VIEW ARTICLE

Ecology and Epidemiology

Environmental Factors Initiating Liberation of Conidia of Powdery Mildews. G. C. Adams, Jr., Assistant professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; T. R. Gottwald(2), and C. M. Leach(3). (2)Research plant pathologist, USDA-ARS, Horticultural Research Laboratory, Orlando, FL 32830; (3)Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 76:1239-1245. Accepted for publication 24 June 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-1239.

Patterns of spore release were examined for Sphaerotheca pannosa on rose, Erysiphe pisi on pea, and E. graminis on brome-grass to determine the importance of environmental factors in removal of conidia from conidiophores of powdery mildews. No conidia of S. pannosa or E. pisi were released in the dark or light (80 μE m^-2 sec^-1) in still air (ambient air velocity <0.1 m sec^-1) at 100% relative humidity (RH) but when the relative humidity was lowered rapidly, conidia of S. pannosa were liberated in light and darkness. E. pisi released conidia in still air when decreasing relative humidity was accompanied by increasing temperature. Liberation of conidia of E. graminis from infected detached leaves was examined in a specially designed spore release apparatus using a linear air velocity of 0.5 m sec^-1. Conidia were liberated in darkness whenever the relative humidity was abruptly reduced or raised. Exposure to unfiltered infrared light also triggered discharge. The evidence for liberation of powdery mildew conidia by an active discharge mechanism is discussed.