Introductory Plant Pathology

Class 11

Naming

Signs and Symptoms

Individual Plants

Leaf Symptoms

Healthy Leaf	Healthy Leaf
Leaf in an incipient stage of infection, no particular taxon of pathogen indicated.	Leaf representing intervienal chlorosis (yellowing to browning between the veins.) Typical symptom of a vascular pathogen.
Leaf representing the mild symptoms of some early bacterial infections; notice around some infection sites there are "Green Islands". The Green Island effect is thought to be due to kinetin imbalance in the leaf tissue surrounding the infection site and is typical of some bacterial infections	Typical of a bacterial infection notice the lesions are vein limited producing an "angular leaf spot" type symptom. This pattern in reflective of the intercellular spread of the bacterium that is anatomically restricted by the plant's veins.
Fungi can be such "thugs" that their ramification through the leaf is not inhibited by veins; thus they often produce an irregular pattern.	This leaf is intended to represent the yellow halos present around leaf lesions where the pathogen is thought to produce a toxin as part of its pathogenic arsenal. It may be of fungal or bacterial origin.
Mosaic pattern typical of some viruses; notice there is a large amount of variation in the subtleness of the pattern

Original image: Botany 2402 University of Arkansas Little Rock
Root cap cells are constantly sloughing off and being replenished. They are a ready nutrient source for rhizosphere organisms. Because of their ephemeral nature, if a parasitic organism uses them as nutrient source that does not automatically make the organism a pathogen; However, it may provide an avenue for ingress.	The Zone of Elongation is a primary area for infection. Many rhizosphere organisms are chemotactically attracted specifically to this area.
As a primary infection focus one can expect a progression of disease symptoms and a pathogen ramifies. From this area, the vascular tissues as well as the outer cortex

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This page is authored and maintained by:

Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln