Powdery mildew on mungbean and other legume species in Australia

Powdery mildew on mungbean and other legume species in Australia

Mungbean is currently Australia’s most widely grown summer legume crop. Powdery mildew remains a consistent challenge to mungbean production across Australia and worldwide. If left unmanaged, this disease can cause grain yield losses of up to 40% in the Australian mungbean paddocks. Despite being easily recognised and present every cropping season, the causal agents remain poorly understood. Legume species in Australia are commonly infected with powdery mildew, though few studies have been undertaken to identify which species of powdery mildew they host. This study aimed to better understand powdery mildew diseases of mungbean and other broad-acre and pasture legume crops in Australia. In this thesis, we provide the precise identification of the species causing powdery mildew in Australian mungbean and black gram paddocks. We identified Podosphaera xanthii and Erysiphe vignae, a newly recognised taxon, as the pathogens causing disease, based on (a) morphology of freshly collected and herbarium specimens; (b) nrDNA ITS sequences; and (c) cross-inoculation studies. We investigated the host range of P. xanthii and revealed that populations of P. xanthii that infect mungbean and cucurbits differ markedly in their host range. This study identified the native Glycine species, G. tabacina, as an alternate host for the soybean powdery mildew pathogen, E. diffusa, in Australia. Glycine tabacina powdery mildew specimens were collected, and the pathogen was identified based on morphology and nrDNA ITS and MCM7 sequences. Cross-inoculation experiments revealed that the E. diffusa isolates infecting G. tabacina in the field were pathogenic to soybean. We also elucidate the precise identification of powdery mildew species naturally infecting fabaceous hosts in Australia, identifying eleven powdery mildew species on more than fifty hosts. The nrDNA ITS sequences and morphology of 34 fresh and 40 herbarium powdery mildew specimens infecting diverse Fabaceae species in Australia were characterised in this study. Together, this work has produced the most comprehensive study of powdery mildew species infecting legume hosts in Australia. The accurate identification of the pathogens in this study and enhanced knowledge of their life cycle, in regard to their host range, provides a significant step forward in improving our understanding of the powdery mildew diseases of mungbean and other broad-acre and pasture legume crops in Australia that will ultimately assist in the development of disease management strategies.

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