Coherent spore dispersion via drop-leaf interactions

TL;DR

This study uncovers how leaf flexibility and raindrop impacts create flow patterns that significantly enhance pathogen spore dispersion, providing insights for better crop disease management.

Contribution

It introduces a theoretical model linking leaf elasticity and fluttering to spore transport, revealing mechanisms behind pathogen dispersion on flexible leaves.

Findings

Flexible leaves generate vortex dipoles increasing spore transport energy.

Shorter, wider leaves promote greater pathogen spread.

Leaf rigidity affects dispersion through damping effects.

Abstract

The dispersion of plant pathogens, such as rust spores, is responsible for more than 20% of global yield loss annually, and poses a significant threat to human health. However, the release mechanics of pathogens from flexible plant surfaces into the canopy is not well understood. In this study, we investigated the interplay between leaf elasticity and raindrop momentum, revealing how it induces flow coherence and enhances spore transport with 2-10 times greater energy compared to impacts on stationary surfaces. We observed that a flexible leaf generates vortex dipoles, leading to a super-diffusive stream flow. We then developed a theoretical model that accurately predicted the average air flux from leaf edges and the vortex strength to be proportional the vibration speed of the leaves. With Lagrangian diagnostics, we further revealed the presence of hyperbolic and elliptical coherent structures around fluttering leaves, providing the dynamical description of spore transport. Our model demonstrated that a leaf aspect ratio (length/width) negatively correlates with dispersion, indicating that shorter and wider leaves promote greater pathogen spread. Additionally, we found that leaf rigidity positively correlates with dispersion due to damping effects. These mechanistic insights would help the construction of physically informed analytical models for improve local crop disease management.