Stem rust

Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by K. C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.

In 1999 a new, more virulent race of stem rust was identified against which most current wheat strains show no resistance. The race was named TTKSK (e.g. isolate Ug99). An epidemic of stem rust on wheat caused by race TTKSK spread across Africa, Asia and the Middle East, causing major concern due to the large numbers of people dependent on wheat for sustenance, thus threatening global food security.

An outbreak of another virulent race of stem rust, TTTTF, took place in Sicily in 2016, suggesting that the disease is returning to Europe. 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. 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. The law banned the planting of barberry near wheat fields and was the first of its kind.

The parasitic nature of stem rust was discovered in the 1700s. Two Italian scientists, Fontana and Tozzetti, first explained the stem rust fungus in wheat in 1767. Italian scientist Giuseppe Maria Giovene (1753–1837), in his work Lettera al dottor Cosimo Moschettini sulla ruggine, also thoroughly studied the stem rust. 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. The brothers were also able to make a connection between the red (urediniospore) and black (teliospore) spores as different stages within the life cycle of the same organism, but the rest of the stages remained unknown.

Anton de Bary later conducted experiments to observe the beliefs of European farmers regarding the relationship between the rust and barberry plants, and after connecting the basidiospores of the basidia stage to barberry, he also identified that the aeciospores in the aecia stage reinfect the wheat host. 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.

Due to the useful nature of both barberry and wheat plants, they were eventually brought to North America by European colonists. Barberry was used for many things like making wine and jams from the berries to tool handles from the wood. Ultimately, as they did in Europe, the colonists began to notice a relationship between barberry and stem rust epidemics in wheat. Laws were enacted in many New England colonies, but as the farmers moved west, the problem with stem rust moved with them and began to spread to many areas, creating a devastating epidemic in 1916. It was not until two years later in 1918 that the United States created a program to remove barberry. 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. The "war against barberries" was waged and called upon the help of citizens through radio and newspaper advertisements, pamphlets, and fair booths asking for help from all in the attempt to rid the barberry bushes of their existence. Later, in 1975–1980, the program was reestablished under state jurisdiction. 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. A barberry testing program was created to ensure that only those species and varieties of barberry that are immune to stem rust will be grown in the quarantine area.