Synergistic Effects of Isolates and Succinate Dehydrogenase Inhibitors Fungicides against Gray Mold on Tomato.

Gray mold caused by is a devastating disease in tomatoes. Site-specific fungicide application is still key to disease management; however, chemical control has many drawbacks. Here, the combined application of a biological agent, , with newly developed succinate dehydrogenase inhibitors (SDHI) fungicides showed stronger synergistic effects than the application of SDHI fungicides alone on tomato gray mold control. 67-1 has been reported as an efficient biological control agent (BCA) for . Little information is currently available about the combination of and fungicides in the control of gray mold. By testing the sensitivity to fungicides with different action mechanisms, isolates showed high tolerance to SDHI fungicides (1000 μg mL) on PDA, and the conidial germination rate was almost not affected under 120 μg mL of fluxapyroxad and fluopyram. In greenhouse experiments, the control effect of the combination of and fluxapyroxad or fluopyram against tomato gray mold was significantly increased than the application of BCA or SDHI fungicides alone, and the combination allows a two-fold reduction of both the fungicide and BCA dose. Further, the biomass of and on tomato plants was determined by qPCR. For , the trend of detection level for different treatments was consistent with that of the pot experiments, and the lowest biomass of was found when treated with combined with fluxapyroxad and fluopyram, respectively. For , qPCR assay confirmed its colonization on tomato plants when mixed with fluopyram and fluxapyroxad. These results indicated that combining 67-1 with the SDHI fungicides could synergistically increase control efficacy against tomato gray mold.