Peronospora radii

Peronospora radii is a floricolous downy mildew which infects plants in the Asteraceae.^[2] It disfigures the inflorescence, mainly causing symptoms in the ray florets, but can also be visible on the leaves. It forms greyish-violet conidia. It has been reported from hosts in the genera Achillea, Anthemis, Argyranthemum, Chrysanthemum, Coleostephus, Cota, Glebionis, Leucanthemum, Matricaria, and Tripleurospermum.^[1]

Peronospora radii
Grey conidiophores of Peronospora radii on an inflorescence of Tripleurospermum maritimum.
Scientific classification
Domain:	Eukaryota
Clade:	Sar
Clade:	Stramenopiles
Clade:	Pseudofungi
Phylum:	Oomycota
Class:	Oomycetes
Order:	Peronosporales
Family:	Peronosporaceae
Genus:	Peronospora
Species:	P. radii
Binomial name
Peronospora radii de Bary, 1864
Synonyms[1]
Peronospora danica Gäumann, 1923

Symptoms

When Peronospora radii infects chamomile it causes more inflorescences to be produced by the plant, and the inflorescences to be larger and malformed. In some plants it causes more severe malformations like the absence of disc florets, and indeterminate growth resulting in a branched inflorescence.^[3]

Economic impact

Since appearing in northern Serbia in 2004, Peronospora radii has become a threat to chamomile cultivation there.^[3]