Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

First Advisor

Raymond W. Schneider


A worldwide collection of 112 isolates of Fusarium oxysporum f. sp. lycopersici (FOL) from tomato was examined for pathogenicity, colony morphology, vegetative compatibility, and isozyme polymorphism. There were no correlations among colony morphology with age of culture, race, vegetative compatibility group (VCG), or geographic origin. Vegetative compatibility group 0030 contained all three races of FOL from throughout the world and all colony morphology types. Vegetative compatibility groups 0031 and 0032 contained races 1 and 2, but their geographic ranges were somewhat more limited. In addition, 50 isolates of FOL were the sole members of their own VCGs. Thus, there was not correlation between VCG and pathotype. Following isozyme analysis, all isolates of FOL and several other formae speciales were assigned to 35 electrophoretic phenotypes (EP). In that many EPs contained more than one race of FOL as well as other formae speciales, no clustering of isolates by race was observed. However, clustering of isolates by VCG was obvious. Vegetative compatibility groups 0030 and 0032 were clustered together on a major branch of the dendrogram while VCG 0031 appeared on a different branch. In addition, principal component analysis offered information regarding the relative position of each isolate with respect to all isolates examined. It was found that the majority of isolates in VCG 0030 were enclosed in the largest cluster, the cluster containing VCG 0032 fell entirely within the former, and the cluster containing VCG 0031 was shifted slightly away from VCG 0030. The majority of the remaining EPs contained single members, were in their own VCGs, and were scattered within other VCG clusters. A collection of 317 nonpathogenic isolates of F. oxysporum from symptomless tomato roots was examined for vegetative compatibility. One hundred and eighty six isolates were assigned to 48 VCGs containing two of 15 members from one to three different collection sites. There were 131 isolates that were single members of their own VCGs. Thus, the composition of the nonpathogenic population of F. oxysporum isolated from symptomless tomato roots is quite diverse.