Unit 4: Diagnosis of Plant Diseases

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Questions and Answers

What is the purpose of using pathogen-tested seeds and propagation materials?

To improve crop yield

To enhance soil fertility

To exclude or eradicate the pathogen (correct)

To increase resistance to pests

How can crop rotation help in disease management?

By enhancing chemical resistance

By promoting weed growth

By introducing different crop varieties

By reducing pathogen levels (correct)

Which agar medium is specifically selective for gram-negative bacteria?

Chocolate agar

MacConkey agar (correct)

XLD agar

Blood agar

What should be done if a plant is already infected with a systemic disease?

Isolate and destroy the plant Signup and view all the answers

What is the primary purpose of disease diagnosis in plants?

To identify a diseased plant from a healthy one Signup and view all the answers

Which of the following components is found in Eosin – Methylene Blue (EMB) agar?

Peptone Signup and view all the answers

Which of the following is NOT a major type of bacterial disease?

Fungal Diseases Signup and view all the answers

What factor should be minimized to reduce mechanical damage to crops?

Handling of crops Signup and view all the answers

What can leaf and fruit spots in tomatoes indicate?

A variety of different diseases Signup and view all the answers

What is the composition of XLD agar primarily designed to isolate?

Salmonella and Shigella species Signup and view all the answers

What is considered a sign of bacterial infection in plants?

Presence of bacterial ooze Signup and view all the answers

Which pathogen is primarily associated with bacterial soft rots?

Erwinia Signup and view all the answers

Why should crops not be worked on when wet?

To avoid infection spread Signup and view all the answers

What is a characteristic of necrotic diseases in plants?

Necrotic leaf spots Signup and view all the answers

What method can be used to diagnose bacterial wilt in a plant?

Cutting the stem and observing exudate Signup and view all the answers

Why is it insufficient to diagnose plant conditions solely based on symptoms?

Many pathogens cause similar symptoms Signup and view all the answers

What is the primary cause of watersoaking in plant tissues?

Bacterial attack Signup and view all the answers

Which bacterium is associated with the fruit spot of pepper?

Xanthomonas campestris pv. vesicatoria Signup and view all the answers

What characterizes undefined (complex) media in microbiology?

Contains at least one ingredient that is chemically indefinable. Signup and view all the answers

What is the main purpose of negative staining techniques in diagnosing bacterial diseases?

To visualize bacteria against a dark background Signup and view all the answers

Which type of culture media does not solidify at temperatures above freezing?

Liquid Media Signup and view all the answers

Which solution is used as part of the negative staining technique?

Congo red Signup and view all the answers

What is a key feature of semi-solid media?

They contain a solidifying agent but do not form a firm substrate. Signup and view all the answers

What is the purpose of Gram staining in the context of bacterial diseases?

To differentiate plant bacteria into gram-positive and gram-negative groups Signup and view all the answers

What is a characteristic visual symptom of bacterial streaming?

Translucent spots resembling drops of water Signup and view all the answers

What distinguishes synthetic media from non-synthetic media?

Synthetic media compositions are chemically defined, while non-synthetic media contain undefined ingredients. Signup and view all the answers

Which of the following is an example of a solid media?

Cooked Meat Signup and view all the answers

Black leg of tobacco is caused by which pathogen?

Pectobacterium carotovorum subsp. atrosepticum Signup and view all the answers

Which method involves direct examination of infected tissues for diagnosing bacterial diseases?

Symptomatology Signup and view all the answers

What type of bacteria are known to form a surface pellicle in liquid media?

Aerobic bacteria Signup and view all the answers

What defines non-liquefiable media?

They remain solid after heat sterilization. Signup and view all the answers

Which of the following types of media is primarily used for research when the exact nutritional requirements are known?

Synthetic Media Signup and view all the answers

What is the function of the cell wall during bacterial cell division?

It constricts to form a cross-wall. Signup and view all the answers

What does generation time refer to in bacterial growth?

The interval between two cell divisions. Signup and view all the answers

Which bacterium causes bacterial wilt in banana crops?

Xanthomonas vasicola pv. musacearum Signup and view all the answers

What is a common symptom of bacterial wilt in plants?

