*2.2.1* Fusarium oxysporum *'formae speciales (f.sp.)' and race*

Host range of plant species are grouped into a *forma specialis* and subdivided into races by cultivar specialization [44]. More than 100 *formae speciales* of *F. oxysporum* causing diseases in different plant species. *Forma specialis* is determined by testing the fungus for pathogenicity on various plants species and race is determined by pathogenicity on cultivars of a single plant species. Molecular tools can identify pathogenic strains and in some cases races of the pathogen. A *forma specialis* of fusarium fungus normally affects only one primary host species, but colonize endophytically in the roots of secondary hosts. Many *formae speciales* were named according to the host plant either the genus name/species name. A reported 106 *formae speciales* and 58 additional host plants which have no *forma specialis* as characterized and races based on cultivar identified 25 of the 106 *formae speciales* (**Table 2**) [67].
