PLSC322 Chapter One

Plant Pathology (Phytopathology)

The study of plant diseases and the suffering of plants.

Learning more about diseases and their causes, and developing controls for plant diseases.

Two main areas of concern for Plant Pathologists

Proved that wheat bunt is caused by a fungus.

Prevost (1807) Discovery

Late blight of potato.

Cause of the 1845-1846 Irish famine

Proved that a fungus caused late blight of potato.

deBary (1861) Discovery

Annihilating diseases

Diseases that may wipe out a crop or species completely (e.g., chestnut blight, Dutch elm disease).

Devastating diseases

Diseases that may be severe for a few years and then gradually subside (e.g., wheat rust, southern corn leaf blight).

Limiting diseases

Diseases that build up to the point that it is not economical to grow a crop in a given field (e.g., many root diseases, nematodes).

Debilitating diseases

Diseases that occur almost annually and weaken crops, resulting in lower yields and poor quality.

Plant Disease

Any progressive disturbance by a pathogen or environment that interferes with the normal function of a plant.

Plant Injury

Damage caused by a transitory (temporary) interaction with an insect, chemical, or unfavorable environmental condition (e.g., lightning).

Initial reaction of diseased tissue

It is invisible and of a chemical nature before visible symptoms appear.

They reduce photosynthesis and may limit transpiration, affecting water movement.

Effect of foliar diseases

Effect of diseases on xylem

Pathogens invade it and interfere with the movement of water and minerals.

Effect of diseases on phloem

They interfere with the movement of photosynthates (food).

Abiotic diseases

Environmental, non-pathogenic, non-infectious, or physiological diseases.

Pathogenic diseases

Infectious diseases caused by biological agents.

Pathogen

A biological agent capable of causing an infectious disease (it is the agent, not the disease itself).

Pathogen, Host, and Environment.

The Disease Triangle (Three Factors)

The host plant must be susceptible, otherwise no disease will develop.

Role of the Host in disease development

Vector

An organism capable of transmitting a pathogen.

Pathogen, Environment, Susceptible host, and Time.

The Disease Pyramid (Four Factors)

Use of resistant cultivars, healthy seed, proper planting dates, crop rotation, and removal of crop debris.

Pest Management techniques (examples)

Ergot poisoning epidemics

A major plant disease issue that occurred historically in the 16th century.

Cell division/differentiation, absorption/translocation, photosynthesis/respiration, food storage, and reproduction.

Functions of a healthy plant

photosythesis

Diseases affecting foliage reduce _________

Water Movement

Foliar Diseases may limit transpiration, affecting ___________

Movement of water and minerals

Pathogens may invade xylem and interfere with the ___________

Carbohydrates

Diseases affecting phloem interfere with movement of _________

Water uptake and plant support

Diseases can affect roots which interferes with ________

strength of the trunk

In trees pathogens can cause wood decay which affects _______

Virulence

The degree of pathogenicity