Molecular Karyotypes of Pathogeic Strains of Fusarium oxysporum

Abstract

Genetic diversity of pathogenic strains of the fungus Fusarium oxysporum was determied by analysis of electrophoretic karyotype, as well as by DNA variation detected by Restriction Fragment Length Polymorphisms (RFLPs) and Random Amplified Polymorphic DNAs (RAPDs). The electrophoretic karyotypes for 130 isolates of the fungus pathogenic to tomato, melon, and banana were analyzed. Electrophoretic karyotype variation, reflected in differences in apparent chromosome number and genome size, was observed even among isolates from the same host and sub specific category. Sub specific categories studied were forma specialis, vegetative compatibility group (VCG) and race. Chromosome number and genome size variation was less for isolates within the same VCG than for the collection of isolates as a whole. RFLP and RAPD analysis were performed on 62 isolates of F. oxysporum from tomato and melon. Polygenetic trees were constructed from genetic diversity data. The results support the hypothesis that isolates belonging to the same VCG originate from a single ancestor compared to other isolates. The results do not support the hypothesis that all isolates belonging to the same forma specialis originate from a common ancestor. These conclusions have profound implication for breeding resistance to diseases caused by particular formae speciales of F. oxysporum.