Plant Diseases Chapter PPA-46

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Questions and Answers

What was responsible for the near complete loss of the American chestnut?

A bacterial infection

A plant parasitic nematode

A viral outbreak

A fungal disease (correct)

How was chestnut blight introduced to the United States?

Through native tree species

Imported Chinese chestnut trees (correct)

Via contaminated soil

Through agricultural practices

What management strategies are currently used against chestnut blight?

Chemical pesticides exclusively

Genetic modification of the trees

Planting only native species

Sanitation and fungicides (correct)

What role did the French wine industry play in disease management?

They introduced the Bordeaux mixture fungicide Signup and view all the answers

Approximately how many acres of chestnut trees died due to the chestnut blight?

30 million acres Signup and view all the answers

Which of the following statements about Chinese chestnut trees is true?

They can tolerate the blight. Signup and view all the answers

What type of pathogen mainly caused the devastation of the American chestnut?

Fungi Signup and view all the answers

After the introduction of chestnut blight, how did the landscape of American forests change?

Many other tree species became dominant. Signup and view all the answers

What is the primary function of sexual spores produced by water molds?

To serve as a survival mechanism under adverse conditions Signup and view all the answers

How often can sporulation occur in water molds during a growing season?

Many times, provided water is available Signup and view all the answers

What is one visible example of a fungal disease mentioned?

Powdery mildew Signup and view all the answers

Which of the following pathogens cannot survive winter in Kentucky?

Cucurbit downy mildew pathogen Signup and view all the answers

How can the variation in fungal spores assist diagnosticians?

Identifying the specific pathogens Signup and view all the answers

Which type of fungal fruiting structure is produced sexually?

Ascocarps Signup and view all the answers

What is a common symptom of cucumber infection by the cucurbit downy mildew pathogen?

Yellow, angular leaf spots Signup and view all the answers

Where are spores of the cucurbit downy mildew pathogen typically produced?

On the undersides of leaves Signup and view all the answers

What is a characteristic of exposed or unprotected fungal spores?

More sensitive to environmental conditions Signup and view all the answers

What happens to a fungal spore once it makes contact with a suitable plant surface?

It germinates and hyphae emerge Signup and view all the answers

How do spores of downy mildew spread to new tissue?

Through water or rain Signup and view all the answers

What is required for plant disease to occur according to the Disease Triangle?

A combination of susceptible host, pathogen, and environment Signup and view all the answers

Which of the following diseases primarily affects solanaceous crops?

Late blight Signup and view all the answers

What is the typical overwintering site for the late blight pathogen?

In infected plant or weed tissue Signup and view all the answers

Which of the following fungi’s reproductive strategies involves both sexual and asexual processes?

Rust fungi Signup and view all the answers

Which structure is a common asexual fruiting body produced by fungi?

Pustules Signup and view all the answers

What structures do plant parasitic nematodes use to pierce plant tissues?

Needle-like mouthparts Signup and view all the answers

Which of the following symptoms is NOT commonly caused by nematode feeding?

Flower wilting Signup and view all the answers

How do plant parasitic nematodes primarily disseminate over long distances?

Movement of infested soil Signup and view all the answers

What does the presence of female nematodes at a feeding site indicate?

Longevity of feeding Signup and view all the answers

Which type of nematode feeds while remaining on the exterior of plant roots?

Stubby-root nematode Signup and view all the answers

What reproductive method can female nematodes use to produce eggs?

Both mating and asexual reproduction Signup and view all the answers

What is a common result of severe root loss due to nematode feeding?

Symptoms resembling nutrient deficiencies develop Signup and view all the answers

What differentiates the feeding behavior of dagger nematodes from that of soybean cyst nematodes?

Dagger nematodes penetrate plant tissues completely, while soybean cyst nematodes do not Signup and view all the answers

What is the primary way bacteria infect plants?

Via wounds or natural openings Signup and view all the answers

Which of the following symptoms are commonly caused by bacterial infections?

Wilting and defoliation Signup and view all the answers

What facilitates the movement of bacteria to infect plants?

Wind or splashing water Signup and view all the answers

What reproductive process do bacteria undergo for rapid multiplication?

Binary fission Signup and view all the answers

How long can some bacteria survive in soil?

Up to five years Signup and view all the answers

What happens to plant tissue once bacteria begin to reproduce inside it?

The tissue degrades and is used as food by bacteria Signup and view all the answers

Which of the following is NOT a common bacterial disease mentioned?

Powdery mildew Signup and view all the answers

What might indicate a serious bacterial infection in plants?

Water-soaked, grey-brown lesions Signup and view all the answers

Powdery mildew is known to cause a white powdery appearance on infected plants.

True Signup and view all the answers

Cedar-apple rust can complete its life cycle using only one host.

