Indigenous fungi as pathogens of crops: some examples from Australia

Several species of Peronosclerospora (Peronosporaceae, Oomycetes) which cause downy mildew on grasses (Poaceae) have been recorded in Australia, with two, Peronosclerospora noblei and P. sargae, being found only on wild grasses indigenous to Australia. The only downy mildew species which has caused significant damage on a cultivated grass crop in Australia was P. sacchari on sugarcane (Saccharum officinarum), but that pathogen is now considered to be eradicated. Separate outbreaks of downy mildew on maize (Zea mays) have been recorded in northern Australia and in southern Queensland over the past 3 decades, both being attributed to Peronosclerospora maydis, a serious pathogen of maize overseas. At that time, the identification of Peronosclerospora species was based on the morphology of the anamorph and/or of the teleomorph but the published descriptions of the asexual spore dimensions of different Peronosclerospora species often overlapped. Recent molecular studies have demonstrated that the downy mildew outbreaks on maize in northern Australia are most likely due to the newly described P. australiensis which is a pathogen of two indigenous, endemic Sorghum species. Similarly, the outbreak of maize downy mildew in southern Queensland was actually caused by P. eriochloae which up until that time had been found only on indigenous Eriochloa species. These recent findings of pathogens on indigenous, endemic hosts causing disease outbreaks on cultivated crops reinforce the need for ongoing taxonomic studies of such pathogens