P-137 - A novel avirulence effector in Fusarium oxysporum f. sp. cepae

Fusarium oxysporum f. sp. cepae (Foc) causes basal rot disease in Allium species, including onions (Allium cepa L.) and shallots (A. cepa L. Aggregatum group). Among Allium species, shallots can be crossbred with onions and are relatively more resistant to Foc than onions. Thus, shallots are potential resources for identifying novel avirulence effectors in Foc and disease-resistance breeding in onions. However, the molecular interactions underlying the relationship between shallots and Foc remain unclear. Hence, we tried identifying avirulence effectors in Foc with the Foc-resistance shallot. This study demonstrated that SIX5, an effector derived from Foc (FocSIX5), acts as an avirulence effector in shallots. We achieved this by generating a FocSIX5 gene knockout mutant in Foc, for which experiments which revealed that it caused more severe wilt symptoms in Foc-resistant shallots than the wild-type Foc and FocSIX5 gene complementation mutants. Moreover, single amino acid substitution (R67K) in FocSIX5 was insufficient to overcome shallot resistance to Foc. In conclusion, this study indicated that the Foc-resistance shallot can be a great resource for identification of avirulence effectors in Foc and disease resistance breeding in onions, which lead to the development of Foc-resistance onion cultivars.