Puccinia Monoica - Life Cycle

Life Cycle

Infection of the host mustard (usually Arabis) plants occurs via wind-borne basidiospores in late summer. Upon germination of the spores, fungal hyphae penetrate the stem of the mustard plant, siphoning off nutrients from its host. However, to reproduce, the fungus must undergo sexual reproduction, facilitated by 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, the fungus forces the infected plant to turn clusters of its leaves into brilliant yellow spring "pseudoflowers", bearing the spermatogonia. Insects visiting the pseudoflowers transfer spermatia from one host plant to another, in the same way that pollinators transfer pollen amongst the true flowers of uninfected plants.

Spermatia transferred in this way, will 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 are referred to as aeciospores and are responsible for infecting the alternate host plant (a grass species: Koeleria, Trisetum, or Stipa).

Upon germination hyphae produced by the aeciospores will penetrate the grass, leading to the production of uredia. The uredia produce urediniospores capable of infecting more grass plants. Ultimately, telia will be produced on the infected grasses. This leads to production of basidia and basidiospores. When released the basidiospores may infect new mustard plants, completing the life cycle.