Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2005
Publication Date: 9/1/2005
Citation: Peterson, P.D., Leonard, K.J., Roelfs, A.P., Sutton, T.B. 2005. The effect of barberry eradication on changes in populations of Puccinia graminis in Minnesota. Plant Disease. 89:935-940.
Interpretive Summary: Stem rust of wheat has been controlled for more than 50 years by breeding resistant wheat varieties as well as eliminating common barberry, the host for the sexual stage of the stem rust fungus. We analyzed stem rust collection data from barberry in Minnesota from 1912 to 2002 for frequency of wheat, rye, and oat forms of stem rust before and after the barberry eradication campaign, which ended in 1980. We also compared wheat stem rust races found in collections from barberry with those found on wheat. After the removal of barberry bushes from the vicinity of wheat fields by the 1930s, most collections from remaining barberry bushes were of rye stem rust rather than wheat stem rust. Common wild grasses growing near barberry bushes in uncultivated areas of southeastern Minnesota were more susceptible to rye stem rust than to wheat stem rust. Since 1990, however, the proportion of wheat stem rust in collections from barberry has increased, perhaps because wheat stem rust adapted to survive better on common grasses. Also, the number of pathogenic races of stem rust found in wheat declined dramatically after barberry eradication. However, the diversity of wheat stem rust races from remaining barberry bushes in uncultivated areas remains as high in 2002 as it was before eradication. This shows that barberry is still a potentially dangerous source of new races that could overcome resistance in current wheat varieties. If the remaining barberry bushes in Minnesota are allowed to spread or if the stem rust fungus has adapted to survive better on common wild grasses, new stem rust races highly virulent to formerly resistant wheat varieties may begin to appear. That could cause severe epidemics with 15-20% losses in wheat yield in the Upper Midwest.
Technical Abstract: Proportions of formae speciales of Puccinia graminis in collections of aeciospores from barberry were determined from cereal rust survey records from 1912 to 2002 in Minnesota. The frequency of P. graminis f. sp. avenae (Pga) in aeciospore collections fluctuated between 0 and 10% from 1920-2002 even though oat was the dominant small grain crop in Minnesota until 1970. In early years, P. graminis f. sp. tritici (Pgt) was common, but the frequency of Pgt in aeciospore collections declined to a low of 4% in the 1980s, while P. graminis f. sp. secalis (Pgs) increased to 96%. After 1990 the frequency of Pgt increased and Pgs declined in aecial collections, possibly indicating a changing proportion of Pgs and Pgt on wild grasses near barberry bushes. Diversity of races among uredinial collections of Pgt from wheat in Minnesota declined sharply from 1912 to 1930 and remained low to 2002. Although the races of Pgt most common in uredinial collections were also most common in the aecial collections in seven of nine decades from 1912-2002, the diversity of races was greater among aecial than uredinial collections. Diversity in aecial collections remained nearly constant for 90 years indicating a continuing contribution of the sexual stage to diversity of Pgt.