Plant Pathology: Principles, Symptoms and Diagnosis MCQs 2026

The arrival or transfer of inoculum to an infection court is called:

1. A Sporulation ✓
2. B Chlorosis ✓
3. C Roguing ✓
4. D Inoculation ✓

The disease triangle in plant pathology consists of:

1. A Susceptible host, virulent pathogen and favorable environment ✓
2. B Seed, fertilizer and irrigation ✓
3. C Soil, tractor and rainfall ✓
4. D Root, stem and leaf only ✓

Koch postulates are used mainly to:

1. A Calculate fertilizer dose ✓
2. B Establish the causal relationship between a pathogen and a disease ✓
3. C Measure crop market price ✓
4. D Classify soil texture ✓

In diagnosis, a symptom is best defined as:

1. A A reproductive structure of the pathogen only ✓
2. B A pesticide label instruction ✓
3. C The visible response of the host plant to disease ✓
4. D A soil nutrient analysis result ✓

Death of plant tissue resulting in brown or black dead areas is called:

1. A Chlorosis ✓
2. B Etiolation ✓
3. C Hypertrophy ✓
4. D Necrosis ✓

Yellowing of normally green plant tissue due to loss or failure of chlorophyll is:

1. A Chlorosis ✓
2. B Scab ✓
3. C Mummification ✓
4. D Gummosis ✓

Wilt symptoms are commonly associated with:

1. A Excess seed dormancy only ✓
2. B Interference with water movement in the plant ✓
3. C Improved xylem flow ✓
4. D Absence of transpiration in all cases ✓

Damping-off is a disease that primarily affects:

1. A Mature dry grain in storage only ✓
2. B Harvested cotton lint only ✓
3. C Seeds and young seedlings ✓
4. D Woody timber after sawing ✓

Primary inoculum is the inoculum that:

1. A Is always produced only by insects ✓
2. B Appears only after harvest ✓
3. C Cannot survive between seasons ✓
4. D Initiates the first infections in a crop season ✓

Secondary inoculum is most important in diseases that:

1. A Spread repeatedly during the same growing season ✓
2. B Have no pathogen involved ✓
3. C Occur only in seed storage without infection ✓
4. D Are caused only by nutrient deficiency ✓

An obligate parasite is a pathogen that:

1. A Can grow only on sterilized metal ✓
2. B Requires living host tissue for growth and reproduction ✓
3. C Never infects plants ✓
4. D Lives only as a mineral particle ✓

A facultative saprophyte is best described as an organism that:

1. A Cannot survive outside distilled water ✓
2. B Requires only living tissue and never survives on dead matter ✓
3. C Usually parasitizes living plants but can also live on dead organic matter ✓
4. D Is always a virus ✓

A polycyclic plant disease is characterized by:

1. A Only one infection cycle for all time ✓
2. B Absence of inoculum ✓
3. C A purely genetic disorder without pathogen ✓
4. D Several infection cycles during one growing season ✓

A monocyclic disease usually has:

1. A One main infection cycle in a growing season ✓
2. B Unlimited cycles every day under all conditions ✓
3. C No survival stage ✓
4. D Only insect damage without infection ✓

Rust diseases commonly show which visible pathogen sign?

1. A Clear sugary honeydew only ✓
2. B Powdery pustules of spores on plant surfaces ✓
3. C Hard insect scales ✓
4. D Root nodules containing Rhizobium only ✓

Powdery mildew is commonly recognized by:

1. A Black watery bacterial ooze only ✓
2. B Complete absence of visible growth ✓
3. C White powdery fungal growth on leaf or stem surfaces ✓
4. D Root knots only ✓

Smut diseases often produce:

1. A Clear viral inclusion bodies visible to naked eye ✓
2. B Only yellow nutrient deficiency bands ✓
3. C Only nematode cysts on leaves ✓
4. D Black masses of powdery spores replacing plant organs ✓

Downy mildew of leaves often produces:

1. A Downy fungal growth mainly on the lower leaf surface ✓
2. B Metallic cankers on fruit only ✓
3. C No sporulation under humid conditions ✓
4. D Only root galls ✓

Bacterial ooze from cut infected tissue is considered:

1. A A symptom caused by host chlorophyll loss only ✓
2. B A sign of a bacterial pathogen ✓
3. C A soil texture class ✓
4. D A maturity index ✓

