Flow Cytometric Analysis of Conidia of Fungi Isolated from Soybean Vascular Tissue

Flow cytometry was used to characterize isolates of Phialophora gregata using the fluorescence intensity of propidium iodide-stained conidia. The isolates differed in their mean fluorescence intensity, ranging from 100.0 to 129.7 arbitrary units (AU). When the number of fluorescent events was plotted against intensity of fluorescence, a single peak was observed. Fluorescent patterns of Acremonium isolates from soybean vascular tissue were compared with those of P. gregata. Their mean fluorescence intensity ranged from 76.4 to 88.0 AU. With some of these isolates, multiple peak histograms were observed, corresponding to multiple spore sizes as well as single and double nucleated conidia. Using flow cytometry, we were able to distinguish P. gregata isolates from those of Acremonium, based on mean fluorescence intensity and/or the presence of multiple peaks. Flow cytometric analysis of propidium-iodide stained conidia of Phialophora isolates should prove to be useful for determining the relative DNA content of different isolates collected from different geographic areas.