Pathogen culture

We collected teliospores of P. horiana from the abaxial side of chrysanthemum leaves infected with white rust and placed the teliospores in 1 mL of sterile water. We adjusted the concentration of the teliospores to 40–60 per field of vision under BA400 microscope (Motic, Xiamen). We removed a drop of teliospore suspension with a sterile straw and then dropped the suspension onto a glass substrate that was placed on a U-shaped rod in a culture dish covered with wet filter paper. The teliospores were allowed to germinate under a temperature of 18–21 °C for 24 h, after which we resuspended the germinated spore suspension in sterile water with 0.05% (w/v) Tween 20 pH (4–6.5). We then sprayed the abaxial side of the plant leaves evenly with the solution before covering the plants with plastic film and moving them into the dark and high humidity. After 16–24 h, we transferred the infected plants to new growth conditions of 17 °C and 50% humidity. The fungi started to release basidiospores, which germinated within 3 h Basidiospores invade leaf surfaces^47–51.