Genetic Relatedness within and between Formae Speciales of Fusarium oxysporum as Measured by DNA-DNA Reassociation Kinetics

Genetic relatedness among 18 formae speciales within Fusarium oxysporum was determined on the basis of DNA-DNA reassociation kinetics. DNA homology values were high (more than 95%) between isolates within the same forma specialis, while isolates of different formae speciales showed lower values (63 to 86%) of DNA homology. Comparatively high homology values (90 to 95%) were observed within isolates of different formae speciales causing disease on the Cruciferae or the Cucurbitaceae plants. Isolates of F. oxysporum consistently showed low homology values (36 to 48%) with isolates of F. solani. These results suggest that formae speciales of F. oxysporum can be differentiated genetically from each other, indicating that the reassociation analysis of DNA may be a useful tool in studies involving classification and phylogeny of subspecific taxa in this species.