All of above
Explanation:Hyperparasitism (coils around pathogen), competition for space/nutrients, produces antibiotics (gliotoxin).
- “Pseudomonas fluorescens” produces antibiotic:
a) Pyocyanin
b) Phenazine
c) Pyoluteorin
d) All of above
Answer: d) All of above
Explanation:Produces multiple antibiotics, siderophores (pyoverdine), HCN, induces systemic resistance.
- 63 “Bacillus subtilis” controls diseases through:
a) Antibiotic production
b) Induced resistance
c) Competition
d) All of above
Answer: d) All of above
Explanation:Produces lipopeptides (surfactin, iturin), activates plant defense mechanisms (ISR via JA pathway).
- “AM fungi” help in disease control by:
a) Improving plant nutrition
b) Physical barrier
c) Induced resistance
d) All of above
Answer: d) All of above
Explanation:Arbuscular mycorrhizae improve P nutrition, form physical barrier in roots, prime defense responses.
- 65. “Biofumigation” uses:
a) Brassica residues
b) Neem cake
c) Castor cake
d) All of above
Answer: d) All of above
Explanation:Decomposition releases volatile compounds (isothiocyanates from brassicas, azadirachtin from neem).
Integrated Disease Management
- “IDM” components include:
a) Cultural methods
b) Biological control
c) Chemical control
d) All of above
Answer: d) All of above
Explanation:Integrated Disease Management uses multiple strategies for sustainable disease control.
- “Economic threshold level” for disease control is when:
a) Cost of control = Loss prevented
b) Disease first appears
c) Disease is severe
d) Always control
Answer: a) Cost of control = Loss prevented
Explanation:ETL: disease level at which control measures become economically justified.
- 67. “Tolerance” in plants means:
a) Infection without yield loss
b) No infection
c) Slow disease development
d) Early symptom expression
Answer: a) Infection without yield loss
Explanation:Tolerant plants get infected but show minimal yield reduction compared to susceptible plants.
- “Escape” from disease occurs due to:
a) Early maturity
b) Plant architecture
c) Environmental conditions
d) All of above
Answer: d) All of above
Explanation:Plants avoid disease by maturing before epidemic, having open canopy, or growing in unfavorable conditions for pathogen.
- 69″Disease triangle” components are:
a) Host, pathogen, environment
b) Host, vector, pathogen
c) Inoculum, environment, time
d) Virulence, susceptibility, environment
Answer: a) Host, pathogen, environment
Explanation:Disease requires susceptible host, virulent pathogen, and favorable environment simultaneously.
Specific Crop Diseases
- “Blast of rice” is caused by:
a) Pyricularia oryzae
b) Magnaporthe oryzae
c) Helminthosporium oryzae
d) Both a and b
Answer: d) Both a and b
Explanation:Teleomorph: Magnaporthe oryzae, anamorph: Pyricularia oryzae. Causes leaf, node, neck blast.
- “Karnal bunt of wheat” is caused by:
a) Tilletia indica
b) Tilletia caries
c) Ustilago tritici
d) Urocystis tritici
Answer: a) Tilletia indica
Explanation:Partial bunt, fishy odor, quarantine significance. Also called partial bunt.
- 73. “Yellow rust of wheat” is caused by:
a) Puccinia striiformis
b) Puccinia graminis tritici
c) Puccinia recondita
d) Uromyces appendiculatus
Answer: a) Puccinia striiformis
Explanation:Stripe rust with yellow uredia arranged in stripes. Cool temperature favor (10-15°C).
- “Downy mildew of grape” is caused by:
a) Plasmopara viticola
b) Peronospora parasitica
c) Sclerospora graminicola
d) Pseudoperonospora cubensis
Answer: a) Plasmopara viticola
Explanation:Oomycete pathogen, controlled by Bordeaux mixture (first fungicide use).
