The rust Puccinia
graminis belongs to the large group of rust fungi that live exclusively
In early spring special spores (teleutospores) that have endured wintertime infest the leaves of the barberry. Inside the leaves they form a mycelium, which penetrates the leaf surface and forms pyknospores (shown here for the pear rust, right picture). Simultanously a sticky sugar syrup is secreted to attract insects, which contribute to the spread of the parasite.
Later in cup-shaped capsules aecidiospores
are formed at the bottom of the leaves to infect the now ripening cereals (left
picture). Because of the high reproduction rate on the the barberry during springtime
there is now a rapid infection of whole fields. The leaves are soon covered
with rust-brown uredospores, which are driven by the wind in clouds over
the fields and infest more and more fields.
Toward the end of summer teleutospores
are again formed to endure wintertime.
Since the late Neolithic all civilizations
have been dependent on cereals, and so parasitic fungi that are able to effectively
infest monocultures must be considered as the greatest enemies of civilization.
Often plant parasites have led to famine: Crop failures triggered the French
Revolution and the potato blight, caused by the fungus Phytophtora infestans,
forced many hundred thousands of Irishmen to emigrate to the United States.
Today pesticides and fungicides protect
us so effectively from famine that it is even possible to practice "bio-farming"
in the "wind shadow" of these chemicals. But bio-farming on a very
large scale will not be possible, because cleverly adapted parasites of the
type of cereal rust are lurking everywhere to get their chance! Perhaps fungus-resistant
crops developed by genetic engineering may help, but so far parasites have always
overcome any new difficulties by mutation and selection.