cereal rusts

Like other Puccinia species, P. graminis is an obligate biotroph (it colonizes living plant cells) and has a complex life cycle featuring alternation of generations. The fungus is heteroecious, requiring two hosts to complete its life cycle – the cereal host and the alternate host. There are many species in Berberis and Mahonia (and their hybrid genus x Mahoberberis) that are susceptible to stem rust, but the common barberry (B. vulgaris) is considered to be the most important alternate host. P. graminis is macrocyclic (exhibits all five of the spore types that are known for rust fungi). P. graminis can complete its life cycle either with or without barberry (the alternate host). P. g. tritici's obligately biotrophic lifestyle involves the dramatic up-regulation of particular gene transcriptions, constituting its biotrophy genomic features. These genomic regions have parallels in other eukaryotic plant pathogens. These parallels – between these independently evolved and unrelated sets of genes – show a strong and broad pattern of convergent evolution around the plant pathogenic lifestyle.

Life cycle on barberry. Due to its cyclical nature, there is no true 'start point' for this process. …

The fungal ancestors of stem rust have infected grasses for millions of years and wheat crops for as long as they have been grown. According to Jim Peterson, professor of wheat breeding and genetics at Oregon State University, "Stem rust destroyed more than 20% of U.S. wheat crops several times between 1917 and 1935, and losses reached 9% twice in the 1950s," with the last U.S. outbreak in 1962 destroying 5.2% of the crop. Stem rust has been an ongoing problem dating back to Aristotle's time (384–322 BC). An early ancient practice by the Romans was one where they would sacrifice red animals, such as foxes, dogs, and cows, to Robigus (fem. Robigo), the rust god. They would perform this ritual in the spring during a festival known as the Robigalia in hopes of the wheat crop being spared from the destruction caused by the rust. Weather records from that time have been reexamined and it has been speculated that the fall of the Roman Empire was due to a string of rainy seasons in which the rust would have been more harsh, resulting in reduced wheat harvests. Laws banning barberry were established in 1660 in Rouen, France. This was due to the fact that European farmers noticed a correlation between barberry and stem rust epidemics in wheat. …