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Influence of Humidity, Red-Infrared Radiation, and Vibration on Spore Discharge by Pyricularia oryzae. C. M. Leach, Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis, 97331; Phytopathology 70:201-205. Accepted for publication 5 September 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-201.

Under controlled conditions in which air temperature and air velocity (0.5 m/sec) 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-infrared radiation (IR). Effects of vibration on spore liberation ranged from negligible to massive: release was greatest at reduced relative humidities and least at saturation; however, even at saturation appreciable numbers of spores were discharged. Red-infrared 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.