Host-Pathogen Interaction Overview
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Questions and Answers

What structure do fungal hyphae form on the host surface in Rhizoctonia solani to initiate infection?

  • Appresorium
  • Ganglion
  • Infection cushion (correct)
  • Rhizomorph

Which of the following is NOT a natural opening through which pathogens may penetrate a host?

  • Lenticels
  • Stomata
  • Wounds (correct)
  • Hydathodes

What is indicated about some germ tubes in relation to light?

  • They are neutral to light.
  • They become dormant in light.
  • They are positively phototropic.
  • They are negatively phototropic. (correct)

What distinguishes a pathogen from a parasite?

<p>Pathogens are capable of causing disease in a specific host. (D)</p> Signup and view all the answers

What is the primary process by which pathogens enter a host through natural openings?

<p>Indirect penetration (B)</p> Signup and view all the answers

What is the role of inoculum in host pathogen interaction?

<p>Inoculum is the part of the pathogen that comes into contact with the host to initiate infection. (C)</p> Signup and view all the answers

What role do environmental factors play in the growth of germ tubes and formation of appresoria?

<p>They influence both growth and formation. (C)</p> Signup and view all the answers

What is required for stomatal penetration by pathogens?

<p>A film of water (C)</p> Signup and view all the answers

Which of the following is NOT a condition for successful infection by a pathogen?

<p>The host must be resistant to disease. (D)</p> Signup and view all the answers

What is the significance of the appresorium formation in fungal pathogens?

<p>It initiates the colonization of host tissue. (B)</p> Signup and view all the answers

How is inoculum potential defined?

<p>The number of infecting particles present in the environment of the infected host. (C)</p> Signup and view all the answers

Which of the following fungal structures is associated with Armillaria mellea?

<p>Rhizomorphs (A)</p> Signup and view all the answers

What factor is considered the most important in determining successful infection?

<p>Inoculum potential. (B)</p> Signup and view all the answers

What is the significance of environmental conditions in the context of pathogen infection?

<p>Conditions can influence pathogen aggressiveness and reproduction. (B)</p> Signup and view all the answers

Which type of inoculum is classified as dormant but can later cause infection?

<p>Sclerotia. (C)</p> Signup and view all the answers

Which statement best describes host pathogen interaction?

<p>It begins as soon as the inoculum contacts the host. (D)</p> Signup and view all the answers

What process is referred to as the initial step of pathogen invasion?

<p>Direct penetration (C)</p> Signup and view all the answers

Which type of pathogen grows only on the surface of the host and uses haustoria for penetration?

<p>Ectoparasite (B)</p> Signup and view all the answers

Which of the following pathogens causes systemic infections in plants?

<p>Fusarium (C)</p> Signup and view all the answers

What characterizes endoparasites with external mycelium?

<p>They produce mycelium both inside and outside the host. (B)</p> Signup and view all the answers

What is the primary function of the haustoria produced by some pathogens?

<p>To extract nutrients from the host cells (A)</p> Signup and view all the answers

Which pathogens are known to colonize within the parenchymatous tissues of plants?

<p>Phytophthora and Ustilago (D)</p> Signup and view all the answers

Which type of parasite specifically invades the host's vascular tissues?

<p>Vascular parasite (B)</p> Signup and view all the answers

The term 'invasion' in the context of plant pathology refers to what process?

<p>The successful establishment and spread of the pathogen within the host (D)</p> Signup and view all the answers

What does the term inoculum potential refer to?

<p>The mass or number of propagules available for infection. (C)</p> Signup and view all the answers

Which of the following factors does NOT influence pathogenesis?

<p>Time of day (A)</p> Signup and view all the answers

Which stage of pathogenesis occurs before the pathogen penetrates the host?

<p>Prepenetration (C)</p> Signup and view all the answers

What conclusion did Withelm (1966) make regarding inoculum potential?

<p>It should solely indicate the density of inoculum. (D)</p> Signup and view all the answers

What is meant by the term 'disease potential'?

<p>The aggregate effect of host and environmental factors on disease. (D)</p> Signup and view all the answers

During which stage do viruses and bacteria often bypass the typical prepenetration activity?

<p>When using vectors or natural openings. (A)</p> Signup and view all the answers

Which of the following is included in the study of pathogenesis?

<p>Aggressiveness of the pathogen (B)</p> Signup and view all the answers

In the context of plant pathogenesis, which external factor is NOT indicated as influential?

<p>Genetic mutations in pathogens (D)</p> Signup and view all the answers

Which fungal structures can exist in a dormant state?

<p>Sclerotia (D)</p> Signup and view all the answers

What is the first stage of the prepenetration process in fungal pathogens?

<p>Germination of spores (B)</p> Signup and view all the answers

Which environmental factor is known to stimulate spore germination?

