PICTURES OF A DANGEROUS PLANT PARASITE

Pyknidium mit Pyknosporen
Aecidium mit Aecidiosporen

   

The rust Puccinia graminis belongs to the large group of rust fungi that live exclusively parasitic.

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.

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