LAUSR

Floricolous downy mildews (Peronospora, Oomycetes) are a small, monophyletic group of mostly inconspicuous plant pathogens that induce symptoms exclusively on flowers. Characterisation of this group of pathogens, and information on their biology, is particularly sparse. The recurrent presence of a disease causing flower malformation, which in turn leads to high production losses of the medicinal herb Matricaria chamomilla in Serbia, has enabled continuous experiments focusing on the pathogen and its biology. Peronospora radii was identified as the causal agent of the disease, and morphologicaly and molecularly characterised. Diseased chamomiles showed severe malformations of the disc and ray florets, including phyllody and secondary inflorescence formation, followed by the onset of downy mildew. Phylogeny, based on ITS and cox2, indicates clustering of the Serbian P. radii with other P. radii from chamomile, albeit in cox2 analyses they formed a separate sub-cluster. Evidence pointing to systemic infection was provided through histological and molecular analyses, with related experiments validating the impact of soil-borne and blossom infections. This study provides new findings in the biology of P. radii on chamomile, thus enabling the reconstruction of this floricolous Peronospora species' life cycle.