Fungal Plant Pathogens and Infection

Fungal Plant Pathogens

• Fungi are eukaryotic microorganisms with a complex cellular construction, including a nucleus, and other organelles.
• Hyphae make up the main fungal body, these are thread-like structures forming a mycelium network.
• Fungi can reproduce through sexual, and asexual means, often by spores that are dispersed by wind, water, insects, other vectors.
• Fungi are primarily saprophytic, feeding on decaying organic matter, or parasitic, feeding on other living organisms and causing plant diseases.

Infection Process

• Inoculation occurs when spores land on a plant.
• Hyphae germination happens under environmental conditions.
• Penetration happens when hyphae enter via stomata, or wound sites.
• Colonization is when fungi spread within the plant.
• Symptom development occurs when visible damage like wilting, spots, or blights occur.
• Reproduction and dissemination: the fungus sporulates on the host plant, spores then disperse to, and infect new hosts, this completes the cycle.

Plant Pathogens

• Rust fungi result in yellow spots on wheat.
• Powdery mildew results in white fungal growth on leaves.
• Fusarium wilt is a soil-borne disease.

Adhesion and Penetration

• For both fungi and parasitic plants, adhesion is the first step to host surface penetration.
• Mucilaginous substances around fungal hyphae and radicles facilitate adhesion via intermolecular forces.
• Structures known as adhesion pads are spore formations that contact moist surfaces, cutinase, and cellulase enzymes aid in adhesion.
• The tip of the hypha then expands, forming an appressorium, a flattened, bulb-like structure improving the penetration process.

Appressorium and Cell Wall

• A penetration peg starts from the appressorium, and progresses through both the cuticle, and cell wall.
• Melanin accumulation is an important factor for fungi such as Alternaria, Colletotrichum, and Magnaporthe to penetrate and reinforce the appressorial structural integrity.
• Melanin traps solutes, helps water absorption and turgor pressure, thus pushing the penetration peg into the host.
• Host penetration effectiveness is affected by the hardness of its cell wall.
• Soft walls allow for easy penetration.
• Hard walls may resist or stop fungal entry.
• Enzymes like cellulases and cutinases help disintegrate plant defenses, thus aiding penetration.
• Certain powdery mildew fungi generate turgor pressures around 2-4 MPa.

Chemical Weapons

• Fungi use a variety of nonspecific chemical weapons to facilitate infection, and then overcome plant defenses.
• These enzymes include cellulases, hemicellulases, and pectinases, proteases, and lipases.
• Oxidative stress agents include reactive oxygen species (ROS).
• Secondary metabolites include compounds like tannins, alkaloids, and phenolic compounds that can disrupt regular cellular functions.
• Phytotoxins and mycotoxins are also included.

Fungal Life Cycles

• Fungi often possess complex, variable life cycles.
• Main types of cells: haploid with one set of chromosomes, diploid with two chromosome sets, or dikaryotic with two nuclei per cell.
• The main goal is to reproduce, survive, and spread.
• Reproduction include sexual for genetic diversity, and asexual for rapid spore spread.
• An example is wheat rust, which affects crops like wheat and barberry; spreading happens through haploid spores.

Reproduction in Fungi

• Fungi primarily reproduce through spores.
• Spores are reproductive structures can arise through asexual or sexual mechanisms.

Asexual Reproduction

• Asexual reproduction in fungi takes place through spores produced by the spore-producing structures
• Sporangium is a structure, where asexual spores grow.
• Zoospores are motile spores release from the sac with flagella.
• Conidia are formed by fragmentation of conidiophores or modified fungal filaments.
• Conidia are created from phialides forming chains at the end of conidiophores.

Sexual Reproduction

• Some fungi reproduce sexually, which involes the fusion of genetic material.
• Zygomycetes create zygospores through the fusion of two gametes.
• Chytridiomycetes use motile gametes that combine inside meiosporangia.
• Ascomycetes produce ascospores inside a sac-like ascus.
• Basidiomycetes grow basidiospores on a club-ended basidium.
• Oomycetes (Chromista) form oospores from the fusion of gametangia of different sizes.
• Mitosporic Fungi or Fungi Imperfecti/Deuteromycetes only reproduce asexually, displaying no sexual reproduction.

Life Cycle Types

• In asexual Reproduction spores types are:
  • Sporangium releases swimming spores (zoospores)
  • Conidia are spores growing from chains or at the tip.
  • Chlamydospores are walled spores.
• Rapid reproduction is useful for survival.
• In sexual reproduction spore types are:
  • Ascospores are present in a sac of ascomycetes.
  • Basidiospores are present on club structures (basidiomycetes).
• Genetic material is combined to provide adaptation.
• Fungi are more adaptable and aggressive utilizing sexual, and asexual cycles, simultaneously.

The Spore Stage

• Most fungi and oomycetes have a life cycle that begins with a spore stage featuring a plain haploid nucleus (1N), with one set of chromosomes.

