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Virulence evolution of Puccinia striiformis f.sp. tritici on wheat in Kenya between 1970 to 1992 and 2009 to 2014

Emergence of new virulent races of Puccinia striiformis f. sp. tritici (Pst) to stripe (yellow) rust resistance genes in wheat (Triticum aestivum L.) has historically resulted in severe yield losses worldwide. We conducted a study to characterize the virulence profiles of Pst races prevalent in Kenya from historic (1970-1992) and recent collections (2009-2014). Pst isolates collected during surveys in Kenya were characterized at the Global Rust Research Centre (GRRC), Denmark. Yellow rust differential sets (wheat lines with known Yr resistance genes), and strain-specific sequence-characterized-amplified-region (SCAR) markers were used to group the Pst isolates as Pst1 or Pst2. Virulence to Yr1, Yr2, Yr3,Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, Yr27, and the seedling resistance in AvocetS were detected. A total of 12 virulence profiles /races were detected in isolates obtained during 1970 to 1992, while six races were detected from samples collected between 2009 to 2014. In both periods, races with virulence profiles Yr2, Yr6, Yr7, Yr8, Yr25, Yr27, Avs and Yr2, Yr6, Yr7, Yr8, Yr17, Yr25, AvS were common. The SCAR results revealed that both Pst1 and Pst2 strains were present in the Pst isolates tested, Pst1 even in isolates from the 1970s. Additional isolates were also identified with neither Pst1 nor Pst2 profiles. From our findings, race analysis is key to understand the race diversity and pre-breeding efforts for effective resistance gene deployment.

Egerton University Njoro, Kenya
Ruth Wanyera, James Owuoche, Julian Rodriguez, Annemarie Justesen, Lesley Lesley, Sridhar Bhavani, Cristobal Uauy, Mogens Hovmøller
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Regulation of Pst and wheat genes in incompatible and compatible reactions

We evaluated Pst-wheat interaction at the transcriptome level between Pst isolate LSW3_2012_SP2 and Avocet/Yr5 (R), and Avocet S (S). For the compatible interaction we used a dataset of 9.3 M Illumina paired-end clean reads in which ?300,000 reads mapped against nearly 9,000 contigs of the PST-78 reference transcriptome, whereas 3.5 M reads mapped against a partial wheat transcriptome of 13,300 contigs. Pst transcripts in the infected wheat tissues amounted to about 10% of the mapped transcripts. In the incompatible reaction, we used a dataset of 13.2 M clean reads and ?27,000 reads mapped against nearly 2,900 Pst transcriptome contigs while 7.7 M reads mapped against 18,800 wheat transcripts. These results show an important differential regulation of genes in both the fungal pathogen and the wheat host. More than 3 times the number of distinct Pst transcripts was identified in the compatible reaction than the incompatible reaction. Genes differentially regulated between the incompatible and compatible reactions will be compared in terms of functionality and GO term classification. To validate Pst transcripts involved in the infection process, we adapted a leaf rust haustorial isolation protocol for characterization of proteins and modified it to protect the integrity of RNA in enriched Pst haustoria. A list of potential effectors present in LSW3_2012_SP2 and verified in haustoria-enriched tissues will be presented.

Agriculture and Agri-Food Canada, Lethbridge Research Centre, Canada
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