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Pathology Flashcards

(103 cards)

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1
Q

What is Plant Pathology?

A

Plant Pathology (Phytopathology) deals with the cause, etiology, resulting losses and control of plant diseases.

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2
Q

What are the objectives of Plant Pathology?

A

The objectives include studying the living entities that cause diseases, non-living entities causing disorders, mechanisms of disease production, interactions between agents and host plants, and methods of disease prevention and management.

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3
Q

What is the scope of Plant Pathology?

A

It comprises knowledge and technologies from Botany, Plant Anatomy, Plant Physiology, Mycology, Bacteriology, Virology, Nematology, Genetics, Molecular Biology, and more.

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4
Q

How is a plant disease defined?

A

A plant disease is a malfunctioning process that interferes with normal physiological activities, producing undesirable outcomes.

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5
Q

What are the types of physiological responses in plant diseases?

A

Responses include disintegration of tissues, effects on growth, nutrient uptake, respiration, photosynthesis, translation, transcription, and reproduction.

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6
Q

What are the two main types of plant diseases?

A

Plant diseases can be infectious (caused by pathogens) or non-infectious (caused by environmental factors).

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7
Q

What are infectious diseases?

A

Infectious diseases are caused by biotic agents termed pathogens, including fungi, bacteria, mycoplasma, spiroplasma, viruses, viroids, nematodes, and parasitic plants.

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8
Q

What are non-infectious diseases?

A

Non-infectious diseases are caused by environmental factors such as temperature extremes, moisture extremes, air pollution, nutrient deficiencies, and soil pH.

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9
Q

What are some examples of abiotic causal agents of plant disease?

A

Examples include temperature extremes, moisture extremes, nutrient extremes, light extremes, soil pH extremes, and air pollution.

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10
Q

What are the effects of pathogens on plants?

A

Pathogens cause morphological and physiological changes, including structural changes like overgrowth and physiological changes affecting growth and nutrient uptake.

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11
Q

What are the five groups of pathogens?

A

The five groups are fungi, bacteria and phytoplasmas, viruses, nematodes, and parasitic higher plants.

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12
Q

What are fungi?

A

Fungi are microscopic organisms that can be saprophytic or pathogenic, causing many plant diseases.

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13
Q

What are some common bacterial diseases?

A

Common bacterial diseases include crown gall, fire blight, soft rot, and ring rot.

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14
Q

How do viruses affect plants?

A

Viruses cause diseases that can be transmitted by insects and lead to symptoms like mosaics and leaf curls.

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15
Q

What are nematodes?

A

Nematodes are microscopic roundworms that can be saprophytic or parasitic, causing diseases in plants.

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16
Q

What are organisms that transmit viruses called?

A

Vectors.

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17
Q

What are the two main types of symptoms caused by viruses?

A

Mosaics and leaf curls.

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18
Q

Can virus diseases be controlled by pesticide chemicals?

A

No, virus diseases are not controlled by pesticide chemicals.

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19
Q

What are nematodes?

A

Microscopic roundworms that live in soil and water.

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20
Q

What do most nematodes feed on?

A

The underground parts of plants (roots, tubers, bulbs, etc.).

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21
Q

How do nematodes spread?

A

Through contaminated planting material, manure, soil, water, machinery, and implements.

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22
Q

What do some nematodes serve as vectors for?

A

Plant viruses.

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23
Q

How do nematodes survive in the soil?

A

As eggs or cysts.

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24
Q

What is an example of a root knot nematode?

A

Root knot nematodes on tomato, potato, beans, and many other plants.

