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The Role of Abscised Cylindrocladium-Infected Azalea Leaves in the Epidemiology of Cylindrocladium Wilt of Azalea. R. G. Linderman, Research Plant Pathologist, Western Region, Agricultural Research Service, United States Department of Agriculture, Ornamentals Research Laboratory, Corvallis, Oregon 97330; Phytopathology 64:481-485. Accepted for publication 15 October 1973. DOI: 10.1094/Phyto-64-481.

Detached azalea leaves, inoculated with either Cylindrocladium scoparium or C. theae, and placed on the rooting medium between rows of azalea cuttings in propagation flats under mist, provided inoculum which induced root and stem rot and death of many cuttings before transplanting. Less severe root and/or stem infections also occurred that did not cause wilt and death of plants until some months after transplanting. Cuttings near the inoculum source (infected leaves) died before those farther away. Of the surviving 9-mo-old azalea plants from each of three propagation flats to which Cylindrocladium-infected leaves were added, 36.2% (C. scoparium flat), and 60.6% and 28.6% (C. theae flats) were infected. Some of the surviving infected plants were stunted and chlorotic and showed dark streaks in the internal stem wood, and the remainder had only root infections and no above-ground symptoms. Direct observations and indirect evidence indicated that in mist propagation flats C. scoparium or C. theae spread from infected "inoculum leaves" to healthy cuttings by: mycelial growth and splash-disseminated conidia. Conidia washed from one C. scoparium inoculum leaf per pot were sufficient inoculum to induce wilt on cuttings subsequently rooted therein. Furthermore, C. scoparium inoculum leaves placed beneath the root ball of azalea cuttings at transplanting induced root and basal stem infections, but these had not progressed to the wilt stage by 8 mo.

Additional keywords: infected carriers.