Pst pathotypes and Yr gene postulation in Tunisian wheat
Yellow rust is a widely distributed wheat disease, that is more damaging in cooler, temperate regions. Epidemics have increased worldwide due to spread of aggressive high temperature tolerant strains PstS1/S2 that reached North Africa and southern France in 2004 and the widely virulent exotic Warrior race that spread in Western Europe in 2011. Resistant varieties are effective solutions to reduce the use of pesticides. However, races of the pathogen quickly overcome resistance genes. Therefore, selection of varieties with durable resistance to yellow rust is paramount for protection of both bread wheat and durum. To conduct a genetic control strategy, it is essential to study the pathotype dynamics and the resistance genes in wheat. We identified the pathotypes using the European and world differential sets that discriminate between 23 avirulence/virulence factors as well as simple sequence repeat (SSR) diversity among 20 Pst isolates collected in Tunisia in 2014. In addition, we postulated resistance genes in 28 Tunisian varieties and accessions at the seedling stage in order to identify the resistance diversity. Race 239 E175V17 was involved in the 2014 epidemic in Tunisia. Genetic analysis revealed that this race is exotic and distinct from the Northwestern European and Mediterranean groups, previously present in Tunisia. Resistance gene postulation indicated the presence of Yr3, Yr6, Yr7, Yr9+Yr4, and Yr25 in Tunisian varieties and accessions. Durum varieties Khiar and Salim, and bread wheat variety Tahent, were resistant to the local Northwestern European and Western Mediterranean pathotypes as well as the Warrior race. These varieties are thus short-term measures to address the yellow rust problem in Tunisia. Gene identifications will be confirmed by molecular and pedigree analyses of the accessions.Yellow rust is a widely distributed wheat disease, that is more damaging in cooler, temperate regions. Epidemics have increased worldwide due to spread of aggressive high temperature tolerant strains PstS1/S2 that reached North Africa and southern France in 2004 and the widely virulent exotic Warrior race that spread in Western Europe in 2011. Resistant varieties are effective solutions to reduce the use of pesticides. However, races of the pathogen quickly overcome resistance genes. Therefore, selection of varieties with durable resistance to yellow rust is paramount for protection of both bread wheat and durum. To conduct a genetic control strategy, it is essential to study the pathotype dynamics and the resistance genes in wheat. We identified the pathotypes using the European and world differential sets that discriminate between 23 avirulence/virulence factors as well as simple sequence repeat (SSR) diversity among 20 Pst isolates collected in Tunisia in 2014. In addition, we postulated resistance genes in 28 Tunisian varieties and accessions at the seedling stage in order to identify the resistance diversity. Race 239 E175V17 was involved in the 2014 epidemic in Tunisia. Genetic analysis revealed that this race is exotic and distinct from the Northwestern European and Mediterranean groups, previously present in Tunisia. Resistance gene postulation indicated the presence of Yr3, Yr6, Yr7, Yr9+Yr4, and Yr25 in Tunisian varieties and accessions. Durum varieties Khiar and Salim, and bread wheat variety Tahent, were resistant to the local Northwestern European and Western Mediterranean pathotypes as well as the Warrior race. These varieties are thus short-term measures to address the yellow rust problem in Tunisia. Gene identifications will be confirmed by molecular and pedigree analyses of the accessions.
