Fitness and cross-resistance of Fusarium fujikuroi strains resistant to prochloraz from field

Bakanae disease is the most notorious seed-borne fungus disease affecting rice. Prochloraz, an imidazole fungicide with broad-spectrum and systemic activity, is the most widely used chemical for the control of this disease at present. Prochloraz-resistant and prochloraz-sensitive strains of Fusarium fujikuroi collected from fields were used in this study to characterize their fitness and cross-resistance between prochloraz and other fungicides. The results showed that most of the resistant strains could be inherited stably. No difference was observed between the resistant and sensitive strains in terms of temperature sensitivity. With regards to mycelial growth rate, conidium production, conidium germination rate and pathogenicity, some of the resistant strains were significantly higher than those of the sensitive ones. There is no cross-resistance found among prochloraz, triazoles and 2-cyanoacrylate fungicides. This study showed that some field F. fujikuroi strains with resistance to prochloraz had a strong fitness, which might develop into dominant population in the fields. In order to slow down the development of fungicide resistance, fungicides with different modes of action should be alternately applied in the field.