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Influence of Relative Humidity and Red-Infrared Radiation on Violent Spore Release by Drechslera turcica and Other Fungi. Charles M. Leach, Professor of Plant Pathology, Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331; Phytopathology 65:1303-1312. Accepted for publication 17 June 1975. DOI: 10.1094/Phyto-65-1303.

The relationship of relative humidity and light to spore release by Drechslera turcica was studied under precisely controlled and monitored conditions of temperature, light, air velocity, and relative humidity. Spore release was triggered (i) by lowering relative humidity from near saturation; (ii) by increasing the relative humidity from a lower to a higher level; and (iii) by exposing sporulating specimens to light. Both infrared and shorter red wavelengths stimulated spore release. Direct observation of spore discharge by utilization of the Tyndall effect, demonstrated that spores are violently propelled into the air. The relationship of relative humidity and light to spore release was studied for miscellaneous other fungi having exposed, nonmucilaginous spores borne singly or in chains on simple sporophores (Phytophthora infestans, Cercospora sp., Stemphylium botryosum, Alternaria tenuis, Cladosporium fulvum, Sphaerotheca fuligena). Spore release in all those tested was similar to that in D. turcica; spores were discharged as the relative humidity was lowered from saturation in the presence of light (infrared lamp); and, all violently discharged their spores when exposed to light from an incandescent lamp. Uredospores of a rust associated with Hordeum vulgare, aeciospores of a rust associated with Senecio vulgaris and basidiospores of Agaricus bisporus also violently released their spores when exposed to light.