For many viral plant diseases, reliable diagnosis commonly requires symptoms plus:

1. A Only smelling the soil ✓
2. B Only measuring fruit sweetness ✓
3. C Serological or molecular testing such as ELISA or PCR ✓
4. D Only counting leaves ✓

Root-knot nematodes are best recognized by:

1. A Powdery spores on leaves ✓
2. B Blue mold on canned food ✓
3. C White rust pustules only on stems ✓
4. D Galls or knots on roots ✓

A typical internal diagnostic feature of Fusarium wilt is:

1. A Brown discoloration of vascular tissue ✓
2. B Silvering of fruit skin only ✓
3. C Black sori replacing grain only ✓
4. D Honeydew on leaf surface ✓

Late blight caused by Phytophthora infestans is favored by:

1. A Hot dry desert winds only ✓
2. B Cool, moist conditions ✓
3. C Complete absence of leaf wetness ✓
4. D Sterile dry seed storage ✓

Alternaria leaf spots are often described as:

1. A Uniform genetic variegation only ✓
2. B Root nodules with nitrogen fixation ✓
3. C Concentric target-like lesions ✓
4. D Clear insect eggs only ✓

Powdery mildew often differs from many other foliar fungi because it can develop with:

1. A Permanent flooding only ✓
2. B No living host tissue ✓
3. C Complete darkness and no host ✓
4. D High humidity without free water on the leaf surface ✓

Disease incidence measures:

1. A The proportion or percentage of plant units that are diseased ✓
2. B The amount of fertilizer applied ✓
3. C The depth of irrigation water only ✓
4. D The price of seed per kilogram ✓

Disease severity measures:

1. A Only the number of healthy plants ✓
2. B The amount of plant tissue or area affected by disease ✓
3. C Only pathogen name spelling ✓
4. D Only soil pH ✓

Any part of a pathogen that can initiate infection is called:

1. A Stomata ✓
2. B Mulch ✓
3. C Inoculum ✓
4. D Compost maturity ✓

Penetration in the disease cycle means:

1. A Entry of the pathogen into host tissue ✓
2. B Removal of diseased plants from the field ✓
3. C Harvesting seed at maturity ✓
4. D Drying grain below safe moisture ✓

The incubation period is the time between:

1. A Sowing and fertilizer purchase ✓
2. B Infection and appearance of symptoms ✓
3. C Harvest and marketing only ✓
4. D Flowering and seed cleaning only ✓

A latent infection is one in which the pathogen:

1. A Has no host interaction at all ✓
2. B Is always killed immediately ✓
3. C Is present but symptoms are not yet visible ✓
4. D Exists only as fertilizer impurity ✓

The hypersensitive response is:

1. A A method of seed grading ✓
2. B A bacterial spore type ✓
3. C A symptom of nitrogen deficiency only ✓
4. D Rapid localized host cell death that can restrict pathogen spread ✓

Systemic acquired resistance refers to:

1. A Broad resistance induced throughout the plant after localized activation ✓
2. B Resistance caused only by adding more irrigation ✓
3. C A market grading standard ✓
4. D The loss of all defense responses ✓

Protectant fungicides are generally most effective when applied:

1. A Only after all plants are dead ✓
2. B Before infection occurs ✓
3. C Only after harvest in every case ✓
4. D Only to the soil surface for viral diseases ✓

Systemic fungicides are distinguished by their ability to:

1. A Act only as inert dust ✓
2. B Kill weeds but not fungi ✓
3. C Move within plant tissues to some extent ✓
4. D Increase pathogen resistance intentionally ✓

Fungicide resistance management commonly recommends:

1. A Repeated use of one site-specific fungicide only ✓
2. B Applying lower than label rates always ✓
3. C Ignoring disease monitoring ✓
4. D Rotating or mixing products with different modes of action ✓

Seed treatment is mainly used to:

1. A Protect seed and young seedlings from seedborne or soilborne pathogens ✓
2. B Increase weed seed contamination ✓
3. C Replace all field scouting ✓
4. D Convert all pathogens to beneficial microbes ✓

Crop rotation helps manage many soilborne diseases because it:

1. A Increases continuous host availability ✓
2. B Reduces survival and buildup of host-specific inoculum ✓
3. C Eliminates all airborne spores instantly ✓
4. D Works only in hydroponics ✓

