Differences in spore size and atmospheric survival shape stark contrasts in the dispersal dynamics of two closely related fungal pathogens

Abstract

AbstractA frequently ignored but critical aspect of microbial dispersal is survival in the atmosphere. We exposed spores of two closely related, morphologically dissimilar, and economically important fungal pathogens to typical atmospheric environments and modeled their movement in the troposphere. We first measured the mortality ofAlternaria solaniandA. alternataconidia exposed to ranges of solar radiation, relative humidity, and temperature. We then measured survival in an advantageous environment over 12 days.A. solaniconidia are nearly 10 times larger thanA. alternataconidia and most die after 24 hours. By contrast, over half ofA. alternataconidia remained viable at 12 days. The greater viability of the smaller spores is counterintuitive as larger spores are assumed to be more durable. To elucidate the consequences of survival rates for dispersal, we deployed models of atmospheric spore movement across North American. We predict 99% of the largerA. solaniconidia settle within 24 hours, with a maximum dispersal distance of 100 km. By contrast, mostA. alternataconidia remain airborne for more than 12 days and long-distance dispersal is possible, e.g., from Wisconsin to the Atlantic Ocean. We observe that the larger conidia ofA. solanisurvive poorly but also land sooner and move over shorter distances as compared to the smaller conidia ofA. alternata. Our data relating larger spore size to poorer survival in the atmosphere and shorter distances travelled likely translate to other fungal species and highlight the potential for starkly different dispersal dynamics among even closely related fungi.