Barley Leaf Billiards: Spore Liberation via Rebound Collision from Jumping-Droplet Condensation

Presenter: Jack Tapocik, Mechanical Engineering

Authors: J. Tapocik, M. Swedat, G. Helm, H. Gruszewski, D. Schmale III, J. Boreyko

Abstract: Droplets growing near one another on nanostructured superhydrophobic surfaces can coalesce and spontaneously jump due to the release of capillary-inertial energy. This self-propelled jumping has been widely studied for enhancing heat transfer, anti-icing, and self-cleaning surfaces. In nature, this phenomenon occurs on wheat leaves during dew cycles, where coalescing droplets detach and transport pathogenic spores, a process that has been documented in previous research on infected wheat plants. We investigate jumping-droplet behavior on barley leaves infected with Puccinia hordei rust spores. Two distinct ejection modes are identified: wet spore ejection, where droplets carry attached spores during launch, and dry spore ejection, where spores are propelled without any droplets being attached. We demonstrate, for the first time, that dry particles can be launched by droplets rebounding from overlying particle clusters. These findings reveal a previously unexplored pathway for pathogen dispersal driven by self-propelled droplet dynamics.