- 75″Black rot of grapes” is caused by:
a) Guignardia bidwellii
b) Plasmopara viticola
c) Uncinula necator
d) Botrytis cinerea
Answer: a) Guignardia bidwellii
Explanation:Fungus causing circular black spots with pycnidia. Also called bitter rot.
Post-Harvest Diseases
- “Blue mold of citrus” is caused by:
a) Penicillium italicum
b) Penicillium digitatum
c) Geotrichum candidum
d) Phytophthora citrophthora
Answer: a) Penicillium italicum
Explanation:Blue-green spores, grows at lower temperature than digitatum (green mold).
- “Stem end rot of mango” is caused by:
a) Botryodiplodia theobromae
b) Colletotrichum gloeosporioides
c) Aspergillus niger
d) Phomopsis mangiferae
Answer: a) Botryodiplodia theobromae
Explanation:Latent infection, symptoms appear during ripening. Also called diplodia stem end rot. - “Soft rot of vegetables” is caused by:
a) Erwinia carotovora
b) Rhizopus stolonifer
c) Botrytis cinerea
d) All of above
Answer: a) Erwinia carotovora - “Aflatoxin” is produced by:
a) Aspergillus flavus
b) Aspergillus parasiticus
c) Both a and b
d) Fusarium moniliforme
Answer: c) Both a and b
Explanation:Carcinogenic mycotoxin in groundnut, maize, cottonseed. flavus produces B1, B2; A. parasiticus produces B1, B2, G1, G2. - “Patulin” toxin is produced by:
a) Penicillium expansum
b) Aspergillus flavus
c) Fusarium graminearum
d) Alternaria alternata
Answer: a) Penicillium expansum
Explanation:Found in rotten apples, apple products. Mycotoxin affecting kidneys, immune system.
Emerging Diseases
- “False smut of rice” is caused by:
a) Ustilaginoidea virens
b) Tilletia barclayana
c) Neovossia horrida
d) Ustilago maydis
Answer: a) Ustilaginoidea virens
Explanation:Emerging disease causing orange-yellow smut balls. Produces mycotoxins (ustiloxins).
- “Sheath rot of rice” is caused by:
a) Sarocladium oryzae
b) Rhizoctonia solani
c) Sclerotium rolfsii
d) Fusarium moniliforme
Answer: a) Sarocladium oryzae
Explanation:Causes discolored lesions on sheath, unfilled grains. Associated with Pseudomonas fuscovaginae.
- 83 “Sheath blight of rice” is caused by:
a) Rhizoctonia solani
b) Sclerotium rolfsii
c) Pyricularia oryzae
d) Xanthomonas oryzae
Answer: a) Rhizoctonia solani
Explanation:Anamorph of Thanatephorus cucumeris. Causes oval lesions with brown margin.
- “Bakanae disease of rice” is caused by:
a) Fusarium moniliforme
b) Fusarium oxysporum
c) Pyricularia oryzae
d) Helminthosporium oryzae
Answer: a) Fusarium moniliforme
Explanation:Causes abnormal elongation, sterile tillers. Produces gibberellins causing elongation.
- 85 “Brown spot of rice” is caused by:
a) Helminthosporium oryzae
b) Cochliobolus miyabeanus
c) Bipolaris oryzae
d) All names for same fungus
Answer: d) All names for same fungus
Explanation:Teleomorph: Cochliobolus miyabeanus, anamorph: Bipolaris oryzae (formerly Helminthosporium oryzae).
Disease Resistance
- “Multiline varieties” were developed by:
a) Jensen
b) Borlaug
c) Vanderplank
d) Browning
Answer: d) Browning
Explanation:A. Browning developed multilines for oat crown rust resistance. Mixture of isolines.
- “Pyramiding of genes” involves:
a) Combining multiple R genes
b) Combining minor genes
c) Combining tolerance genes
d) All of above
Answer: a) Combining multiple R genes
Explanation:Stacking major resistance genes in single cultivar for broader spectrum, delayed resistance breakdown.
