NUCLEAR-DNA CONTENT OF BASIDIOSPORES OF SELECTED RUST FUNGI AS ESTIMATED FROM FLUORESCENCE OF PROPIDIUM IODIDE-STAINED NUCLEI

The relative nuclear DNA content of basidiospores of five species of Puccinia, two of Uromyces, and one of Melampsora was estimated from the fluorescence intensity of propidium iodide-stained nuclei. Relative to the nuclear fluorescence of P. graminis, taken as 1.0, other fungi had the following fluorescence values: M. lini (one collection), 2.5; P. coronata (two collections), 1.1; P. hordei (11 collections), 1.7; P. recondita (six collections), 2.0; P. sorghi (one collection), 0.8; U. appendiculatus (one collection) 6.9; U. reichertii (one collection), 1.6; and U. vignae (one collection), 4.3. Assuming that the basidiospore nuclei were all haploid and in the same stage of the nuclear cycle, the fluorescence values give an estimate of relative genome size among these fungi. Because of their smaller genome sizes, P. graminis, P. coronata, and P. sorghi may be more suited for mapping genetic loci than the other fungi measured. In some cases, DNA content within a species differed among collections from different uredinial hosts. Thus, within P. coronata, a collection from A vena sativa had less fluorescence than a collection from A. sterilis, within P. hordei, a collection from Hordeum bulbosum had more fluorescence than collections from three other species of Hordeum; and within P. recondita, a collection of Triticum durum had less fluorescence than collections from four species of Aegilops. This suggests that each rust fungus may have diverged in genome size during evolution on different host species, a possibility in need of further investigation.