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Induced Autofluorescence in Fungi and Its Correlation with Viability: Potential Application of Fluorescence Microscopy. Cathy H. Wu, Graduate research assistant, Agricultural Research Service, U.S. Department of Agriculture, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907; H. L. Warren, plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907. Phytopathology 74:1353-1358. Accepted for publication 22 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-1353.

A microscopic test based on cytoplasmic autofluorescence induced by specific stresses was developed. Conidia of 15 species of fungi were subjected to heat stress that resulted in death of the conidia. Conidia of seven of the 15 heat-stressed species were induced to autofluoresce brightly. As with natural autofluorescence, the artifically induced autofluorescence was inversely related to viability in these seven species. Also an increase in percentage of fluorescent conidia and a reciprocal decrease in percentage of germination was observed when conidia of Colletotrichum graminicola were incubated in Tween-80 (0.0- 2.0%) or different relative humidities (0, 53, and 100%). The correlation between natural or induced autofluorescence and conidial germination of C. graminicola was highly significant (r=- 0.982). Thus, fluorescence microscopy may complement or replace germination assays or vital stain tests to determine viability of fungal propagules. The procedure is precise, rapid, and easy, and has potential applications in mycological, pathological, and ecological studies of fungi.