Roguing means:

1. A Applying fertilizer in bands ✓
2. B Drying seed in sunlight only ✓
3. C Removing diseased or off-type plants from a field ✓
4. D Measuring leaf area index ✓

Field sanitation in disease management includes:

1. A Leaving all diseased residues on the surface ✓
2. B Planting only susceptible cultivars ✓
3. C Encouraging alternate hosts near the crop ✓
4. D Removing infected debris, volunteer hosts and contaminated materials ✓

Plant quarantine aims to:

1. A Prevent introduction and spread of exotic pests and pathogens ✓
2. B Increase movement of infected planting material ✓
3. C Replace laboratory diagnosis ✓
4. D Measure pesticide residue only ✓

ELISA is commonly used in plant disease diagnosis to detect:

1. A Soil bulk density only ✓
2. B Pathogen antigens using specific antibodies ✓
3. C Leaf area by photography only ✓
4. D Fungicide spray volume only ✓

PCR assists diagnosis by:

1. A Increasing pathogen virulence in the field ✓
2. B Measuring only crop yield ✓
3. C Amplifying specific pathogen nucleic acid sequences ✓
4. D Replacing all sampling needs ✓

Microscopic examination is especially useful for:

1. A Determining market price ✓
2. B Testing tractor horsepower ✓
3. C Measuring irrigation canal length ✓
4. D Observing spores, hyphae, bacterial streaming or other diagnostic structures ✓

A moist chamber is used in diagnosis to:

1. A Encourage sporulation from diseased tissue ✓
2. B Dry the sample as fast as possible ✓
3. C Sterilize all pathogens instantly ✓
4. D Measure fertilizer concentration ✓

Isolation into pure culture is important because it:

1. A Prevents any further observation ✓
2. B Helps identify culturable pathogens and supports pathogenicity testing ✓
3. C Is used only for nutrient deficiency ✓
4. D Always proves viral infection ✓

Selective media are used to:

1. A Increase all contaminants equally ✓
2. B Replace host symptoms completely ✓
3. C Favor growth of a target pathogen while suppressing contaminants ✓
4. D Make viruses visible to naked eye ✓

Gram staining separates bacteria mainly on the basis of:

1. A Leaf color intensity ✓
2. B Root depth ✓
3. C Spore size in fungi only ✓
4. D Cell wall staining response ✓

Integrated disease management is best described as:

1. A Combining resistant varieties, cultural, biological and chemical methods wisely ✓
2. B Using only one pesticide repeatedly ✓
3. C Ignoring disease diagnosis ✓
4. D Planting only susceptible hosts ✓

Disease forecasting systems are based mainly on:

1. A Seed color alone ✓
2. B Weather data, crop stage and pathogen biology ✓
3. C Market demand only ✓
4. D Tractor speed only ✓

Anthracnose diseases often show

1. A only powdery mildew white mats ✓
2. B sunken necrotic lesions on fruits/leaves ✓
3. C only smut of wheat heads ✓
4. D only rust uredinia exclusively ✓

A disease epidemic is favored when

1. A host, pathogen and environment align over large area/time ✓
2. B pathogen is absent ✓
3. C host is fully resistant everywhere ✓
4. D weather never favors infection ✓

Seed-borne diseases are managed partly by

1. A ignoring seed health ✓
2. B healthy seed and seed treatment ✓
3. C using only diseased seed ✓
4. D banning all certified seed ✓

Crop rotation helps against some soil-borne diseases by

1. A increasing the same host every season ✓
2. B breaking pathogen life cycles on non-host crops ✓
3. C guaranteeing more inoculum ✓
4. D eliminating all beneficial microbes always ✓

Resistant varieties are a cornerstone of

1. A increasing pesticide dependency always ✓
2. B eliminating breeding programs ✓
3. C ignoring genetics ✓
4. D economical and environmentally sound disease management ✓

Fungicides are chemicals used to

1. A kill only insect eggs always ✓
2. B fertilize nitrogen deficiency ✓
3. C manage fungal (and some oomycete) diseases ✓
4. D raise soil pH only ✓

Bordeaux mixture is a classic

1. A nitrogen fertilizer ✓
2. B herbicide for grasses only ✓
3. C copper-based fungicide/bactericide preparation ✓
4. D insect growth regulator only ✓

