Genetic Diversity of Fusarium oxysporum Isolates from Common Bean and Distribution of Mating Type Alleles

Fusarium wilt caused by Fusarium oxysporum Schltdl. f.sp. phaseoli (Fop), is one of the important diseases of the common bean in Iran and many of the bean growing countries. Incidence of the disease has been reported in tropical and semi-tropical regions of the world. This study was carried out to characterize genetic diversity of F. oxysporum isolates from the common bean by vegetative compatibility test and random amplified polymorphic DNA (RAPD) analysis, as well as determining the frequency of mating type alleles (idiomorphs) in F. oxysporum population. In the present study, a total of 82 Fusarium sp. isolates collected from the major common bean growing areas of Tehran province were purified and identified. Among the isolates, 20 (24.4%), which were identified as F. oxysporum, were selected for the study. Nitrate non-utilizing (Nit) mutants were used to identify vegetative compatibility groups (VCGs). Ten VCGs were identified based on heterokaryon formation, 6 of which were single isolate VCGs. In order to study genetic diversity by RAPD, 6 random primers were used. Amplicons were analyzed and a dendrogram was created. The 20 isolates were grouped into 10 fingerprint groups. The results of VCGs and RAPD analyses suggest high genetic diversity among the 20 F. oxysporum isolates obtained from the bean samples. To determine the frequency of mating type alleles (MAT1-1 and MAT1-2) in F. oxysporum isolates, PCR was carried out using two pairs of specific primers. Among the tested isolates, two isolates were identified as MAT1-1 and 15 isolates as MAT1-2. There may be a direct relationship between the existence of both mating types idiomorphs and the large genetic diversity among the isolates.