Wilting and stunted growth Signup and view all the answers

Which of the following bacteria is responsible for crown gall disease?

Agrobacterium tumefaciens Signup and view all the answers

Which plant disease is caused by Pectobacterium carotovorum?

Soft rot of vegetables Signup and view all the answers

In plant bacteriology, what is the significance of discussing plant pathology?

It is essential for developing sustainable agricultural practices. Signup and view all the answers

What did J.C. Davine's research in 1863 contribute to the understanding of bacterial diseases?

He linked rod-shaped bacteria to anthrax infections. Signup and view all the answers

Study Notes

Diagnosis of Plant Diseases Caused by Bacteria

Disease diagnosis involves identifying diseased plants by their signs and symptoms; essential for effective disease management.
Symptoms alone are insufficient for diagnosis due to overlapping symptoms caused by different pathogens (e.g., fungi and bacteria can cause soft rots).
Common bacteria associated with soft rot include Pseudomonas, Dickeya, Bacillus, Pectobacterium, and Erwinia.

Major Types of Bacterial Diseases

Vascular Diseases: characterized by wilting.
Necrotic Diseases: associated with necrotic leaf spots.
Soft Rot Diseases: involve tissue maceration and ooze.
Tumor Diseases: include galls and hyperplasia.

Signs of Bacterial Diseases

Signs are physical evidence of pathogens in unhealthy plants, such as bacterial ooze and specific odors.
Bacterial ooze forms in droplets from water-soaked lesions, indicating bacterial presence.

Diagnostic Methods for Bacterial Diseases

Symptomatology: Direct inspection of infected tissues supported by visual and microscopic examination.
Staining Techniques:
- Negative Staining: Identify leaf lesions, showing bacteria as colorless rods against a dark background.
- Gram Staining: Differentiates bacteria into gram-positive and gram-negative for bacterial disease classification.

Management of Bacterial Diseases

Employ clean transplants and monitor crops regularly.
Implement crop rotation to reduce pathogen levels and control disease spread.
Use resistant plant varieties and minimize mechanical damage.
Apply registered bactericides under favorable weather conditions and rotate chemical treatments to avoid resistance.
For infected plants, isolate and destroy them; avoid excessive handling. Systemic infections require complete destruction of the plant.

Cultivation and Growth Media for Bacteria

Chocolate Agar: Enriched medium for isolating pathogenic bacteria; contains lysed red blood cells.
Eosin-Methylene Blue (EMB) Agar: Selective for gram-negative bacteria, differentiates lactose fermenters.
Xylose Lysine Deoxycholate (XLD) Agar: Used for isolating Salmonella and Shigella species.
MacConkey Agar: A selective medium for gram-negative bacteria.

Classification of Culture Media

By Chemical Composition:
- Synthetic Media: Chemically defined compositions.
- Non-synthetic Media: Contains undefined ingredient compositions.
By Physical State:
- Liquid Media: Solutions that flow freely.
- Semi-solid Media: Intermediate consistency, useful for testing bacterial motility.
- Solid Media: Firm surfaces allowing formation of discreet bacterial colonies.

Cell Division and Multiplication of Bacteria

Bacteria reproduce via binary fission, where a single cell replicates its DNA and divides into two daughter cells.
Generation Time: Time required for a bacterium to divide and multiply under optimal conditions.

Importance of Plant Bacteriology

Plant bacteriology helps understand the interplay between plant diseases and agriculture sustainability.
Significant bacterial diseases in the Philippines include:
- Bacterial wilt of solanaceous crops (Ralstonia solanacearum).
- Soft rot of vegetables (Pectobacterium carotovorum).
- Crown gall of roses (Agrobacterium tumefaciens).
- Bacterial spot of pepper (Xanthomonas axonopodis pv. vesicatoria).

Historical Background

1863: J.C. Davine observed rod-shaped bacteria in anthrax-infected animals, marking an important milestone in bacteriology and the understanding of plant diseases.

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Description

Explore the key concepts surrounding the diagnosis of plant diseases caused by bacteria. This quiz covers symptoms, signs, and the essential functions of healthy versus diseased plants. Perfect for those studying plant pathology and disease management.