Germination, and Hyphal Growth

• Spores germinate into hyphae, also containing haploid nuclei.
• These hyphae may grow further haploid spores as is often seen imperfect fungi, or go through additional development.

Fusion and Zygote Formation

• A hypha can, occasionally, mix into another to create a fertilized hypha.
• In this case the nuclei combine, the forming a diploid nucleus or zygote (2N), with two sets of chromosomes, as often seen oomycetes.

Diploid Mycelium, and Spores in Oomycetes

• Oomycetes have zygotes which divides into a diploid spore and mycelium.
• This mycelium creates gametangia, undergoing meiosis, and reproduction, which then reverts to zygote the stage.

Dikaryotic Phase in Ascomycetes, and Basidiomycetes

• A phase often found in basidiomycetes, and ascomycetes as a whole, with an (N+N) dikaryotic phase, whereas after fertilization, and the paired nuclei, and cytoplasm separates.
• Dikaryotic hyphae reside exclusively inside fruit bodies which, as ascogenous hyphae in ascomycetes.
• The two nuclei in one cell combines into a zygote (2N).

In Basidiomycetes

• The life cycle initiates with haploid spores that start the haploid hyphae.
• Fertilization forms a dikaryotic mycelium with the main body of fungus.
• The mycelium asexually multiplies dikaryotic spores, creating new dikaryotic mycelia.
• Nuclei ultimately merge, forming the creation of diploid cells, that either divide mitotically, or perform as zygotes.
• The zygotes goes through meiosis, thereby forming haploid basidiospores for reproduction.

Deuteromycetes

• Deuteromycetes only multiply asexually constantly multiplying the haploid spore.
• Haploid spores give rise to mycelium that makes further spores.
• Oomycetes repeat the cycle for every season.
• The sexual cycle happens rarely, and only once each season.

Processes Related To Reproduction In Fungi

• It can happen when heterokaryosis containing the two distinct nuclei form after fertilization or anastomosis.
• Armillaria mellea (Oak Root Fungus) – are created, heterokaryotic mycelia, increasing pathogenicity causing root disease in woody plants.
• Parasexuality is when in heterokaryotic cells produce diploid cells lacking meiosis.
• Aspergillus niger is a parasexual cycle that has been used in genetic studies.
• Vegetative Incompatibility is how fungi avoid mixing with incompatible hyphae, and stops distribution throughout fungi.
• Cryphonectria parasitica (Chestnut Blight Fungus) is an Incompatible fungus, influencing disease of chestnut trees.
• Heteroploidy possesses varying chromosome numbers, genetic variation/diversity is often observed.
• Ustilago maydis (Corn Smut) create spore cells often observed from infected fields.

Myxomycota (Myxomycetes) Diseases

• Myxomycetes are known as slime molds, belonging to the Protozoa species.
• These organisms are defined by a plasmodium, it has multiple nuclei, but lacks all other cell walls.
• They produce zoospores that each have a flagella, and in a resting state it produces specialized spores.
• They grow on low land vegetation like strawberries, and turf, it's most often observed in saturated temperature locations.
• Causes the existence of decaying components, bacteria and the growth of micro flora.
• It’s often found in soil components, on plantlife, they also originate crust-ended structures of plantlife.
• Most spores are distributed via climate events, or the tools used on site to start fresh crops.

Plasmodiophoromycetes Diseases

• Crucifers, are what’s often referred as “clubroot”, those that have that disease often display symptoms that include cereal with damaged roots.
• Hosts are bound as parasites since they stay in resting spores to ensure other, and uninfected soil.
• Characteristics of pathogens are that live cells still support cell tissue, the cell also divides.
• These are commonly moved via fertilizer, from foreign plants, this also spreads several disease.
• Green leafs become discolored yellowish green.
• Growing slows and halts, causing non marketable crops.
• Swelling occurs, that makes them susceptible secondary infection.
• Pathogens and disease development are often brought upon because plasmodiophora.
• Then it will enlarge all cell types, so to affect nutrients in the water.
• Keep high the level so that its well avoid these from contaminated.
• Use fumigants in the ground, keep PH above normal as well.

Oomycetes Diseases

• This species has glucans with both of their mycellium.
• Create both and asexual zoospores and also asexual.
• Pyruim, and also what stems, stem and root damage as well.
• Several diseases may impact plants, and various kinds of others.

True Fungi Groups

• Hytridiomycota (Chytridiomycetes) lack a true mycelium and has a thick “chitin-wall”.
• It resides within a host requiring stable and free water access.
• Can create diseases in most of the components for plant life, such as Olpidium that can affect some plants.
• Causes spot related issues in corn.
• Cell division can cause cell damage that allows transmission of viruses, like Olpidium.
• Symbiotes are an example for mycelium formation, forming spores.
• These are also land based, exist in various stages from weak all stages.
• They may result in soft components that trigger plant structure damage.

