CHAPTER 4 Plant Pathogen Relationship Weapon of Attack

Plant Pathogen Relationship Parasite – An organism living on or in another living organism and obtaining food from the host Obligate parasite – only live (grow and reproduce) on or in the living host Nonobligate parasite – can live either on living or dead host Facultative parasite – most of the time live on the dead host, but under certain condition can live on the living host (become parasite)

Saprophyte – an organism that uses dead organic material for food Obligate Saprophyte – only live on the dead host Nonobligate Saprophyte – can live either on dead or living host Facultative saprophyte - most of the time live on the living host, but under certain condition can live on the dead host (become saprophyte)

Weapon of attack Mechanical weapon  Appressorium (fungus)  Stylet (Nematodes) Chemical weapon  Enzymes  Microbial toxins  Growth regulators

Mechanical Weapon Some fungi and nematodes penetrate plant surface using special structures Before penetrate into the plant, they must adhere to the plant surface first.

Chemical weapon- Enzymes a. Enzymes that degrade cell wall substances Cutinase  degrade cutin Pectinase  degrade pectice substances Cellulase – degrade cellulose Hemicellulases – degrade hemicelluloses Ligninases – degrade lignin

b. Enzymes That Degrade Substances Contained in Plant Cells Proteolytic enzymes – degrade proteins Amylases – degrade starch Lipases, phospholipases – degrade lipids

Chemical weapon- Microbial toxins Substance produced by plant pathogenic microorganism and caused toxicity to plant Seriously damaging and killing the plant cells. Affecting permeability of cell membrane, inactivating enzymes and interrupt enzyme reaction.

a)Non host specific Toxin that affect a wide range of host plants i. Tabtoxin Produced by bacterium Pseudomonas syringe ii. Phaseolotoxin Produced by bacterium Pseudomonas syringe iii. Tentoxin Produced by fungus Alternaria alternata

Host-Specific The toxin specific to only certain particular host i. Victorin / HV Toxin produced by Cochliobolus victoriae (fungus) ii. T-Toxin produced by T-race of Cochliobolus victoriae (fungus) iii. HC-Toxin produced by Cochliobolus carbonum iv. AM-Toxin produced by apple pathotype of Alternaria alternata –

Chemical weapon- Growth regulators A natural substance that regulates the enlargement, division, or activation of plant cells. All plant already naturally produce this growth regulator. Plant pathogen will produce the same growth regulator and caused hormonal imbalance in plant.

Example of hormones:  Auxins  Gibberalins  Cytokinins  Ethylene  polysaccharides

Hormonal imbalance will lead to abnormal plant growth such as  Stunting  overgrowths  excessive root branching  stem malformation