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25
What are parasitic higher (flowering) plants?
Plants that live as parasites on other plants, deriving nutrition from them.
26
What is the most common example of a parasitic plant?
Dodder (strangleweed, devil’s hair).
27
What does dodder do to host plants?
It entwines the stems and other parts, drawing nutrition through tube-like structures.
28
What is another example of a parasitic plant?
Dwarf mistletoe on pines.
29
What is pathogenesis?
Pathogenesis is the chain of events that lead to the development of disease in the host, from initial contact between the pathogen and its host to the completion of the syndrome.
30
What is a disease cycle?
A disease cycle is a sequence of distinct events that occur in succession, leading to the development and perpetuation of the disease and the pathogen.
31
What are the primary events in a disease cycle?
The primary events are: 1) Survival of the pathogen, 2) Dissemination of the pathogen, 3) Inoculation, 4) Penetration, 5) Host Recognition, 6) Infection, 7) Invasion, 8) Colonization, 9) Growth and reproduction of pathogens.
32
What is the survival of the pathogen?
Survival of the pathogen is the first link in the infection chain or disease cycle, involving primary and secondary inoculum.
33
What is primary inoculum?
Primary inoculum is the propagules that cause the initial infection in the crop.
34
What is secondary inoculum?
Secondary inoculum is produced from primary infections and causes secondary infections, spreading the disease.
35
How can pathogens be disseminated?
Pathogens can be disseminated through autonomous (direct) or passive (indirect) dispersal methods.
36
What is autonomous dispersal?
Autonomous dispersal occurs through soil, seed, and planting material during normal agronomic operations without external agencies.
37
What is passive dispersal?
Passive dispersal happens through animate (e.g., insects) and inanimate (e.g., air, water) agents.
38
What is inoculation?
Inoculation is the initial contact of a pathogen with a site of the plant where infection is possible.
39
What are the two types of inoculum?
The two types of inoculum are primary inoculum and secondary inoculum.
40
What is penetration?
Penetration is how pathogens enter plant surfaces, either directly, through natural openings, or through wounds.
41
What is host recognition?
Host recognition is the process by which pathogens recognize their hosts and vice versa, triggering responses in both.
42
What is infection?
Infection is the process by which pathogens establish contact with susceptible cells or tissues of the host and procure nutrients.
43
What are the factors necessary for infection?
Factors necessary for infection include moisture, temperature, stage of plant growth, disseminating agents, and duration of spore release.
44
How is Dutch elm disease spread?
Dutch elm disease is spread from tree to tree by insects.
45
What is the duration of spore release in fungi?
Some fungi produce spores during the entire rainy or dry season, while others produce only one crop of spores during a short period in early rainy season.
46
Why can fungi with a short spore release period be more easily controlled?
A fungus which produces spores for only a few days can be more easily controlled since the infection period is very short.
47
What factors influence the dispersal of fungal spores?
Dispersal of fungal spores frequently occurs daily and corresponds closely to current critical environmental events that favor infection or pathogen reproduction, e.g., moisture, temperature.
48
How do various pathogens invade hosts?
Various pathogens invade hosts in different ways and to different extents.
49
What is subcuticular colonization?
Some fungi produce mycelium that grows only in the area between the cuticle and the epidermis.
50
How do powdery mildews invade plants?
Powdery mildews produce mycelium only on the surface of the plant but send haustoria into the epidermal cells.
51
How do fungi spread within plant tissues?
Most fungi spread into all the tissues of the plant organs they infect, either by growing directly through the cells as intracellular mycelium or by growing between the cells as intercellular mycelium.
52
How do bacteria invade plant tissues?
Bacteria invade tissues intercellularly, although when parts of the cell walls dissolve, bacteria also grow intracellularly.
53
What is the growth behavior of fungi and parasitic plants in infected hosts?
They continue to grow and branch out within the infected host indefinitely until the spread of the infection is stopped or the plant is dead.
54
How do vascular wilt pathogens invade plants?
Fungi causing vascular wilts often invade plants by producing and releasing spores within the vessels.
55
How do other pathogens increase in number within infected tissues?
These pathogens invade and infect new tissues within the plant by reproducing at a rapid rate.
56
What defines plant disease?
Plant disease occurs when a pathogen induces a reaction in the body of its host plant, resulting in abnormalities.
57
What are symptoms of plant disease?
Symptoms are the plant's expression of being diseased, including blights, cankers, galls, rots, necrosis, and spots.
58
What are signs of plant disease?
Signs are the physical evidence of the pathogen, such as conks, mildew, mycelium, ooze, pycnidia, and rhizomorphs.
59
What are pathogenic symptoms?
Symptoms due to the visible pathogen or its structure may be called pathogenic symptoms.