Quarantine in plant pathology aims to

1. A prevent introduction and spread of dangerous pathogens ✓
2. B maximize free movement of all pests ✓
3. C ignore SPS rules ✓
4. D import only diseased plants ✓

Symptoms differ from signs in that symptoms are

1. A identical terms always ✓
2. B only soil colors ✓
3. C plant's reaction (spots, wilt, mosaic) while signs are pathogen structures ✓
4. D only weather reports ✓

Mosaic symptoms on leaves often suggest

1. A only rust pustules ✓
2. B viral infection ✓
3. C only smut balls ✓
4. D only bacterial streaming always ✓

Hyperplasia and hypertrophy refer to

1. A abnormal cell division and cell enlargement in diseased tissues ✓
2. B normal photosynthesis rates ✓
3. C standard seed germination only ✓
4. D tractor horsepower ratings ✓

Incubation period is the time between

1. A harvest and marketing only ✓
2. B infection and appearance of symptoms ✓
3. C ploughing and sowing only ✓
4. D ETL and pesticide spray only ✓

Primary inoculum starts

1. A only secondary spread within canopy ✓
2. B the first infections in a season/cycle ✓
3. C only postharvest packing ✓
4. D only cold storage condensation ✓

Secondary inoculum spreads disease

1. A only across geological eras ✓
2. B only via tractor manuals ✓
3. C during the same season from infected to healthy plants ✓
4. D only in seed catalogs ✓

Integrated disease management combines

1. A only calendar spraying forever ✓
2. B only one pesticide forever ✓
3. C host resistance, cultural, biological and chemical tools as needed ✓
4. D ignoring scouting ✓

Hot-water seed treatment is sometimes used against

1. A certain seed-borne pathogens (e.g., some smuts) ✓
2. B adult whitefly swarms in fields ✓
3. C soil salinity crystals ✓
4. D canal silt load ✓

Soil solarization uses

1. A night frost only ✓
2. B diesel burners in roots ✓
3. C ocean tides in orchards ✓
4. D solar heat under clear plastic to reduce soil pathogens/weeds ✓

Mycotoxins are

1. A toxic metabolites of certain fungi in infected/stored produce ✓
2. B plant hormones only ✓
3. C insect pheromones only ✓
4. D nitrogen fertilizers ✓

Ergot of cereals/grasses produces

1. A sclerotia that can be toxic if consumed ✓
2. B only beneficial yogurt cultures ✓
3. C only rhizobium nodules ✓
4. D only mycorrhizal vesicles always ✓

Black tip of mango is often associated with

1. A physiological disorder linked to pollution/boron issues in some regions ✓
2. B only stem rust of wheat ✓
3. C only rice blast fungus ✓
4. D only potato cyst nematode ✓

Dieback in trees often indicates

1. A healthy vigorous flush only ✓
2. B increased fruit set always ✓
3. C progressive death of twigs from tips due to biotic/abiotic causes ✓
4. D improved root nodulation ✓

A canker on woody plants is

1. A a localized necrotic lesion on stem/branch ✓
2. B a beneficial graft union ✓
3. C a type of drip emitter ✓
4. D a fertilizer grade ✓

Soft rot of vegetables is commonly caused by

1. A bacteria that macerate tissues ✓
2. B only rust fungi of wheat ✓
3. C only powdery mildew ✓
4. D only stem borers ✓

Disease forecasting helps farmers by

1. A eliminating all weather data needs ✓
2. B guaranteeing zero disease always ✓
3. C replacing resistant varieties forever ✓
4. D timing management when risk is high ✓

The best long-term strategy against many airborne rusts includes

1. A planting only highly susceptible landraces ✓
2. B never scouting fields ✓
3. C relying on a single failed chemical forever ✓
4. D resistant cultivars and monitoring ✓

Plant pathology is the study of

1. A only tractor engines ✓
2. B plant diseases and their management ✓
3. C only dairy lactation ✓
4. D only canal hydraulics ✓

A plant pathogen is

1. A always a beneficial pollinator ✓
2. B a soil texture class ✓
3. C an irrigation schedule ✓
4. D an organism capable of causing disease in plants ✓

