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Historical Significance

Stem rust is one of the major diseases of wheat and barley and, therefore, a potential threat to the world food supply. Wheat is the largest food crop in the world, and barley is the sixth largest. Together, they account for more than 25% of the world food supply. It is estimated that more than $5 billion are lost to cereal rusts (leaf rust, stem rust, and stripe rust) each year. Cereal rusts have probably been a problem since the first cereal crops were grown in the Fertile Crescent. Spores of P. graminis have been found in archeological sites in Israel dating from 1300 B.C. Wheat, barley, and barberry all originated in the Fertile Crescent, so this complex relationship in the stem rust life cycle has an ancient history.

Wheat stem rust was a serious problem in ancient Greece and Rome. Rust was observed and recognized as early as the time of Aristotle (384-322 B.C.). The ancient Romans sacrificed red animals such as dogs, foxes, and cows to the rust god, Robigo or Robigus, each spring during the festival called the Robigalia in hopes that the wheat crop would be spared from the ravages of the rust (Figure 27). This festival was incorporated into the early Christian calendar as St. Mark's Day or Rogation on April 25. Historical weather records suggest that a series of rainy years, in which rust would have been more severe and wheat harvests reduced, may have contributed to the fall of the Roman Empire.

Figure 27

Although the parasitic nature of stem rust was not known until the 1700s, farmers in Europe had recognized much earlier that barberry was somehow connected to stem rust epidemics in wheat. Laws banning the planting of barberry near wheat fields were first passed in Rouen, France, in 1660.

The Italian scientists Fontana and Tozzetti independently provided the first detailed descriptions of the stem rust fungus in wheat in 1767. Persoon named it Puccinia graminis in 1797. By 1854, the Tulasne brothers recognized that some autoecious (single host) rust fungi could produce as many as five spore stages. They were the first to link the red (urediniospore) and black (teliospore) stages as different spores of the same organism, but the remaining stages of P. graminis remained a mystery.

Anton deBary was puzzled by the lack of infection when basidiospores of P. graminis were placed on wheat plants. Using the farmers' belief that barberries increased wheat rust, he successfully inoculated barberries with the basidiospores and observed the remaining spore stages develop on the alternate host. Once the heteroecious nature of the life cycle was established, many other known rust fungi were discovered to be heteroecious, and their hosts could be paired up.

Both wheat and barberry plants were brought to North America by the European colonists. Barberry has a number of practical uses including a yellow dye from the bark, jams and wines from the berries, tool handles from the wood, and fast-growing, thorny hedges to help retain animals. As in Europe, farmers began to recognize the connection between barberry and stem rust epidemics in wheat. Barberry laws were enacted in several New England colonies in the mid-1700s. However, barberry continued to spread as pioneer farmers moved west. From farmyard plantings, barberry spread into fencerows and woodlots. Barberry bushes can be 3 m (9 ft) high and produce abundant berries that are attractive to birds and animals that feed on them and spread their seeds.


Figure 22	Figure 28

After the devastating 1916 North American stem rust epidemic, a cooperative state and federal barberry eradication program was established in 1918 (Figure 22). This program was partially motivated by the concern about food supplies during war. A "war against barberries" was established that enlisted help from the general population through radio and newspaper ads, extension pamphlets, and booths at fairs urging them to aid in the destruction of barberries. Even school children were encouraged to help find sites where barberry bushes existed (Figure 28). From 1975 through 1980, the program was gradually returned to the jurisdictions of various states. A federal quarantine is still maintained against sale of stem rust-susceptible barberry in states that were part of the barberry eradication program. A barberry testing program was established to ensure that only barberry species and varieties, such as the popular ornamental Japanese barberry, that are immune to stem rust will be grown in the quarantine area.

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