Evaluation and Characterization of Some Egyptian Fusarium oxysporum Isolates for their Virulence on Tomato and PCR Detection of (SIX) Effector Genes

Abstract

The genus Fusarium is comprises of different species which are furtherer divided into small groups called formae speciales according to their host specificity. It is remarkable that while an isolate belonging to particular formae speciales is considered highly pathogenic in a certain plant species, the many other isolates belonging to the same formae speciales may have no harm effect or even a beneficial relation to the same host plant. Traditionally, bioassays conducted under green house conditions were used to distinguish pathogenic and non-pathogenic isolates. However, such these techniques have some limitations due to the time consuming and the inconsistency of obtained results. In contrary, molecular identification techniques are candidate to play an important role in the characterization process of Fusarium isolates as well as with many other organisms. Recently, the ability of a Fusarium isolate to infect particular plant species was found to be dependent on specific genes encoding host determining ‘virulence factors’ that distinguish virulent from avirulent strains. More recently, eight fungal proteins were identified from xylem sap of infected plants, encompassing the small secreted proteins called Six1, Six2, Six3, Six4, Six5, Six6, Six7 and SIX 8. In the present study, the linkage between virulence potential of fifteen pathogenic isolates in addition to one non-pathogenic isolate, Fo162 , of Fusarium oxysporum and the presence of secreted in xylem effector genes (SIX) was determined. The results showed that the tested isolates were varied regarding to their pathogenicity potential toward tomato plants under greenhouse conditions. On the other hand, the amplicons of SIX1, SIX5 and SIX 7 were detected with most hyper virulent isolates while no amplicons for any tested SIX genes were observed with the non-pathogenic isolate (Fo162) as well as with the most hypo virulent isolates. These results, suggested that SIX1, SIX5 and SIX6 may play a distinct role in virulence potential of these Fusarium oxysporum isolates toward tomato plants under Egyptian conditions.