The disease triangle consists of

1. A only fertilizer bag, tractor and diesel ✓
2. B seed, flower and fruit only ✓
3. C ETL, IPM and pesticide brand only ✓
4. D susceptible host, virulent pathogen and favorable environment ✓

A biotroph pathogen

1. A only feeds on dead organic matter ✓
2. B never infects plants ✓
3. C is always a virus-free saprophyte ✓
4. D obtains nutrients from living host tissues ✓

A necrotroph typically

1. A only lives as a mutualist mycorrhiza ✓
2. B never causes lesions ✓
3. C kills host tissue and feeds on dead matter ✓
4. D is identical to all viruses ✓

Fungi cause many crop diseases; fungal structures for survival often include

1. A only animal antibodies ✓
2. B spores and sometimes sclerotia ✓
3. C only tractor filters ✓
4. D only fish scales ✓

Bacteria that cause plant disease often enter through

1. A intact cuticle with zero openings always ✓
2. B only seed coat of mango exclusively ✓
3. C wounds and natural openings (stomata, hydathodes) ✓
4. D PTO shafts of tractors ✓

Plant viruses are typically transmitted by

1. A insect vectors, sap, seed or vegetative propagation ✓
2. B only canal water velocity meters ✓
3. C only soil pH meters ✓
4. D only ploughshares without contact ✓

Nematodes damaging crops are often

1. A beneficial honey bees ✓
2. B microscopic roundworms attacking roots or other tissues ✓
3. C large vertebrate grazers only ✓
4. D fungal rust spores ✓

Rust diseases of cereals are caused by

1. A only bacteria of citrus canker ✓
2. B only nematodes of potato cyst ✓
3. C fungal pathogens (Puccinia and related) ✓
4. D only viruses of tobacco mosaic ✓

Stem rust, leaf rust and stripe rust of wheat are

1. A bacterial soft rots only ✓
2. B viral mosaics only ✓
3. C nematode galls only ✓
4. D important fungal rust diseases ✓

Loose smut of wheat is characterized by

1. A replacement of grains by black spore masses ✓
2. B only leaf yellow mosaic without smut ✓
3. C bacterial ooze on citrus ✓
4. D whitefly honeydew only ✓

Karnal bunt of wheat is a

1. A viral disease of banana only ✓
2. B bacterial wilt of tomato only ✓
3. C insect pest of cotton only ✓
4. D fungal disease affecting grains ✓

Downy mildew diseases are associated with

1. A only powdery white always identical to rust ✓
2. B only smut balls ✓
3. C only viral inclusions ✓
4. D oomycete pathogens under humid conditions ✓

Powdery mildew appears as

1. A black smut replacing all grains always ✓
2. B white powdery growth on leaf surfaces ✓
3. C bacterial streaming only ✓
4. D nematode cysts only ✓

Blast disease is especially important on

1. A date palm only ✓
2. B apple only ✓
3. C rice ✓
4. D cotton lint only ✓

Cotton leaf curl disease is associated with

1. A only stem rust fungus ✓
2. B only loose smut ✓
3. C only root-knot nematode alone ✓
4. D a virus complex transmitted by whitefly ✓

Red rot of sugarcane is a

1. A viral mosaic of tobacco only ✓
2. B fungal disease of stalks ✓
3. C bacterial citrus canker only ✓
4. D insect bollworm damage only ✓

Smut diseases generally produce

1. A only green mosaic without spores ✓
2. B black powdery spore masses in affected parts ✓
3. C only bacterial ooze threads ✓
4. D only nematode eggsacs ✓

Damping-off of seedlings is often caused by

1. A only adult bollworms ✓
2. B only fruit flies ✓
3. C soil-borne fungi/oomycetes in wet conditions ✓
4. D only stem borers of rice ✓

Wilt diseases (e.g., Fusarium wilt) typically

1. A only spot leaves without systemic effect ✓
2. B increase root nodules beneficially ✓
3. C block vascular tissues and cause wilting ✓
4. D are always viral mosaics ✓

Citrus canker is a

1. A bacterial disease ✓
2. B fungal rust ✓
3. C viral leaf curl only ✓
4. D nematode cyst disease ✓

Early blight of potato/tomato typically shows

1. A only smut of maize ✓
2. B target-spot leaf lesions (Alternaria) ✓
3. C only rust pustules of wheat ✓
4. D only root knots of tomato exclusively ✓