1. CAUSES OF PLANT DISEASES
CHAPTER 2

2. Factors Affecting Biotic Abiotic
Climatic, temperature & other physical factors
Biotic
Insects, nematodes, mites, fungus, bacteria &virus

3. Abiotic Factors Caused by non living factors such as:
Nutritional abnormalities
Pesticide exposure
Environmental pollutants
Extreme weather conditions

4. 1. Nutritional Abnormalities
Often nutrient abnormalities show up as discoloration of foliage
Common discoloration symptoms include:
Yellowing
Chlorosis

5. Nutrient Deficiencies
Plants require several major (N, P, Ca, Mg) and minor (iron, copper, Zn) elements for normal growth.
Deficiency or lack of any of these essential nutrients results in disease symptoms in the plant.
The symptoms in this photo occur due to a lack of molybdenum (minor plant nutrient)

6. Mineral Toxicity
Presence of excessive available amounts of certain minerals in the soil can lead to mineral toxicity to the plants.
The extent of injury depends on the mineral, its concentration, & the species of the plant.
The plant in this photo has received too much copper, which has proved toxic and led to yellowing.

7. 2. Pesticide Exposure
Some pesticides, if improperly used, can cause serious damage to plants.
However, the most common type of chemical injury to plants is due to soil residues or spray drift of herbicides.
Examples of pesticide toxicity are:
2,4-D damage to beans and tomatoes
glyphosate (Roundup) damage to fruit trees

8. The common symptoms of herbicide exposure are curling and cupping
This plant was exposed to the herbicide 2,4-D

9. 3. Environmental Pollutants
High levels of fluoride in water or fluorine gas in the air can cause symptoms like this.
The damage is concentrated towards the margins of the leaf where fluorine tends to accumulate.

10. Air Pollution
Certain chemicals, such as O3, SO2, and NO2 are released into the air from factories, power plants, and automobile exhausts.
These chemicals can accumulate in the atmosphere insufficient concentration to cause damage to plants.
Ozone damage appears in the form of chlorosis, spots, and bleaching of young leaves.
This is common in certain regions of the country where there is a high ozone concentration in smog
Some of the air pollutants responsible for acid rain cause damage to vegetation in certain regions.

11. Ozone Damage on Morning
Glory Plant
Ozone Damage of
marijuana leaves

12. 4. Extreme Weather Conditions
Extremes of weather can also lead to plant injury
Cold injury
Low temperatures, like frost or freeze, can damage the exposed or sensitive organs (buds, flowers, young fruits) or may kill the entire plant.
As the new branch tips began to expand, a period of cold was severe enough to kill the growing tips
Heat injury
In this case the temperature was high enough and damage the plant tissue
When plants or plant parts are exposed to high temperatures for prolonged periods, symptoms of scorching or scalding may develop

13. High/Low Soil Moisture
Due to excessive watering, poor drainage or flooding may cause plants to turn yellow and be stunted.
Potted indoor plants may show poor development or root rots.
At the other extreme, low moisture or drought conditions can lead to poor development, wilting, and death of plants

14. High/Low Light Intensity
High light intensity is usually not a problem but low light conditions, especially for indoor plants, can lead to etiolation (tissue are yellowish)
A normal and an etiolated shoot under sun and
artificial lighting

15. Biotic Factors Caused by living factors such as : Fungi Bacteria
Viruses
Nematodes
Parasitic Plants

16. 1. Fungi Largest pathogen group More than 8000 pathogenic species
Vegetative growth through production of hyphae
Reproduce via spores

17. Fungal Hyphae

18. 2. Bacteria About 200 pathogenic species
Can be seen with a light microscope
Simple, unicellular
Reproduce by binary fission

19. 3. Virus Can only be seen using an electron microscope
Extremely simple- nucleic acid with a protein coat
Reproduce by taking over host reproductive machinery
Often associated with insect vectors

20. 4. Nematodes Parasitic worms Very complex compared to other pathogens
Usually seen only with a light microscope
Reproduce by eggs

21. 5. Phytoplasmas
A prokaryotic organism that lack a cell wall and survive in the phloem of plant
Round or elongate
Usually seen only with an electron microscope
Reproduce by binary fission