Impact of tricyclazole and azoxystrobin on growth, sporulation and secondary infection of the rice blast fungus, Magnaporthe oryzae.

Rice blast, caused by Magnaporthe oryzae B. Couch sp. nov., is one of the most destructive rice diseases worldwide, causing substantial yield losses every year. In Italy, its management is based mainly on the use of two fungicides, azoxystrobin and tricyclazole, that restrain the disease progress. The aim of this study was to investigate and compare the inhibitory effects of the two fungicides on the growth, sporulation and secondary infection of M. oryzae. Magnaporthe oryzae mycelium growth was inhibited at low concentrations of azoxystrobin and relatively high concentrations of tricyclazole, while sporulation was more sensitive to both fungicides and was affected at similarly low doses. Furthermore, infection efficiency of conidia obtained from mycelia exposed to tricyclazole was affected to a higher extent than for conidia produced on azoxystrobin-amended media, even though germination of such conidia was reduced after azoxystrobin treatment. This study presents for the first time detailed azoxystrobin and tricyclazole growth-response curves for M. oryzae mycelium growth and sporulation. Furthermore, high efficacy of tricyclazole towards inhibition of sporulation and secondary infection indicates an additional possible mode of action of this fungicide that is different from inhibition of melanin biosynthesis.