Characterization of Fusarium oxysporum Isolates from Common Bean and Sugar Beet Using Pathogenicity Assays and Random-amplified Polymorphic DNA Markers

Fusarium wilt is an economicallyimpor tant fungal disease of common bean and sugar beet in the Central High Plains (CHP) region of the USA, with yield losses approaching 30% under appropriate environmental conditions. The objective of this studywas to characterize genetic diversityan d pathogenicityof isolates of Fusarium oxysporum obtained from common bean and sugar beet plants in the CHP that exhibited Fusarium wilt symptoms. A total of 166 isolates of F. oxysporum isolated from diseased common bean plants were screened for pathogenicityon the universal susceptible common bean cultivar UI 114 . Onlyfour of 166 isolates were pathogenic and were designated F. oxysporum f.sp. phaseoli (Fop). A set of 34 isolates, including pathogenic Fop, F. oxysporum f.sp. betae (Fob) isolates pathogenic on sugar beet, and non-pathogenic (Fo) isolates, were selected for random-amplified polymorphic DNA (RAPD) analysis. A total of 12 RAPD primers, which generated 105 polymorphic bands, were used to construct an unweighted paired group method with arithmetic averages dendrogram based on Jaccard’s coefficient of similarity. All CHP Fop isolates had identical RAPD banding patterns, suggesting low genetic diversityfor Fop in this region. CHP Fob isolates showed a greater degree of diversity, but in general clustered together in a grouping distinct from Fop isolates. As RAPD markers revealed such a high level of genetic diversityacross all isolates examined, we conclude that RAPD markers had onlylim ited usefulness in correlating pathogenicityamong the isolates and races in this study