Aeciospore ejection in the rust pathogen Puccinia graminis is driven by moisture ingress

Abstract

Fungi have evolved an array of spore discharge and dispersal processes. Here, we developed a theoretical model that explains the ejection mechanics of aeciospore liberation in the stem rust pathogen Puccinia graminis. Aeciospores are released from cluster cups formed on its Berberis host, spreading early-season inoculum into neighboring small-grain crops. Our model illustrates that during dew or rainfall, changes in aeciospore turgidity exerts substantial force on neighboring aeciospores in cluster cups whilst gaps between spores become perfused with water. This perfusion coats aeciospores with a lubrication film that facilitates expulsion, with single aeciospores reaching speeds of 0.053 to 0.754 m·s⁻¹. We also used aeciospore source strength estimates to simulate the aeciospore dispersal gradient and incorporated this into a publicly available web interface. This aids farmers and legislators to assess current local risk of dispersal and facilitates development of sophisticated epidemiological models to potentially curtail stem rust epidemics originating on Berberis.

Bueno-Sancho et al. use high-speed videography and mathematical modelling to examine aeciospore dispersal mechanics of the stem rust fungus Puccinia graminis. Their model shows that aeciospore ejection is driven by peridium rupture and moisture ingress, with dispersal projections encapsulated in a web interface to help assess risk of disease spread to nearby cereal crops.