Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Plant Pathology and Microbiology

First Advisor

Charlotte R. Bronson

Second Advisor

Lois H. Tiffany


Mutants of Cochliobolus heterostrophus (Dreschsler) Dreschsler, the incitant of southern corn leaf blight, were identified that will enable researchers to gain a better understanding of fungal pathogenesis. Survivors of mutagenesis were screened on maize seedlings for loss of their ability to cause wild-type symptoms. Several survivors were identified that caused smaller lesions than wild type. Most grew more slowly on media than wild type. Therefore, studies were conducted to establish the minimum growth needed by C. heterostrophus to cause wild-type lesions. Even moderate reductions in vigor were shown to have dramatic effects on the ability of this fungus to cause disease. Mutants with colony diameters 80% of wild type or less caused lesions significantly smaller than wild type. One of the mutants had no apparent growth abnormalities, yet caused only poorly conidiating flecks on maize. Genetic analysis revealed that the mutant phenotype was controlled by a single locus, Les1. This is the first report of a gene in C. heterostrophus affecting lesion size. Also, a conidiation mutant was identified in which the phenotype was controlled by a single locus, Con1, which is the first conidiation gene identified in C. heterostrophus.



Digital Repository @ Iowa State University,

Copyright Owner

Peggy Rae Thorson



Proquest ID


File Format


File Size

66 pages