Coffee rust genome measured using flow cytometry: does size matter?

The genome size of most rust species is unknown due, in part, to technical constraints, especially the difficulty in accessing spores to extract the nuclei for cytometry. Using the urediniospores of coffee rust, Hemileia vastatrix, an improved methodology involving flow cytometry was developed for accurate measurement of the nuclear genome size. The results revealed that the genome of this primitive rust fungus is unusually large - measuring 1C-value=075pg (7335Mb) - significantly bigger than other species quantified thus far in the more advanced rust lineages. The evolutionary consequences and the potential ecological constraints of this large genome size are discussed in relation to the epidemiology of coffee rust.