Influence of Humidity, Red-Infrared Radiation, and Vibration on Spore Discharge byPyricularia oryzae

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Abstract
Under controlled conditions in which air temperature and air velocity (0.5 m/s) were kept constant, spore liberation from diseased rice culms was triggered by vibration and by increasing and decreasing relative humidities. Increasing relative humidity consistently triggered greater spore release than did decreasing relative humidity, and small increases near saturation were more effective than were increases at lower RH. Spore release when relative humidity was lowered from and returned to saturation exhibited a characteristic bimodal distribution: a peak associated with decreasing RH and a peak associated with increasing relative humidity. Spore discharge by P. oryzae, a fungus that liberates its conidia at night, was little influenced by exposure to red-IR radiation. Effects of vibration on spore liberation ranged from negligible to massive: release was greatest at reduced relative humidities and least at saturation; even at saturation appreciable numbers of spores were discharged. Red-IR radiation had little influence on vibrational release of conidia. The violent nature of spore discharge by P. oryzae was confirmed visually by using special illumination.