Wheat stem rust, a devastating disease of wheat and barley caused by the fungal pathogen Puccinia graminis f. sp. tritici, was largely eradicated in Western Europe during the mid-to-late twentieth century. However, isolated outbreaks have occurred in recent years. Here we investigate whether a lack of resistance in modern European varieties, increased presence of its alternate host barberry and changes in climatic conditions could be facilitating its resurgence. We report the first wheat stem rust occurrence in the United Kingdom in nearly 60 years, with only 20% of UK wheat varieties resistant to this strain. Climate changes over the past 25 years also suggest increasingly conducive conditions for infection. Furthermore, we document the first occurrence in decades of P. graminis on barberry in the UK . Our data illustrate that wheat stem rust does occur in the UK and, when climatic conditions are conducive, could severely harm wheat and barley production.
The objective of this study was to investigate the re-emergence of a previously important crop pathogen in Europe, Puccinia graminis f.sp. tritici, causing wheat stem rust. The pathogen has been insignificant in Europe for more than 60 years, but since 2016 it has caused epidemics on both durum wheat and bread wheat in local areas in southern Europe, and additional outbreaks in Central- and West Europe. The prevalence of three distinct genotypes/races in many areas, Clade III-B (TTRTF), Clade IV-B (TKTTF) and Clade IV-F (TKKTF), suggested clonal reproduction and evolution by mutation within these. None of these genetic groups and races, which likely originated from exotic incursions, were detected in Europe prior to 2016. A fourth genetic group, Clade VIII, detected in Germany (2013), was observed in several years in Central- and East Europe. Tests of representative European wheat varieties with prevalent races revealed high level of susceptibility. In contrast, high diversity with respect to virulence and Simple Sequence Repeat (SSR) markers were detected in local populations on cereals and grasses in proximity to Berberis species in Spain and Sweden, indicating that the alternate host may return as functional component of the epidemiology of wheat stem rust in Europe. A geographically distant population from Omsk and Novosibirsk in western Siberia (Russia) also revealed high genetic diversity, but clearly different from current European populations. The presence of Sr31-virulence in multiple and highly diverse races in local populations in Spain and Siberia stress that virulence may emerge independently when large geographical areas and time spans are considered and that Sr31-virulence is not unique to Ug99. All isolates of the Spanish populations, collected from wheat, rye and grass species, were succesfully recovered on wheat, which underline the plasticity of host barriers within P. graminis. The study demonstrated successful alignment of two genotyping approaches and race phenotyping methodologies employed by different laboratories, which also allowed us to line up with previous European and international studies of wheat stem rust. Our results suggest new initiatives within disease surveillance, epidemiological research and resistance breeding to meet current and future challenges by wheat stem rust in Europe and beyond.
The objective of this study was to determine whether genetically differentiated groups of Puccinia triticina are present in Europe. In total, 133 isolates of P. triticina collected from western Europe, central Europe and Turkey were tested for virulence on 20 lines of wheat with single leaf rust resistance genes, and for molecular genotypes with 23 simple sequence repeat (SSR) markers. After removal of isolates with identical virulence and SSR genotype within countries, 121 isolates were retained for further analysis. Isolates were grouped based on SSR genotypes using a Bayesian approach and a genetic distance method. Both methods optimally placed the isolates into eight European (EU) groups of P. triticina SSR genotypes. Seven of the groups had virulence characteristics of isolates collected from common hexaploid wheat, and one of the groups had virulence characteristics of isolates from tetraploid durum wheat. There was a significant correlation between the SSR genotypes and virulence phenotypes of the isolates. All EU groups had observed values of heterozygosity greater than expected and significant fixation values, which indicated the clonal reproduction of urediniospores in the overall population. Linkage disequilibria for SSR genotypes were high across the entire population and within countries. The overall values of R ST and F ST were lower when isolates were grouped by country, which indicated the migration of isolates within Europe. The European population of P. triticina had higher levels of genetic differentiation compared to other continental populations.
Abstract:In 1995-2004 we investigated leaf rust virulence in Slovakia on Thatcher near isogenic lines (NILs) with genes Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. According to reaction of leaf rust isolates resistance genes Lr9 and Lr19 were completely effective to all examined pathotypes in all years. The resistance genes Lr24 and Lr28 were also completely effective to all examined pathotypes till the year 2001. In the year 2001 we detected 20% and 10% virulent isolates on NILs Lr24 and Lr28, respectively. According to the reaction of investigated isolates from the territory of Slovakia on NILs, resistance genes Lr2c, Lr3a, Lr11, Lr17, Lr21, Lr23 and Lr26 were mostly ineffective. During the 1994-2004 period we detected 16 races of leaf rust (races 2, 2SaBa, 6, 6SaBa, 12, 12SaBa, 14, 14SaBa, 57, 57SaBa, 61, 61SaBa, 62SaBa, 77, 77SaBa, 77/57SaBa). The most frequently determined races were 61SaBa and 77SaBa, which occurred in all years. Among frequently determined races we can assign race 12SaBa as well. According to the field tests in 2001-2004 good resistance to leaf rust was displayed by the cvs Arida (Lr13, Lru), Eva (Lr3, Lru) and Solara (Lru).
Abstract:In 2001-2004 virulence of the wheat leaf rust population in the Czech Republic was studied on Thatcher near-isogenic lines with Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. Samples of leaf rust (180 in total) were obtained from different parts of the Czech Republic.Resistance genes Lr9 and Lr19 were effective to all tested isolates like in the previous years. Unlike the previous years virulence on Lr24 and Lr28 was observed. Relatively effective were also Lr1, Lr2a, Lr24, Lr28 and Lr2b. Other Lr genes were defeated by the majority of the tested samples. Our results transformed to the numbers of physiologic races indicate that race 61SaBa prevailed like in the previous years, followed by races 61, 2, 12Sa-Ba, 2SaBa, 14, 77SaBa, 12, 57, 6, 53, 53SaBa, 77, and 14SaBa. Twenty-one winter wheat cultivars registered in 2001-2004 were tested with 8 leaf rust isolates. Out of them 15 showed resistance at least to one rust isolate. High resistance recorded in field trials for cvs Batis and Ilias, which were susceptible to all tested rust isolates at the seedling stage, demonstrates the importance of field (partial) resistance.
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