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Characterization of Endophytic Fungi in Healthy Leaves of Nicotiana spp.. Harvey W. Spurr, Jr., Research Plant Pathologist, Southern Region, Agricultural Research Service, U.S. Department of Agriculture, Oxford Tobacco Research Laboratory, Oxford, N. C. 27565; Ronald E. Welty, Research Plant Pathologist, North Carolina State University, Raleigh 27607, Professor and Associate Professor of Plant Pathology. Phytopathology 65:417-422. Accepted for publication 23 October 1974. DOI: 10.1094/Phyto-65-417.

Endophytic fungi were studied in healthy appearing tobacco leaves from field-grown plants. Surface sterilization with sodium hypochlorite was reaffirmed as adequate for removing or destroying epiphytes on leaves. Proximal and distal portions of the leaves had similar endophytic populations. Endophytic fungi were frequently observed in cross sections of tobacco leaf tissues, and in sections with the epidermis removed. They were varied in morphology, were found in all leaf tissues, and increased in number with leaf growth and development. Certain differences in endophytic populations appeared to be host-specific. Alternaria spp. were frequent endophytes in all of the Nicotiana spp. examined. Penicillium, Aspergillus, and Cladosporium spp., respectively, were next most frequent. Most endophytic Alternaria isolates from healthy appearing leaf tissues were unable to induce symptoms under conditions favoring the brown-spot pathogen, A. alternata. Endophytes were not found in young seedlings in the plant bed protected with ferbam fungicide. After these seedlings were transplanted and the fungicidal treatment discontinued, endophytic fungi became established in the leaves. The number of endophytes changed as the tobacco leaves grew and developed. Alternaria spp. steadily increased in number or frequency whereas Cladosporium spp. fluctuated. The frequency pattern of endophytic fungi was similar in leaves from four different stalk positions. The influence of endophytic fungi in disease development and senescence are discussed.