False Signup and view all the answers

Spores of the powdery mildew fungus survive winter on healthy plant tissues.

False Signup and view all the answers

Armillaria root rot is particularly aggressive towards newly transplanted and older stressed trees.

True Signup and view all the answers

Rust pathogens are only found in dry climates.

False Signup and view all the answers

Cedar-apple rust produces different spore types during different seasons.

True Signup and view all the answers

Infection by the powdery mildew pathogen occurs when rain splashes spores onto new plant growth.

True Signup and view all the answers

The unique structure known as galls is produced by cedar-apple rust on apple trees.

False Signup and view all the answers

Viruses in plants often lead to immediate death of the host plant.

False Signup and view all the answers

Insects can transmit plant viruses multiple times during a growing season.

True Signup and view all the answers

Rose rosette virus is transmitted by insects such as thrips.

False Signup and view all the answers

Plant viruses can move in and out of plant tissue as easily as fungal and bacterial pathogens.

False Signup and view all the answers

Tomato spotted wilt virus can infect a wide variety of plant species.

True Signup and view all the answers

The tobacco mosaic virus primarily infects only tobacco plants.

False Signup and view all the answers

Symptoms of rose rosette infection can appear immediately after infection.

False Signup and view all the answers

Once a plant is infected with TSWV, it does not transmit the virus to insects.

False Signup and view all the answers

Infected seeds or pollen can contribute to the spread of plant viruses.

True Signup and view all the answers

Infected plants can sometimes exhibit lesions on stems as a symptom of TSWV.

True Signup and view all the answers

Chlorosis is a symptom commonly associated with plant viral infections.

True Signup and view all the answers

The mites responsible for spreading rose rosette virus can move through wind currents.

True Signup and view all the answers

Certain viruses can remain viable in dormant plant tissue for extended periods.

True Signup and view all the answers

Once inside an insect's gut, plant viruses can only be carried for short periods.

False Signup and view all the answers

Virus-infected plants do not provide a source for vectoring mites after they are infected.

False Signup and view all the answers

Thrips acquire the tomato spotted wilt virus during their adult stage.

False Signup and view all the answers

Mosaic symptoms on plants are characterized by a uniform green color throughout.

False Signup and view all the answers

Mottle symptoms present as an irregular pattern of light and dark areas on plant leaves.

True Signup and view all the answers

Mummy refers to soft, wet tissue on fruits caused by pathogens.

False Signup and view all the answers

Necrosis is the death of plant tissue and is a symptom associated with multiple pathogen groups.

True Signup and view all the answers

Stunting symptoms indicate that a plant is growing larger than normal.

False Signup and view all the answers

Vein clearing symptoms manifest as yellowing of the entire leaf surface.

False Signup and view all the answers

Watersoaking involves wet, dark, or greasy lesions that are typically sunken.

True Signup and view all the answers

Scab lesions are characterized by a smooth surface appearance.

False Signup and view all the answers

Witches’ broom symptoms involve an abnormal brush-like shoot development.

True Signup and view all the answers

Wilt symptoms are associated with drooping leaves and reduced plant health.

True Signup and view all the answers

Exclusion techniques aim to prevent pathogen introductions to areas where they currently exist.

False Signup and view all the answers

Fungicides are usually pathogen-specific and are effective in managing only fungal pathogens.

True Signup and view all the answers

Resistance refers to selecting plants with increased tolerance to pathogens.

True Signup and view all the answers

Avoidance strategies include the practice of using diseased plants for crop rotation.

False Signup and view all the answers

Fungicides can reverse disease symptoms once applied to affected plants.

False Signup and view all the answers

Reducing plant stresses can be an effective common practice for pathogen avoidance.

True Signup and view all the answers

Quarantine is a common practice used in the avoidance strategy to manage plant pathogens.

True Signup and view all the answers

Antibiotics are primarily used to manage fungal pathogens in plants.

False Signup and view all the answers

Powdery mildew is known to infect numerous landscape and garden ______.

plants Signup and view all the answers

Spores of the powdery mildew pathogen survive winter on infected plant ______.

debris Signup and view all the answers

Organisms that cause disease are referred to as ______.

pathogens Signup and view all the answers

Cedar-apple rust is caused by a group of fungi known as ______.

rusts Signup and view all the answers

A plant disease is an abnormality caused by a living ______.

organism Signup and view all the answers

The pathogen of cedar-apple rust overwinters as galls on ______.

juniper Signup and view all the answers

One of the most notable historical impacts of plant disease was caused by the late blight of ______.

potato Signup and view all the answers

The galls produced by the cedar-apple rust release slimy 'horns' comprised of ______ during spring rains.

spores Signup and view all the answers

Plant pathogens utilize hosts for nutrients and/or reproduction at the hosts' ______.

expense Signup and view all the answers

In late summer, apple lesions produce another spore type that infects ______.

juniper Signup and view all the answers

Armillaria root rot is particularly aggressive towards ______ and older stressed trees.

newly transplanted Signup and view all the answers

Disease-causing organisms include fungi, oomycetes (water molds), bacteria, viruses, and ______.

nematodes Signup and view all the answers

Throughout the season, powdery mildew produces additional ______ causing subsequent infections.

spores Signup and view all the answers

On a global scale, plant diseases cause an estimated ______ billion in annual losses.

