Pathogenicity and genetic diversity of Fusarium oxysporum isolates from corms of Crocus sativus

•Three different formae speciales iridiacearum, croci and saffrani are present in saffron corms rot caused by Fusarium oxysporum.•Fusarium oxysporum f. sp. iridiacearum infects all the iridaceae crops tested, Fusarium oxysporum f. sp. croci attacks Crocus sp. species, Fusarium oxysporum f. sp. saffrani is pathogenic only to saffron.•Differences on cellophane degradation response were obtained suggesting different physiological traits on virulence of our isolates.•ISSR markers clearly separated F. oxysporum f. sp. croci, F. oxysporum f. sp. saffrani and F. oxysporum f. sp. iridiacearum from the other formae speciales tested but not among them.•None of the mycotoxins studied were detected neither by HPLC analysis nor by PCR assay on these isolates.

Crocus sativus is a triploid sterile plant and autumnal flowering geophyte with corms. As a subterranean organ, the corm is susceptible to diseases caused by fungi, bacteria, nematodes and viruses. Fusarium corm rot incited by F. oxysporum is the most destructive disease in saffron, having caused severe yield losses in saffron producer's countries. Infected plants die off early, resulting in reduction of corm yield, quality and flower and stigma production. Little is known about the formae speciales attacking saffron and less about the relationship among the fungus and the possible hosts. In this study we investigate the formae speciales which colonize saffron and their relationship with some members of iridaceae such as C. vernus (ornamental crocus), gladiolus and narcissus using pathogenicity tests; we determine whether different pathogenic isolates of F. oxysporum can be distinguished by ISSR, and we analyze the genetic relationships and variability among some isolates of these pathogens. We found two formae speciales iridiacearum and croci which attack different iridaceous crops and Crocus sp., respectively and we suggested the creation of a new formae speciales saffrani which shows only pathogenicity on saffron corms. From ISSR analysis, the unweighted paired group method with arithmetic averages cluster analysis (UPGMA) was used to discriminate the F. oxysporum isolates, we were able to differentiate among f. sp. from saffron corms and other formae speciales of F. oxysporum but not among formae speciales iridiacearum, croci and saffrani. Furthermore, we searched for fum1, tri5, tri7 and tri13 genes using PCR assays, however, all the isolates from saffron corms were negative.

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