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).
STAGES IN THE DEVELOPMENT OF A DISEASE
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.
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.
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.
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.
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.