Search

Wheat yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici ( Pst ), is one of the most devastating diseases of wheat worldwide. Pst populations are composed of multiple genetic groups, each carrying one or more races characterized by different avirulence/virulence combinations. Since the severe epidemics in 2017, yellow rust has become the most economically important wheat foliar disease in Uruguay. A set of 124 Pst isolates collected from wheat fields in Uruguay between 2017 and 2021 were characterized phenotypically, and 27 of those isolates were subsequently investigated in-depth by additional molecular genotyping and race phenotyping analyses. Three genetic groups were identified, PstS7 , PstS10 , and PstS13 , with the latter being the most prevalent. Two races previously reported in Europe, Warrior ( PstS7 ) and Benchmark ( Pst S10), were detected in four and two isolates, respectively. A third race, known as Triticale2015 ( PstS13 ), that was first detected in Europe in 2015 and in Argentina in 2017 was detected at several locations. Additional virulence to Yr3 , Yr17 , Yr25 , Yr27 , or Yr32 was detected in three new race variants within PstS13 . The identification of these new races, which have not been reported outside South America, provides strong evidence of the local evolution of virulence in Pst during the recent epidemic years., Competing Interests: The author(s) declare no conflict of interest.

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici , is a major threat to wheat ( Triticum spp.) production worldwide. The objective of this study was to determine the virulence of P. striiformis f. sp. tritici races prevalent in the main wheat growing regions of Kenya, which includes Mt. Kenya, Eastern Kenya, and the Rift Valley (Central, Southern, and Northern Rift). Fifty P. striiformis f. sp. tritici isolates collected from 1970 to 1992 and from 2009 to 2014 were virulence phenotyped with stripe rust differential sets, and 45 isolates were genotyped with sequence characterized amplified region (SCAR) markers to differentiate the isolates and identify aggressive strains PstS1 and PstS2 . Virulence corresponding to stripe rust resistance genes Yr1 , Yr2 , Yr3 , Yr6 , Yr7 , Yr8 , Yr9 , Yr17 , Yr25 , and Yr27 and the seedling resistance in genotype Avocet S were detected. Ten races were detected in the P. striiformis f. sp. tritici samples obtained from 1970 to 1992, and three additional races were detected from 2009 to 2014, with a single race being detected in both periods. The SCAR markers detected both Pst1 and Pst2 strains in the collection. Increasing P. striiformis f. sp. tritici virulence was found in the Kenyan P. striiformis f. sp. tritici population, and different P. striiformis f. sp. tritici race groups were found to dominate different wheat growing regions. Moreover, recent P. striiformis f. sp. tritici races in East Africa indicated possible migration of some race groups into Kenya from other regions. This study is important in elucidating P. striiformis f. sp. tritici evolution and virulence diversity and useful in breeding wheat cultivars with effective resistance to stripe rust.