[7] An outbreak of another virulent race of stem rust, TTTTF, took place in Sicily in 2016, suggesting that the disease is returning to Europe.

[5] Comprehensive genomic analysis of Puccinia graminis, combined with plant pathology and climate data, has pointed out the potential of the re-emergence of stem wheat rust in UK.

The fungal ancestors of stem rust have infected grasses for millions of years and wheat crops for as long as they have been grown.

An early ancient practice by the Romans was one where they would sacrifice red animals such as foxes, dogs, and cows to Robigus (fem.

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.

This was due to the fact that European farmers noticed a correlation between barberry and stem rust epidemics in wheat.

[2] Italian scientist Giuseppe Maria Giovene (1753–1837), in his work Lettera al dottor Cosimo Moschettini sulla ruggine, also thoroughly studied the stem rust.

[10] Thirty years later it received its name, Puccinia graminis, by Persoon, and in 1854 brothers Louis René and Charles Tulasne discovered the characteristic five-spore stage that is known in some stem rust species.

Upon de Bary's discovery of all five spore stages and their need for barberry as a host, John Craigie, a Canadian pathologist, identified the function of the spermogonium in 1927.

[2] Due to the useful nature of both barberry and wheat plants, they were eventually brought to North America by European colonists.

Ultimately, as they did in Europe, the colonists began to notice a relationship between barberry and stem rust epidemics in wheat.

The program was one that was supported by state and federal entities and was partly prompted by the threat it posed to food supplies during World War I.

Once this happened, a federal quarantine was established against the sale of stem rust susceptible barberry in those states that were part of the program.

[11] South Africa itself has an ongoing problem with various stem rust outbreaks which requires better response, including an indigenous breeding for resistance program.

[12] There is considerable genetic diversity within the species P. graminis, and several special forms, forma specialis, which vary in host range have been identified.

[25] The first QCC race (since renamed QCCJ or QCCJB) was detected in the northwest Great Plains in 1988, and by 1990 was over 90% of Pgs on barley in the United States.

[24] TPMK was the worst at 69% of Pgs on wheat in 1997 in the United States – being absent only from the southern Great Plains and the west, but then was down to 10% in 1998.

Spores that land on green wheat plants form a pustule that invades the outer layers of the stalk.

Five to ten days later, cup-shaped structures filled with orange-yellow, powdery aeciospores break through the lower leaf surface.

[2] So important is its role in maintenance of prevalence that since the near extermination of the alternate host from the northern Great Plains in the United States, epidemics in crops have become rare.

[24] Like other Puccinia species, P. graminis is an obligate biotroph (it colonizes living plant cells) and has a complex life cycle[27] featuring alternation of generations.

[2] 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.

[2] P. g. tritici's obligately biotrophic lifestyle involves the dramatic up-regulation of particular gene transcriptions, constituting its biotrophy genomic features.

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.

Urediniospores are formed in structures called uredinia, which are produced by fungal mycelia on the cereal host 1–2 weeks after infection.

[2] Each teliospore undergoes karyogamy (fusion of nuclei) and meiosis to form four haploid spores called basidiospores.

A pycniospore can fertilise a receptive hypha of the opposite mating type, leading to the production of a mycelium that is dikaryotic.

[1] This occurs in areas that have unsuitable conditions for year-round survival of Puccinia graminis – typically temperate regions where hosts are absent during either the winter or summer.

AvrSr35 came first, followed by the selective pressure of widespread adoption of Sr35 wheat races, followed by the evolution of virulence on Sr35 by way of nonfunctionalization mutations of AvrSr35.