Puccinia monoica

Puccinia monoica
Puccinia pseudoflowers produced on Arabis
Scientific classification
Kingdom:	Fungi
Phylum:	Basidiomycota
Class:	Urediniomycetes
Subclass:	Incertae sedis
Order:	Uredinales
Family:	Pucciniaceae
Genus:	Puccinia
Species:	Puccinia monoica

Puccinia monoica is a parasitic rust fungus of the genus Puccinia that inhibits flowering in its host plant (usually an Arabis species) and radically transforms host morphology in order to facilitate its own sexual reproduction.

Infection of host plants (including Arabis and several other members of the mustard family) occurs via wind-borne basidiospores in late summer. Upon germination of the spores, fungal hyphae penetrate the stem of the mustard plant and siphon off nutrients. However, in order to reproduce sexually, the fungus must facilitate the transfer of spermatia from the spermatogonia on this plant to receptive hyphae borne in the spermatogonia on another infected mustard plant. To accomplish this, the fungus sterilizes the host plant, preventing it from producing true flowers. Instead, it forces the infected plant to grow clusters of leaves into brilliant yellow "pseudoflowers" bearing the fungal spermatogonia. Insects visiting the pseudoflowers transfer spermatia from one host plant to another, in the same way that pollinators transfer pollen between the true flowers of uninfected plants.

Spermatia transferred in this way fuse with receptive spermatogonial hyphae on the recipient plant. The resulting hyphae subsequently form aecia. At this time, the pseudoflowers lose their green colour and stop producing nectar. Spores produced in the aecia, referred to as aeciospores, are responsible for infecting P. monoica's alternate host plant (a grass species of Koeleria, Trisetum, or Stipa).

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