A) Changes in cell permeability:

• Toxins kill plant cells by altering the permeability of plasma membrane, thus permitting loss of water and electrolytes and also unrestricted entry of substances including toxins.
• Cellular transport system, especially, H + / K + exchange at the cell membrane is affected.

B) Disruption of normal metabolic processes :

• Increase in respiration due to disturbed salt balance
• Malfunctioning of enzyme system Ex: Piricularin inhibits polyphenol oxidase
• Uncoupling of oxidative phosphorylation

C) Interfere with the growth regulatory system of host plant :

• Ex: Restricted development of roots induced by Fusarium moniliforme