Genetic diversity of Fusarium oxysporum f.sp. niveum responsible of watermelon Fusarium wilt in Tunisia and Spain

  Fusarium wilt is a serious disease, caused by Fusarium oxysporum f. sp. niveum (FON) and responsible of significant yield losses in watermelon crop in Tunisia. Thirty-nine FON isolates were collected from different infected watermelon fields in Tunisia and were identified on the basis of morphological features and by using one pair of species-specific primers Fn-1/Fn-2. Genetic diversity of the twenty-six FON isolates, originated from Spain and Tunisia, was studied by applying Inter simple sequence repeat genotyping. PCR amplification appears to be efficient to identify FON isolates amplifying only a single PCR band of approximately 800 bp. The RAMS study using two, bi and four trinucleotide microsatellites primers, showed a different genetic similarity degree among FON isolates. Seventy-one bands were amplified by four ISSR primer combinations. Diversity in the banding patterns obtained by DNA fingerprinting was always >50% and allowed us to distinguish all the isolates tested, according to number and size of the fragments, which ranged from 300 to 2800 bp. The genetic similarity values are comprised between 8 and 97%. UPGMA grouped the 45 genotypes into six main clusters at a similarity index value above 0.5, showing a relative genetic homogeneity and no correlation has been found among FON isolates and their origins. The most abundant Cluster VI comprising thirty-nine FON isolates