A FLOW VISUALIZATION STUDY OF SPORE RELEASE USING A WIND TUNNEL-MOUNTED LASER-LIGHT SHEET

A phase Doppler anemometry system in combination with a laser light sh eet was used in a low-speed recirculating wind tunnel to examine the f low field around an individual leaf. Turbulence similar to that encoun tered near the surface of the earth in a neutral stability boundary la yer was generated using a grid at the upwind end of the wind tunnel te st section. Individual healthy and diseased plant leaves were introduc ed into the tunnel with the leaf tip pointing downwind. The Mie-scatte red radiation from the spores departing the diseased leaf was captured on videotape. Image processing software was used to enhance the visua l quality of the individual frames from the videotape and to make spor e velocity calculations. Three main vortex regions around the leaf wer e identified. The importance of these regions to the separation of the spores from the leaf surface and their subsequent downwind movement w as analyzed.