Australia: A continent without native powdery mildews?

Abstract

In contrast to Eurasia and North America, the powdery mildews (Ascomycota, Erysiphales) are largely understudied in Australia. There are over 900 species known globally, with less than 50 recorded from Australia. Some of these records are doubtful as the identifications were presumptive, being based on host plant-pathogen lists from overseas. Australian herbaria contain many undetermined powdery mildew specimens and an outdated nomenclature is still in use. The Department of Agriculture-sponsored Modern Diagnostics Project identified the Erysiphales as a diagnostic gap that was addressed by a 5-day workshop in 2018. This resulted in (i) an up-to-date list of all the taxa that have been identified in Australia based on published DNA barcode sequences prior to the workshop; (ii) precise identification of 117 specimens freshly collected from across the country; and (iii) precise identification of 30 herbarium specimens collected between 1975 and 2013. Identifications were done based on both morphology and DNA barcodes. Altogether, 39 species representing 10 genera were confirmed in Australia, including two genera and ten species newly recorded during the project. In Eurasia and North America the number of powdery mildew species is more than 10 time greater. Interestingly, powdery mildew infections have been recorded on only eight native Australian plant species in the genera Acacia, Acalypha, Eucalyptus, Ixodia, Jagera, Senecio and Trema. All but one of these infections were caused by polyphagous species that infect many other host plants both overseas and in Australia. The data indicates that (i) the native Australian vegetation may have evolved without being exposed to any native powdery mildews; and (ii) all the species of the Erysiphales that are known to occur in Australia may have been introduced since the European colonisation of the continent.