Ascomycetes and Deuteromycetes or (Mitosporic Fungi)

• Display characteristics such as haploid myceliums with separations and the multiplication, that come from bodies bearing structure.
• It is the main and primary factor with many diseases, vascular wilts, and soft rots.
• Important distinctions comprise of ascomytes spores with a lack of all sex traits.
• Many were once recognized, DNA then finds its classification amongst ascomyetes.
• May find connection between members of the classes.
• Taphrina impacts deformity.

Plant Diseases with Fungal Families

• Fusarium can impact and cause damage to an assortment of roots.
• Phytophthora It’s responsible for several diseases that range from death in oak, or potatoes having issues in blight.
• Puccinia may impacts grasses.
• Both can cause damage to growth cycle depending upon climate.
• Ustilago is an agent from smut infections, which mostly impacts cereal croplife.
• Verticillium It can hurt many crops like tomatoes, or even potatoes.
• Pleosporade is something that harms several forms of life, leading to multiple problems.
• Magnaporthaceae can result in bad diseases, commonly called rice.
• Erysuphaceaw can cause fungi and mild damage to plant’s leaves .
• It is another family of oomycetes, or some kind of mildew issue.

Types of Disease

• Rust Fungi or (Puccinia spp.) have both steam and leaf damage that may require all plant structure damage.
• Has a complicated state with multiple spore forms, and primary, and secondary phases.
• Powdery Mildew Fungi have cereal, vine damage this also forms several damage that causes surfaces to fade.
• Results in a wind like effect upon plant like in this structure.

Fungi That Causes Plasmopara Viticol

• This causes yellow pigment damage to all vegetations, while forming harm to most vegetation.
• The damage leads to rain like damage.
• This is just a form the grey mold disease affecting numerous areas.
• Effects are spores.
• Spores will form and can infect all openings.
• Damage may take places via contaminated liquid often, to live with soil damage.

Control of Fungal Disease in plants

• Controls needs to be tailored made to each response that one receives.
• The cycle is well implemented as well, it allows one to know the correct measure it applies.
• It’s essential for control damage ,and this helps maintain the damage.
• Chemicals may impact the fungicide that it is implemented.
• Soil agents that can prevent it from causing further damage.
• Spores move to spread via insects.
• This is the process for better damage in insects.

Disease Management and Controls

• Integrated damage management can prevent multiple damage that helps structure issues to multiple elements in various areas.
• Its better to maintain resistance is better in the system as well.
• One must consider a factor when it comes, it will impact certain effects for targets etc.
• Most people need to remain obedient to some regulations to prevent.
• They have to stay protected to the soil, and to make sure plant life stays health.

Virus Management

• Virus transmission impacts multiple components via several plant life.
• Several compounds impact responses in a plants system.
• RNA reduces factors depending those can allow damage to continue.

For Nematodes

• It has the ability to diffusion damage to a region.
• Often found and use in multiple bacteria.

Mechanisms of Pathogen Invasion

• Recognition of the host includes pathogen associated with recognition along proteins and effector-triggered immunity.

Invasion and Manipulation The Host Machinery

• Contains suppression and gene expression.

Types of Effectors (Host Manipulation)

• Fungi produces effectors to change cell function suppressing plant mechanisms of defense.
• Tissue enzymes damage the cell structure by cell degradation
• It can create hormone plant increase.
• It’s required that they must often target and take the nutrients, so the fungi can penetrate and colonize plant cells.
• Necrotrophs damage it right away , it takes place using enzymes, bacteria and toxins.
• T3SS is where the damage spreads over plant life.
• Toxins also breakdown and cause damage.

Host Plant Defense

• It takes place in multiple stages:
• SA levels grow quickly.
• Applications affect resistance for SA
• In SAR and catalase these bind to SA with the protein that often.
• Also part ways for HA

Virus and Replication of plants

• Upon the entry system the plant needs support for reproduction.
• Carry’s RDRP since it doesn’t.
• Multiple travel in several distances.
• Proteins change the dimensions to plant.

Plant Defense Mechanisms

• They use defensive mechanisms of what ever components.
• Multiple levels are used from bartering, cell wall damage, etc.
• Proteins can be encoded to detect molecules from pathogens

R Gene Expression

• Is expressed so it allows defense and for signals to connect.
• These are made well after gene that form the process for expression.
• What happens here is a strong gene is expression.
• Is stimulated from compounds used in multiple elements.
• This is often induced after the components in some forms.

Resistance Gene

• With the genes available one may help multiple plants become resistance againts different damages.
• Several of the areas are in the system.
• Can stop certain pathogens so that they often work.

Biosensors

• Is to work as a transducer that will sense damage in plant life.
• Several sensors are used instead of something that that old tool.
• Bioreceptors includes multiple factors, all this will provide factors for what select the method.
• The types that are based on all systems.
• The electro that the various sensors that electro sensors.
• This also applies on every stage of process.
• They should have a sufficient immune response on every.
• There includes several processes for damage depending, and with this and various electro. -It helps the test become specific from what’s needed.

Electroc Biosensors

• May have several plant types and may come from those kinds of systems for the set goal in site.
• Some are used and can be useful.