Atmospheric Concentration of Cladosporium Spores

Abstract

The authors propose a hypothesis to explain the daytime double maxima which commonly occur in Cladosporium spore concentration. The mature spores become airborn as the infected leaves are jarred and vibrated by the increasing morning turbulence. The number of spores increases until the spore source is depleted. This occurs in the forenoon. The number of airborne spores is now constant. Further turbulence carries them ever higher into the air over the fields. This increases the air volume in which the spores are carried. In effect, the concentration of the spores is lowered, accounting for the midday minimum. During the afternoon or early evening, turbulence lessens. The spores begin to settle, occupying less air volume and giving rise to the 2nd maximum. Gradually the spores settle out of the air, and their number falls to the night-time minimum. Rain evidently has 2 effects on the concentration of airborne Cladosporium spores. A light, misting rain that wets the leaves without vibrating them washes the spores down onto the leaf surface, not into the air. At the same time the mist scrubs the airborne spores from the air, reducing their number. Conversely, the heavy, wind-driven drops of thunderstorms and summer showers increase the number of airborne spores. Not only do these turbulent storms jar and whip infected leaves but the wind-driven drops are extremely efficient in detaching any remaining conidia.