Saprophytic growth of the alder rust fungus Melampsoridium hiratsukanum on artificial media

The first axenic culture of a free living saprophytic stage of the exotic rust fungus Melampsoridium hiratsukanum is reported. Colonies were obtained from one-celled, dikaryotic urediniospores on eight nutrient media out of twelve. Modified Harvey and Grasham (HG) and Schenk and Hildebrandt (HS) media HG1 and SH1 and their bovine serum albumin (BSA)-enriched derivatives gave abundant mycelial growth, but modified Murashige and Skoog (MS) QMS media and their BSA-enriched modifications performed poorly, colony growth being low on QMS-1 and QMS1+BSA, and nil on QMS-5 and QMS-6, with or without BSA. Colonies initially grew poorly when subcultured for one month in purity, but much better after re-transfer to fresh media later: presumably because only the most exploitative genotypes survived, best able to cope with an uncongenial medium. Stabilised cultures survived, and remained vegetative, but only few reproductive colonies produced spore-like bodies. Though the agarised medium remains an inhospitable environment for this biotrophic parasite, it is shown that non-living media can nevertheless sustain the growth and sporulation of this fungus outside its natural hosts and habitat. Axenic culture promises important advances in basic and applied research on this rust, leading to a better understanding of its nutrition, metabolism, diversity and pathogenicity.