- 88″Marker-assisted selection” uses:
a) DNA markers linked to traits
b) Morphological markers
c) Biochemical markers
d) All markers
Answer: a) DNA markers linked to traits
Explanation:Molecular markers (RAPD, SSR, SNP) linked to resistance genes enable early selection.
- 89 “R genes” typically encode:
a) NBS-LRR proteins
b) PR proteins
c) Enzymes
d) Hormones
Answer: a) NBS-LRR proteins
Explanation:Most cloned R genes encode nucleotide-binding site leucine-rich repeat proteins that recognize avr gene products.
- 90 “Durable resistance” lasts for:
a) Many years over large area
b) One season
c) Few years
d) Under all conditions
Answer: a) Many years over large area
Explanation:Resistance remains effective despite widespread cultivation and pathogen evolution.
Historical Aspects
- “Father of Plant Pathology” is:
a) Anton de Bary
b) Louis Pasteur
c) Robert Koch
d) E.J. Butler
Answer: a) Anton de Bary
Explanation:Demonstrated fungal nature of potato late blight (1861), established mycology basis of plant pathology.
- “First recorded plant disease” was:
a) Wheat rust
b) Grape downy mildew
c) Potato late blight
d) Ergot of rye
Answer: a) Wheat rust
Explanation:Mentioned in Bible, Homer’s Iliad, Roman rituals to rust god Robigus.
- 93 “Irish famine” was caused by:
a) Potato late blight
b) Wheat rust
c) Rice blast
d) Grape downy mildew
Answer: a) Potato late blight
Explanation:Phytophthora infestans caused famine (1845-49) killing 1 million people, emigrating 1.5 million.
- 94 “First fungicide” discovered was:
a) Bordeaux mixture
b) Sulfur
c) Copper sulfate
d) Lime sulfur
Answer: a) Bordeaux mixture
Explanation:Pierre-Marie-Alexis Millardet (1885) accidentally discovered while preventing grape theft.
- 95 “First virus discovered” was:
a) Tobacco mosaic virus
b) Potato leaf roll virus
c) Cucumber mosaic virus
d) Tomato bushy stunt virus
Answer: a) Tobacco mosaic virus
Explanation:Dmitri Ivanovsky (1892) showed infectious agent passed through bacteria-proof filter. Beijerinck called it “contagium vivum fluidum”.
Miscellaneous Important Diseases
- “Wilt of pigeonpea” is caused by:
a) Fusarium udum
b) Fusarium oxysporum
c) Rhizoctonia bataticola
d) Phytophthora drechsleri
Answer: a) Fusarium udum
Explanation:Vascular wilt causing yellowing, wilting, vascular browning. Host-specific ( udum f. sp. udum).
- “Tikka disease of groundnut” is caused by:
a) Cercospora arachidicola
b) Cercospora personata
c) Both a and b
d) Phoma arachidicola
Answer: c) Both a and b
Explanation:Early leaf spot ( arachidicola: larger spots), Late leaf spot (C. personata: smaller spots with yellow halo).
- 98 “Purple blotch of onion” is caused by:
a) Alternaria porri
b) Stemphylium vesicarium
c) Botrytis allii
d) Peronospora destructor
Answer: a) Alternaria porri
Explanation:Causes purplish lesions with concentric rings. Favored by high humidity, moderate temperatures.
- “Damping off disease” is caused by:
a) Pythium
b) Rhizoctonia
c) Fusarium
d) All of above
Answer: d) All of above
Explanation:Pre-emergence (seed rot) and post-emergence (stem rot) damping off in seedlings.
- “Club root of crucifers” is caused by:
a) Plasmodiophora brassicae
b) Albugo candida
c) Peronospora parasitica
d) Alternaria brassicicola
Answer: a) Plasmodiophora brassicae
Explanation:Protist pathogen causing gall formation on roots. Survives long as resting spores in soil.
