Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/7/2001
Publication Date: 3/1/2002
Citation: KOLMER, J.A. VIRULENCE PHENOTYPES OF PUCCINIA TRITICINA IN THE SOUTH ATLANTIC STATES IN 1999. PLANT DISEASE. 2002. v. 86. p. 288-291. Interpretive Summary: Leaf rust is an important disease that occurs on wheat throughout the United States. The disease is caused by a fungus called Puccinia triticina. The fungus infects leaves of the wheat plants and each infection can produce thousands of spores that spread to other wheat plants locally. The spores can also be carried hundreds of miles in the atmosphere, infecting wheat plants in different states. The fungus is ver genetically diverse. Different collections of the fungus differ in ability to attack wheat cultivars that have different resistance genes. Races of the fungus are identified by testing collections of the fungus on wheat plants that vary in a single leaf rust resistance gene. In 1999, we found 21 different races of leaf rust in Georgia, South Carolina, North Carolina, and Virginia. Of the 253 collections that were tested, the most common race, designated as MBRK, was widespread throughout this region of the United States. The second most common race, TLGF, was also widespread in the South Atlantic States in 1999. We also found that leaf rust races in the South Atlantic States are different from those found in the Great Plains region of the United States. The research is important because it shows that wheat cultivars grown in the South Atlantic region need to have a diversity of resistance genes for leaf rust, since the same races attack wheat in the four state region. Breeders will use this information as they create various cultivars with different resistance genes.
Technical Abstract: Collections of Puccinia triticina, were made from rust infected wheat leaves in Georgia, South Carolina, North Carolina and Virginia in 1999. Single-uredinial isolates derived from the leaf rust collections were processed for identification of virulence phenotypes on seedling plants in greenhouse tests. Twenty-one virulence phenotypes from 253 isolates were described based on infection type to 16 Thatcher wheat lines near-isogenic for leaf rust resistance genes. Virulence phenotype MBRK (virulent to leaf ruse resistance genes Lr1, Lr3, Lr3ka, Lr11, Lr30, Lr10, Lr14a, and Lr18) was the most common phenotype in all four states at 38.7% of all isolates. Phenotype TLGF (virulent to Lr1, Lr2a, Lr2c, Lr3, Lr9, Lr11, Lr14a, and Lr18) was the second most common phenotype overall at 33.8% of isolates. Twenty-nine isolates selected on the basis of seedling virulence phenotypes were also tested for virulence to adult wheat plants with the resistance genes Lr12, Lr13, Lr22b, and Lr34. Almost all isolates were avirulent to Lr12 and almost all isolates were virulent to Lr13. All isolates had lower infection types to the Thatcher line with Lr34 compared to Thatcher. The widespread occurrence of the predominant P. triticina virulence phenotypes throughout the region indicated that the South Atlantic states should be considered as a single epidemiological area for wheat leaf rust. Some virulence phenotypes, which occurred at lower frequencies, were found primarily in the mountains of North Carolina or in breeding plots in Georgia. Localized populations of P. triticina may develop in the South Atlantic region due to overwintering of leaf rust infections, or specific selection by leaf rust resistance genes in wheat cultivars.