A Wind Tunnel for Controlled-Environment Studies of Ascospore Release byVenturia inaequalis

Abstract

We designed and built a bench-top wind tunnel for the study of ascospore release by Venturia inaequalis in controlled environments. Compressed air was forced through a column of water to adjust relative humidity. Air then entered one end of a 102-mm-diameter tube at the rate of 20 liters/min, passed over a platform holding a leaf sample bearing pseudothecia of V. inaequalis, and exited the tunnel through a 2- x 10- mm orifice 20 cm downwind of the sample. Ascospores exiting the orifice impacted on a clear plastic tape borne on a clock cylinder that revolved once in 6, 12, or 24 h. Temperature of the leaf sample was recorded by a data-logger. Light was directed to the leaf sample through a fiber-optic bundle coupled to a 150-W quartz-halogen lamp. The quality and intensity of the light could be adjusted by colored or neutral density filters at the source. Simulated rain was applied to the leaf sample at the rate of 5.3 cm/h through a fine-spray nozzle located 50 cm above the sample. The temperature of the simulated rain, as well as a water jacket surrounding the tunnel, was controlled by passing the water supply through a controlled-temperature bath. The tunnel maintained temperatures as low as 1.0 ± 0.2°C for 6 h, and could operate for up to 24 h continuously. Utility of the wind tunnel and reproducibility of obtained results was demonstrated using ascospores of V. inaequalis and Guignardia bidwellii.