60
What is mildew?
Mildew pathogens appear as white, brown, purple or gray patches on leaves, stem or fruits.
61
What are the symptoms of smut?
The plant parts affected by smut can be recognized by the presence of black and purplish black dust powder.
62
What is a sclerotia?
A compact, hard mass of inactive vegetative part of fungus, often black or dark brown, found on the surface of the affected part of the plant.
63
What is scab in plants?
Scab is a rough or crust-like lesion or a brown spot on the skin of the affected part.
64
What does rust look like on plants?
Rust appears as red, brown, yellow or black colored powdery deposition on some parts of plants.
65
What are blotches in plant disease?
Blotch symptoms are large irregular, discolored, superficial lesions on fruits and leaves.
66
What is exudation in plant disease?
A viscous fluid along with bacteria oozes out and forms a thin smear on the surface of the plant.
67
What are white blisters?
A transparent bulge or swelling on the upper surface of the leaf, common in mustard and other cole crops.
68
What are spots in plant disease?
Limited areas of affected parts of the plant become dead and turn brown or yellow.
69
What are physical change symptoms?
Changes in size, color, and texture observed on the whole plant or parts due to internal disorders.
70
What is chlorosis?
The phenomenon of changing green pigments of leaf into yellow due to the influence of pathogens.
71
What is overgrowth in plants?
Affected portions of the plant increase in size abnormally due to the pathogen's biochemical activity.
72
What is dwarfing in plants?
Dwarfing occurs when the inhibition of growth results in the dwarfing of any part or the whole plant.
73
What is die-back in plants?
Dying of plant parts, especially stem or branches from tip to back.
74
What is wilt in plants?
Leaves and other green parts lose turgidity and become droopy and flaccid.
75
What is necrosis?
Necrosis causes death of affected parts, with the appearance depending on the affected plant and pathogen.
76
What is blight in plants?
Blight shows a burnt appearance and results in sudden death of the whole plant or parts.
77
What is damping-off?
When the stem is attacked at the soil surface, causing the plant to topple due to weakness.
78
What are miscellaneous symptoms of plant disease?
Includes premature dropping of leaves, destruction of specific parts, or replacement of normal structures by the pathogen.
79
How do pathogens attack plants?
Pathogens attack plants by acquiring the ability to live off the substances manufactured by host plants.
80
What are the two ways pathogens attack plants?
1. Mechanical forces exerted by pathogens 2. Chemical weapons.
81
What are mechanical forces in pathogen attack?
Only some fungi, parasitic higher plants, and nematodes can exert mechanical pressure on the plant surface.
82
What are chemical weapons in pathogen attack?
Substances secreted by pathogens that are involved in the production of disease, including enzymes, toxins, growth regulators, and polysaccharides.
83
What role do enzymes play in pathogen attack?
Enzymes catalyze reactions in living cells and help pathogens derive energy from host tissue.
84
What is cutin?
The main component of the cuticle in host plants, which many fungi and a few bacteria can degrade.
85
What are pectic substances?
Main components of the middle lamella that are degraded by pectinase enzymes produced by pathogens.
86
What is cellulose?
A polysaccharide consisting of chains of glucose, degraded by cellulolytic enzymes produced by phytopathogenic organisms.
87
What is lignin?
An amorphous polymer found in the middle lamella and secondary cell wall, degraded by ligninases secreted by white rot fungi.
88
What is starch in the context of plant pathogens?
The main reserve polysaccharide in plant cells, degraded by amylases.
89
What are toxins?
Harmful or poisonous substances that affect the metabolism of the host.
90
What are pathotoxins?
Toxins that play a major role in disease production and produce symptoms characteristic of the disease.
91
What are phytotoxins?
Substances produced in the host plant due to host-pathogen interactions, suspected to play a role in disease.
92
What are vivotoxins?
Substances produced in the infected host by the pathogen that function in disease production.
93
Effect of toxins on host tissues
94
Changes in cell permeability: Toxins kill plant cells by altering the permeability of plasma membrane
thus permitting loss of water and electrolytes and also unrestricted entry of substances including toxins. Cellular transport system
95
Disruption of normal metabolic processes
96
• Increase in respiration due to disturbed salt balance
97
• Malfunctioning of enzyme system Ex: Piricularin inhibits polyphenol oxidase
98
• Uncoupling of oxidative phosphorylation
99
Interfere with the growth regulatory system of host plant Ex: Restricted development of roots induced by Fusarium moniliforme
100
GROWTH REGULATORS
101
Growth regulators are of two types: growth promoting substance and growth inhibiting substance. Auxin
gibberellins and cytokinnins are growth promoting substance whereas dormin
102
POLYSACCHARIDES
103
Fungi
bacteria and nematodes release varying amounts of mucilaginous substances that coat their bodies and provide interface between the outer surface of pathogen and its environment. In vascular wilts

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