James Kolmer

Population Biology of Cereal Rust Fungi and Genetics of Rust Resistance in Cereals

My research has dealt with the population genetics and biology of cereal rust fungi, with particular regard to how the use of host resistance genes selects rust genotypes. In North America, at least four major groups of the wheat leaf rust fungus, Puccinia triticina have been delineated by testing isolates for virulence to wheat lines which are near-isogenic for leaf rust resistance genes, and also by using DNA based RAPD and AFLP markers. One group of P. triticina isolates are found primarily in eastern North America, and also the Pacific Northwest Region. Two other groups of P. triticina are found in the Great Plains region, while a fourth group consists of isolates that are presently rarely found in North America, but were the most prevalent genotypes in the 1930s -1940s. Regional populations of P. triticina have most likely developed due to the use of wheat cultivars that differ for resistance genes in the different regions of North America. Collections of P. triticina from different parts of the world have also been characterized for virulence and molecular polymorphism. Populations of the crown rust fungus of oats, Puccinia coronata, and the wheat stem rust fungus, P. graminis have also been characterized for virulence in different regions of North America.

A second aspect of my research has dealt with the genetics of leaf and stem rust resistance in wheat. Many spring wheat cultivars in the US and Canada have leaf rust resistance genes Lr13 and Lr34. In recent years, cultivars with these resistance genes have suffered higher levels of rust infection since many P. triticina genotypes are now virulent to Lr13 and produce intermediate levels of infection on lines with Lr34. Wheat cultivars from North America and other parts of the world are genetically examined to determine their leaf and stem rust resistance genotype. Effective genes for rust resistance from different sources can then be transferred to locally adapted wheat germplasm.

In the future, my research will continue to characterize current populations of the leaf rust fungus P. triticina in North America, and will also examine the genetic relationships between different groups of P. triticina that occur on lower ploidy relatives of wheat. Fitness differences between isolates that differ for virulence to resistance genes derived from wheat relatives will also be examined. Genetic analysis of rust resistance in wheat cultivars will continue in an ongoing effort to characterize and improve wheat germplasm for rust resistance.