- Normal cell division, differentiation and development.
- Uptake of water and nutrients from the soil.
- Synthesis of food from sunlight by photosynthesis.
- Translocation of water and food to the sites of necessity through xylem and phloem
- Metabolism of synthesized material
A diseased plant fails to perform one or more of these functions. The effect of a disease on functioning of an organ depends on which cells or tissues were first attacked by the pathogen. Thus, disease can be defined as malfunctioning process that is caused by continuous irritation by a pathogen (Dimond, 1959).