RELATIVE NUCLEAR-DNA CONTENT OF RUST FUNGI ESTIMATED BY FLOW-CYTOMETRY OF PROPIDIUM IODIDE-STAINED PYCNIOSPORES

Flow cytometry was used to estimate the relative nuclear DNA content o f pycniospores from 85 collections of 13 species of rust fungi. For a given sample, 10,240 fluorescent events were measured. Sufficient pycn iospores could be obtained from as little as one well-developed pycnia l cluster, Numbers of fluorescent events plotted against intensity of fluorescence usually exhibited a single well-defined peak with coeffic ients of variation of 10% or less. Results confirmed and extended data for small numbers of basidiospores obtained earlier with the microsco pe photometer. DNA content relative to that of a Puccinia hordei stand ard was estimated to be as follows (in order of increasing DNA content ): P. lagenophorae, 53%; P. graminis, 56%; P. coronata, 64%; P. sorghi , 84%; P. hordei, 101%; P. recondita, 105%; Uromyces hippomarathricola , 107%; U. reichertii, 120%; Tranzschelia pruni-spinosae, 150%; P. all ii, 164%; P. helianthi, 185%; U. vignae, 336%; and U. appendiculatus, 346%. Within P. hordei, collections from Hordeum bulbosum had higher D NA content than collections from other telial host species; within P. recondita, collections from each of four telial host species differed, suggesting that these fungi are diverging genetically on some telial host species.