Molecular identification of formae specialis and racial identity in Iranian strains of Fusarium oxysporum f. sp. lycopersici: detection of avirulence genes

Fusarium oxysporum f. sp. lycopersici (Fol) is the causal agent of vascular wilt in tomato, an important plant disease in Iran. Four monogenic resistance genes in tomato are used for identification of races of Fol and their corresponding avirulence genes Avr1, Avr2 and Avr3 were identified in pathogen one of which, Avr2, is f.sp. specific. Hence they can serve as reliable markers for racial identity and f.sp discrimination. These markers have been used for strains from other countries except Iran. Furthermore, a point mutation in Avr3 can lead to enhanced virulence of Fol on a susceptible tomato cultivar. To identify forma specialis and racial identity, Avr genes were studied in a collection of Iranian strains. Results revealed that PCR assay is very efficient in distinguishing between non-pathogenic and low virulence strains and in the vast majority of strains, avirulence genotype was consistent with Fol race1. Furthermore, to determine whether allelic variation of Avr3 could separate strains of different degrees of virulence, Avr3 wassequenced in Fol strains with high and low virulence. The resultsrevealed that allelicvariation of Avr3 was not correlated with degree of virulence in Iranian strains.