Study on sensitivity of Phytophthora nicotianae to flumorph and combinatory fungicide

To investigate the effects of Phytophthora nicotianae to flumorph and delay the development of its flumorph resistance, the sensitivity of P. nicotianae to flumorph was determined by a colony growth rate method. In addition, the effects of Phytophthora nicotianae on a combinatory fungicide (flumorph + metalaxyl) were evaluated by the Wadley method. The combination ratio of the fungicide with a high antibacterial activity was selected and the synergistic effects of the flumorph and metalaxyl combination and Bacillus amyloliquefaciens ZY-9-13 were evaluated by the Abbott model. The results showed that the EC₅₀ values of 71 strains of P. nicotianae to flumorph ranged from 0.428 5 to 0.760 8 μg/mL with a mean of 0.588 4 μg/mL. The sensitivity distribution was unimodal, and there was no resistant isolate in the 71 strains. The additive effect of the combinatory fungicide at a volume ratio of 1:10 was the most effective (EC₅₀=0.398 7 μg/mL). The growth of B. amyloliquefaciens was not affected by the fungicide. The combined application of the fungicide at different concentrations and ZY-9-13 (10¹⁰ cfu/mL) had better inhibitory effects comparing with a single application of each fungicide, and there existed a synergistic effect between them.