PLANT PATHOLOGY

Course CodeBHT206
Fee CodeS2
Duration (approx)100 hours
QualificationStatement of Attainment

Plant production is reduced significantly every year, due to pathological problems. To control these problems is to increase productivity, and for the horticultural business; that means increased profit margins.

PLANT PATHOLOGY IS NOT simply a study of pests & diseases. Some pests are in fact not pathological problems, and there are pathological problems which are not pests or diseases.

PLANT PATHOLOGY is about problems in plants caused by physiological damage or irritation at a cellular level. (ie: It is concerned with problems which affect parts of the plant cell, leading to malfunctions in the normal processes which occur within the plant).

Lesson Structure

  1. Introduction
    • Overview of plant disease
    • Diagnosis of problems: nutritional, environmental, pathological
    • Symptoms
    • Common terminology
  2. Types of Diseases
    • Morphological changes
    • Necroses
    • Hypoplases
    • Hyperplases
    • Types of pathogens: viruses, bacteria, actinomycetes, fungi, nematodes
    • Techniques for diagnosing plant diseases: optical equipment, preparing pathogens for observation, culture methods, inoculation, etc
    • Plant viruses; detection and diagnosis
    • Plant nematodes
    • Case study: Australian plant nematodes
    • Main types of diseases
    • Spots
    • Rots
    • Cankers
    • Galls
    • Mildews
    • Rusts
    • Moulds
    • Wilts
    • Scabs
    • Others
    • Using a key to diagnose diseases in plants
  3. The Lifecycle of a Disease
    • Inoculation
    • Penetration
    • Infection
    • Growth and reproduction
    • Dissemination
    • Methods of penetration by bacteria and nematodes
    • Lifecycle of nematodes
    • Fungal biology
    • Role of insect spreading fungal and bacterial pathogens
  4. Control Techniques
    • Sanitation
    • Resistant Plant Varieties
    • Biological Controls
    • Soil Drenches/dips
    • Chemical Controls
    • Nematicides
    • Soil fumigants
    • Contact poisons
    • Fungicides and the environment
    • Systemic fungicides
    • Misters, dusters, blowers, sprayersSpray maintenance and cleaning
    • Natural controls: cultural, physical, biological, etc
    • Terminology
  5. Selected Pathogen Diseases Ornamentals
    • Fungi affecting turf
    • Phytopthera cinnamomi
    • The process of tree decay: Shigo
    • Case study: how phytopthera cinnamomi kills a susceptible Eucalyptus
    • Peach powdery mildew
    • Rose powdery mildew
    • Honey fungus on rhododendrons and azaleas
    • Petal blight on rhododendrons and azaleas
  6. Selected Pathogen Diseases Crops
    • Sclerotinia rot in vegetables
    • Nematodes and citrus production
    • Citrus diseases: scaly butt, lemon crinkle, citrus canker
    • Brown rot
    • Fire blight
    • Apple fruit rot caused by trichoderma harzianum
    • Prunus necrotic ringspot virus in cut flower roses
    • Potato and tomato blight
    • Club root
  7. Non-Infectious Diseases
    • Nutritional disorders
    • Lack of water
    • Excess water
    • Other environmental problems
    • Disorders caused by man: mechanical damage, pollution
    • Case Study: Air pollution
    • Other disorders: genetic, disturbed growth
    • Non parasitic turf problems
  8. Special Project

Aims

  • Describe a range of pathological problems that affect plants.
  • Describe symptoms of a range of diseases that affect plants.
  • Describe disease life cycles and explain how this knowledge can be applied in disease control
  • Explain the methods used to control diseases
  • Identify and describe a range of common pathogens that affect ornamental plants.
  • Identify and describe a range of common pathogens that affect crop plants
  • Identify and describe a range of non-infectious diseases and problems that affect plants
  • Demonstrate a comprehensive knowledge of a particular plant pathogen.

UNDERSTANDING DISEASES

 

STAGES IN THE DEVELOPMENT OF A DISEASE

1) Inoculation
Inoculation occurs when the pathogen comes into contact with the plant. The actual organisms which come in contact with the plant are called the "inoculum." Any part of the pathogen which can attack the plant is called inoculum. If the inoculum lays dormant over winter and then infects the plant in spring, this is called the "primary inoculum," and it is causing a "primary infection." Inoculum produced from this infection is called "secondary inoculum" and can cause "secondary infection" of the plant.

Inoculum may be present in the soil or in dead plant material near to the plant being affected (e.g. rotten or mummified fruit left on the plant), or it may be brought into the area with seeds, new plants, soil, on the wheels of a car, on boots or shoes, or even carried by the wind. Inoculum can survive on weeds or infected plants nearby, and move onto cultivated plants when conditions are favourable.

2) Penetration
Pathogens move into plants by breaking through the plant surface, by entering through wounds, or through natural openings (such as stomata). Some fungi only penetrate through one of these methods, while bacteria mainly enter through wounds. Viruses and some microorganisms (mycoplasmas and some bacteria) enter through wounds made by a disease carrier (which is known as a vector). Aphids, for example, carry viruses. They inject their mouthpiece into the plant creating a wound and placing the virus inside the plant. New plants are infected as the aphids moves from plant to plant.

3) Infection
This is the process by which the pathogen establishes contact with the cells or tissues which it is going to affect. In this stage the pathogen grows and invades parts of the plant which it will infect. Changes to the plant can be either obvious or obscure at this point. You might see discolouration or necrosis as the disease moves through the plant, or it may be that the changes are microscopic and necrosis or other symptoms are not seen until the next stage (growth and reproduction).

4) Growth & Reproduction

The pathogen now grows and develops within the part of the plant which it inhabits. It then begins to reproduce itself.

5) Dissemination
Spores or new organisms produced in the growth and reproduction stage are moved to other places where they can sooner or later infect a new plant. This is mostly carried out by agents such as wind, water, insects, animals or man. However, appropriate temperature and humidity conditions must be prevailing.

 
 
 

OPPORTUNITIES

 
This course will teach you to understand diseases that can affect plants. Diseases come in many forms including fungi, bacteria, viruses and other things. All affect plants in different ways, and develop in different ways. Different disease organisms each have unique ways of coming into contact with and infecting plants. Once the infection starts, they all develop within the plant differently, and eventually move on to infect other plants.
 
When you understand this life cycle that an organism progresses through, you are then in a position to see opportunities to interrupt and hence stop the progression of a disease. 
 
Some people use their knowledge of plant pathology to better manage plants they are growing (eg. gardeners and farmers); while others may use that knowledge to devise targeted treatments for managing diseases. Anyone who develops or supplies products for disease control; whether natural or chemical, can benefit from this course, just as much as anyone who grows plants.  
 

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