Distribution of Puccinia striiformis f. sp. tritici Races and Virulence in Wheat Growing Regions of Kenya from 1970 to 2014

Abstract

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst), is a major threat to wheat (Triticum spp.) production worldwide. The objective of this study was to determine the virulence of Pst 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 Pst isolates collected from 1970 to 1992 and from 2009 to 2014 were virulence phenotyped using stripe rust differential sets, and 45 isolates were genotyped with sequence characterized amplified region (SCAR) markers to differentiate among 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, Yr27 and the seedling resistance in genotype Avocet S were detected. Ten races were detected in the Pst 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 Pst virulence was found in the Kenyan Pst population, and that diverse Pst race groups dominated different wheat growing regions. Moreover, recent Pst races in east Africa indicated possible migration of some race groups into Kenya from other regions. This study is important in understanding Pst evolution and virulence diversity and useful in breeding wheat cultivars with effective resistance to stripe rust. Keywords: pathogenicity, Puccinia f. sp. tritici stripe (yellow) rust, Triticum aestivum

Global dispersal and diversity of rust fungi in the context of plant health

“…PstS2 was first reported in Europe in 2000 [31], where only a relatively small wheat area was affected due to widespread deployment of PstS2-resistant cultivars [34,35]. Subsequent studies indicated East Africa as putative origin of PstS1/PstS2 [12], first detection of PstS1 dating back to an isolate sampled in Kenya in 1974 [36]. The fact that PstS1 has not been reported in P. striiformis populations outside North America and Australia since 2000 (except few samples in East Africa) may suggest an accidental, human-mediated spread of this strain, rather than random airborne spore movements around the globe between 2000 and 2002.…”

Past, Current and Future of Wheat Diseases in Kenya

“…Stripe rust race 134 with virulence for Yr7, 6, 9+ genes were present in Ethiopia, Kenya, Syria, and Yemen [34]. Thirteen races with virulence corresponding to stripe rust resistance genes Yr1, Yr2, Yr3, Yr6, Yr7, Yr8, Yr9, Yr1 7, Yr25, Yr27, and Avocet S are present in wheat-growing regions of Kenya [35], these races belong to either strain Pst1 or Pst2 which might have been present much earlier than 1982 and 1970.…”

“…SCAR markers SCAR1265 and SCAR1400 were developed in wheat to identify powdery mildew (B. graminis) gene Pm21, which was located on 6AL/6Vs same locus for gene Yr26 [115]. Species-specific sequencecharacterized-amplified-region (SCAR) markers have been used to characterize stripe rust races in Kenya [35].…”