39 Journal of Wheat Research 7(1):39-47 Homepage: http://epubs.icar.org.in/ejournal/index.php/JWR Research Article Article history Received: 14 January, 2015 Revised : 20 February, 2015 Accepted: 25 February, 2015 Citation EM Al-Maaroof, M Hovemoler, R Ali, H Mahmood, A Naser, L Muhammed. 2015. Detection of Yr27 virulence in Puccinia striiformis f.sp. tritici populations on wheat in Iraq. Journal of Wheat Research 7(1):39-47 *Corresponding author Email: ealmaaroof@yahoo.com @ Society for Advancement of Wheat Research Detection of Yr27 virulence in Puccinia striiformis f.sp. tritici populations on wheat in Iraq Emad Al-Maaroof 1 , Mogens Hovemoler 2 , Rizan Ali 1 , Hazha Mahmood 1 , Azad Naser 3 , Laith Muhammed 3 Faculty of Agricultural Sciences, Sulaimani University Sulaimania- 46 001, IKR- Iraq 1 Sulaimani University, Sulaimania-46 001, Iraq, 2 Aarhus university, DK-4200 Slagelese, Denmark, 3 Ministry of Agriculture, Baghdad 10001, Iraq Abstract This study was conducted to detect any possible changes in virulence spectrum of Puccinia striiformis f. sp. tritici population in Iraq. Biological trap nurseries of yellow rust were planted at different locations representing most of wheat growing areas in Iraq. The plants were exposed to the natural population of the pathogen in the felds. Disease was scored as severity and infection type on each genotype at different stages of wheat development. Yellow rust development was calculated on the local susceptible wheat cultivars Araz, and Saberbeg. yellow rust samples collected from the commercial wheat felds at different locations were sent to the Global Rust Center for race analyses. Virulence analysis of Puccinia striiformis f. sp. tritici population, revealed detection of virulence against the known resistance genes Yr2, Yr6, Yr7, Yr9, Yr18, YrA, Yr21, Yr25, Yr27, Yr28, Yr29 and Yr31 at adult plant stage in Sulaimania, while virulence against the known resistance genes Yr1, Yr2, Yr4, Yr5, Yr7, Yr9, Yr SD, YrSu, YrND, Yr32, YrA, Yr21, Yr27, Yr28, Yr31, were detected in the natural populations of P. striiformis f. sp. tritici at adult plant stage in Nineveh. Out of 34 rust samples sent to GRRC for race analysis, 12 samples were only recovered while 22 samples were failed to recover. Breakdown of resistant genes Yr27 and Yr25 was further confrmed at seedling stage. Infection rate value of yellow rust during the epidemic on Saber Beg (r- value= 0.337) was higher than Araz (0.187). Keywords: Yellow Rust, Triticum aestivum, Resistance genes, Pathogen variability, Iraq 1. Introduction The trans-boundary wheat rust diseases could have potential devastating effects on wheat production in Iraq. Stripe or yellow rust of wheat, caused by Puccinia striiformis f.sp. tritici (Pst ), is currently considered to be the most important biotic constraint to sustainable wheat production in Iraq (Al-Maaroof et al., 2003b). Yield losses of 10-60% in Iraq are common, if susceptible cultivars are grown (Al-Maaroof et al., 2012). The pathogen has the ability to evolve rapidly into new races and to migrate long distances by air-borne dispersal (Chen et al., 2002). Yellow rust infection was formerly restricted in some wheat felds in the northern parts and It has never been seen in the middle and South of Iraq. The disease appeared periodically both on the rain fed areas and irrigated wheat felds (Al-Beldawi et al., 1993). The disease was observed for the frst time in some wheat felds in the middle zone in 1988. Later on it has rapidly spread on the susceptible cultivars in this area and then moved to wheat growing area’s in the South (Al- Maaroof et al., 2003a). Many outbreaks of yellow rust were observed in all wheat growing areas particularly in the irrigated felds in the last decades. The most severe epidemic form was recorded in 1998, which has caused signifcant decline in the national grain production.