Disease Lesion Mimic Mutants in Corn

Disease Lesion Mimic Mutants

Disease lesion mimic mutants are a class of mutants in plant species that cause the formation of lesions resembling disease symptoms without the presence of a pathogen.
Lesion mimic mutants (abbreviated Les or les to indicate dominant or recessive mutants) are common in plant species.
Over 50 lesion mimic loci have been identified in the corn genome and research suggests more than 200 may exist.

Lesion Formation

The formation of lesions on plant tissue is part of a defense system against attacks by pathogens.
Lesions are formed when the plant responds to the presence of a pathogen by triggering the rapid death of the cells surrounding the infection site, known as the hypersensitive response.
This response is an active process in which the cells undergo programmed cell death.
Lesion mimic phenotypes in plants have generally been attributed to mutations that cause the triggering of the hypersensitive response mechanism independent of the presence of a pathogen or affect the control of this process once it has been initiated (hence the term, disease lesion mimic mutants).
This is true of some mutations; however, the sheer number of lesion mimic loci in corn and their presence throughout the genome suggest that pathways other than disease response could be involved as well.
Recent research has shown that lesion mimic phenotypes can be caused by mutations associated with a variety of pathways.

Appearance of Lesion Mimics

Frequency and Timing

Lesion mimic mutations do not occur at high frequencies so symptoms will often appear on an individual plant surrounded by unaffected plants.
The majority of lesion mimic mutants in corn will begin expressing visual symptoms within a few weeks of emergence.
A smaller number of lesion mimic mutants will show up around the time of tasseling.
Symptoms can appear similar to those of a residue-borne foliar disease because they can begin on the lower leaves and spread up the plant.

Phenotypes

Phenotypes associated with lesion mimic mutants vary in the size, number, and color of lesions.
In most cases, lesions appear only on leaf tissue, but some mutants will produce lesions on the leaf sheath and stalk.

Factors Affecting Phenotypic Expression

Light and Temperature

Expression of lesion mimic mutants is often light and temperature dependent, with intense light and high temperatures often favoring higher levels of expression. Low night temperatures are also known to favor expression in some cases.

Field Conditions

Expression of lesion mimic mutants appears to be favored by saturated soils and environmental stresses. Symptoms tend to be observed more frequently in corn following corn and in irrigated fields.

Hybrid Genetics

Hybrid genetics are known to have a large influence on the expression of lesion mimic mutants, although symptoms have been observed in numerous hybrids from multiple seed companies.

Management Considerations

Yield of affected plants can be reduced due to the loss of photosynthetically active leaf area. Yield impact varies based on the amount of leaf area affected.
Since symptoms are caused by a genetic mutation and not a fungal pathogen, fungicides have no effect.
Lesions can often resemble those caused by various fungal and viral diseases of corn. A diagnostic lab can test a sample to determine whether or not the symptoms are due to a pathogen.

References

Johal, G.S., S.H. Hulbert, and S.P. Briggs. 1995. Disease lesion mimics of maize: a model for cell death in plants. BioEssays 17:8.
Johal, G.S. 2007. Disease lesion mimics mutants of maize. Online. APSnet Features. doi: 10.1094/APSnetFeatures-2007-0707.
Moeder, W. and K. Yoshioka. 2008. Lesion mimic mutants. Plant Signaling & Behavior. 3(10):764-767.