38 Signup and view all the answers

Affected plants are referred to as ______.

hosts Signup and view all the answers

Saprophytic organisms obtain nutrients from ______ organic material.

dead Signup and view all the answers

The American chestnut was nearly wiped out by a fungal disease known as ______.

chestnut blight Signup and view all the answers

Chinese chestnuts are tolerant to the ______, while American chestnuts are not.

blight Signup and view all the answers

Disease management strategies against chestnut blight include the use of resistant ______.

varieties Signup and view all the answers

The first fungicide used in the wine industry was the ______ mixture.

Bordeaux Signup and view all the answers

Approximately ______ million acres of chestnut trees died due to chestnut blight.

30 Signup and view all the answers

Fungi, bacteria, viruses, and ______ are examples of different types of pathogens that affect plants.

oomycetes Signup and view all the answers

In urban areas, American chestnut trees once provided high-quality ______ for construction.

hardwood Signup and view all the answers

In the late 1800s, chestnut blight was accidentally introduced to the United States through imported ______ trees.

Chinese chestnut Signup and view all the answers

Plant disease diagnostics begins with the observation of ______.

symptoms Signup and view all the answers

Fungi and bacteria can cause leaf spots that are similar to those caused by ______.

herbicides Signup and view all the answers

To confirm diagnoses, identification of signs such as mycelial growth and fruiting structures requires the use of a ______.

microscope Signup and view all the answers

Examination of surrounding plants can provide vital information regarding disease ______.

spread Signup and view all the answers

Patterns of injury or symptoms can give clues as to whether variety- or species- specific infections are ______.

possible Signup and view all the answers

Information regarding soil makeup, disturbances, and soil drainage patterns can assist in differentiating ______ maladies from diseases.

abiotic Signup and view all the answers

Diagnosing plant problems may require submitting samples to a ______ laboratory for further analysis.

commercial Signup and view all the answers

Several steps to disease diagnostics include examining vital site information and examining ______ tissue.

diseased Signup and view all the answers

A single plant species can have numerous cultivars or ______, which can vary in many traits.

varieties Signup and view all the answers

Symptoms may differ with plant species or ______, which is vital for diagnosis.

cultivar Signup and view all the answers

Critical information like irrigation practices and ______ date can aid in making accurate diagnoses.

planting Signup and view all the answers

In some cases, symptoms develop on plant parts that are different from the infected ______.

tissue Signup and view all the answers

A root rot pathogen may cause symptoms like dieback and ______, indicating potential troubles with the plant.

wilting Signup and view all the answers

It may be necessary to submit symptomatic plant samples to a diagnostic ______ if the cause cannot be determined.

laboratory Signup and view all the answers

Determining if a problem is present can depend on assessing normal versus abnormal plant ______.

appearance Signup and view all the answers

Collecting additional information can lead to a more complete ______ of plant health issues.

diagnosis Signup and view all the answers

Study Notes

History and Significance

American chestnut trees were devastated by chestnut blight, a fungal disease introduced in the late 1800s through Chinese chestnut imports.
Approximately 30 million acres of American chestnuts died within 40 years due to their lack of tolerance to the blight.
Disease management strategies now include resistant varieties, sanitation, and fungicides.

Pathogens

Fungi reproduce via spores which can be created sexually or asexually; their variation helps in pathogen identification.
Fungal reproductive structures can be visible (e.g., mushrooms) or microscopic (e.g., pycnidia, acervuli).
Downy mildew and late blight are diseases caused by water molds, which are host-specific.

Conditions for Disease Development

Plant disease is influenced by a susceptible host, a viable pathogen, and a favorable environment, forming the Disease Triangle.
Spores germinate on contact with a plant surface under optimal conditions, leading to infection.

Fungi

Fungi require suitable conditions to grow; sporulation can happen multiple times in a season when water is available.
Water molds can produce spores prior to dormancy and can survive harsh conditions.

Water Molds

Downy mildew affects various plants; infection results in angular leaf spots and can cause defoliation.
Late blight primarily infects potatoes and tomatoes, characterized by water-soaked lesions that lead to defoliation.

Bacteria

Around 200 bacterial types are known to cause plant diseases; they are single-celled and reproduce rapidly through binary fission.
Common bacterial diseases include bacterial wilt and fire blight, with symptoms such as leaf spots and wilting.
Bacteria spread via water, wind, and insects, often requiring wounds or natural openings to infect plants.

Plant Parasitic Nematodes

Nematodes are microscopic roundworms that primarily infect plant roots, causing stunted growth and reduced yields.
Infestation symptoms include chlorosis, root galls, and dieback due to their feeding on plant cell contents.
Key examples include soybean cyst nematodes and stubby-root nematodes, which can feed externally or penetrate tissues.

Plant Diseases Overview

Powdery Mildew: A fungal disease affecting many plants; spores survive winter on infected debris. Spring rains facilitate spread to new growth, leading to a white, powdery appearance.
Cedar-Apple Rust: A fungi-induced disease requiring multiple hosts; galls on juniper overwinter, producing spores in spring that infect apple trees, creating lesions that later infect junipers.

Armillaria Root Rot

Affects recently transplanted and stressed trees, causing root decay.

Viruses

Extremely small pathogens necessitating powerful magnification for observation. Viruses can persist in host plants for years, avoiding rapid mortality.
Common vectors include insects which acquire and transfer virus particles during feeding, enabling multiplication of viruses inside insects.

Common Viral Diseases

Tobacco Mosaic Virus: Named after the first observed symptoms in tobacco, infects over 100 plant species, leading to symptoms like mottling and stunting.
Rose Rosette Virus: Carried by rose leaf curl mites, causing witches' broom, leaf reddening, and excessive thorn development.
Tomato Spotted Wilt Virus (TSWV): Infects thousands of species, transmitted by thrips. Symptoms include wilting, lesions, and mottling on fruit.

Symptoms of Plant Pathogens

Mosaic and Mottling: Nonuniform coloration often seen with viral infections.
Necrosis: Tissue death observed in various pathogens.
Stunting: Reduced plant growth affecting size and vigor, ensuing from viral or nematode infections.
Wilt and Scorch: Common symptoms related to both fungal and viral infections.

Plant Disease Diagnostic Techniques

Techniques include prevention (exclusion), pathogen management (avoidance), and selection of resistant plant varieties.
Exclusion: Prevent pathogen entry through quarantine and inspection, utilizing disease-free plant materials.
Avoidance: Use certified plants, inspect before planting, reduce stress, and rotate crops.

Protection Against Plant Diseases

Implement protective measures tailored to specific pathogen threats. Fungicides mainly serve to limit fungal infections but do not cure existing diseases.
Resistance: Selecting disease-resistant plant varieties to mitigate the impact of common pathogens.

Understanding these principles aids in the identification and management of plant diseases, enhancing plant health and productivity.

Plant Diseases Overview

Pathogens causing plant diseases include fungi, water molds (oomycetes), bacteria, viruses, nematodes, phytoplasmas, and parasitic seed plants.
Major historical impact example: Late blight of potato led to the Irish potato famine in 1845, resulting in about one million deaths.
Losses from plant diseases globally are estimated at $38 billion annually.

American Chestnut and Chestnut Blight

The American chestnut was nearly wiped out by chestnut blight, a fungal disease introduced in the late 1800s through Chinese chestnuts.
Approximately 30 million acres of American chestnut trees died within 40 years due to their susceptibility.
Management of chestnut blight now includes resistant varieties, sanitation, and fungicide applications.

Disease Development and Symptoms

Symptoms of plant disease arise after a pathogen infects a host and may result from complex interactions between biotic and abiotic factors.
Common disease indicators include notable symptoms on specific plant parts, which can mislead diagnostics if not appropriately assessed.
Examples of diseases:
- Powdery mildew: Infects various plants, characterized by white powdery growth.
- Cedar-apple rust: Requires multiple hosts; overwinters on juniper and affects apple trees in spring.

Plant Disease Diagnostics

Diagnosis begins with observing affected plants and the environment, often necessitating microscopic examination.
Recognizing the impact of abiotic factors (e.g., weather, soil conditions) is crucial for accurate diagnosis.
Key diagnostic steps:
- Examine the site for clues about environmental conditions affecting plant health.
- Ask questions about plant history, caretaking practices, and unusual occurrences (herbicide applications, irrigation practices).
- Identify the specific plant parts exhibiting symptoms, as issues may not originate from the visibly affected areas.

Management and Research

Disease management strategies evolved significantly since the introduction of the Bordeaux mixture fungicide to tackle issues in agricultural systems.
Continuous research is being conducted for better management options against persistent diseases, like chestnut blight.

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Description

Explore the complex world of plant diseases with insightful contributions from experts. This chapter discusses the challenges posed by pathogens, strategies for managing them, and the historical impact on species such as the American chestnut. Learn about resistant varieties and effective sanitation methods.