<p>Optimal moisture (C)</p> Signup and view all the answers

How do thick-walled spores differ from thin-walled spores during germination?

<p>Thick-walled spores contain more food material (C)</p> Signup and view all the answers

What is the role of root exudates in spore germination?

<p>They stimulate germination of some spores (D)</p> Signup and view all the answers

Which of the following propagules undergoes germination without a resting period?

<p>Thin-walled spores (C)</p> Signup and view all the answers

What happens to the germ tube after it elongates over the host surface?

<p>It enters directly into the host or proliferates into hyphae (A)</p> Signup and view all the answers

Which type of chemical is known to inhibit the germination of fungal spores?

<p>Malic acid secreted from plant leaves (C)</p> Signup and view all the answers

What type of barrier primarily prevents viruses from directly penetrating the host cells?

<p>Morphological barriers like cutin and cellulose (B)</p> Signup and view all the answers

How do fungi penetrate the cuticularized epidermal wall?

<p>By exerting physical force and chemical actions (A)</p> Signup and view all the answers

What actions do bacterial pathogens primarily employ to penetrate host barriers?

<p>Exhibiting chemical action without physical force (A)</p> Signup and view all the answers

In which part of the plant does direct penetration by pathogens typically NOT occur?

<p>Thick bark on mature stems (A)</p> Signup and view all the answers

What is the primary role of the cutin and cuticular waxes in plant defense?

<p>Act as a protective morphological barrier (D)</p> Signup and view all the answers

Which of these pathogens is associated with a direct penetration strategy through physical force?

<p>Nematodes and fungi (C)</p> Signup and view all the answers

What occurs after a fungal pathogen's infection peg pierces the epidermis?

<p>The infection hypha contacts pectic substances and cellulose. (C)</p> Signup and view all the answers

Which of the following is true regarding the barriers that pathogens encounter when penetrating plant tissues?

<p>Viruses lack the means to penetrate due to strong barriers. (D)</p> Signup and view all the answers

Flashcards

Host-Pathogen Interaction

The relationship between a plant (or other host) and a pathogen (disease-causing organism), leading to potential disease development.

Parasite

An organism that lives in or on another organism (host) and benefits from it, potentially causing harm.

Pathogen

An organism that causes disease in a host, deriving essential resources.

Inoculum

The portion of a pathogen that contacts the host to initiate infection; the infectious material like spores, etc.

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Inoculum Potential

The number of infectious particles in the environment of the host, a key factor in infection success.

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Susceptibility

The tendency of a host to develop disease.

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Disease Proneness

A host's predisposition to infections.

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Pathogenesis

The development of disease, from the initial infection.

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Inoculum Potential

Energy of pathogen available for infection at host surface; determined by inoculum density, nutrients, environment, genetics, plant exudates, and residues.

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Disease Potential

Factors beyond inoculum density affecting disease development, including host susceptibility, environment, nutrients, etc.

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Pathogenesis

Sequence of disease development from pathogen-host contact to complete symptoms.

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Prepenetration Stage

Interaction of host and pathogen before pathogen enters the host.

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Penetration

Pathogen's entry into the host.

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Post-penetration Stage

Events after pathogen has entered the host.

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Inoculum Density

The mass or number of pathogen propagules on the host surface.

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Host Susceptibility

Plant's tendency to develop disease.

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Fungal Spore Germination

The process where fungal spores change from a resting state to an active growth stage, requiring energy.

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Spore Types

Different forms of fungal propagules, including conidia, sporangiospores, and more. Different types of spores have different traits.

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Germ Tube Growth

The elongation of a tube from a germinating spore to enter or further grow on a host surface to generate hyphae

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Environmental Factors (Spore Germination)

Moisture, temperature, light, chemicals, and biological factors which either encourage or hinder spore germination.

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Host exudates

Chemicals released by the host plant which can stimulate or inhibit spore germination.

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Prepenetration Stage

The steps before a fungal pathogen penetrates the host, including spore germination and germ tube growth.

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Active Mycelium

Fungal growth stage where the fungus is actively growing, searching for a host or nutrients.

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Dormant Mycelium

Fungal growth that's not actively growing but is capable of growth under the right conditions.

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Infection Cushion (Rhizoctonia)

A structure formed by fungal hyphae on the host surface, increasing the chances of infection by building strength.

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Rhizomorphs (Armillaria)

Rope-like strands formed by fungal hyphae, used by the fungus for infection.

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Appressorium

A specialized structure formed at the tip of a germ tube to penetrate the host.

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Indirect Penetration

Entry of a pathogen through natural openings (stomata, lenticels) or artificial ones (wounds, insect punctures).

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Stomata

Minute pores on leaves and green stems, often used for pathogen entry.

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Germ Tube

Elongated tube growing from a spore to reach and penetrate the host.

