DISEASE IN
PLANTS
INTRODUCTION
Estimated annual crop losses worldwide
31-42%
Lower in the more developed countries
Higher in the developing countries
Average of total losses, 36.5%
14.1% caused by diseases ($220 billion)
Should be added 6-12% losses of crops after harvest
Not yet include losses caused by environmental factors
Freezes, droughts, air pollutants, nutrient deficiencies, and toxicities
10.2% caused by insects
12.2% caused by weeds
Concept of disease in plants
Disease in plants can be defined as:
The series of invisible and visible responses of plant cells and tissues to a pathogenic microorganism or environmental factor that result in adverse changes in the form, function, or integrity of the plant and may lead to partial impairment or death of
plant parts or of the entire plant.
In some disease, hyperplasia or hypertrophy occur to produce abnormal amorphous overgrowths (tumors) or abnormal
organs.
Types of plant diseases
leaf spot, blight, canker, damping-off, dieback, mosaic, rot, scab, shot hole, vascular wilt, downy mildew, powdery
mildew, rust, smut, gray mold, anthracnose, chlorosis, stunting, blast, gall
Schematic diagram of the shapes and sizes of certain plant pathogens in relation to a plant cell.
Infectious, or biotic, plant diseases
Diseases caused by fungi
Diseases caused by prokaryotes (bacteria and phytoplasma)
Diseases caused by parasitic higher plants and algae
Diseases caused by viruses and viroids
Diseases caused by nematodes
Diseases caused by protists
Pests: Living things that affect humans, animals, or plants adversely
Methods of penetration and invasion by fungi
Methods of penetration and invasion by
bacteria
Mechanical inoculation and early stages in the systemic distribution of viruses in plants
etration and invasion by nematodes
Means of dissemination of fungi and bacteria
Forms and locations of survival of fungi and bacteria between crops
Noninfectious, or abiotic, plant diseases
too low or too high a temperature
lack or excess of soil moisture
lack or excess of light
lack of oxygen
air pollution
nutrient deficiencies
mineral toxicities
soil acidity or alkalinity (pH)
•
Other factors may cause plant disorder
– Chemical agents
– Wind
– Mechanical injury
– Ice storm
– Electric storm
