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Isolates of recently spreading races of yellow rust from wheat and triticale in Europe were analysed using virulence phenotypic data of 2605 isolates sampled in 12 countries between 2000 and 2014. A subset of 239 isolates was investigated by microsatellite markers. At least three races of non-European origin, termed 'Warrior', 'Kranich' and 'Triticale aggressive', were identified in the post-2011 population. The Warrior race was already present in high frequencies in the first year of detection in most European countries and to a large extent it replaced the pre-2011 European population. In contrast, the two other exotic races were localized to certain regions and/or crop type. The presence already of at least six multilocus genotypes of the Warrior race and five genotypes of the Kranich race in the first year of detection and across large areas is consistent with a hypothesis of aerial spread from genetically diverse source populations. A comparison with reference isolates sampled from six continents suggested that the Warrior and Kranich races originated from sexually recombining populations in the centre of diversity of the yellow rust fungus in the near-Himalayan region of Asia. However, the Triticale aggressive race was most similar to populations in the Middle East/Central Asia. The study illustrated the potential role of sexual Puccinia striiformis populations as a reservoir for new races replacing distant clonal populations. [ABSTRACT FROM AUTHOR]

A unique collection of spore samples of Puccinia striiformis, often referred to as the 'Stubbs collection', has been stored in liquid nitrogen from 18 to 45 years. A subset of samples representing 35 countries and 28 years was investigated to assess recovery rate, race identity and previously undetected virulence. A new method for recovery using an airbrush sprayer and Novec™ 7100 for inoculating the host plants was highly successful. Ninety-six percent of 231 isolates were recovered. Virulence phenotyping was done using differential sets of wheat genotypes representing specific-resistance genes. A total of 181 samples represented single genotypes (isolates), whereas 40 samples consisted of at least two genotypes. Race identity was confirmed for 102 of 181 single-genotype isolates. The virulence phenotype was updated for additional 44 isolates based on improved resolution of results because of updated and more informative wheat-differential sets. The remaining 35 isolates showed discrepancies for one or more virulences when compared with past results. Additional virulences corresponding to Yr17, Yr25 and Yr27, respectively, which were not assayed originally, were discovered. The value of biological collections for research and plant breeding is discussed along with the challenges of maintaining collections of biotrophic microorganisms. [ABSTRACT FROM AUTHOR]