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Environmental Influence (germ tube)

Environmental factors (light, chemicals, moisture) play a role in germ tube growth and appressorium formation.

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Penetration (of a host)

The act of a pathogen entering into a host, whether directly or indirectly.

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Direct Penetration

Pathogens directly entering plant tissues through the cuticle or uncuticularized surfaces.

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Cuticle Barriers

Protective layers (cutin, waxes) on plants that pathogens must overcome for direct entry.

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Penetration Hypha

Specialized fungal structure that pushes against the plant wall, creating an opening for infection.

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Infection Peg

The narrow tip of the hypha that pierces through the weakened plant cell wall.

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Chemical Barriers

Presence of toxins or lack of nutrients at the host surface to hinder pathogen entry.

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Biological Barriers

Naturally occurring organisms (like microbes) that compete with pathogens for space and resources.

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Morphological Barriers

Physical plant structures (cuticle, cell walls) that hinder pathogen entry.

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Indirect Penetration

Pathogen entry through wounds or with the help of vectors (insects, etc.)

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Direct Penetration

Initial mechanical then chemical process of a pathogen entering the host cell wall, softening it to facilitate entry.

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Ectoparasite (Ectotrophic)

Pathogen grows on the surface of the host plant, only sending haustoria into epidermal cells.

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Endoparasite with external mycelium

Pathogen grows inside the host and produces external mycelium penetrating the host plant repeatedly.

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Subcuticular Parasite

Pathogen colonizes the space between the cuticle and the outer epidermal wall

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Parasites in Parenchyma

Pathogens colonize different tissues within the cortex, pith, and mesophyll.

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Vascular Tissue Parasites

Pathogens that target xylem vessels and tracheids, causing vascular wilts.

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Post-Penetration/Invasion

The stage after successful penetration; pathogen establishing the infection within the host.

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Local vs. Systemic Infection

Some pathogens cause infections confined to a specific area (local), while others spread throughout the plant (systemic).

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Study Notes

Host Pathogen Interaction

  • Pathogens are parasites, but not all parasites are pathogens.
  • A parasite relies on a host for vital resources.
  • A pathogen causes disease.
  • Host-parasite interactions, often termed host-pathogen interactions, describe the disease interaction.

Inoculum

  • Infection begins when the inoculum (infectious agent) contacts the host.
  • Inoculum includes virus particles, bacterial cells, actively growing fungi, dormant fungi, sclerotia, and spores.
  • Successful infection requires a susceptible host, a strong pathogen, and favorable environmental factors.
  • Host susceptibility and disease proneness are considered.
  • The pathogen must be aggressive and capable of rapid multiplication.
  • Favorable environmental conditions are needed for the pathogen, but not the host.

Pathogenesis

  • Pathogenesis describes the disease progression from initial contact to disease symptoms.
  • Genetic host responses and environmental factors (temperature, humidity, etc.) influence pathogenesis.
  • Host vigor, age, and nutritional status are important.
  • The aggressiveness of the pathogen (inoculum potential) and disease potential play a part.
  • Pathogenesis involves prepenetration, penetration, and post-penetration.

Prepenetration

  • This phase includes interactions before actual pathogen entry.
  • Key processes include spore germination, germ tube growth, and appressorium formation in fungi.
  • Environmental conditions (moisture, temperature, light) affect spore germination.

Penetration

  • This stage involves the pathogen's entry into the host.
  • Penetration can occur through natural openings (stomata, lenticels) or artificial ones (wounds, insect punctures).
  • Direct penetration is through cuticles, epidermis.
  • Indirect penetration occurs through natural openings.

Post Penetration (Invasion)

  • Successful penetration leads to invasion.
  • The pathogen must overcome internal host barriers to establish infection.
  • Various factors affect how the pathogen invades and multiplies within the host.

Host Pathogen Categories

  • Ectoparasites/Ectotrophic: The pathogen grows on the host surface and extends haustoria into host cells. Example: Powdery mildew.
  • Endoparasites with external mycelium: Pathogen lives inside the host but produces external mycelium. Example: Corticium solani.
  • Subcuticular parasites: Pathogen grows between the cuticle and the outer host wall. Example: Venturia inaequalis.
  • Parasites in parenchyma: Pathogen invades and grows within the host's parenchyma (mesophyll, cortex). Example: Albugo.
  • Vascular parasites: Pathogens infect the vascular tissues (xylem, tracheids). Example: Fusarium.
  • Endobiotic: Pathogens grow and multiply within host cells. Example: Synchytrium endobioticum.
  • Systemic infections: Pathogens infect the entire plant. Example: Smuts.

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Host Pathogen Interaction PDF

Description

Explore the critical concepts of host-pathogen interactions, including the roles of pathogens and inoculum in disease progression. This quiz delves into how different factors contribute to the success of infections and the pathogenesis process. Ideal for students studying microbiology and disease mechanisms.

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