According to the source of origin, toxins are divided into 3 broad classes namely, pathotoxins, vivotoxins and phytotoxins.

1. Pathotoxins:

• These are the toxins which play a major role in disease production and produce all or most of the symptoms characteristic of the disease in susceptible plants.
• Ex: Victorin: Cochliobolus victoriae (Helminthosporium victoriae), the causal agent of Victoria blight of oats. This is a host specific toxin.

Other examples:

a) Selective :

T- toxin: Helminthosporium maydis race T

HC-toxin: Helminthosporium carbonum

HS- toxin: Helminthosporium sacchari

Phyto-alternarin: Alternaria kikuchiana

PC- toxin: Periconia circinata

b) Non-selective :

Tentoxin: Alternaria tenuis

Tabtoxin or wild fire toxin: Pseudomonas tabaci

Phaseolotoxin: Pseudomonas syringae pv. Phaseolicola

c) Produced by plant or plant X pathogen interaction :

Amylovorin: Erwinia amylovora (Fire blight of apple and pears)

2) Phytotoxins:

• These are the substances produced in the host plant due to host-pathogen interactions for which a causal role in disease is merely suspected rather than established.
• Ex: Alternaric acid – Alternaria solani

3) Vivotoxins:

• These are the substances produced in the infected host by the pathogen and / or its host which functions in the production of the disease, but is not itself the initial inciting agent of the disease.
• Fusaric acid – Wilt causing Fusarium sp.
• Lycomarasmin – Fusarium oxysporum f.sp. lycopersici
• Piricularin – Pyricularia oryzae