Molecular and genetic study of wheat rusts

Puccinia triticina, Puccinia graminis and Puccinia striiformis cause leaf, stem and yellow rust, respectively. Wheat rusts can cause losses as high as 70%. The rusts ability to evolve fungicide resistance has resulted in the use of resistant cultivars as the primary method of control. Breeding resistant cultivars is a long process and requires an accurate picture of the current and future pathogen population. Differentiation of wheat rust pathotypes using conventional plant pathology techniques is time consuming, labour intensive and requires the services of a highly skilled and experienced plant pathologist. Modern molecular biology techniques have the potential to aid the conventional techniques and provide fast, accurate same-day results. Microsatellite markers were used to differentiate P. triticina and P. striiformispathotypes. Amplified fragment length polymorphisms (AFLP) were used to differentiate stem rust P. graminis pathotypes. Phylogenetic trees were created for leaf and stem rust pathotypes. Field isolates of leaf, stem and yellow rust were collected from eleven sites across the Western Cape Province. Microsatellite markers were used to type leaf and yellow rust isolates. AFLP markers could not be used on field isolates due to the presence of plant DNA. Novel alleles found in the Leaf and yellow rusts isolates prevented the assigning of a specific pathotype to each isolate. UVPrt10 (25.2%) and UVPrt9 (21.5%) were the most prevalent leaf rust pathotypes. Only 6E16A+ was identified in the yellow rust isolates. Pathotype incidence was similar to previous studies. The prevalence of multiple pathotypes with a variety of virulence genes in the rust population shows that breeding lines with single major resistance genes will not be effective and breeding programmes should concentrate on lines that exhibit quantitative resistance. Key words: Prevalence, microsatellite, amplified fragment length polymorphisms (AFLP), phylogeny, Puccinia.